Flat Roof in NSW?
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Typical Flat Roof Waterproofing Costs NSW
Torch on membrane, per m2$90 - $180
Liquid applied membrane, per m2$70 - $160
Single ply sheet system, per m2$100 - $200
Localised repair$600 - $6,000
Fall correction screed, per m2$60 - $150
New outlet or overflow$400 - $1,500
Typical small roof, stripped and redone$8,000 - $25,000
Roof inspection and report$400 - $1,200
Figures on this page are indicative 2026 NSW estimates only and vary with roof area and geometry, the number of penetrations and upstands, substrate condition and whether the existing membrane is stripped or overlaid, insulation and fall correction, access and height, outlet and flashing work, and any structural repair found once the old surface is removed. Quotes should always be obtained for your specific property. Building, licensing, work health and safety and consumer protection requirements are set by legislation, the National Construction Code and Australian Standards and are periodically updated, so confirm the current position with the relevant authority and your contractor before relying on any figure.
Flat Roof Waterproofing Services NSW 2026 - Get Quotes
A flat roof is never actually flat, and the ones that fail early are the ones built as though it should be. Every flat roof needs a fall toward its outlets so water leaves rather than sits, and where that fall is missing or reversed, water ponds and the membrane underneath ages several times faster than the rest of the roof. Standing water is the single best predictor of how long a membrane will last. Two roofs with identical systems and identical installers can differ by fifteen years on that alone. Before comparing quotes on membrane type or price per square metre, go up after rain and see where the water goes. Two other things are worth settling before you compare prices. Ask whether the job is an overlay or a full strip and what evidence that decision rests on, because an overlay traps whatever moisture is already in the build up. And read the warranty exclusions rather than the headline term, since many membrane warranties exclude ponding water outright and a roof that holds water may carry no effective cover at all. Post your job on The Quote Yard to reach New South Wales membrane specialists.
At a Glance - Membrane Systems Compared
| System | Cost per m2 | Typical Life | Strength | Weakness |
|---|---|---|---|---|
| Torch on bitumen | $90 - $180 | 15 - 25 years | Robust, proven | Open flame, seams |
| Liquid applied | $70 - $160 | 10 - 20 years | No seams, complex shapes | Thickness depends on application |
| Single ply sheet | $100 - $200 | 20 - 30 years | Consistent thickness | Welded seams, detailing |
| Overlay on sound existing | Lower | Shorter than new | Avoids strip cost | Hides what is beneath |
| Localised repair | $600 - $6,000 | Buys time | Cheap now | Rarely the last one |
| Metal deck replacement | Higher | Long | No membrane at all | Needs adequate pitch |
Ponding Water Is What Kills Flat Roofs
Every membrane system has a stated design life, and that figure assumes water drains off the roof rather than standing on it.
Standing water attacks a membrane in several ways at once. It keeps the surface permanently wet, which accelerates chemical breakdown in bitumen and softens some liquid systems. It concentrates ultraviolet damage at the waterline where wet meets dry. It holds debris and organic matter that traps moisture and encourages growth. It adds weight, and a pond a hundred millimetres deep across a modest area weighs a great deal more than most owners assume. And when it freezes, which happens on winter mornings across the Blue Mountains, Southern Highlands and Central Tablelands, it expands and works at any weakness it finds.
The practical consequence is that fall matters more than membrane choice. A roof with adequate fall to well placed outlets will get the upper end of a membrane's stated life. A roof where water sits for days after every storm will fail well before the lower end, whatever system was laid and whoever laid it. This is why fall correction at $60 to $150 a square metre belongs in the conversation even though it adds cost, and why an owner replacing a membrane without asking why the last one failed early is likely to repeat the outcome. Go up two days after heavy rain and look for dark staining, silt lines or standing water, because those marks tell you what any inspection will confirm. Roof inspections sit at roof inspection cost.
