Built-Up Roofing in Missoula, MT

A built-up roof is laid in layers, and each layer has to be down and bonded before the next one goes on. That order is the whole system. Skip a ply, or lay one onto a damp surface, and the roof carries the flaw for its life. In Missoula, MT the weather window decides how many plies can go down in a day, because snow covers the ground about 120 days a year and a day of rain stops hot asphalt work. We plan a BUR job by ply count and by forecast, and the plan shows which day each layer closes.

BUR fails in recognizable ways. Blisters, where trapped moisture or air has raised the plies. Splits, where thermal movement has pulled the felts apart along a line. Alligatoring, a cracked surface of the asphalt. Bare spots where gravel has blown or washed away. Ridging at insulation joints, where the board moved and the roof followed.

Summer swings past 30 F work the membrane in July, and about 45 all-day freezes work it in winter. Splits tend to line up with insulation joints and deck seams. We map them on the roof plan, probe the edges and look for the dark staining that signals moisture below. The findings sheet separates surface repairs from ones that reach the insulation.

Flashings on BUR are their own item. Base flashing is built up from felts and a cap flashing, and it can split at corners. Where the roof meets a wall, the flashing carries thermal movement every day. We press each corner and probe each seam, then photograph the result. A cracked corner repaired with new plies and mastic lasts longer than a bead of sealant.

BUR is heavy, and gravel adds more. Missoula's design ground snow load is 40 psf, with roof loads calculated under ASCE 7-16, and the deck must carry the roof, the snow and any drift. The heavy snow that collapsed much of the former Bonner mill roof in 2011 is the reminder. We check what the existing deck can carry before any recover goes on, and we weigh the gravel removed in a tear-off.

Drift areas behind parapets and rooftop units get attention. Drains must be open before the first thaw, because ponded meltwater adds weight and soaks seams. Modified bitumen is lighter and often replaces BUR when weight is the problem.

Snow removal is a hazard for gravel roofs, since shovels scrape the surface and move stone. We advise against owner-led shoveling and mark the drain lines so a trained crew knows where to clear if loads grow.

BUR is durable and repairable, and its redundancy is real. It is also heavy, slow and smelly to install. Single-ply systems such as TPO install faster and weigh less. The owner decides by weighing the deck's capacity, the fire rules, the noise and odor tolerance and the budget. Montana's 2021 IECC with Montana amendments sets the insulation level, which affects the cost of any new assembly. We compare the options with prices and show the recover versus tear-off numbers next to each.

A last point on moisture. BUR traps water well, and saturated board under it can sit for years. An infrared scan and core cuts map it before a recover is priced. If the board is saturated across a drainage zone, the cheaper recover path closes, and the findings sheet says why.