Other roofing products, include:
- Curved Roofs.
- Solar Units.
- Pressed Metal Tiles.
- Standing Seam Cladding.
COP v24.12:Other-Products;
There are two main methods to clad curved buildings.
- Draped sheets, known as spring curving.
- Pre-curved sheets, either roll-curved or crimp curved.
Which system is used depends on the design of the structure and profile selected. Spring curving can be used on wider radii, while pre-curving can generally be done down to a 300mm or 400mm radius.
Curved flashings are described in 8.5.6 Curved Flashings
Where a barrel curved roof is below the specified minimum roof pitch recommended for the profile, side laps should be sealed over the crest of the arch with lap tape or silicone sealant until the minimum pitch is reached. Avoid double lapping because condensation can become trapped in the lap, which can cause accelerated corrosion with all metal products.
If the width and height of the roof are known, this information can be used to obtain the radius of curvature and subsequently the sheet length and the length of seal required for any profile.
IMPORTANT NOTE: The seal length (s) is required on each side of the crest (b).
15.1.1A Spring Curving Calculator
Definitions
Width = w=w
Height = h=h
Radius of curvature = r=r
Minimum pitch = p=p°
Sheet length = l=l
Length of seal = s=s
The Code of Practice Online provides an interactive tool for these calculations. This tool is only available online at 15.1.1A Spring Curving Calculator
Enter width and height to calculate:
Full Calculation Details and Example
Formula
Example
Start with : w = Width of roof
w
= 12
Start with : h = Height of roof
h
= 5
To find r the radius of curvature
r =
4h²+ w² 8h
=
(4 x 25) + 400) 40
= 12.5
To find l the sheet length
Find the length y
y = r - h
= 12.5 - 5
= 12.5
Find the length x
x =
w 2
=
20 2
= 10
To find the tangent of angle A
tan A =
x y
=
10 7.5
= 1.33
To find angle A
A = aTan(
x y
)= aTan(1.33)
= 53°
Find the arc length c b
c b =
2 π r A° 360
=
2 x 3.1412 x 12.5 x 53 360
= 11.56
Find the sheet length l
l = cb x 2
= cb 23.12 + 100mm
= 23.12
To find the length of seal
p = Min Pitch for corrugate = 8°
p = Min Pitch for corrugate = 8°
s = r x (tan 8°)
= 12.5 x 0.1405
= 1.76
N.B. This length of seal is required on each side of the crest.
15.1.1B Curved Roof: Sealed Lap Pitch
| Profile | Pitch |
|---|---|
| Corrugate | 8° |
| Symmetrical Low Trapezoidal | 4° |
| Asymmetrical Low Trapezoidal | 3° |
| Secret-fix Tray | 3° |
End laps must not be placed in the region of the curve where the roof pitch is below the minimum pitch for the profile in 7.1.1A Minimum Pitch for Generic Metal Roofing.
Because of limitations in manufacturing pre-curved sheets, end laps are often required. Transverse laps should be sealed at both edges to prevent the ingress of both rainwater and condensation, in accordance with 14.12.1 Sealing End Laps.
Penetrations should be placed at the apex, or where the pitch is greater than the minimum for the profile.
Barrel curved roofs have no ridging to allow water vapour to exit at the ridge, so other means of venting the ceiling space should be considered. (See 10.10 Ventilation Pathways.)
Provision for expansion should be provided in the same manner as required for straight lengths, but the configuration of curved roofs means that some expansion will be taken up by a springing of the profile further up, which results in less movement. When the total sheet length is considered for expansion, positive fixing should be used at the crown, and provision for expansion accommodated on the slopes. Sealed and fastened end laps do not act as an expansion joint.
When curved roofs are unlined and used as canopies or exposed eaves, the underside of the sheeting becomes an unwashed area. Therefore, it needs to be washed and regularly maintained to comply with the durability requirements of the NZBC and the supplier's warranty. Because pre-painted cladding is not intended for use in this type of micro-climate without regular maintenance, the underside of the soffit should be lined in all severe and very severe environments. (see 16 Maintenance )
Spring curving, also known as draping or arching of roofs, is a method of providing continuous lengths of roof cladding over a curved roof structure without pre-curving the sheets. It is best suited to corrugated profiles, or symmetrical roofing profiles of low rib height and narrow pan width, which can follow a curve without excessive panning or distortion. Asymmetrical rib products have greater minimum radii, which are limited by their pan width and rib height.
Because symmetrical profiles do not have a large rain-water carrying capacity they are limited in maximum radius and length. Maximum radius is limited by the need to provide adequate drainage at the top of the curvature and minimum radius is limited by the need to avoid distortion without pre-forming.
Continuity over a minimum of three purlins is required for successful spring curving and therefore any interruption such as a penetration may affect the ability of the sheet to drape curve.
Purlins must be accurately positioned with the top faces tangential to the radius of the arch and should be within a 5 mm tolerance to avoid purlin creasing. Roof traffic should be restricted to avoid damage, particularly in the low pitched region or in highly visible areas, particularly in the low-pitched region or in highly visible areas. Some purlin creasing or canning is to be expected with stronger profiles at minimum radii.
For convex roofs, the minimum radii should be adhered to because the pans are in compression, whereas with concave roofs the pans are in tension and the panning or distortion of these roofs will be less.
15.1.7C Typical Radius for Spring Curved Asymmetrical Profiles
NOTE: These figures are typical only and design should be checked with the manufacturer.
The tables above for recommended radii assume the cladding is draped over an arc where the base chord is parallel to the ground. When the base chord is on an incline, the maximum radius can be increased.
The two top purlins should be spaced to enable the sheeting to follow an arc that minimises purlin marking.
Draped curved roofs or curved ridges should be fixed by fastening each sheet first to one side of the roof and then pulling it down to be fixed on the other side. Where sheets are end-lapped, alternate sheets should be laid in sequence to avoid cumulative errors and be laid from opposite sides of the roof to ensure squareness is maintained.
