TPO wins bids because the sheet is fast to lay and the seams are welded, not glued. It loses jobs when the bid ignores the snow. Post Falls averages about 59 inches a year, the City of Coeur d'Alene sheet carries a 60 psf ground snow load, and a TPO roof here spends a long winter under drift pockets and frozen drains. The membrane brand matters less than whether the insulation, the attachment and the edge metal were priced for that load.
If you are the GC comparing three TPO bids in Coeur d'Alene, ID, look at the lines under the membrane. That is where they differ.
The Call: Why Owners Pick TPO
Three reasons come up. The membrane is light and arrives in wide rolls, so a crew covers a large roof quickly. The seams are hot-air welded into a single sheet, which is stronger than a glued lap when the weld is done right. And white TPO reflects heat, a minor benefit in a place with a July mean near 70 F but a useful one on summer afternoons.
The call against TPO is just as plain. It is a single-ply, so it has no redundancy: one failed weld can leak. It does not tolerate poor workmanship at cold temperatures. And it has less margin for foot traffic and abuse than a thicker system. We recommend it when the roof is large, the traffic is light and the schedule is tight.
What It Costs: Five Lines That Move the Bid
Insulation thickness. Attachment method, whether mechanically fastened, adhered or ballasted. Membrane thickness, which is a gauge choice with a price step. Edge metal and flashing count. And drains, because every additional drain is a penetration with a sump and a flashing. We list each line, and the owner can adjust them.
Tear-off is the other swing. Taking off the old roof and hauling it away costs more than a recover over a sound existing roof, though a recover only works when the insulation below is dry. We ask for an infrared scan and a set of core cuts first, so the decision between replacement and recover rests on the roof and not on a guess.
What the City Sheet Says: Snow, Wind and Ice
The City of Coeur d'Alene Building Services sheet is what your submittal is checked against. For a TPO roof, the 115 mph wind number sets the fastener density at corners and perimeters, where uplift is highest. The snow number sets the insulation and deck demands, and the ice barrier requirement shapes the low-slope and edge details.
Idaho enforces the 2018 International Building Code statewide, and the City can amend it within limits. We read the sheet for each job and detail the perimeter and corners to it. A TPO roof that passes inspection on paper but lifts at the edge in a windstorm costs more than the one that was fastened properly. The November 2015 windstorm, which cut power to about 238,000 customers across the region, is a good reminder.
Where It Fails First: Seams, Drains and Details
Welds fail where the crew rushed or the weather was wrong. Cold sheet needs the right heat, speed and pressure to fuse, and a weld made at the edge of the temperature range can look fine and peel later. We probe every seam after it cools. The second failure point is the drain: a sump set high leaves water standing, and a standing pond sits on the membrane for months. The third is the detail work, the corners, curbs and pipe boots, which are cut and welded by hand.
Snow adds to each of these. A drift pocket behind a parapet holds meltwater against the flashing. A frozen scupper pushes water back under the sheet. We locate the drains and scuppers first, since a roof that drains in January is a roof that lasts.
Attachment: Fastened, Adhered or Ballasted
The attachment choice is a cost line and a risk line. Mechanically fastened TPO is the quickest and the lightest, with plates and screws set in rows through the sheet into the deck. It flutters a little in wind, and the plates need to be set tight to the deck so they do not wear the membrane. Fully adhered TPO is bonded to the substrate, which resists billowing and gives a smoother surface, and it costs more in material and labor. Ballasted TPO sits under stone, adds weight to the deck and suits roofs that were designed for it.
With a 60 psf snow load already in the structure, adding ballast is a conversation with the engineer, not a field decision. We run the fastener pattern to the wind zone on the city sheet and price an adhered alternate for roofs where flutter is a concern. We also set a cover board over the insulation when hail or traffic is a worry, which adds a line but protects the sheet from below.
Where It Fits: Warehouses, Retail and Flex Space
TPO suits big, flat roofs with few penetrations. Tilt-up buildings at Riverbend Commerce Park in Post Falls, such as a 50,000 square foot shell built for up to five tenants, are the type of building where a welded single-ply gets priced. Retail centers like the Village at Riverstone along Northwest Boulevard are the kind of project where we price it, as are light industrial buildings in Hayden.
It fits less well where roofs carry heavy traffic, chemical exhaust or grease. For those, PVC is the stronger choice, and EPDM or modified bitumen may beat both on rough use.
Schedule: The Welding Window
TPO can go on in cold weather with care, but the margin shrinks as the temperature drops. Coeur d'Alene has logged minus 30 F, and a January day averages near 31 F. We schedule large TPO installs between the spring thaw and the first hard freeze, and we prefer to keep the roof open for as little time as possible. When a winter job is unavoidable, we change the method, slow the welding and test more seams. A short season costs more per square foot than a long one, and we price it that way.
Closeout is where the bid pays off. We walk the finished roof with the GC, probe the seams, photograph every flashing and hand over the warranty paperwork the maker requires. Punch items get fixed before the crew leaves, because a callback in January costs more than a day in October. The owner also gets a drain-by-drain note listing which outlets to watch through the first thaw.
Commercial Roofing Questions
How thick should the TPO sheet be?
Thicker for traffic, hail and wind. We bid two gauges as alternates so the owner sees the price step. For a warehouse with few visits, the thinner sheet can be enough.
Can TPO go over the old roof?
Yes, if the old roof is dry and the deck can carry the extra layer. We scan and core first. A wet roof gets torn off.
Does white TPO hold snow longer?
A little. It does not absorb winter sun the way a dark sheet does. We check drains and scuppers so melt has a path.
What breaks a TPO warranty?
Unapproved penetrations, ponding past the stated limit, chemical exposure and repairs outside the maker's methods. We follow the maker's details and keep a record.
TPO or PVC for a restaurant?
PVC, in most cases, because it resists grease. TPO can be used with an exhaust curb detail and a grease management plan. We price both.