Flat and low-slope
Flat roofs, and what has to change below 1 in 4
We build and replace flat and low-slope roofs across Nanaimo, Lantzville, Cedar and Gabriola Island. Below a slope of 1 in 4 a shingle or a metal panel is the wrong covering, so we use a fully sealed membrane instead: two-ply torch-on SBS, TPO or EPDM.
A flat roof is not really flat, and that is the whole job. Water leaves a steep roof on its own; on a low-slope deck we have to give it somewhere to go and seal every square inch it sits on until it gets there.
Where the covering has to change
Profiled metal begins at 1 in 4 and modified bituminous membrane ends there, so 1 in 4 is the line. Asphalt shingles cannot go below 1 in 6 under any method. A deck at 1 in 5, 1 in 12 or dead level is a membrane roof, whatever is on it now.
The three systems we install
Two-ply torch-on SBS is the workhorse: a base sheet and a granulated cap, fully bonded, and the easiest of the three to repair years later. TPO is a single-ply heat-welded sheet, light in colour and quick to install over a large area. EPDM is a single-ply rubber membrane that stays flexible in cold and suits small, awkward decks. We pick from the deck size, the number of penetrations and how the roof gets walked on.
Drainage decides how long it lasts
Nanaimo takes 1,000 mm of rain a year and a one-day rainfall of 91 mm on the 1-in-50 event. A low-slope roof that ponds is a roof holding that water on the membrane and the seams until it evaporates. We set the slope with tapered insulation where the framing will not give it to us, and we size and place drains, scuppers and overflows so a blocked outlet is not the only way off the roof.
Flashing heights and the perimeter
Most flat-roof leaks we get called to are at an edge, not in the field. Membrane has to turn up the parapet or the wall and terminate above where water can stand, with the counter-flashing over top and the edge metal locked in against a 0.50 kPa design wind. Curbs at skylights, hatches and mechanical units get the same treatment, because a 200 Pa driving rain finds a short upstand long before it finds a seam.
Decks, patios and the roof you walk on
A flat roof over living space, or one used as a deck, carries traffic the membrane was not designed to take on its own. We put a walkway pad, pavers or a floating deck over the membrane so foot traffic lands on the surface above it, and we keep those surfaces liftable so the roof underneath can still be inspected and repaired.
Where the permit answer sits
The City of Nanaimo issues building permits under Building Bylaw 2016 No. 7224. The Regional District of Nanaimo exempts a roofing repair or replacement where no structural changes are made. Adding tapered insulation or reframing to build slope can cross that line, so we confirm the answer with the authority that covers the address before the work is booked.
What's included
Two-ply torch-on SBS membrane roofing
TPO single-ply membrane roofing
EPDM rubber membrane roofing
Tapered insulation and drainage correction
Parapet, curb and scupper flashing
People also ask
How long does a flat roof last here?
A well-drained two-ply torch-on roof gives us 20 to 30 years on this coast. A roof that ponds after every storm gives us far less, and the difference is drainage rather than the membrane brand.
Can a flat roof be shingled instead?
Not below a slope of 1 in 6, and we would not use asphalt between 1 in 6 and 1 in 4 unless the low-slope method is applied in full. Below those slopes water stands long enough to work back under a lap.
Is water sitting on the roof after rain normal?
A film that clears within a couple of days is ordinary. A puddle that is still there a week later means the slope or the drain is not doing its job, and we would rather correct that than keep patching around it.
Can a new membrane go over the old one?
Sometimes, on a single sound layer with a dry deck. We check for trapped moisture first, because a wet layer sealed under a new membrane blisters it from below and we would be back on the roof within a few seasons.
Keep exploring
- What a new roof costsInstalled price by material, and what moves it on a given roof.
- Permits by communityWho issues the permit for an address, and what each authority asks for.
- Where the work isThe communities covered across the Regional District of Nanaimo.
- Metal roof systemsStanding seam and profiled metal from a slope of 1 in 4 with no upper limit, detailed for a 2.1 kPa ground snow load and a 0.50 kPa design wind.
- Roof repair and leak tracingFlashing, valleys, penetrations and laps. Finding where water enters a roof, which is almost never directly above the stain on the ceiling.
- Nanaimo Roofers home