Because extra uplift load will be imposed on the end fasteners of convex spring curved roofs, through the torsional action of the sheets on the fasteners, screws and load spreading washers should be used on the penultimate and the last purlins. This torsional uplift must also be considered when designing purlin to rafter connections and other structures below.
Low tensile metals and G 300 coated steel can be formed into a number of simple and compound shapes. Generally, roll curving is applied to corrugated profiles, and crimp curving to trapezoidal profiles.
A curve can be rolled in the centre of a straight length of roof cladding to provide a ridge, but for ease of fitting and transport, a lap is often required at the first purlin down from the ridge, and an end lap is formed at that point. This should be sealed in the same manner as is required for any transverse lap.
As pre-curved sheets are typically formed from medium-strength (G300) material, the lower strength of this material must be considered when considering purlin spacings and roof traffic.
Fitting curved sheeting requires considerable care to ensure a satisfactory and aesthetically pleasing job. Setting out requires first checking that the materials delivered on site are within specified tolerances, and before commencing work the building should be checked for squareness.
Both roll curving and crimp curving will produce a curve with the effective cover dictated by the forming process. It is critical that the material is run to the correct width before being presented to the curving tool, or the effective cover of the straight portion will not match that of the curve. A variation of only 2mm between the straight and curved portion of a sheet will make it very difficult, or impossible, to install.
The curving process can cause dimensional changes, which can lead to misalignment, so the sheets should be kept square with the building. Some minor saw-toothing at the gutter end is to be expected when fitting curved sheeting. When multiple curves are required that cannot be provided on one sheet, the sheets should be fixed in the order shown below.
Roll curving is typically used for corrugated profiles. Pre-curved corrugated roof cladding is used for bull-nosed veranda roofs, ridges, or roofs where the radius is less than the minimum required for sprung or draped curved roofs.
The sheets are passed through offset curving rolls, which progressively form curves in a wide range of radii down to 300 mm. There is, however, a straight portion of about 80 mm at each end of the sheet which may need to be trimmed off if a true curve is required.
Circular barns have been successfully clad with 0.4 mm steel for many years, but 0.55 mm steel or 0.9 mm aluminium should be used for roll-curved roofs subject to foot traffic. As roll curving is normally done with G300 steel or H34 aluminium, the lower yield strength of these materials must be taken into account when setting purlin spacings.
If the edge of the sheet is too flat or long, and at tight radii, rippled edges may result, and these should be dressed out using a dressing tool, or trimmed off before the sheet is installed.
Crimp curving is applicable to all profiles, but it is most suited to trapezoidal profiles.
Crimp curving is produced by pressing a small crimp in either the tops of the ribs or the pans of the sheeting, progressively shortening it at these points and thereby causing it to bend. The radius can be altered by the spacing of the crimps and the angle of the bend by the number of crimps.
As crimp Curving is normally done with G300 steel or H34 aluminium, the lower yield strength of these materials must be taken into account when setting purlin spacings.
Structures mounted on the roof requires consideration of all the factors contributing to the performance of the roof cladding.
Some structures which are commonly mounted on roofs include air conditioning units, aerials, photovoltaic systems, and solar water heating units.
Design and installation of these structures should consider at least three areas of performance:
- Structure – the effect of mounting the structures and roof traffic for ongoing maintenance; see 3.7.5 Dead Loads and 3.7.4 Roof Traffic.
- Durability – corrosion may result from issues such as wet contact, capillary action, unwashed areas, material compatibility, and runoff; see 4.10 Other Causes of Corrosion.
- External Moisture – penetrations influence roof drainage and can affect weatherproofing of the cladding; see 9.3 Penetration Durability and Compatibility.
Metal tiles, shingles and shake panels are press formed to provide a variety of shapes resembling clay tiles, wooden shingles or shakes. They are interlocked or overlapped laterally and longitudinally and are clipped or fastened to timber or steel battens.
Metal tiles, shingles and shakes are metallic coated steel are manufactured from metallic coated steel, although aluminium or other metals can also be used.
Pressed metal tiles made from steel invariably have an additional protective coating applied over the metallic coated steel. This may be an organic paint coating applied by either the steel manufacturer before the tiles are formed or by the tile manufacturer after the tiles are formed. An alternative coating can be provided by applying crushed stone or ceramic granules to the base metallic coated steel and attached by an adhesive coating; normally, a clear acrylic coat is used.
These coatings give protection to the metallic coated steel base, as well as providing a decorative finish.
Pressed metal roofing tiles are installed by fixers, trained and appointed by the manufacturers or their representatives, and they are not normally supplied to other installers.
The principles behind detailed requirements for fixings, flashings, corrosion, compatibility, and maintenance as described elsewhere in this COP should also be applied to the design and installation of pressed metal tiles.
Exceptions result from the specific differences between tiles and other forms of metal roof cladding, and include the height of laps and specific dimensions of metal shingles and shakes prescribed in this section.
Steel based metal tiles, shakes, and shingles must have hot-dipped galvanised fasteners that are compatible with the base metal and provide a service life equivalent to the durability of the panel.
Panels are fastened to the roof structure by fixing horizontally through the front of the panel; and because the fixings are in shear, they provide wind uplift resistance suitable for very high wind design loads.
Tiles with a minimum upstand of 25 mm must not be laid on roof structures less than 12° unless approved in writing by the tile manufacturer, the B.C.A. or the Territorial Authority.
Tiles, shakes or shingles with an upstand of less than 25 mm must not be laid on roof structures less than 15°.
N.B. The pitch of the roof is not the same as the pitch of the tiles because this varies with the height of the batten and the height of the upstand. If the minimum pitch cannot be complied with, a method approved in writing or a producer statement should be given before work is commenced.
Permeable self-supporting underlay must be installed on all new roofs as specified in section 4.3. of this Code of Practice.
The underlay must be installed horizontally with a minimum overlap of 75mm.
The first length of underlay should be positioned so that it lays over the eave batten and the fascia, and into the gutter.
When pressed metal tiles are installed, the underlay is laid horizontally on top of the rafters before the battens are fixed, and so there is an air space between the underlay and the tiles, except at the eave.
