Metal roof and wall cladding should be installed as described in this section to comply with the NZBC and to qualify manufacturers' warranties.
COP v24.12:Installation;
The roofing contractor or supervisor must inspect a set of consent drawings and specifications, before starting to install metal roof or wall cladding. Any decisions departing from it should be agreed on and written confirmation signed before work begins.
Minor changes should be recorded by the council on the consent application, major changes must be approved by the council before execution.
Where specific details are not drawn, the roofer and the main contractor should agree on the execution of these details before commencement.
The roofing contractor is required to have safety provisions in place that satisfy the HSW Act before work is commenced
The supporting structure should be inspected; the purlins and girts should be checked to see they are in a true plane and securely fixed, all trimming completed for penetrations, and any work by other trades is completed.
Where roof and wall cladding intersect with other materials, the sequencing of work and responsibilities for weatherproofing must be agreed upon with the main contractor prior to installation.
The profile must be suitable for the strength requirements of the building, and appropriate for the minimum pitch, and the material selected must be suitable for the environment and be compatible with adjacent building materials. See 4 Durability.
Aluminium requires special installation details to achieve durability. See 14.20 Fixing Aluminium Sheeting for more details.
Measuring should take place once sufficient structure is in place to enable accurate calculation of lengths required. It is beneficial to make more than one measurement of any run to identify discrepancies and avoid errors.
Cladding materials should be ordered with enough time to allow for manufacture and transport. Profile, thickness, colour, grade, and any requirements for labelling of bundles should all be clearly identified.
Do not mix products; different manufacturers use different paint formulations. Where different brands of pre-painted material are used on the same building, differences in colour, gloss, and weathering performance may appear immediately or over time.
Load safety and protection is primarily the driver’s responsibility.
Short sheets should be packed on top of longer ones, which should have end and edge protection to avoid cut-end damage to the sheets below them. Dunnage should be evenly spaced in vertical alignment. Bundles must be placed and secured to protect against damage from other materials.
For sheets that are exposed on the underside in situ, such as for unlined wall cladding applications, or have double-sided or fleece-lined coatings, protection must be given to prevent the dunnage from damaging the bottom sheet. This is normally achieved by the application of a short slip sheet with paper overlay.
On longer distances, extra protection or packaging may be required to protect the material from fretting during transport.
For longer lengths, when a long boom is required for off-loading, a suitable boom should accompany the load unless otherwise arranged.
Check the delivery to make sure you have the right product, delivered in prime condition. If there is any concern about the condition of the product, the supplier should be contacted before installation commences.
Ensure all components needed to complete the installation, including fasteners and accessories, are onsite before commencing installation.
Set out a flat area and supporting dunnage to ensure sheets will not be damaged by site debris.
When unloading by crane, ensure the lifting boom has a spreader bar and that tightening strops do not damage sheet laps. Slings or strops should be nylon with leather sleeves to prevent fraying or cutting and damaging slings. Single slings and chains should not be used to lift packs of cladding.
When unloading by hand, lift each sheet off the stack without sliding over under sheets, as that may cause damage to the paint.
The person receiving the roof is responsible for identifying a safe and convenient landing point for the load, in association with the main contractor. The mobile or truck mounted crane operator has the duty of declining any loading instruction which he deems unsafe. Under no conditions should the load be traversed directly above any person
Bundles or packs of roof cladding must remain banded when being lifted by a crane.
They must be placed adjacent to the portal frame and not mid-span on the purlins. Bundles must be placed so that their weight is spread over the entire area of the roof and should be positioned with the laps in the direction of laying.
Workers receiving a bundle of roof cladding on the roof must have sufficient mobility to avoid the load, and use tag lines to control the swinging of the load while it is out of reach.
Packs must be securely fixed to the structure.
Close stacked sheets may deteriorate quickly if water enters the pack. This happens because the metal exposed to moisture without air forms bulky, unstable, and loosely adherent, hygroscopic compounds. See 4.10.7 Crevice Corrosion/Wet Storage Stain.