Falls, Outlets and Where Water Actually Goes
A flat roof needs a fall toward its outlets so water leaves rather than sits on the surface. That fall is the single biggest determinant of how long a membrane lasts. Falls are created either by the structure itself or by a screed laid over it. Fall correction belongs in the original scope, not deferred.
Screed correction costs $60 to $150 a square metre. Outlets placed at high points instead of low points are a common and expensive design error. Water then gathers away from the drain instead of toward it. A membrane over an uncorrected fall repeats the last failure.
Overflow provisions matter because a blocked outlet on a parapeted roof turns the roof into a shallow tank. Overflow provisions sit at roof and gutter plumbing. Deflection in the structure under load can flatten a fall that was adequate on paper. Older timber framed roofs are especially prone to that. A membrane laid over an uncorrected fall repeats whatever failed last time.
Silt lines and dark staining show where water has been sitting. Condition reports sit at building inspection. Ask any contractor what they intend to do about fall before discussing membrane brands. A new membrane over an unchanged fall problem repeats the failure. Silt lines and dark staining record where water has been sitting.
| Issue | What It Causes | Remedy |
|---|---|---|
| Inadequate fall | Ponding across the surface | Screed correction |
| Outlet at a high point | Water gathers elsewhere | Relocate or add outlets |
| Blocked outlet, no overflow | Roof holds water | Install overflow provision |
| Structural deflection | Fall flattens over time | Structural assessment |
| Debris accumulation | Holds moisture, blocks drains | Regular clearing |
| Reversed fall at an edge | Water runs to the wrong place | Rebuild that section |
Choosing Between Membrane Systems
Torch on bitumen at $90 to $180 a square metre is the established system on Australian flat roofs. Sheets are bonded with an open flame and lapped at the seams. It is robust and well proven, and its weak points are the seams and the hot work involved. Upstand height is the number to ask about at a threshold.
Fire safety procedures matter a great deal on an occupied building. Liquid applied membranes at $70 to $160 cure into a continuous film and handle complex shapes without joins. Penetrations and upstands become much simpler to detail properly. Penetrations get counted and priced on a proper quote.
Their weakness is that film thickness depends entirely on how generously the product was applied. A thin coat looks identical to a correctly applied one. Single ply sheet systems at $100 to $200 offer factory consistent thickness and long service life. Seams are heat welded together instead of simply being lapped. Overflow provisions matter most on roofs enclosed by a parapet.
Where a roof has enough pitch, replacing it with metal deck removes the membrane question entirely. Pitched roof options sit at roofing services. Systems must be compatible with the substrate below and any insulation used. Replacing the roof outright sits at roof replacement cost. Two layer build ups perform differently from single layer ones.
| System | Suits | Ask About |
|---|---|---|
| Torch on bitumen | Large simple areas | Hot work safety procedure |
| Liquid applied | Complex shapes, many penetrations | Coat count and spread rate |
| Single ply sheet | Long life, larger roofs | Seam welding method |
| Insulated warm roof build up | Habitable space below | Condensation risk |
| Overlay system | Sound existing substrate | What is underneath |
| Metal deck conversion | Where pitch allows | Structural implications |
Leaks Start at the Details, Not in the Middle
Membranes rarely fail across an open field of roof, and an owner comparing quotes on price per square metre is comparing the part least likely to cause a problem.
The failure points are consistent across every system. Upstands where the membrane turns up a parapet or wall need adequate height and a proper termination at the top, because a membrane finished too low lets water behind it during driving rain. Penetrations for vent pipes, air conditioning units, aerials, solar mounting feet and cable entries each need individual detailing, and a roof with twenty penetrations carries twenty potential leaks. Outlets need the membrane dressed into them rather than finished near them. Movement joints have to be carried through the membrane and not covered over. Changes of direction at internal corners concentrate stress. Door thresholds onto a roof terrace are a recurring weak point because the level needed for access conflicts with the upstand height needed for waterproofing. Two things follow for an owner. A quote that itemises penetrations, upstands and terminations is describing the work that matters, where one quoting only an area rate is not. And where solar panels or plant are being added to an existing membrane, the mounting method needs settling before anybody drills, because penetrating a sound membrane carelessly is a common way to ruin one. Flashing work sits at roof flashing repair cost.