Roof framing should provide support and fixing for the tile battens that will satisfy the design load wind requirements. Installers should check that the framing has been erected to an accurate and even line before roof fixing is started.
An inspection and any rectification to the framing alignment must be carried out before roof fixing is commenced.
Tiling battens must be:
- H1.1 boric treated when used in attic roof construction;
- H1.2 treated when used in skillion roof construction;
- Douglas fir with a moisture content of less than 20%;
- KD Pinus Radiata with a moisture content of less than 18%;
- a minimum of 50 mm x 40 mm for 900 mm rafter spacing; and
- a minimum of 50 mm x 50 mm for 1200 mm spacing.
Copper preservative timbers must not be used with Zincalume coated tiles. Battens required for rafter spacings greater than 1200 mm must be specifically designed and be spaced to suit the tile module.
Battens at 370 mm centres must be fixed to the rafters or trusses over the underlay using fasteners to comply with Tables 10.1.5.A, B and
N.B. Battens at different centres may require different values.
15.3.1.5A Batten Installation
- Battens must have square cut ends and must be butt jointed over the centre line of the rafter.
- Adjacent rows of battens must not be joined on the same rafter and must span at least three rafter spacings at the roof edge.
- A batten must be installed immediately behind the fascia as fixing for the eaves tiles.
- Eaves tiles must overhang the gutter by a minimum of 30 mm.
Eaves tiles are recommended to overhang the gutter by 40 mm.
Because an eaves-tile batten is installed immediately behind the fascia the position of the next batten up the rafter will be less than that of the normal tile batten spacing. The position of this batten may vary depending on the pitch of the roof.
The edge of the roof should be taken as 20% of the roof width measured from the fascia, barge, hip or ridgeline, and will apply all around the periphery of each roof plane.
The batten layout is marked on the rafters by placing nails at the line of the batten fronts. The roofing underlay is laid over this, onto the rafters. The battens are then laid from the lowest part of the roof upwards, using the marker nails to locate the front edge of the batten. The marker nails are removed before the tiles are laid.
15.3.1.5.1A Pullout resistance in kN required for battens for buildings with ceilings
cpe = -0.9, cpi = 0, cp = 0.9
| Purlin/ batten size | Max span | Wind Zone 0.61kPa | Wind Zone 0.61kPa | Wind Zone 0.82kPa | Wind Zone 0.82kPa | Wind Zone 1.16kPa | Wind Zone 1.16kPa | Wind Zone 1.50kPa | Wind Zone 1.50kPa |
|---|---|---|---|---|---|---|---|---|---|
| mm x mm | mm | Low 32m/s | Low 32m/s | Medium 37m/s | Medium 37m/s | high 44m/s | high 44m/s | Very high 50m/s | Very high 50m/s |
| M | P | M | P | M | P | M | P | ||
| 50 x 40 | 900 | 0.2 | 0.3 | 0.3 | 0.4 | 0.3 | 0.5 | 0.5 | 0.7 |
| 50 x 50 | 1200 | 0.2 | 0.4 | 0.3 | 0.5 | 0.5 | 0.7 | 0.6 | 0.9 |
M = main body of the roof P = periphery
15.3.1.5.1B Pullout resistance in kN required for buildings without ceilings (but with a permeable
windward wall)
cpe = -0.9, cpi = 0.2, cp = 1.1
| Purlin/ batten size | Max span | Wind Zone 0.61kPa | Wind Zone 0.61kPa | Wind Zone 0.82kPa | Wind Zone 0.82kPa | Wind Zone 1.16kPa | Wind Zone 1.16kPa | Wind Zone 1.50kPa | Wind Zone 1.50kPa |
|---|---|---|---|---|---|---|---|---|---|
| mm x mm | mm | Low 32m/s | Low 32m/s | Medium 37m/s | Medium 37m/s | high 44m/s | high 44m/s | Very high 50m/s | Very high 50m/s |
| M | P | M | P | M | P | M | P | ||
| 50 x 40 | 900 | 0.2 | 0.3 | 0.3 | 0.5 | 0.4 | 0.6 | 0.6 | 0.8 |
M = main body of the roof P = periphery
15.3.1.5.1C Pullout resistance in kN required for buildings without ceilings (and with a dominant
windward opening)
cpe = -0.9, cpi = 0.8, cp = 1.7
| Purlin/ batten size | Max span | Wind Zone 0.61kPa | Wind Zone 0.61kPa | Wind Zone 0.82kPa | Wind Zone 0.82kPa | Wind Zone 1.16kPa | Wind Zone 1.16kPa | Wind Zone 1.50kPa | Wind Zone 1.50kPa |
|---|---|---|---|---|---|---|---|---|---|
| mm x mm | mm | Low 32m/s | Low 32m/s | Medium 37m/s | Medium 37m/s | high 44m/s | high 44m/s | Very high Very high 50m/s 50m/s | |
| M | P | M | P | M | P | M | P | ||
| 50 x 40 | 900 | 0.4 | 0.5 | 0.5 | 0.7 | 0.7 | 1 | 0.9 | 1.3 |
| 50 x 50 | 1200 | 0.5 | 0.7 | 0.6 | 0.9 | 0.9 | 1.3 | 1.1 | 1.7 |
M = main body of the roof P = periphery
15.3.1.5.1D Tile Batten Fastener Requirements
| Fastener | Size | No. | kN |
|---|---|---|---|
| Gun nail | 90 x 3.15 | 1 | 0.4 |
| Ringshank nail (gun/hand) | 90 x 3.2 | 1 | 0.6 |
| Gun nail | 90 x 3.15 | 2 | 0.7 |
| Twist Shank Nail | 90 x 3.3 | 1 | 0.9 |
| Purlin Screw c/s head | 10g x 100 | 1 | 2.5 |
| Type 17 screw | 14g x 100 | 1 | 7.3 |
Valley gutters must be made of the same metal or coating as the roof tiles or a compatible material, and when the roof tile is painted or coated the valleys must also be painted.