Water can infiltrate deeply into a bundle of close-stacked sheets. The extent and severity of wet storage stain is usually proportional to the time the sheeting has been wet, however, the time to onset can be very variable, and occur more rapidly in warm conditions.
Sheets can be dried by filleting sheets or cross-stacking them on a slope to allow water to drain and air to circulate between them. Only use a dry, well-ventilated environment for long-term storage.
A patchy visual appearance of the paint can also result from wet stack storage of pre-painted steel products. This is known as blooming.
Blooming results from water swelling the paint and flattening or suppressing gloss components. The gloss distortion is typically temporary and will dissipate with time, and exposure to heat/sunlight. This can be demonstrated by the application of boiling water to an affected surface bringing the appearance back to normal
Installation of roofs presents many hazards including laceration, electrocution, puncture, and falling from a height. Prudent PPE and installation practices must be employed, and the guidelines of Worksafe: Working at Height in New Zealand must be followed. See 13 Safety
Don’t handle any roofing products roughly or carelessly; roofing products perform best when handled correctly.
- Don’t drag or slide new sheets over other sheets or rough surfaces.
- All equipment and materials taken on to the roof should be clean and care taken to prevent damaging the surface.
It must not be assumed that it is safe or permissible to stand on any roof structure or roof cladding.
The manufacturer of the roof sheeting must provide technical literature stating the point load limitations of the profile. The information must indicate the positions on the sheet where persons may safely walk or stand without causing damage or, alternatively, indicate the necessity to provide temporary walkways.
For roofs tested in accordance with MRM testing standards see 17.1 Metal Cladding Testing, a Restricted Access roof will withstand a 100 kg point load applied to the rib or over two pans, and an Unrestricted Access roof will withstand a 100 kg point load to a single rib at mid span. It must be taken into account that a worker laden with tools may weigh more than 100 kg, and impact loads can also contribute to exceeding this limit.
When access to the roof is necessary after construction, it is best practice to in the pan of the profile when walking up the roof, and follow purlin lines when traversing roofs.
If ribs are too close together, so workers cannot place their feet in the pan, their weight must be spread evenly over at least two ribs when walking up the roof.
Translucent sheeting must not be walked on unless it is designed specifically for that purpose.
- Anyone walking on the roof should wear flat rubber-soled footwear to prevent marking.
- Put an old mat or piece of carpet at the base of the ladder so that shoes can be cleaned before going up on the roof, or dirty shoes should be removed and replaced at base of the ladder.
- Smooth soled or open tread pattern shoes with good grip on smooth surfaces should be worn when working on a roof. Avoid the closely ribbed type which will carry swarf and other objects.
Strippable film is a clear pressure sensitive polyethylene plastic film that is applied to some roofing products to assist in protecting the surface from damage and scratching during forming, transportation, handling, storage, and erection.
Strippable film is designed to provide some protection to the product before and during installation on the building. It is not designed to protect against corrosion, humidity, or chemicals.
Strippable film must be removed before prolonged exposure to sunlight, as that may make it extremely difficult to remove. Prolonged exposure and wet conditions can also cause the film adhesive to whiten and breakdown, leaving residue on the painted surface when the film is removed. Once removed from the sheet for installation, strippable film must be collected and removed from the site.
Product with film applied must be stored at temperatures of less than 50°C and out of direct sunlight to avoid prolonged UV exposure.
The product needs to be kept dry to prevent moisture ingress between the film and the painted surface. In the long term moisture ingress may cause issues to the painted surface; and in the shorter term cause the film adhesive to whiten and breakdown, leaving residue on the painted surface when the film is removed.
Sheets should not be laid with a double lap, as this can cause accelerated corrosion in the lap area. If the remaining area of a roof or wall section to be covered is less than a standard sheet width, the sheet should be cut lengthwise to fit the gap.
Similarly, when replacing a roof without removing existing flashings, for example apron or chimney flashings behind cladding, the area of the retained flashing should be reduced by cutting back to the minimum practically achievable.