Penetrations, Upstands and Terminations
Upstands where a membrane turns up a parapet or wall need adequate height and a sealed termination at the top. Finishing too low lets driving rain get behind it. Every penetration is a potential leak, and a roof carrying vents, air conditioning plant, aerials and solar feet has many. Moisture testing settles the overlay question at modest cost.
Each one needs detailing individually rather than generally. Outlets need the membrane dressed down into them rather than stopped nearby. That junction is where a great many leaks actually begin. Existing layers add weight the structure may not have.
Movement joints must carry through the membrane instead of be covered over. Covering a movement joint simply relocates the tear. Door thresholds onto a roof terrace conflict with upstand heights, since access wants a low level and waterproofing wants a high one. Trafficable roof areas sit at balcony waterproofing and repair. Accredited applicator status is what many system warranties require.
Adding solar or plant to a sound membrane needs the mounting method settled before anybody drills. Supporting structure sits at carpentry services. Box gutters within a flat roof have their own requirements and failure modes. Those are covered at box gutter repairs and maintenance. Core sampling through the build up is inexpensive against the consequence.
Overlay or Strip It Back
An overlay lays a new membrane over the existing one, avoiding strip and disposal costs. It works where the substrate beneath is genuinely sound. The risk is that an overlay hides whatever is underneath, including trapped moisture and deteriorated decking. The warranty exclusions matter far more than the headline term.
Any trapped moisture then has nowhere to go. Wet insulation under an old membrane will keep the new one damp from below and shorten its life considerably. Core samples taken through the build up settle the question. Product cover and workmanship cover are two separate documents.
Multiple existing layers add weight and eventually exceed what the structure was designed for. Ask how many layers have already been laid up there. A full strip reveals the substrate and allows falls to be corrected properly. Repairing a concrete deck beneath sits at concrete repair. A walkway keeps foot traffic off the membrane where a roof is used.
Stripping also exposes structural repairs that were invisible beforehand, which is where budgets move. Chasing an active leak sits at roof leak repairs. Ask for moisture testing before accepting an overlay recommendation. Testing is inexpensive relative to the consequence of guessing. Surface temperatures on a dark membrane run well above ambient in summer.
| Factor | Favours Overlay | Favours Full Strip |
|---|---|---|
| Substrate condition | Dry and sound | Moisture detected |
| Existing layers | One only | Two or more |
| Falls | Already adequate | Need correcting |
| Structural load | Capacity available | Already near limit |
| Budget | Constrained now | Whole life view |
| Warranty wanted | Shorter accepted | Full term sought |
What AS 4654 Sets Out
External above ground waterproofing in Australia is governed by AS 4654, which comes in two parts covering materials and design and installation, and the National Construction Code references it. An owner does not need to read the standard, though knowing what it addresses makes quotes easier to interrogate. It deals with minimum falls so water drains rather than ponds. It sets requirements for upstand heights at parapets, walls and thresholds, which is why a contractor proposing to finish a membrane low at a doorway should be asked how that complies. It covers termination and flashing of membrane edges. It addresses the treatment of penetrations and outlets. It deals with substrate preparation and compatibility between membrane, primer and substrate. And it covers movement joints and where they must be carried through. Two practical points follow. A quote referencing AS 4654 is not automatically better, but a contractor who cannot say how the detailing complies when asked directly is a concern on a job of this cost. And where a roof is part of a building with habitable space below, the consequences of a failure extend well past the roof itself, which is the argument for specifying properly and not cheaply. The standard itself comes from Standards Australia, with the Code maintained by the Australian Building Codes Board.