Where secret gutters are used or where the flashings are unseen, they must have a durability of 50 years.
The valley must have a minimum upstand of 20 mm, and the fasteners must not penetrate the valley.
For valley sizing, see 5.5.7 Valley Capacity Calculator.
Metal Tiles are classified as a Type B roof cladding as they cannot be walked on indiscriminately without the risk of damage.
Persons authorised to walk on a metal tile roof must walk only in the pan of the tile where the batten supports it, and wear flat, soft-soled shoes to prevent damage to the tiles and surface coatings.
Other trades must be made aware by the contractor or site supervisor of the method of walking on pressed metal tiles without causing damage, and that the cost of repairing damaged tiles is their responsibility.
The valley boards installed between the valley jack rafters to support the valley and tile battens are required to be set with their outer edge at a minimum of 90 mm from the centre line of the valley. Valley boards are required to support a point load of 1.1.kN, which is taken to be the weight of a tradesperson with a bag of tools.
Valleys are installed so water discharges over the back and into the eaves gutter. The valleys are held in position by clips specially designed to allow for expansion, or by compatible nails and washers placed alongside the valley or bent over the top lip of the valley.
Under no circumstances must the fasteners penetrate the valley surface.
Joints cannot have an overlap of less than 200 mm.
The top end of the valley should be turned up against the hip or ridge battens to the height of the batten. Where two valleys meet over a dormer, they are cut, shaped, joined, and sealed so that they form a continuous valley.
The tile edge should be bent down to a minimum of 5 mm from the valley floor.
The gap between tiles on opposing sides of the valley must be a minimum of 70 mm.
Valley boards and boards supporting flashings must be H.3 treated, and all metal and timber should be separated by underlay .
Standard flashings are supplied for most locations on a roof, and are in two styles, only one of which is used on any one roof. All flashings and roofing accessories are made of the same base metal as the tiles.
- Long accessories are 2 m long with fixing holes every 500 mm and there are specific accessories for ridges, hips, barges, aprons and walls.
- Short accessories are 400 mm long trims and can be used for most flashing applications on a roof.
Special flashings are made as required by the manufacturer or the roofer from uncoated steel, and subsequently factory coated using the same coating process as used for tiles.
Tiles must be turned up to a minimum of 40 mm against the battens, hip board or where they butt against a vertical or an inclined surface.
The ridge trim cap or side flashings must cover the tile turn-ups by a minimum of 35 mm.
Ridge tiles are bent up and then cut to form a turn-up that fits under the ridge/hip cap or short accessory. To ensure a watertight joint, a tight fit is required between the tile and the ridge cap.
Tiles should be turned up against the battens or hip board by a minimum of 40 mm. See 15.3.5.1A Ridge and Hip: Short Trim Installation and 15.3.5.1B Ridge and Hip: Long Trim Installation.
Tile ends are turned up a minimum of 40 mm and installed against a batten that will be covered by a barge cover or under a metal fascia. If a hidden gutter is used, tile edges should be turned down into the gutter by a minimum of 20 mm.
The wall cladding flashings must be positioned before the tiles and must be designed so that the turned up tile can be inserted behind the flashing.
All preparatory work of under-flashing, fixing of eaves, gutters and valley gutters must be completed, and all tiling battens must be in place before laying tiles.
Flashings at the ends of roofs, where the roof does not end past the wall require a stop-end flashing that ensures water is directed into the gutter. Sufficient material should be left standing out from the wall so that cladding installers can ensure a weatherproof finish.
Tiles cut for penetrations through the roof should be provided with up-stands and over-flashed for drainage from above without restricting the water flow.
The flashing should finish 15 mm beyond the tile head lap above the penetration and should be wide enough to cover the nearest tile rib or up-stand. When the construction is solid masonry or brickwork, and flashings cannot be installed under the wall cladding, a chase should be cut and an over-flashing installed in the chase to provide weather protection.
A long-run tile is a hybrid roof cladding providing the appearance of pressed metal tile with the fixing attributes of long-run profiled metal cladding.
The minimum pitch is 8˚, and underlay and battens are fixed in the same manner as for pressed metal tiles.
The module or step size of the profile can be adjusted, and the pitch of the tile can be varied to suit any batten spacing on an existing roof or to alter the roof appearance.
Maximum sheet length is 7 m however transverse laps are possible.
The material is pre-painted metallic coated steel with a yield strength of G250 Mpa. It is fixed with nails or screws at the front of the tile.
Sheets should be back-laid, working from right to left which prevents creep at the gutter line due to the back-step in the underlap of the profile.
Longrun tile can be curved to a 250 mm radius.
The requirements of 13 Site Practice also apply to the installation of metal tiles. In addition all gutters, valleys, roof channels and the roof should be left clean and free from debris on completion of the work.
The roofing supervisor will establish when the roof should be installed after all sub-trade work has been completed.
All preparatory work of under-flashing, fixing of eaves, gutters and valley gutters must be completed, and all tiling battens must be in place before laying tiles.
If substantial work, such as texturing walls, is to be carried out on a wall above or adjacent to where metal tiles are to be laid, they should be installed after such work has been completed.
Tiles should be inspected and selected, as tiles of a different colour match should not be installed on the same plane of a roof. If more than one pallet of tiles is required for one job, the colour uniformity should be checked.
Tiles damaged during installation must be removed and replaced, and any deformed tiles or tiles with surface damage must be rejected.
Tiles should be laid from the ridge down to avoid unnecessary traffic and can be laid broken bond or straight down the roof.
The eave gutter tiles should project over the edge of the fascia to ensure that water discharges directly into the gutter system and tiles should be laid so they prevent any water penetrating into the roof cavity.
Before tiles are laid, the direction of lay should be determined by:
- Taking into account whether the profile can be laid only one way or both ways;
- Appearance, so that laps face away from the line of sight;
- Allowing for prevailing weather exposure.
Installation of perimeter tiles (excluding eaves tiles) can be completed before the main body of tiles are laid.
