Ponding Water on Wellington Flat Roofs and Decks
Flat and low-slope roofs are everywhere in Wellington now: inner-city apartments in Te Aro, townhouses in Kilbirnie, modern homes with roof decks in Island Bay and Khandallah. They suit tight sections and steep hillsides, but they depend on water draining away quickly. When it sits there in puddles after rain, something needs attention.
If you have noticed ponding, cracking or blistering, look for a company that offers membrane and flat roof repairs for Wellington buildings covering butynol, TPO and torch-on systems. The right fix depends on the membrane, the age of the roof and whether the problem is the surface, the joins or the structure underneath.
Why water ponds
A flat roof is never quite flat. It needs a fall towards outlets, and over time timber substrates can sag, outlets can block with leaves and grit, and repairs can build up ridges that trap water. Standing water speeds up wear on the membrane, finds any weak seam and adds weight to the structure.
Things to look for after rain
- Puddles still sitting a day or more after the rain has stopped
- Outlets and scuppers partly blocked with debris
- Seams lifting, especially at corners and upstands
- Blisters or bubbles in the membrane surface
- Cracking where the membrane turns up a wall or parapet
Deck roofs need extra care
Where a flat roof doubles as a deck, the membrane is often covered by tiles, timber or pavers. Furniture legs, pot plants and barbecues can all damage it. Check that drainage gaps under the decking are clear and avoid fixing anything through the membrane without advice.
Repair or reroof?
A small split or failed seam can usually be repaired. Widespread blistering, membrane that has gone brittle or a substrate that has softened from long-term leaks usually means the roof needs replacing. A roofer can test the condition of the membrane and the boards underneath before recommending either option.
Keeping outlets clear is the single most useful thing you can do yourself, and it is worth doing after every big southerly when debris has been blown across the roof.
More on this site: Salt Air and Steel Roofs on Wellington's South Coast and Restore or Replace? Deciding on a 1970s Roof in Lower Hutt.