Key takeaways
- Fixing type, spacing and edge distance are product-specific, so the cladding manufacturer’s installation instructions govern what you can substitute on site.
- Clearances at the base of a wall, around openings and at horizontal junctions exist to let water drain and air move, and packing them with sealant defeats the purpose.
- Ground level and the finished floor level relationship determines how much of the wall is exposed to splash, so it must be resolved before the frame goes up.
- Dissimilar metals in fixings and flashings cause galvanic corrosion that typically appears well after practical completion, when the builder is still the first call.
- The condensation requirements in the NCC and the ABCB Condensation in Buildings handbook are relevant to cladding because a wall that cannot dry is a wall that will show it.
Cladding failures on residential work rarely trace back to the sheet itself. The product is usually the one the designer specified, delivered in good condition, installed by a trade that has done it many times. What fails is the interface: the fixing that was substituted because the specified one was not on the ute, the base clearance that was lost when the landscaper raised the ground level, the opening that was sealed hard because that is how it has always been done.
Fixings and clearances are the part of cladding work that nobody photographs and nobody inspects closely, because by the time anyone looks, they are covered. That is exactly why they are worth slowing down for. A wall that drains and dries will tolerate a lot of ordinary site conditions. A wall that cannot drain will eventually show it, and it will show it after practical completion, when the call comes to the builder.
This article deals narrowly with fixings, clearances and ground levels across cladding types. It is not a comparison of cladding materials and it does not attempt to reproduce any manufacturer’s installation instructions. It sets out how the requirements fit together so you can reason about a detail on a job that no article anticipated.
Why fixing type and spacing are product-specific, not trade convention
Every cladding product has a fixing schedule that has been tested and, in most cases, tied to the product’s compliance evidence. The type of fixing, the diameter, the length, the spacing along the support, the spacing between supports and the minimum edge distance are all part of that schedule. Change one and you have changed a system that was tested as a whole.
The reason this matters is not bureaucratic. Cladding is a diaphragm that has to resist wind pressure and suction, and it has to hold its own weight plus any insulation, sarking and framing tolerances that sit behind it. A screw at wider centres than specified might hold the sheet on a still day and let go in a storm event with the right combination of pressure and fatigue. The failure will be localised, often at a corner or an edge, and it will look like a product fault when it is a fixing fault.
Two habits cause most of the trouble. The first is substituting a fixing because the specified one is unavailable, without checking whether the substitute has the same corrosion protection, head type and load capacity. The second is treating edge distance as a suggestion. Fixings placed too close to the edge of a sheet or a batten can tear out under load, and the tear-out happens at the point where the wind pressure is highest.
The related detail work on steel and timber frames is worth reviewing before you set out cladding fixings, because the substrate condition determines whether the cladding fixing can do its job. The PointCPD articles on cold-formed steel framing fixing details and timber framing nail plate fixing schedules cover the frame side of that interface.
Corrosion protection and dissimilar metals
Cladding sits in the most aggressive part of the building envelope. It is exposed to wind-driven rain, salt in coastal areas, and constant wetting and drying. Fixings and flashings are small components with a high surface-area-to-volume ratio, so they corrode faster than the sheets they hold.
The mechanism that catches builders most often is galvanic corrosion. When two dissimilar metals are in contact in the presence of moisture, the less noble metal becomes the anode and corrodes preferentially. A stainless steel flashing fixed with a galvanised screw, or an aluminium sheet in direct contact with a mild steel bracket, sets up a cell that will quietly consume the smaller component. The joint looks fine at handover and shows staining or a loose fixing years later.
In coastal locations, the corrosion category is more severe and the specified coating or material class will reflect that. The practical rule is to fix and flash with materials in the same corrosion class as the sheet, and to use isolating tape or washers wherever the manufacturer requires them at a dissimilar metal interface. If you are unsure what the current requirement is for your location, check the manufacturer’s installation instructions and the corrosion section of the relevant Australian Standard, rather than relying on what was specified on the last job.
The mistake that costs the most. Raising the finished ground level after the cladding is on, so the base of the wall loses its clearance and sits in soil or paving. Water then wicks up behind the sheet, the bottom of the frame stays wet, and the repair involves removing cladding, replacing the bottom plate or bottom track, and redoing the landscaping that caused it.
Base clearances, ground level and the finished surface
The clearance at the base of a clad wall is there for two reasons: to keep the bottom of the sheet and the frame out of the splash zone, and to let the cavity or the back of the sheet drain and dry. The specific clearance is set by the manufacturer’s instructions and, where the cladding is part of a system with a drained cavity, by the design of that system. It is not a number to guess.
What matters on site is that the clearance is measured from the finished ground surface, not from the slab or the frame. This is where the sequencing goes wrong on residential jobs. The cladding is set out from the slab, the base clearance looks generous, and then the landscaper or the concreter brings the ground up to the finished level and the clearance disappears. On sloping sites the problem is worse, because the ground level at the low end of the wall can be well above the level at the high end.