Graphite pencils must not be used to mark AZ coated steel products as carbon can cause premature corrosion failure of the coating.
Finishing of tile cuts and bends must leave straight lines up the roof section, to provide a true line for flashings.
When cutting tiles for their installation at ridges, hips, valleys and barges, avoid damage to the surface finish by using a guillotine or metal shears. When cutting the tile lengthwise, it must be bent before cutting to reduce the amount of distortion that occurs as the profile is flattened during bending.
Tiles turned up and down for ridges, hips, valleys and barges must be bent using a bender specifically designed for this purpose. Tiles must be turned up at ridges, hips and barges by a minimum of 40 mm, and down into the valleys to a minimum of 5 mm from the valley floor.
Standing Seam or Tray roofing is similar to trough section in that it is secret fixed, but it consists of just a single pan per sheet, compared to the two or three pans of a trough section.
Tray roofing may be designed to be self-supporting on purlins, or installed on solid sarking. With the former, sheets clip together, the latter has its side ribs clipped to the adjacent sheet.
Tray roofing designed to be fully supported by sarking is referred to in the COP as standing seam roofing. Clauses in this section headed Tray Roofing will apply to both types, clauses headed Standing Seam Roofing, including Load/Span tables, will only apply to generic standing seam roofing profiles
The profiles and fixing methods for tray roofing date back to traditional methods used to hand-fabricate metal roofs, predominantly in Europe and often from non-ferrous metal, prior to the development of roll forming technology. A by-product of this heritage is that, in addition to the secret clips fastening the main roof, flashings should also be installed on clips with minimal use of exposed rivets and fasteners.
In Europe, the installation of tray roofing is done by Spenglers, who serve a 4-year apprenticeship. We do not have the same qualification in NZ, but installers of tray roofing must have specific training and experience in the product if they are to achieve the expected high standard of workmanship
Traditionally standing seam roofs were manufactured from sheets of copper or pure zinc (sometimes even lead) and these materials are still popular being naturally durable and weathering to a natural patina. They are also very malleable which allows more variation in intersections and terminations, and they can be soldered.
More common in the New Zealand market are pre-painted steel and aluminium substrates. To increase its formability, Steel is normally supplied in Medium Strength G300 grade and Aluminium in hardness grade H34.
See 4.16 Materials for a more thorough discussion of roofing material.
Self-support tray roofing profiles resemble a single tray trough section but the ribs are generally narrower and the installation techniques are more sophisticated. Standing seam profiles generally have rib heights of 25 mm – 45 mm. Pan widths for both types vary from 300 mm to 500 mm.
Traditional standing seam shapes are angle-seamed, double-seamed, or roll cap. The angle seam is the most popular and the double seam is the least popular. The roll cap replicates old roofs with a capped joint installed over a longitudinal batten.
One of the features of standing seam roofs is that they can be formed by folding rather than roll-forming. This makes it possible to install roofs to buildings that are round or sinusoidal in plan, to have “random” pan widths, or to vary rib width discretely so that ribs are spaced equidistant from associated architectural features such as penetrations and windows.
All tray roofing, including standing seam profiles, must have clearance between adjacent pans to allow for timber shrinkage and transverse thermal expansion of the pan. The non-existence of this clearance gap can cause excessive canning or quilting.
15.4.2F Standing Seam Cladding on a Round Building.
Source: UK Guide to Good Practice in Fully Supported Metal Roofing and Cladding 3rd Edition; © Federation of Traditional Metal Roofing Contractors
Some manufacturers have the facility to curve their trays in a concave or convex shape.
Tray and particularly standing seam profiles lend themselves to many variations in installation details. Installers are generally specialist and highly trained and may modify or improvise a detail to suit the needs of a situation. Because of this, the demarcation between design and Installation is not clear cut.
The following information on design and installation is generally applicable to all tray roofing including self-support, apart from the sections on sarking and load tables. Sections particular to standing seam are headed as such, but there is a large amount of cross-over in many areas.
15.4.3A Roof-Wall Junction Without Needing Prickles
All tray roofs can be seamed at the junction of roof and wall, without the need for prickles.
The malleable nature of the metal used to manufacture tray roofing, the wide pan, and the vertical rib, give many options for achieving weathertightness. Generally, options that work with a trapezoidal profile will equally work for tray roofing but are most likely to be installed on secret grab fasteners rather than being riveted. The elimination of primary and secondary fasteners is another attribute abetting weathertightness, as are the tight laps and the water carrying capacity of the wide pan.
The wide pan of tray roofing makes it impractical to have longitudinal flashings cover two pans, and because of the vertical rib and fastening techniques, longitudinal flashings covering a single pan are acceptable.
Perhaps the most outstanding feature of all tray roofs is the minimisation of visible fasteners. Apart from the secret fixing clips, attachment of flashings to the roof should be achieved by crimping to the cladding or other flashings or to a grab flashing wherever possible.
Clips for standing seam roofing are normally single clips, fastened to the substrate with screws or annular grooved nails. The sole of the clips should have a rebated or countersunk hole for the fastener, and rounded edges, to ensure thermal movement of the sheet does not cause damage by rubbing against sharp edges.
Wall cladding laid horizontally may need additional support and the standard bracket to resist gravity loads.
As the style of roofing replicates hand-formed products of yesteryear, and because the sheets themselves are relatively flexible, end laps are more common in tray roofs, and more acceptable, than with other profiles. In practice, staggered end laps are often used with tray roofing as an architectural design feature.
15.4.6A Staggered End Laps
Source: UK Guide to Good Practice in Fully Supported Metal Roofing and Cladding 3rd Edition, © Federation of Traditional Metal Roofing Contractors
Sarking is commonly CPD (Construction Panel Directive), Stress grade 11, 15 mm ply laid on supports at 800 centres, or 17 mm ply at 900 centres. Ply should be laid with face grain at a right angle to supports. Edges of sheets not held by plastic tongue or T&G should be supported. Fasteners should not be closer than 10 mm from sheet edges.