If a roof sheet lap requires extra protection, for instance when over the apex of a barrel curved roof where pitch is less than the minimum stipulated for the product, laps should be sealed rather than double-lapped. Lap tape is preferred over gunned sealant for this purpose, as it is less likely to become displaced while positioning the sheet.
Underlay support if required must be installed before laying of roof sheets commences, and underlay may be cut to length before use.
Laying should commence considering building sequence, prevailing weather, and architectural details. It is not necessary to face laps away from prevailing wind direction as roofs must be designed to withstand weather from any quarter. On critical jobs or when using curved sheets, it is advisable that side laps face away from the line of sight.
Sheets should be laid square to the nearest architectural feature, and regularly checked to correct any misalignment of sheet or squareness of structure. Laying out of square will result in saw-toothing of the eaves line. Saw-toothing of greater than 5 mm may be trimmed back to form a straight line.
Black lead pencils must never be used for marking aluminium/zinc, and unpainted or pre-painted steel products. The carbon in the pencil promotes corrosion which will etch the surface of the material, leaving a permanent mark. Use a pencil of any colour other than black, a marker pen, or crayon.
Cut pre-painted steel material with care to avoid marring the high-quality finish. Cut by shear only — use nibblers or hand shears. Friction blades and high-speed saw blades must not be used on metal cladding. These blades will damage both the metallic coating and the pre-painted steel surface by creating excessive heat, and generate large amounts of hot swarf which will get embedded into the coating surface
All debris must be swept off the job at the end of each day. Prevention of swarf damage is far easier than its cure. (See 14.19.4.1 Preventing Swarf Damage).
The length of the overhang of sheeting into a gutter or spouting depends on the pitch of the roof and the site exposure to wind and rain.
The recommended minimum overhang for roof sheets is 50 mm measured on the rake. When the ends are not baffled by spouting, the recommended minimum is 70 mm.
14.11A Minimum Overhang14.11A Minimum Overhang
Underlay must not overhang the fascia by more than 20 mm or, if eaves flashings are used, terminate on the upper side of the flashing. Do not drape underlay into the gutter.
- Soldering cannot be used on aluminium-zinc materials; use only neutral cure silicone rubber or MS polymer sealants.
- Pre-align the pieces to be joined and pre-drill if possible.
- Thoroughly clean off surplus sealant and swarf using a dry, lint-free cloth or plastic scraper.
- Apply two beads of sealant close to each edge of the joint.
- Align pieces together and fasten with rivets at 50 mm centres.
End laps in profiled metal roofing should be avoided where possible. When unavoidable, the end lap of should be sealed with a double bead of sealant as in the illustration below. Alternatively, self- adhesive closed cell tape can be used in the same position.
Side laps should be fitted evenly and snugly without excessive gaps or tension. Sheets exhibiting edge wave should be reported to the supplier immediately. Where a sheet width exceeds the distance to the next architectural feature, it should be slit to width; not given multiple overlaps to decrease its effective cover width.
The durability of fasteners should equal or exceed that of the material being fastened, and the fastener metal or coating must be compatible with the cladding material if in contact. Fasteners used pre-painted steel products should be factory colour matched before installation.
The traditional New Zealand roof fastener was until 1980 the "Lead Head", a flat-headed smooth shank steel nail with a lead head cast on it. Lead heads often 'backed out' causing leaks, the shanks were prone to corrosion, and lead is incompatible with modern metallic coatings.
Spiral Shank nail fasteners have a galvanised shank, and the spiral shank has over twice the withdrawal resistance of a smooth shanked nail. They are however still prone to backing out, and the under-head seal is not as robust as the neoprene seals used on modern roofing screws.
The COP recommends using screws rather than driven fasteners, in all cases.
Screw fasteners should be long enough to give adequate penetration into the supporting structure. Generally, 30 mm embedment is required for screws into timber or three threads engagement for screws into steel. Refer to roofing manufacturers for specific recommendations.
Fasteners should be:
- a minimum of Class 4 for Severe Environments,
- Class 5 for Very Severe Environments,
- manufactured and coated with materials compatible with the material being fastened, and
- fitted with low-carbon, non-conducting sealing washers.
