A flat roof is never truly flat. It relies on a gentle fall to move water to an outlet, and on a continuous membrane with every seam, upstand and outlet sealed. When any of those is missing, water sits on the roof, finds the weakest joint and turns up inside, often well away from where it got in. Membrane roofs and decks over bedrooms are one of the most common sources of hidden water damage we see in Auckland homes built from the 1990s onward.
We install and replace membrane systems on flat and low-pitch roofs, enclosed decks, box gutters and parapet cappings. Many jobs combine a membrane section with a longrun roof elsewhere on the house, and we make sure the junction between the two is detailed properly rather than left to sealant.
Pricing: every roof gets a free on-site measure and an itemised written quote, with a fixed price agreed before any work starts.
Signs your membrane roof or deck is failing
Membranes rarely fail across the whole surface at once. Problems start at seams, outlets, edges and anywhere the membrane turns up a wall. Look for these early warnings before they become ceiling stains:
- Water ponding for more than a day after rain, which points to inadequate fall or a sagging substrate
- Bubbles, blisters or soft spots underfoot, which can mean moisture trapped beneath the membrane
- Lifting or open seams, especially at laps and corners
- Cracking or shrinkage pulling the membrane away from upstands and parapets
- Blocked or undersized outlets with no overflow, so heavy rain backs up behind them
- Staining or swelling on soffits, ceilings or the framing below the deck
Membrane systems we work with
There is no single best membrane. The right choice depends on whether the area is a roof or a trafficable deck, what substrate it sits on, how much foot traffic it will take and how complicated the shape is. The systems used on New Zealand homes are typically covered by a BRANZ Appraisal or CodeMark, which sets out where and how they can be used.
Butynol is a synthetic rubber sheet that has been used on New Zealand roofs and gutters for decades. TPO is a thermoplastic sheet with heat-welded seams. Torch-on is a bitumen-based membrane, usually laid in two layers, with a mineral cap sheet that resists UV and foot traffic. Liquid-applied membranes suit small, awkward areas with lots of penetrations. We explain the trade-offs for your roof rather than defaulting to one product.
- Butynol: flexible, proven on gutters and smaller roofs, glued and lap-jointed
- TPO: heat-welded seams, light colours available, suited to larger flat roofs
- Torch-on: tough two-layer bitumen system, common on trafficable decks
- Liquid-applied: seamless coating for small or complex areas and detailing
How It Works
Falls, substrate and outlets: where most failures start
Every appraised membrane system specifies a minimum fall. Several published BRANZ Appraisals for TPO and torch-on membranes set 1:30 for roofs and 1:40 for decks on a plywood substrate, with different figures for concrete. If an existing roof or deck has less fall than its membrane needs, re-covering it with the same product just repeats the problem. Correcting the fall means rebuilding the substrate with firring or tapered framing, which we price as a separate line so you can see it.
The substrate under the membrane matters as much as the membrane itself. Plywood must be the right grade and thickness, fixed and dry before laying, because moisture locked under a new membrane causes blistering. Outlets need to be sized for Auckland rainfall and paired with an overflow, so a blocked outlet shows itself as water spilling outside rather than inside the house. Internal gutters are covered in more detail on our spouting page.
What affects the cost of a membrane roof
Membrane work is priced on the area, but the details usually drive the total. Your written quote breaks out each item, including:
- Removal of the old membrane and any rotten plywood or framing underneath
- Building up falls where the existing roof or deck is too flat
- Number of penetrations, outlets, upstands and parapet cappings
- Choice of system and whether the area needs to be trafficable
- Access, scaffolding and protection of the rooms below while the roof is open
Consent, licensing and weathertightness
Replacing a membrane with a comparable system in the same position can fall under the Schedule 1 exemption for repair and replacement, as long as the existing roof has met its Building Code durability requirement. A membrane that failed within 15 years, or work that changes the structure, falls or outlets, may need building consent. On a home, consented work that affects weathertightness is restricted building work, so it has to be done or supervised by a Licensed Building Practitioner.
Decks over living spaces deserve extra care. If you have a home from the leaky building era with an enclosed deck or parapets, we may recommend a roof inspection before quoting so the extent of any hidden damage is known up front.
Membrane roofs in Auckland conditions
Auckland's intense summer UV ages exposed membranes, and short, heavy downpours test outlets and overflows. Flat roofs are common on modern infill housing, terraced homes and renovated villas with flat-roofed rear extensions in suburbs such as Grey Lynn, Mt Eden and Ponsonby. Exposed sites on the North Shore and Hibiscus Coast also see stronger wind loads on membrane edges and cappings, so edge fixing is part of our specification. Annual checks of outlets and seams are the cheapest way to make a membrane last.
Why Choose Cheeky's Roofers for Membrane Roofing
Falls measured before we quote
We check the actual fall with a level so you know whether a straight re-cover will work or the substrate needs rebuilding.
System matched to the job
We recommend butynol, TPO, torch-on or liquid membrane based on use, substrate and shape, not habit.
Overflows as standard
Every outlet we install has an overflow path, so a blockage cannot quietly flood the room below.
Photos of what is underneath
When the old membrane comes off you see photos of the substrate before it is covered again.
Membrane Roofing FAQs
How long does a butynol or membrane roof last?
It depends on the system, UV exposure, foot traffic and maintenance. Each appraised product states its expected durability in its BRANZ Appraisal or product literature. Keeping outlets clear and checking seams yearly makes the biggest difference.
Can you lay a new membrane over the old one?
Sometimes, but only when the existing membrane and substrate are sound, dry and the system manufacturer allows it. In most failures we see, the substrate needs attention, so stripping is the safer option.
Why does water pond on my flat roof?
Usually the fall is too shallow or the substrate has sagged. Appraised systems specify minimum falls, commonly 1:30 for roofs and 1:40 for decks on plywood. Correcting the fall is part of a lasting fix.
Is butynol or torch-on better for a deck?
Torch-on with a mineral cap sheet is widely used on trafficable decks. Butynol is often chosen for gutters and roofs with little foot traffic. We recommend based on how the area is used.
Do I need consent to replace a membrane roof?
Like-for-like replacement can be exempt, but early failure or changes to falls, structure or outlets can need consent. We confirm this before quoting.
Can you fix a leak in a membrane without replacing the whole roof?
Yes, if the leak is at a local seam or outlet and the rest is sound. If the membrane is failing widely, patching only delays the cost. See our roof repairs service for smaller fixes.
Membrane Roofing by Area
Local membrane roofing information for your part of Auckland:
Related Roofing Services
Membrane Roofing Guides
See the re-roofing cost guide or every service we offer.
Sources and further reading
- BRANZ Appraisal 792: TPO roofing membrane (minimum falls)
- BRANZ Appraisal 819: membrane roofing and decking (minimum falls)
- Viking Torch-On product technical statement
- ARDEX Butynol BRANZ Appraisal 436
- building.govt.nz: Exemption 1.1 general repair, maintenance and replacement
- building.govt.nz: Restricted building work