15.4.7A Ply Sarking Fixing Pattern
| Wind Zone | Edges fix at 75 mm centres | Body fix at 150 mm centres |
|---|---|---|
| Up to High Wind Zone | 60 x 2.8 nails or 8g x 40 mm screws | 60 x 2.8 nails or 8g x 40 mm screws. |
| Very High and Extra High | 75 x 3.15 nails or 10g x 40 mm screws | 75 x 3.15 nails or 10g x 40 mm screws |
To allow for expansion, maintain a 3mm gap between sheets. At the gutter line, the ply should be cut flush. Dormer valleys and valleys into spouting can be recessed or flat laid.
Because of their relatively narrow ribs, tray roofing generally self ventilates less than other roof profiles. This puts more responsibility on the designer to consider ventilation of the ceiling space. Ventilation is particularly important for fully supported profiles; the ply must have a gap at the apex to allow for egress of air and a gap at the bottom, or soffit vents, to allow air ingress.
Clip spacings for proprietary tray roofing must be set out as per the manufacturer's data for the design wind load of the building.
15.4.9A Generic Standing Seam Clip Spacing
| Rib Height | Max Pan Width | NZS 3604 Wind Zone | |||
|---|---|---|---|---|---|
| Medium | High | Very High | Extra High | ||
| 25 mm | 300 mm | 500 mm | 500 mm | 500 mm | 500 mm |
| 400 mm | 500 mm | 500 mm | 500 mm | 500 mm | |
| 500 mm | 400 mm | 400 mm | 400 mm | N/A | |
| 32 mm | 300 mm | 600 mm | 600 mm | 600 mm | 600 mm |
| 400 mm | 600 mm | 600 mm | 600 mm | 600 mm | |
| 520 mm | 600 mm | 600 mm | 600 mm | 400 mm | |
| 38 mm | 300 mm | 600 mm | 600 mm | 600 mm | 600 mm |
| 400 mm | 600 mm | 600 mm | 600 mm | 600 mm | |
| 500 mm | 600 mm | 600 mm | 600 mm | 400 mm | |
Wind-induced noise can also be an issue in high-wind areas with winds above 20m/s. It can be minimised by specifying a narrower pan width and closing clip centres. Further noise reduction can be gained by putting a concave shape into the pan, which can be achieved by:
- installing longitudinal stringers (e.g., a 10 mm batten) under the centre of the tray
- installing strips of compressive material along the purlins.
Geotextile mat layers have the most significant effect on noise attenuation, but the added cost of such should be weighed against the expected benefits
The wide flat pan of tray roofing makes it easy to achieve secure penetration details. Proprietary rubber boot flashings can be used for small pipe penetrations, but a more aesthetically pleasing solution is to make up a flanged upstand in pre-painted steel or colour matched malleable metal, and fit a “Chinese hat” to the penetration to allow for thermal movement and weatherproofing.
15.4.10B Avoiding Long Back Trays
Avoiding the use of long back trays helps achieve an aesthetically attractive solution for penetrations
Install grab flashings at verges, hips and ridges, and to wall cladding intersections, to minimise exposed rivets and fasteners.
Oil canning, panning, or quilting, is the term used to describe visible waviness of the pan of a metal roof.
Oil canning is one of the most controversial aspects of tray roofing. Some people accept it as an innate feature of a tray product, others want a flat tray with no visible waviness. It may not be obvious, but it is always present in tray roofing to some extent. The visibility of canning is affected as much by the lighting, line of sight, cleanliness, and gloss levels of the roof, as it is by the degree of canning present in the product.
Clients expecting no canning should be informed of the reality, particularly if the roof runs at an acute angle to one’s line of sight. Canning can also be induced by stretching the material or excessive foot traffic. The substrate must be true to plane and not convex.
The most effective ways to minimise canning in a highly visible situation is to use a profile with a narrower pan and use material with a low-gloss or textured surface.
With self-support tray roofs, excessive foot traffic will accentuate purlin lines, because of the ductility of the metal (grade G300) and the wide flat pan.
Tray roofing is a predominantly flat, secret fixed profile with one tray per sheet and vertical ribs. The roofing sheets are clip-fastened, using hidden clips. Tray cladding which is installed on sarking by traditional methods with hand-formed side lap seams is known as standing seam cladding.
With a wide tray profile, it is important to have matching distances from adjacent ribs to any major architectural details. Prior to commencing the lay, the roofer must determine what the predominant features are on a given face and set the roof out to maximise the symmetry of side flashings and matching rib lines. With fully supported profiles, sheets can be folded to varying widths to achieve symmetry across a number of architectural features.
- Install the eaves grab flashing to which the sheets will be crimped and any other flashings that may be behind the cladding, for example, window jamb flashings.
- Fit the netting and/or underlay. On flat roofs requiring underlay support, using twine is preferable to netting as the joins in the latter may imprint through the medium strength iron through foot traffic.
- Form stop-ends in the sheets.
- Then the sheets can be laid, starting from a distance from the barge to give equal cover distance to the opposing barge and other architectural features and penetrations. Fasteners should be annular grooved nails or screws, with clips at centres specified by the manufacturer to suit the product and wind zone.
Pre-painted tray roofing will usually be supplied with strippable film to give temporary protection from scratching. The film should be removed from underlaps while laying, and removed entirely before UV sets the adhesive making it difficult to remove without leaving glue residue on the sheet. Traffic across sheets should be kept to a minimum, particularly with self-supporting products.
Non-ferrous tray roofing expands at about twice the rate of ferrous metals. Supported angle seam and double seam profiles must be installed using a balance of sliding clips to allow for expansion, and fixed clips to withstand gravity loads.
The position of the fixed clips depends on the roof pitch. The width of the fixed clip portion should be sufficient to install five clips at the required spacing.
Steel based angle seam and double seam profiles up to four metres in length can be laid without sliding clips. Roll cap and self-support tray roofing have clip systems that can accommodate thermal movement, and also do not require special sliding clips.
15.4.13.3B Using Clipped Flashings Minimises the Need for Rivets
Using clipped flashings to minimise the use of rivets is a feature of a well-installed standing seam roof.