Profiled washers should have an EPDM sealing washer.
Screw fasteners are identified by their length, gauge pitch (threads per inch) and their drill point. The drill point may be type 17 for driving into timber or drill point for driving into steel. Reduced diameter drill points, which can be used for either function, are also available.
Secret-fixed roofs will be attached to the primary structure by a proprietary clip that is screwed or nailed to the purlins. These profiles offer the advantages of fewer penetrations through the cladding, and thermal expansion is unimpeded.
Clip and bracket fasteners can be purpose made to provide the same attributes to most flashings.
Rivets should have a minimum diameter of 4 mm.
Use aluminium rivets for galvanised sheets and aluminium/zinc-coated steel products; monel rivets are incompatible with aluminium and zinc products.
Sealed rivets are preferred over unsealed rivets, as they do not require adding sealant on the face to achieve weatherproofing.
14.13.4A Rivet Setting
Blind rivets are placed through a pre-drilled hole then are set by rivet tool withdrawing the mandrel. This expands the rivet pin, clamping the material between the rivet pin and the rivet head. The pin eventually snaps free.
The correct depth setting on a screw gun is provided either by the depth gauge or by a clutch torque adjustment, and an adjustment should be made every time a different screw or material thickness is to be drilled. Resilient washers under fastener heads will only seal properly with the right adjustment.
Experienced operators can, in most instances, drive screws correctly by using a variable speed screw gun; however, a depth set gun will give more consistent results.
Type 17 screws driven into timber will 'part' the fibres rather than cutting them which provides a self-locking action against withdrawal. Screws driven completely through timber will, therefore, not have the same pull-out resistance as screws with embedded tips.
Impact drivers and poorly fitting nut drivers can both damage the protective coating on the screw head which will affect durability. It is the roofer’s responsibility to ensure the method of installing screws does not cause damage.
Screw points, method of driving, and thread design all have an impact on pull-out capacity; so in critical situations, the specific screw and method of installation must be specified.
Fasteners should be of grade and type suitable for the application, installed at spacings required by design loads and manufacturer’s recommendations.
On buildings constructed to NZS 3604, a consistent fixing pattern should be used on all fastener rows; for other buildings, higher fastener density may be required around the periphery. All purlins must be fastened to so that they each contribute to resisting uplift loads. See 3.9 Fastener Requirements and Overhangs.
Rivets on flashings should be placed at 50 mm centres.
Roof fasteners should be placed at the crest of the profile. Wall cladding fasteners can be placed at the crest or the pan. Pan fixing of wall cladding is more popular as the screw lines are less visible.
N.B. The pullover design values established by testing for pan fixing are more than twice those for crest fixing.
Fasteners should be seated snugly to give a good seal, without distorting the roofing profile. Any “pigtails” created by the drilling process must be removed before seating the screw.
All roofing and cladding are subject to expansion and contraction due to temperature extremes. This is particularly evident with darker colours and long spans where the expansion may be as much as 8 mm for a 10 m sheet. Screws fitted with profiled washers to allow for thermal expansion must be installed centrally through a 9 mm diameter pre-drilled hole in the roof sheeting.
On most pierce fixed roofs, mode of failure is likely to be pull-over. Where profiled load spreading washers are required to eliminate this, it is important that the specified washer is used. When fastening to light gauge steel purlins, thread strip out may be the lower failure point. The pull-out failure point is very dependent on drill point, thread shape, and pitch; it is essential in such cases to use a correctly specified fastener.
Stop-ends are required at the upper end of all roofing sheets, on horizontal metal wall cladding and at the lower edge of penetrations
Stop-ends for trapezoidal profiles are of two types, i.e. 'dog-eared' or 'pull-up'.
Stop-ending tools should be in good condition so that they do not mark the coating. This is particularly important when using pre-painted material.
Stop ending can cause distortion of the pan adjacent to the turn-up, which can cause contact and mark the turndown of the cover flashing onto the pan of the cladding. This can be avoided by technique and experiment, often standing in the pan adjacent to the end being stopped will prevent the pan from becoming convex at this point.