What to Look for Before You Call Anybody
A flat roof tells an owner most of what a contractor will charge to find out, provided somebody goes up and looks at the right time. Wait until two days after solid rain, because a dry roof hides the single most important piece of information. Look for standing water and note roughly how deep and how wide, then look for the marks left where water has been sitting previously, which show as dark staining, silt lines or a change in surface texture. Check every outlet for debris and see whether the membrane runs down into it or stops nearby. Look at where the membrane turns up against walls and parapets and note how high it goes and whether the top edge is sealed or simply stopped. Count the penetrations, meaning vents, aerials, air conditioning feet, solar mountings and cable entries, since each is a detail somebody has to price. Look for blisters, splits, open seams and any area where the surface has gone brittle. Check the ceiling below for staining and note where it sits relative to the roof above. Photograph all of it with the date. An owner arriving with that information gets comparable quotes instead of three contractors guessing, and where access is unsafe the same questions belong in a paid inspection instead. Roof inspection sits at roof inspection cost.
Compliance and Who Does the Work
AS 4654 governs external above ground waterproofing and the National Construction Code references it. Falls, upstands, terminations and penetrations all sit within it. Waterproofing is licensed work in New South Wales and the person applying the membrane needs the relevant licence. Ask to see the licence rather than assuming it exists. Membrane work on an occupied building involves height safety obligations for the contractor. Those height safety obligations are set out by SafeWork NSW.
Hot work using an open flame on a torch on system carries fire risk and needs a procedure. Ask what their fire safety procedure is before work starts. Licensing status can be confirmed through NSW Fair Trading before engaging anybody. Smaller roofing work sits at roof repairs. The exposure period between strip and membrane needs a weather plan.
Lifespans, Warranties and the Ponding Exclusion
Membrane systems are sold with warranties that sound generous, and the exclusions are where an owner should spend their reading time.
The most important exclusion on flat roof membranes is ponding water, which many manufacturer warranties either exclude outright or limit to water clearing within a stated period after rain. An owner whose roof holds water for days may find a warranty claim declined on exactly that basis, which is another reason fall correction belongs in the original scope instead of being deferred. Other common exclusions include damage from foot traffic where no walkway was specified, penetrations made after installation by other trades, failure to maintain outlets and drains, and ultraviolet degradation where a protective coating was specified and not maintained. Warranties also separate into two kinds that owners frequently conflate, being the manufacturer's product warranty and the installer's workmanship warranty, and a leak at a badly detailed upstand is a workmanship matter rather than a product one. Several practical steps follow. Ask for both warranty documents before signing and check what maintenance each requires, since many are conditional on periodic inspection and cleaning. Ask whether the installer is accredited by the manufacturer, because some system warranties require that. Keep records of maintenance. And on a strata building, make sure the documents go to the owners corporation and not to one owner's filing. Rights under consumer guarantees are set out by the ACCC.
| Ask Every Contractor | Why It Matters | A Good Answer |
|---|---|---|
| What are you doing about fall | Ponding decides lifespan | A specific plan |
| Overlay or strip, and why | Hidden moisture matters | Based on testing |
| How are upstands terminated | Common failure point | Height and method named |
| How many penetrations | Each is a potential leak | Counted and priced |
| What system and thickness | Varies enormously | Product and spec stated |
| What does the warranty exclude | Ponding often voids it | In writing, read it |
The Membrane Systems Specified in Australia
Flat roof membranes come from a defined set of manufacturers, and a quote naming the system tells an owner considerably more than one quoting a rate.
On torch on bitumen, Ardex, Bitumode, Polyfin and Nuralite supply most of what goes onto Australian roofs, generally as modified bitumen sheet in one or two layer build ups. For liquid applied systems, Ardex, Sika, Bostik, Crommelin and Parchem cover the polyurethane and acrylic ranges, with Kemperol and Triflex appearing on more demanding specifications. Single ply sheet systems come mainly from Sarnafil, Cosmofin and Danosa, typically in PVC or TPO. Protective and reflective coatings come from Dulux Acratex, Crommelin and Sika. Insulation for warm roof build ups is supplied by Kingspan and Bondor. Primers, bond breakers and reinforcing fabrics belong to the same system as the membrane and should come from the same manufacturer. Several points matter more than the brand. A system installed by an applicator accredited by that manufacturer is what many warranties actually require. Two layer torch on build ups perform differently from single layer ones and cost accordingly. Liquid systems depend on stated spread rates being achieved rather than approximated. And compatibility between the membrane, the primer and any existing surface is a question worth asking directly where an overlay is proposed. Roof plumbing sits at roof and gutter plumbing.
