Why Missoula decks fail — and how we build them differently.
We tear out a lot of Missoula decks every year. They almost all fail the same way. Shallow footings — surface anchors, 18-inch concrete pucks, deck blocks set on grade — that heave and tilt within five winters as the freeze-thaw cycle works on whatever didn't reach below the frost line. Ledgers nailed (not lagged) directly to siding with no flashing, slowly rotting the rim joist and the framing behind it. Joist hangers missing or undersized for the load. No hold-down hardware where the deck attaches to the house.
Missoula's frost line is 36 inches. That number isn't optional. Every footing we pour goes to 36 inches minimum — usually deeper on bench lots up in Pattee, Linda Vista, or upper South Hills where the geotech recommendations push deeper. We pour concrete, set Simpson post bases in the wet concrete, and let the footings cure before posts go in. There is no faster way that lasts. The shortcut decks fail; ours don't.
The ledger problem on Missoula homes
The single most common deck failure we see in Missoula is rotted ledger and rim joist behind a deck that's been attached to the house for 10–15 years without proper flashing. Water gets behind the ledger every time it rains, runs down the framing, and slowly destroys everything wood it touches. By the time you can see anything from the outside, the framing behind is gone.
On every deck we build in Missoula, the ledger gets:
- Siding cut back, sheathing exposed
- Peel-and-stick membrane (Vycor or equivalent) applied directly to sheathing
- Z-flashing or PVC head flashing at the top of the ledger
- Ledger bolted (not nailed) with proper lag pattern and hardware
- Continuous flashing detail integrated with siding above
It adds maybe a half-day of labor to a deck build. It's the difference between a deck that lasts 25 years and a deck that destroys your siding in 10.
Materials for Missoula decks
- Composite (Trex, TimberTech, Deckorators) — Our most-recommended for new Missoula decks. No sealing, no rot, no annual maintenance. The Missoula freeze-thaw cycle ages cedar fast; composite shrugs it off. Higher upfront cost than cedar but pays back in lifetime maintenance.
- Cedar — Still has a place. Looks great on mountain-modern Missoula homes — Rattlesnake, Linda Vista, Grant Creek custom builds. Requires sealing every 1–2 years (more on south-facing exposures) to maintain that look. Lasts 15–20 years with proper care.
- Pressure-treated — Budget option. Functional but doesn't age as gracefully as composite or cedar. We use it on framing under composite decks but rarely as the visible decking surface for Missoula homeowners spending real money on a deck.
- Cedar railings with composite decking — Common compromise. Real cedar look on the railings and posts where it shows, low-maintenance composite on the floor where you walk.
Missoula deck permits
Any deck more than 30 inches above grade requires a building permit in both the City of Missoula and Missoula County jurisdictions. So do attached decks of any height. We pull the permit, post it on site, schedule the footing inspection (before concrete) and the final inspection. Most clients don't realize that footing inspection happens before the concrete pours — too many homeowner-built decks fail final because they buried the hole and the inspector can't verify depth. We handle the inspection sequence so this doesn't happen.