14.16A Dog-eared Stop-ends
A 'dog-eared' or full stopend is made by cutting the rib back to the height of the profile so the material can be dressed and “wrapped around” 90°. It is not possible to dog-ear stop-end many profiles because of the shape of their rib.
To create dog-eared stop-ends:
- Slit all ribs to a length equivalent to their height.
- Cut away the tops of the ribs at a slight upwards angle and remove.
- Insert turn-up tool to full depth and turn up more than right angles.
- Knock dog's ears flat on a stop-end tool as shown.
- Ensure tray is lying flat
The rib height should be added to the sheet length when the material
is ordered to provide an allowance for a full stop-end.
is ordered to provide an allowance for a full stop-end.
14.16B Pull-up Stopends
A 'pull-up' stop-end is not cut back but pulled up to the maximum allowable height without tearing the metal. No extra material allowance is required for a 'pull-up' stop-end.
14.16C Corrugate Stop-ends
Stop-ends for corrugate should be pulled up to the full height of the profile, and on low pitches at exposed sites, additional weathering may be provided by the use of filler blocks. See 8.8 Profile Closures.
All roof cladding with a pitch of less than 8° must be provided with turn-downs after the roof is fixed, using special tools to ensure water flows directly into the gutter.
Where profiles that prevent turning down the pan (such as deep corrugated) are fixed at pitches of less than 8°, an 8.5.5.4 Eaves Flashing must be installed.
14.17A Profile Turndown
Providing a profile with a downturn will provide a positive drip edge and minimise the amount of sediment build-up at the gutter line.
Distortion should be avoided because it causes ponding and the collection of dirt, which in turn causes corrosion.
The periphery of all roof planes should be sealed with a flashing.
Longitudinal flashings must cover one or two crests according to requirements. There should be a gap between the downturn and the adjacent rib to prevent capillary action and to allow for pressure equalisation. Both vertical and horizontal faces of the flashing should be fastened to other cladding or preferably, through the cladding to the structure.
Transverse flashings may be notched over the ribs of the profile, or for lower trapezoidal profiles or corrugate they can be fitted with a soft edging which is dressed into the pan of the profile. All soft edging must be colour matched to the roof before installation. Soft edging can be solid aluminium, solidly backed, or perforated to allow ventilation. The leading edge of transverse flashings must be through fastened to the primary structure, not riveted to the cladding.
Excessive downforce on a rib or corrugate crest can cause a compression fold, or “ding” in the apex of the crest.
Most roofs designed to Restricted Access criteria will incur some damage during installation or by subsequent traffic. If this is unacceptable, roofs should be designed to Unrestricted Access criteria and roof access and usage by other trades must be strongly managed and supervised.
A small ding in a sheet will not normally cause any structural problems and may be aesthetically acceptable, however deeper dings can cause cracking of the sheet and lead to leaks.
To restore a damaged rib load capability to the original levels all damage must be repaired with a cap flashing.
For aesthetic reasons, any damage may be unacceptable. However, if the roof cladding is not visible, ribs can be repaired by using a sealed and riveted saddle cap.
It is technically acceptable to have two dings or creases on one sheet within one purlin spacing, providing two adjacent ribs are not damaged. Any greater level of damage requires the sheets to be replaced, and the person who causes the damage must report it and be responsible for its repair.
Ponding will create a prolonged time of wetness and increased build-up of debris. Ponding will detract from a coated steel product’s life and will invalidate the product warranty.
The installation of penetrations must be done in such a way that they do not cause ponding. See External Moisture: Penetrations.
On low pitched roofs, careless or excessive foot traffic may cause rib damage and localised ponding. This can be minimised by installing temporary protection in critical areas, such as entry points, where the roof is accessed by other trades, or there is a step-down in the roof. It is the main contractor’s responsibility to ensure that other trades do not damage the roof.
It is recommended to design to Unrestricted Access-criteria or better if roofs are highly visible or need to be regularly accessed by maintenance personnel.