Crimp sheet at ends to eaves flashing with eaves crimping tool, and cut and fold rib to close rib ends. Remove strip film, if applicable, and for standing seam roofs lock adjacent sheets together with rib purpose made closer tool.
Warm roofs are where insulation is in direct contact with the roof cladding. It can be divided into three main categories:
- insulated panels,
- composite or site assembled systems, and
- roofs with insulation sprayed on after installation.
Insulated or sandwich panels are factory-made laminated products using different core materials permanently bonded by adhesive or foam to metal skins to act as a single structural element.
The manufacturing process for bonded panels consists of roll forming the flat or profiled sheeting, followed by the adhesion of the insulation core to both surfaces or skins.
There are three methods to do this:
- Continuous production by injecting foaming insulation between 2 metal skins as they are being roll-formed.
- Continuous production by glueing pre-formed panels of insulation to roll-formed metal skins.
- Individual panel production by glueing insulated panels to roll-formed sheets
The structure and composition of an insulated panel are chiefly determined by its end use.
Three types of profiles are used on insulated panels. This is largely determined by the spanning requirements and ease of maintenance.
Flat continuously produced panels suffer minor undulations in the metal skins that arise from built-in tensions in the metal coil and are introduced during panel manufacture. Panning can be minimised by using a matt finish or forming minor ribs or swages on the flat face of the panel.
The facings or skins of composite panels are typically metallic coated, pre-painted steel or aluminium, and are either profiled or flat on either or both sides of the panel. The internal skin is also known as the liner skin or sheeting.
The metal facing is commonly made from grade G300 steel of 0.40 – 0.63 BMT thickness, with a pre-painted organic finish over a metallic coating. Cool room panels have a galvanised Z275 metallic coating, while interior/exterior structural insulated panels have an aluminium/zinc coating of AZ150 or AZ200. Paint coatings are specifically developed to assist in bonding the insulation to the panel
Aluminium facings are used in very humid conditions or severe marine environments and can be supplied plain or pre-painted.
The core can be made from different types of material with different insulating values, fire ratings, and strengths. The most common are EPS (Expanded Polystyrene), PPS (Phenolic/Polystyrene), PIR (Polyisocyanurate), and mineral fibre.
EPS
EPS foam is mainly used for applications where high fire resistance is not a requirement.
PPS
PPS may be used where greater fire resistance is required.
PIR
PIR foam is increasingly specified because of its fire-resistant properties and better insulation efficiency.
Mineral Fibre
Mineral-fibre insulation may be selected for applications where fire resistance and/or acoustic insulation properties are of prime importance.The insulation thickness of a profiled roof panel varies from 30 mm to 300 mm. To achieve the same insulating value as a flat panel, a profiled roof panel needs to be thicker. The through fasteners or fixing clips are thermal bridges, but it has been shown that these are unlikely to decrease the R-value by more than 2%.
Different cores will also have different values for thermal insulation and noise attenuation, as will the details of panel joints and interfaces with other materials.
The nett insulation value of a panel must be calculated and stated by the manufacturer.
Since we say it won't increase by more than...we can stay with the top value.
R-values are the reciprocal of U-values. We will stick with R-value because that is the most commonly used value for roofs and walls.
Insulated panels are integral units in which the insulation layer together with the two metal skins act as a beam to resist wind and point loads. The bonded insulation core material contributes to the panel's strength by effectively increasing the web depth of the profile and resisting buckling; the depth of the core largely determines the panel's resistance to deflection. Panel stiffness is also affected by skin thickness and profile shape.
Insulated panels are excellent at supporting normal foot traffic without damage because the foam core provides continuous support to the external sheeting. The number and strength of the fasteners under wind suction loads can limit the maximum purlin spacing.
Where roof lights are required, the maximum purlin spacing will be limited by the strength of the roof light sheeting; it can be extended by using mid-span supports. Polycarbonate or G.R.P. barrel vault roof lighting may be used for greater spans or proprietary systems may be supplied by the manufacturer.
Insulated panels do not have inherently good acoustic insulation properties. Sound can be lessened by using sealed joints, but where higher levels of acoustic attenuation or absorption are required, it may be necessary to install additional acoustic lining systems.
Metal facings are effectively impervious to penetration by vapour, and panel cores have a closed cell structure which does not permit significant transmission or absorption of vapour. However, to prevent the possibility of interstitial condensation, it is necessary to fasten and seal all laps and gaps, side-lap joints, transverse laps, and joints and ridges that are exposed to the internal environment.
When insulated panels are used as cold store insulation, a complete and continuous vapour barrier is essential to prevent inward moisture vapour pressure. Any discontinuity will result in a build-up of ice which can destroy the panel.
The bottom skins of composite panels have an integral side lap with a re-entrant sealing space which acts as a vapour control, but in high-risk applications such as food processing buildings, textile mills, and indoor swimming pools an additional sealer strip is required in the side lap joint.
Thermal bowing can occur when the two skins are at significantly different temperatures such as north-facing walls, e.g., when a cool room roof panel is in direct sunshine. The effect is accentuated when the external surface is a dark colour and is more severe for aluminium facings.
The use of insulated panels for roof and wall cladding requires the same or similar detailing for Structure, Durability, External Moisture, and other design considerations as those for single-skin roof and wall cladding.
In most applications insulated panels can be installed by workers operating off the already installed sheet, negating the need for safely mesh. Many panels are installed using underslung safety nets. Other than that, all safety precautions should be followed as for any other cladding material.
Due to their inherent stiffness, insulated panels do not have the flexibility to follow uneven structures. Insulated panels are supported on purlins or girts, which should be accurately erected to a maximum tolerance of 3 mm and a deflection limit of l/600.
Insulated panels can accommodate penetration openings of 350 mm diameter or 300 mm square without the need for additional structural supports or trimmers. Where larger holes are required, trimmers should be in place before the erection of the panels.