How Long Systems Last
Torch on bitumen typically runs fifteen to twenty five years where water drains properly. Ponding water shortens that figure substantially. Liquid applied systems generally give ten to twenty years depending on product and applied thickness. Coat count and applied thickness deliver the upper end. Sheet systems in a single ply reach twenty to thirty years and cost more upfront. The welded seams remain the critical detail on those systems.
Protective coatings extend life where they are specified and maintained instead of forgotten. Reflective coatings sit at painting services. Foot traffic without a designated walkway shortens life and voids many warranties. Designate a walkway if the roof gets used at all. Clearing outlets and debris twice a year is the cheapest maintenance available. Clearing the outlets and drains sits at gutter cleaning.
| Factor | Effect on Life | Owner Action |
|---|---|---|
| Ponding water | Shortens it most | Correct the fall |
| Blocked outlets | Creates ponding | Clear twice yearly |
| Foot traffic | Wears the surface | Designate a walkway |
| Later penetrations | Introduces leaks | Use the original installer |
| Protective coating | Extends it | Maintain as specified |
| Debris and growth | Holds moisture | Remove regularly |
| Item | Cost | Note |
|---|---|---|
| Torch on bitumen, per m2 | $90 - $180 | Established system |
| Liquid applied, per m2 | $70 - $160 | Seamless, thickness critical |
| Single ply sheet, per m2 | $100 - $200 | Longest life |
| Fall correction screed, per m2 | $60 - $150 | Price it explicitly |
| New outlet or overflow | $400 - $1,500 | Each |
| Small roof, stripped and redone | $8,000 - $25,000 | All in |
| Situation | What It Means | Practical Response |
|---|---|---|
| Mid century walk up block | Marginal original falls | Correct falls this time |
| Terrace rear addition | Awkward wall junction | Detail the upstand properly |
| Coastal exposure | Salt and driving rain | Shorter maintenance cycle |
| Frost prone region | Standing water expands | Eliminate ponding |
| Western Sydney heat | Hard thermal cycling | Protective coating |
| Strata building | Common property | Owners corporation decision |
Getting the Sequence and the Weather Right
Membrane work is more weather dependent than most trades and an owner who understands the sequence can spot a program that is about to cause problems. The work runs in a fixed order. Strip or preparation comes first, which is when hidden substrate problems appear and when a budget frequently gets revised. Any structural or decking repair follows. Fall correction screed goes down next and needs its own curing time, which is genuinely days rather than hours and is the step most often compressed. Priming follows, then the membrane itself, then detailing at penetrations, upstands and outlets, then any protective coating. Most systems cannot be applied to a damp substrate or in rain, and several have minimum and maximum temperature ranges that rule out both cold mornings in the Southern Highlands and the hottest part of a Western Sydney afternoon. Two consequences follow for an owner. A roof is exposed between strip and membrane, which means a contractor needs a plan for protecting it if weather turns, and asking what that plan is before work starts is reasonable. And a program with no allowance for weather delay on a job of this kind is optimistic and not efficient, particularly through a Sydney spring. Where the building is occupied, the exposure period matters more again. Leak repairs sit at roof leak repairs.
Regional Considerations Across New South Wales
Sydney's mid century walk up blocks carry parapeted flat roofs with falls that were often marginal when built. Many are on their third membrane. Rear additions on inner suburb terraces bring small flat roofs terminating against old brickwork. That junction against old brickwork needs particular attention. Coastal exposure along the Central Coast and Northern Beaches brings salt and driving rain that find any weak termination. Maintenance intervals shorten noticeably on roofs exposed to that weather.