Gutters must be installed with adequate fall to ensure water is transported to appropriately located downpipes. Fall and joints should be constructed so that water does not pond to a depth of more than 5 mm. Regular gutter cleaning and maintenance is required to remove leaves and other debris that may restrict water flow to downpipes. Vertical downpipes are parrallel to wall and adjacent vertical references such as window jambs.
A gutter protection system (or any other product) that entraps debris or water between itself and any steel product surfaces, restricting coated steel’s ability to dry, is not recommended and is an exclusion in the product warranty.
Swarf is the term given to the metal debris arising from cutting or piercing operations when using friction saws, drills, or other tools on roofing and cladding products. In this context, swarf may also include any other discarded steel objects such as rivet shanks, nails, screws, and nuts which may come into contact with cladding products.
Steel swarf particles left on the surface will corrode and cause rust stains which will detract from the finished appearance of a project. These stains are often mistaken for early deterioration of the roofing and cladding itself. See 4.14 Swarf Staining and Cut Edge Corrosion.
Cutting
- Cut only by shear; power shears or hand snips produce the least amount of debris.
- Power nibblers give a clean cut but generate debris which if left is prone to corrosion.
- Do not use metal friction blades or reciprocating saws which produce fine hot particles which can embed deeply into the coating surface and corrode rapidly.
If metal grinding is taking place near the surface of an installed or uninstalled roof, careful masking of nearby coated steel surfaces must be executed.
Clean-up
Swarf should be swept or hosed from the job progressively and certainly no less than at the end of each day. Swarf that has become stuck must be removed carefully, avoiding action which is likely to remove or change the appearance of the paint or metal coatings.
When sweeping or hosing into a gutter, clean out the gutter before leaving the job to prevent premature corrosion. On completion of the job, give a final wash or sweep down.
If the coating is severely damaged by swarf corrosion, the area should be painted or replaced. The whole visible area should be repaired, as air drying paints weather more rapidly and in a different manner to pre-painted roofing and cladding products. If swarf particles are painted over, rust bleed-through is likely to occur.
A common cause of swarf complaints arises because other trades have used grinding equipment in the vicinity of a newly completed roof. Wind carried swarf can contaminate large areas some distance from the cutting site. Main contractors should be aware of the likelihood of such damage, and project planning should include scheduling of all cutting or grinding work to be completed before laying the roof cladding.
Colour match paint is designed for matching accessories to the pre-painted material; it is not designed for repairing marks or blemishes. The term touch-up paint should never be used. Fasteners and accessories requiring colour matching should be painted before installation.
Air-dried paints used to disguise marks weather at a rate different from that of pre-painted material, sometimes dramatically so, and will often become more apparent than the mark they are intended to disguise. Minor scratches are best left alone, and they will not affect the performance of the pre-painted product due to the self-healing qualities of the primer and metallic coating. They become less evident as the coating weathers.
Minor scratches may be described as scratches that do not extend to the metallic coating, are less than 3 mm in width, and are not visually noticeable from a distance of 3 m. This characterisation will, however, vary with the concentration of the scratches, and the visibility of the area affected.
Extensive coating damage to any pre-painted steel product can only be rectified by replacement or repainting of the affected sheets.
Profiled metal roofing and wall cladding are readily paintable using good quality primers and water-based acrylic topcoats. Metallic coated roofs can be painted immediately after installation; however, dirt, grease, and any loose materials must be cleaned off, so the surface is clean and dry before applying the first coat.
An effective method for painting metallic coated roofing is to apply a good quality galvanised iron primer and two water-based acrylic topcoats, following the manufacturer’s recommendations.
Pre-painted products can be painted after exposure to weather. Normally, 6–12 months of exposure is required to achieve surface modification of the surface to allow the new coating to adhere.
Edge laps of unpainted metallic coated sheets steel do not require lap priming.
Sunscreen containing titanium dioxide or zinc oxide can accelerate the degradation of organic materials including auto finishes and pre-painted cladding surfaces. This damage is irreparable, so prevention of its occurrence is the only defence. For more information contact the material supplier.