The fix is procedural rather than technical. Set the finished ground level before you set out the cladding, and mark it on the frame at each corner. Where the finished level is not yet known, hold the base of the cladding up and detail the gap so it can be closed later without trapping water. Never let the gap be closed with soil, mulch, paving or a garden bed that sits against the sheet.
The same logic applies to the relationship between the finished floor level and the external ground level. The difference between them determines how much of the wall is in the splash zone and how the base of the wall is detailed. That relationship is fixed by the design, but it is verified on site, and it is verified before the frame is clad.
Clearances that drain versus clearances that trap
| Clearance that works | Clearance that fails |
|---|---|
| Base of wall held clear of the finished ground surface | Base of wall bedded into soil or paving so water wicks up behind the sheet |
| Open drained joint at the base of the cavity | Sealant run along the base to ‘keep the insects out’ |
| Head flashing with an upstand and a drip | Head flashing sealed hard to the sheet with no drip |
| Penetrations sealed and independently flashed | Penetrations relying on sealant alone |
| Openings detailed so water sheds outward | Openings packed solid with mortar or sealant |
How clearances actually drain: cavities, weepholes and open joints
A drained and ventilated cavity behind cladding is a managed air space. Water that gets past the outer sheet runs down the back of it, reaches the base, and leaves through an opening. Air moves through the same openings, which lets the cavity dry. Block any part of that path and the system stops working.
Sealant is the usual culprit. Running a bead of sealant along the base of a cavity to keep insects or draughts out closes the drain. The correct approach, where the manufacturer requires it, is an open drained joint or a purpose-made closure that maintains the opening. If vermin or insect screening is needed, it must be a product that still lets water and air through.
Weepholes and drained joints at the base of a wall are only useful if the cavity behind them is clear. Mortar droppings, offcuts, insulation batts pushed into the base and packaging left in the cavity all block the path. A cavity that is blocked at the base fills with water, and the water finds the path of least resistance, which is usually into the frame or through a penetration into the interior.
At the top of the wall, the head flashing does the same job in reverse. It needs an upstand against the sheet, a fall to the outside and a drip that clears the face of the cladding below. A head flashing that is sealed hard to the sheet with no drip will hold water against the fixing line and eventually stain or corrode it.
Openings, penetrations and horizontal junctions
Openings are where the cladding is cut, and cuts are where water gets in. Every window, door, meter box and penetration needs a flashing detail that sheds water outward, and the cladding around it needs the clearance to allow the flashing to work.
The common mistakes are consistent. Sealant is used as the primary weatherproofing rather than as a secondary defence, so the detail relies on a bead that will fail before the building does. The flashing is installed with no fall, or with a fall the wrong way. The cladding is cut tight to the opening with no allowance for movement, so the sheet cracks at the corner. And the flashing is fixed through in a way that punctures the upstand below the level that water can reach.
Horizontal junctions between cladding and a different material, or between cladding and a slab edge, need the same treatment: a flashing that laps correctly, a clearance that lets water out, and no reliance on sealant alone. Lap direction matters. Water runs downhill, so the upper element always laps over the lower one, and the flashing always tucks behind the element above and over the element below.
Penetrations for services are the ones most often left to the last trade on site. A pipe or cable that penetrates the cladding without an independent flashing will leak, and the leak will track along the fixing line before it shows inside. Detail the penetration as part of the cladding installation, not as a repair afterwards.
Sequence for setting out cladding fixings
- 1Confirm the product and the instructionsMatch the cladding product to the current manufacturer’s installation instructions before any fixing is ordered.
- 2Set out the frameLocate studs or girts and confirm the substrate is straight and within tolerance so fixings land in the middle of members.
- 3Establish the base and ground lineSet the finished ground level and the base clearance before the first sheet goes on.
- 4Fix to the specified patternFollow the specified spacing, edge distance and fixing type for the product and the wind classification.
- 5Detail openings and junctionsFlash, clear and drain every opening and horizontal junction as the cladding goes up, not afterwards.
- 6Inspect before lining or lock-upPhotograph the drainage path and clearances while they are still visible.
Condensation, drying and the wall’s ability to manage moisture
Cladding is the outer skin of a wall that has to manage moisture from several directions at once: rain from outside, water vapour from inside, and construction moisture trapped during the build. The condensation provisions in the NCC and the ABCB’s Condensation in Buildings handbook explain the principles behind the detailing that keeps a wall able to dry.
The relevant point for cladding fixings and clearances is that a wall which cannot dry will fail at its fixings. Moisture held against a fixing line accelerates corrosion and, in timber frames, creates the conditions for decay. That is why the clearances at the base and the drainage path through the cavity are not optional extras. They are the wall’s drying mechanism.
Two practical consequences follow. First, do not install a vapour barrier on the outside of a wall that is designed to dry outward, and do not install a vapour barrier on the inside of a wall that is designed to dry inward. The design determines which way the wall dries, and the cladding and sarking must match. Second, do not block the cavity at the top or the bottom. Ventilation at both ends is what drives the drying.
On NSW residential projects, the energy and thermal performance requirements that sit alongside these details are set through BASIX, and the cladding specification often forms part of how the design meets them. The guide to how NSW builder CPD works explains why these requirements are treated as core knowledge for licensed builders rather than specialist content.