Purpose-designed high thread-type fasteners are required to spread upwards loads and maintain the weather seal between the metal skin and the washer. Through fixings for roof panels may be rib fixed or located on a mini-rib within the trough, and should be set snugly to achieve a weatherproof seal without distorting the rib profile. Care must be taken not to over-drive the fasteners as this can cause damage to the G300 outer skin of the panel which can result in water ingress issues
Insulated roof panels with trapezoidal ribs are through-fixed with a load spreading washer on the rib and require lap fixing and sealing at the side laps to the manufacturer’s recommendations.
The maximum practical length of panels for transport and handling efficiency is restricted to approximately 25 m. Where a transverse joint is required, there are two options:
- Butt End Lap
- Waterfall Junction
Butt End Lap
The lining and insulation are butt-jointed over the purlin, and a 150 mm overlap of the top sheet is formed in the external weather skin only, using three or more lines of sealant and fasteners. The sealant should be butyl tape, silicone or MS sealant, or self-adhesive closed cell tape according to the specifications of the manufacturer and should be positioned at the top and bottom of the lap. To provide a secure seal with flat or wide pan profiles, additional sealed rivets or stitching screws are required through the top skins only.
The challenge with this detail is that there are four layers of material to consider at the side/end junction. While successful in many instances, problems developing later are very difficult to remedy.
Waterfall Junction
A waterfall step can be achieved by putting a step in the rafter or by increasing purlin cleat heights,
The first challenge of this detail is that the cold skin of the upper sheet cannot rest on the upper surface of the lower sheet, so a thermal break must be created. The second challenge is that any gap between the upper and lower sheets must be adequately insulated to ensure that the thermal efficiency of the system is not compromised.
Flashings detailing is similar to that used with single-skin roof and wall cladding. The main exception is that internal joints should be designed and sealed so that water vapour cannot impregnate the system.
The panels at the ridge and other edges of the roof should be sealed and the lining closed with a metal trim mounted on the ridge purlins as detailed by the manufacturer. Any gap between the ends of the composite panels should be insulated to eliminate cold spots or cold bridging. They can be sealed using in-situ injected foam or mineral fibre. In high-humidity applications, the liner trim should be sealed to the panels. At end-laps or gaps, foam should be injected to provide a vapour-tight seal.
Where required by the manufacturer, eaves panels should have the ends turned down to prevent capillary action on the underside of the sheet. A metal flashing may also be installed to cover the exposed end of the insulation and metal liner when panel ends are visually exposed.
Site-assembled or built-up warm roof systems are also known as composite systems. They are not a true warm roof, as the ribs are typically not in contact with the insulation, but they have many of the same attributes as warm roofs.
The advantages of composite systems are that they offer longer runs without the need for roof laps or waterfall junctions, and when the time comes for the replacement of the outer weather-proofing roof sheet, the system allows for it to be done without disturbance to the operations within the building.
Acoustic boards can be laid within the system to increase sound absorption either from within the building or from outside. Installation of the under-liner sheets can make a building largely watertight allowing other trades to continue below while the roof is completed.
There are three main types.
- Bespoke systems that incorporate layers of material and insulation above the purlin.
- Proprietary systems that are built up by layer above the purlin, such systems can be sandwich-type or post and rail.
- Overlay systems that are used for re-roofs over existing roofing.
Composite systems typically incorporate a sealed vapour control layer under the insulating layer, and an absorbent roofing underlay under the top skin. They may be designed as closed systems, or ventilation may be introduced between the insulation and the top surface. The insulation material may be expanded foam, mineral wool, or fibreglass blanket. Top surfaces may be profiled metal or membrane.
Post and rail systems allow thicker insulation to be used, increasing thermal and fire performance.
Composite systems are normally laid layer by layer to form the desired system. Typically, they comprise a metal base layer to provide support for the insulation, which is overlaid by a vapour check layer, insulation, underlay, and the top roofing sheet.
Post and rail systems are often used for over-laying existing roofs in good, safe condition. Another form of overlay uses custom cut blocks as pan infills, over which is laid a continuous insulating layer. These forms of roof repair avoid the need for removal and replacement of an existing roof, allowing the building tenants’ operations to continue uninterrupted.
When installing composite systems, it is important that the vapour control layer is correctly installed and sealed to manufacturers requirements, and insulation is laid correctly without gaps. Bulk insulation must be able to loft up to its design thickness to achieve the design R-value.
Warm roofs can also be constructed by applying spray foam after installation.
Spray foam is typically polyurethane closed cell foam applied in thicknesses according to the insulation requirement. It can also be applied to walls, ceilings, and under floors. Spray foam may be applied to any roofing profile. It has a greater insulation value per millimetre than other insulation materials, so is particularly suitable for flat roofs and skillion roofs where there is limited air space.
Spray foam is non-absorbent (less than 1%) and has strong contact with all adjacent building elements. This makes it an effective vapour check, so internal moisture issues must be considered when using this or any other non-permeable system.
When sprayed foam is applied directly to the underside of profiled metal sheet roofing on a lined building, the ceiling space must be adequately ventilated by other means. (See 10 Internal Moisture.)
Installation with underlay.
Polyurethane Spray foam may typically be applied directly to any type of purpose-made bituminous or synthetic building wrap, including foil-backed, excluding polyethylene sheet which is not a suitable substrate as there is inadequate adhesion.
The typical procedure for application is:
1. Check the building to confirm that the wrap is not loose or floppy, is properly attached to the studs, and is not sagging between purlins.
2. Spray a “flash-coat” of Polyurethane Spray Foam over the building wrap or cladding contacting the timber or metal framing. Allow to set — it will take 5-10 minutes depending on the ambient conditions. The "Flash-coat" will tension the building wrap, give it some rigidity, and assist with the curing and adhesion of subsequent layers.
3. Spray the first pass of Polyurethane Spray Foam onto the flash-coat. Do not exceed 25-30 mm with this pass. This will render the building wrap/foam composite rigid and able to take the balance of the foam with no distortion.
4. Spray the second pass of Polyurethane Spray Foam to the desired thickness to achieve the required R-value (or up to a maximum of 100mm per pass).
