What does a guest mean when she writes that the sleeping loft smells musty but everything looks fine? That is the review that started this one, and the answer sat about two feet above the ceiling drywall, inside a 25-year-old cedar roof. The owner runs a two-bedroom cedar-clad rental near Issaquah, books roughly 190 nights a year at an average of $240 a night, and reads every review the morning it posts. Three guests in one wet season used the same word, and then a faint brown ring showed up on the loft ceiling. She called around, and the roofing companies Issaquah WA she got out to look all reached the same finding: the shakes were decaying from the underside rather than leaking from the top. The short version of this case study is that cedar has to dry from both faces, and a roof deck that will not let it dry fails early no matter how good the shakes were.
The Review Said Musty Not Leaking
A leak is obvious. Stains spread, a bucket comes out, and everyone knows what to call it. A musty smell is subtler and it shows up months or years earlier, which is why it often reaches a review page before it reaches anybody’s repair list. Her first responses were the sensible ones: a dehumidifier in the loft, a new mattress, a note asking the cleaner to crack the window between stays. The smell did not budge. The case we see most often on Eastside cedar begins right here, with an owner treating the air in the room when the trouble is in the assembly overhead.
By the time the brown ring appeared, the roof had been damp for years rather than days. Cedar that stays wet underneath goes soft and dark long before it starts passing water through to the room below. The stain was the last symptom in the sequence, not the first.
Cedar Has To Dry From Underneath
A shake takes on water in every storm and gives it back when the weather turns. Both faces have to take part in that exchange. Nail shakes down onto a continuous plywood deck with a solid membrane beneath them and the top face dries in an afternoon while the bottom face stays saturated for weeks at a stretch, right through a Puget Sound winter. A cedar roof wants to breathe on both sides. The traditional answer is spaced sheathing, what crews around here just call skip sheathing, meaning rows of 1×4 boards laid with a gap between them so air can move across the back of every course. Installers will tell you that gap does more for service life than the grade of the shake does.
Solid Sheathing Traps What Rain Leaves Behind
The roof on this cabin went on in 2001, built the fast way, and it was not unusual for its era. Plywood deck, felt, shakes straight on top, no vented gap anywhere in the stack and a ridge that was closed off tight. On a garage that assembly might have lasted fine. Under a heated sleeping loft in a rainforest climate, with warm indoor air pushing up into a cold cavity all winter, it had two sources of moisture and one escape route, and the escape route was blocked. When the crew pulled the first courses, the top faces still looked respectable while the backs were black and crumbling in the hand.
Cedar deck details compared. Service life figures are typical ranges for an example Pacific Northwest scenario, not measured results from this property.
| Deck Detail | Effect On Underside Drying | Typical Service Life |
| Shakes fastened direct to solid plywood | Drying happens on the top face only | Roughly 15 to 20 years |
| Solid deck with breathable underlayment | Some vapor movement, still no air gap | Roughly 20 to 25 years |
| Spaced skip sheathing, 1×4 with gaps | Air crosses the back of every course | Roughly 30 to 40 years |
| Vented batten grid over a solid deck | Continuous drainage and drying gap | Roughly 30 to 40 years |
Look at that middle column on any bid you are handed. Two proposals can name the identical shake, the identical fastener and the identical warranty term while describing completely different roofs, because the difference lives in the deck line nobody reads. The line item that decides how long the roof lasts is usually the cheapest one on the page.
The Repair Bill Against The Booking Loss
Run the arithmetic rather than arguing about it. Say the reinstall across roughly 1,800 square feet of cedar comes to $27,500 with the deck rebuilt in skip sheathing and the ridge and eave opened up, the loft ceiling patched and repainted for another $900, and six working days on site in the shoulder season that knock out four booked nights at $240 each, which is $960 of revenue gone. Call it $29,360 all in. Spread across a 35-year assembly that works out to roughly $840 a year, against a roof that had already quit at 25. Substitute your own square footage and nightly rate and the shape of the answer holds.
What I cannot tell you is what the musty reviews themselves cost her. Nobody tracks the booking that never happens because a guest read one word in a review from last March, and any figure I put on that would be invented. Her own guess was two or three weekends across the season, and she is the first to admit it is a guess.
Rebuild The Deck Detail Or Repeat The Problem
A reinstall only earns its price if what sits under the shakes changes. Same deck, same result in another twenty years. Read the proposal line by line: deck type, underlayment, how the ridge and the eave actually vent, and what the warranty excludes. In August 2026, Roofing Contractor Magazine made the point that a warranty’s real value sits in its exclusions rather than its headline term, since a 30-year warranty carrying a ponding exclusion is functionally a zero-year warranty on a roof that ponds.
Cedar warranties have their own version of that clause, and it is usually tied to ventilation, so ask which conditions void coverage before anyone starts tearing off. If you own a cedar-roofed rental on the Eastside, ask any of the roofing companies Issaquah WA owners short-list to put the deck and ventilation detail in writing, not just the shake grade and the price. The loft on this property has come through two wet seasons dry, and the reviews have gone back to mentioning the coffee.