Frost on winter mornings across the Blue Mountains, Southern Highlands and Central Tablelands expands standing water and works at weaknesses. Ponding matters more in those areas. Western Sydney heat cycles membranes hard through summer, with surface temperatures well above ambient. Venting the space below sits at roof ventilation. Outlets need clearing twice a year at minimum on a treed site.
Where Flat Roofs Turn Up Across New South Wales
Flat roofs sit on a particular set of buildings in this state, and each brings its own pattern of problems worth recognising.
Sydney's walk up apartment blocks from the middle decades of last century frequently carry flat or very low pitch roofs with parapets, and many are now on their second or third membrane with original falls that were never good. Rear additions on terraces and semis across the inner suburbs are the other large group, typically a small skillion or flat roof added to the back of a nineteenth century house, often with the membrane terminating awkwardly against old brickwork. Mid century houses on the north shore and in the eastern suburbs were built with genuinely flat roofs as an architectural choice, and those roofs are now well past any original membrane. Newer apartment buildings carry podium decks, roof terraces and planter boxes, which are waterproofed areas with traffic and landscaping over them and a far higher consequence when they leak. Garages, carports and outbuildings across the state carry small flat roofs where the economics are different again. Two points hold across all of them. A flat roof over habitable space has consequences a shed roof does not, which should shape the specification. And on any strata building the membrane is almost always common property, which makes this an owners corporation matter rather than an individual one, and strata repairs sit at strata common area repairs.
What Flat Roof Waterproofing Costs
Torch on bitumen at $90 to $180 a square metre covers the established system on most Australian flat roofs. Area and complexity move it within the band. Liquid applied at $70 to $160 suits complex roofs with many penetrations. Thickness and coat count drive both price and performance. Single ply at $100 to $200 costs more upfront and lasts longer. The economics favour it on larger roofs and longer holds.
Localised repairs at $600 to $6,000 buy time and are rarely the last repair on an aged membrane. Taking water away sits at downpipe repairs and replacement. Fall correction at $60 to $150 and new outlets at $400 to $1,500 are separate items worth pricing explicitly. Waterproofing in other applications is covered at waterproofing services.
A small roof stripped and redone commonly lands between $8,000 and $25,000. New guttering sits at gutter and downpipe installation. Membrane specialists will ask about drainage first. Ten minutes on the roof after rain answers a great deal.
What to Look Out For
Go up two days after heavy rain and look for standing water before you commission anything. Those marks predict the lifespan better than any brochure. Be wary of an overlay recommended without moisture testing of what lies beneath. Trapped water shortens the new membrane from below. Check whether the warranty excludes ponding, because many do. A roof that holds water may have no effective cover at all.
Ask how upstands terminate and how many penetrations are being detailed. Area rates hide the work that actually matters. Confirm the licence before engaging anybody, since this is licensed work in New South Wales. Building disputes have a pathway through NCAT if needed.
How to Get Useful Quotes
Give the approximate roof area and say what the current surface is if you know it. System and area together drive most of the price. Say whether water sits on the roof after rain and roughly how long it takes to clear. That answer shapes the whole scope. Count the penetrations you can see, including vents, aerials, air conditioning and solar mountings. Every one of those needs detailing on its own merits.
Describe what sits below, whether habitable rooms, a garage or an unoccupied space. What sits below affects how the roof should be specified. Mention parapets, doorway thresholds and any box gutters. Those details are where quotes tend to diverge most. Have each quote state the system and thickness, say whether it is overlay or strip and on what evidence, set out how falls are being handled, price penetrations and upstands separately and attach both warranty documents. Pin those five down and the quotes become comparable, and skylights sit at skylight installation and repairs.
Flat Roof Waterproofing Across New South Wales
We connect you with waterproofing specialists across New South Wales for flat roof leak investigation, membrane repair, threshold and upturn rebuilds, balustrade fixing repairs, concrete cancer works and full strip and remembrane projects, from Sydney metropolitan and the Eastern Suburbs through the Inner West, North Shore, Northern Beaches, Western Sydney, the Hills district and the Sutherland Shire, out to Newcastle, the Hunter, the Central Coast, Wollongong, the Illawarra and regional New South Wales.