Aluminium is a naturally durable material with proven performance over a long period.
Most metals compatible with Galvanised and Aluminium/Zinc coatings are compatible with aluminium. However, to acquire the required fastener durability, use aluminium or stainless screws rather than painted steel screws.
Aluminium has approximately twice the thermal expansion of steel, therefore, expansion provisions must be executed as for steel of twice the length.
Being soft and frequently requiring oversize holes for expansion, aluminium is typically fastened with fasteners equipped with load spreading washers, as is reflected in published span tables. Installers must adhere to published fastening systems to meet design load/span expectations.
Painted aluminium products perform differently than uncoated aluminium as the paint coating affects reactions with the atmosphere, and reduces the aluminium surface area that can be sacrificed to defend against localised corrosion.
Pit corrosion can result from damage to the paint coating and exposure to corrosive substances. It is necessary to protect against wet contact with concrete, treated timber, steel, stainless steel, and butyl rubber.
- The front edge of the spouting or gutter must be higher than the crest of the roofing profile.
- Eaves flashings of painted or unpainted aluminium must be used. Underlay should terminate on the top of the eaves flashing.
- When re-roofing with aluminium, the existing support members must be inspected to ensure all staples, wire netting, nails, or other materials likely to damage the aluminium have been removed.
- Galvanised netting or mesh must not be in contact with the underside of aluminium roofs. If present, it must be separated by a 5 mm non-compressible barrier of inert non-absorbent, non-reactive material. Alternatively, self-supporting underlays may be used. Plastic strapping can be used for supporting underlays, stapled with stainless steel staples to the vertical face of the purlins.
- In a wet environment, aluminium must be separated from a corrosive surface such as concrete, butyl rubber, or CCA treated timber by using a 5 mm rigid strip of an inert non-absorbent material, an open woven geotextile layer, or PVC netting. Plastic coated steel netting is not recommended under aluminium sheeting.
- The design of the ceiling cavity must prevent the saturation of support members from internal or ground moisture. (See 10 Internal Moisture.)
- All screws should be fitted with a profiled or bonded washer. Fixing screws shall be aluminium or Grade 304 stainless steel. Stainless steel screws must be fitted centrally through pre-drilled oversized holes (9 mm) for roofing and walls, regardless of sheet length.
- For sheet lengths over 10 m, the capacity to allow for thermal expansion must be in accordance with the tables in 7.3 Thermal Expansion And Contraction.
The roofing contractor should notify the main contractor, architects or owner when he has completed the scheduled work. It is prudent if he records any damage to the sheets (or lack thereof) at this point, particularly if subsequent trades accessing the roof. Damage of any sort caused by other trades is not the responsibility of the roofer.
All gutters, valleys, roof channels and the roof cladding should be left clean and free from debris on completion of the work, and any roofing related debris on site should be safely removed.
14.22A Hand Seamers
Hand Seamers are used to hand fold small flashings, by progressively working along the edge of a sheet.
14.22B Seaming Pliers
Various shapes of seaming pliers may be required to execute complex sheet metal work, particularly with standing seam roofs.
14.22C Crimping Tools
These can be used to form a small end in downpipes, or by reducing the length of a down-turn on a flashing to cause a curve in the adjacent surface.
14.22D Shears (Straight and Curved)
Shears are normally purchased in left-hand and right-hand sets. Both may be required to cut through complex shapes. They may be solid or articulated (“aviation snips”)
14.22F Portable Folding Machine
Portable folding machines are useful for onsite sheetmetal work.
14.22H Joint Sealing by Hand Seaming
All metal joints that are to be sealed should be mechanically joined. Seaming is one acceptable method of joining two pieces of metal.
The two pieces are folded so each hooks into the other and then they are locked together by the means of a hand seamer or groover.
The material allowance depends on the hook dimension, but it is usually 6 mm. That means the extra allowance for the is 18 mm, because there are four thicknesses of material.
This type of seam can be used on a flat surface or round surface.
14.22I Setting Hammer
A nylon faced hammer can be used to reduce damage when dressing flashings.