Inspection points before the cladding is covered
The clearances and drainage details are only inspectable during installation. Once the cladding is on and the landscaping is done, you cannot see whether the base clearance was maintained or whether the cavity is clear. Build the inspection into the programme rather than trying to reconstruct it later.
Before sheeting, confirm the frame is straight, the substrate is within tolerance and the finished ground level is known. During installation, check that the fixing pattern matches the instructions, that edge distances are respected, and that flashings are lapped and fixed correctly. At the base, confirm the cavity is clear and the drainage opening is unobstructed. At the head, confirm the upstand, fall and drip are in place.
Photograph each of these stages with a tape or a level in the frame so the clearance is visible. If a dispute arises later, the photographs are the evidence that the detail was built as designed. If the detail was not built as designed, better to find out before the sheet goes on than after the owner moves in.
Worked example: a builder in western Sydney
A builder in western Sydney completes a two-storey dwelling with a lightweight cladding system over a drained cavity. The cladding is installed correctly, with the base clearance set from the slab. The finished ground level is not yet constructed because the landscaping is a separate contract.
Months later, the landscaper brings the ground up to the design level, which is higher than the level the builder assumed, and paves to within a short distance of the wall. The base clearance is gone. Water splashing off the paving sits against the base of the cladding and wicks into the cavity. The bottom of the frame stays wet through the winter.
The problem surfaces as a musty smell inside and staining at the base of the internal lining. The builder attends, finds the base of the wall wet, and the repair involves removing the bottom course of cladding, inspecting and likely replacing the bottom plate, reinstating the drainage detail at a higher level, and reworking the paving to restore the clearance. None of the trades did anything wrong in isolation. The failure was in the sequencing and in the assumption about finished levels.
The lesson is not to avoid lightweight cladding on sloping or landscaped sites. It is to fix the finished ground level before the cladding is set out, to record it on the frame, and to make the base detail adjustable so that a later change in ground level does not trap the wall. The same discipline applies to openings and penetrations: resolve the detail before the sheet goes on, not after.
What to carry into the next job
Treat the manufacturer’s installation instructions as the fixing schedule, not as a suggestion, and keep a copy on site. Confirm the corrosion class for the location and match fixings, flashings and accessories to it. Resolve the finished ground level before you set out the cladding, and mark it so the clearance is measured from the right surface. Keep the drainage path open at the base and the head, and never rely on sealant as the primary weatherproofing at an opening.
These are the details that carry the most risk and attract the least attention. They are also the ones that a licensed builder is expected to reason about, not just follow. If you want to work through the current requirements in a structured way, the PointCPD course catalogue includes the NSW builder CPD courses that cover cladding, waterproofing and durability, and you can start from the PointCPD home page.
Questions builders ask
Can I substitute a different cladding fixing if the specified one is not available?
Only if the substitute has been confirmed as equivalent for the product and the application. Fixing type, diameter, length, corrosion protection and head type all form part of the tested system, so a substitution needs to be checked against the manufacturer’s installation instructions rather than decided on site. If you cannot confirm equivalence, wait for the specified fixing.
How do I set the base clearance for cladding on a sloping site?
Measure the clearance from the finished ground surface at every point along the wall, not from the slab. On a sloping site that means the base of the cladding steps or is held high enough to maintain the clearance at the highest ground level. Mark the finished level on the frame at each corner before setting out.
Why can’t I seal the base of a drained cavity to keep insects out?
Because the opening at the base is the drain and the ventilation path for the cavity. Sealing it traps water and stops the wall drying, which accelerates corrosion at the fixings and can lead to decay in a timber frame. Where screening is required, use a closure that still allows water and air to pass.
What causes corrosion at cladding fixings when the sheets themselves look fine?
Fixings and flashings are small components with a high surface area relative to their volume, so they corrode faster than the sheets. Galvanic corrosion occurs where dissimilar metals are in contact in the presence of moisture. Match the corrosion class of fixings and flashings to the location and use isolating washers or tape where the manufacturer requires them.
When should I inspect the cladding clearances and drainage details?
During installation, before the cladding is covered and before the landscaping is built up against the wall. Once the sheet is on and the ground is finished, the base clearance and the cavity condition are no longer visible. Photograph the base, head and opening details with a tape or level in frame so the clearance is recorded.
Does a wall that cannot dry affect the cladding fixings?
Yes. Moisture held against the fixing line accelerates corrosion and, in timber frames, creates the conditions for decay. The clearances at the base and the drainage path through the cavity are the wall’s drying mechanism, which is why they are part of the condensation and durability requirements rather than optional detailing.
Sources
- Drone weight categories and requirements · Civil Aviation Safety Authority
- Drone weight categories and requirements · Civil Aviation Safety Authority
- BASIX · NSW Planning Portal
- Condensation in buildings handbook · Australian Building Codes Board
Published 25 July 2026. General information for builders, not legal, financial or engineering advice for a specific job. Check current requirements with the relevant regulator or standard before relying on them.