▶ Sydney Inner City 18 areas
▶ Greater Sydney 25 areas
Western Sydney
South Western Sydney
Northern Sydney
The Hills District
Inner West
St George
▶ Sydney Coastal 23 areas
Northern Beaches
Eastern Suburbs
Harbour Suburbs
Sutherland Shire
▶ Hunter & Central Coast 19 areas
Central Coast
Hunter Valley
Port Stephens
▶ Illawarra & South Coast 18 areas
Illawarra
Shoalhaven
Sapphire Coast
▶ North Coast 19 areas
Mid North Coast
Coffs Coast
Northern Rivers
▶ Blue Mountains & Highlands 17 areas
Blue Mountains
Southern Highlands
▶ Regional NSW 21 areas
Central West
Riverina
New England
Far West
Flat Roof Waterproofing FAQs - NSW 2026
What does flat roof waterproofing cost in NSW?
Torch on bitumen runs $90 to $180 per square metre, liquid applied $70 to $160 and single ply sheet $100 to $200. Localised repairs are $600 to $6,000, fall correction $60 to $150 per square metre, and a small roof stripped and redone commonly lands between $8,000 and $25,000.
Why does ponding water matter so much?
It keeps the membrane permanently wet, concentrates ultraviolet damage at the waterline, holds debris and adds weight. Two roofs with identical systems and installers can differ by fifteen years on drainage alone, which is why fall matters more than membrane brand.
Which membrane system should I choose?
Torch on bitumen suits large simple areas and is well proven. Liquid applied handles complex shapes and many penetrations without joins. Single ply gives factory consistent thickness and the longest life. Substrate, geometry and budget decide between them.
Can I just overlay the old membrane?
Only where the substrate beneath is genuinely dry and sound, which needs testing rather than assuming. An overlay traps whatever is underneath, and wet insulation will keep the new membrane damp from below. Ask how many layers are already there.
Where do flat roofs actually leak?
At the details rather than the open field. Upstands finished too low, penetrations for vents, aerials, air conditioning and solar feet, outlets the membrane stops short of, movement joints covered rather than carried through, and door thresholds onto roof terraces.
What is AS 4654?
The Australian Standard for external above ground waterproofing, referenced by the National Construction Code. It covers minimum falls, upstand heights, terminations and flashings, penetration and outlet treatment, substrate compatibility and movement joints.
How long should a membrane last?
Torch on bitumen typically fifteen to twenty five years, liquid applied ten to twenty depending on applied thickness, and single ply twenty to thirty. Those figures assume water drains properly, and ponding shortens all of them substantially.
Does the warranty cover ponding?
Frequently not. Many manufacturer warranties exclude ponding outright or limit cover to water clearing within a stated period after rain, so a roof holding water may have no effective cover. Read the exclusions before signing anything.
Who is responsible in an apartment block?
The membrane on a strata building is almost always common property, making it an owners corporation matter rather than an individual owner's. Warranty documents should go to the owners corporation, and repairs are funded through the scheme.
Is waterproofing licensed work in NSW?
Yes, and the person applying the membrane needs the relevant licence. Work at height on an occupied building also carries safety obligations, and torch on systems involve hot work with an open flame that requires a fire safety procedure.
Flat Roof Waterproofing Specialists - NSW
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For Tradies - NSW
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Figures on this page are indicative 2026 NSW estimates only and vary with roof area and geometry, the number of penetrations and upstands, substrate condition and whether the existing membrane is stripped or overlaid, insulation and fall correction, access and height, outlet and flashing work, and any structural repair found once the old surface is removed. Quotes should always be obtained for your specific property. Building, licensing, work health and safety and consumer protection requirements are set by legislation, the National Construction Code and Australian Standards and are periodically updated, so confirm the current position with the relevant authority and your contractor before relying on any figure.