The room sits under the north slope of a 1970s split-level in Issaquah, finished and carpeted, holding a few hundred graded books and a shelf of sealed consoles. Through one wet season the owner watched slipcases bow at the corners and a sealed box swell at the seam until the shrink wrap went slack, while the ceiling above all of it stayed clean and dry. By the time roofing companies issaquah wa get a call like that one, the covering has usually been failing at the deck for years without leaking in any way a person could spot from a step stool. The argument here is plain, and it runs against how most homeowners think about a roof: on a shaded cedar slope, moisture ruins what you store underneath long before it stains anything.
Cardboard Curled While The Ceiling Stayed Dry
Cardboard is a moisture instrument nobody buys on purpose. A slipcase takes on water vapor from the air, swells along the grain, gives some of it back when the room dries out, and after enough of those cycles the board simply stays curled. The graded slabs held up better, although two of them fogged on the inside of the case. Sealed consoles were the worst of it, because a printed sleeve under shrink wrap shows every millimeter of movement at the seam. Nothing ever dripped. That is the case we see most often on the Eastside: the storage fails first, the ceiling holds out for another year or two, and the owner spends that year blaming a humidifier he does not own.
A Cheap Hygrometer Beat The Naked Eye
He bought a fourteen dollar hygrometer, set it on the shelf beside the long boxes, and wrote down a number after every rainy stretch. The room read 68 percent, then 71, then 74 after four straight days of rain, and it never dropped back under 60 even during a dry week. The U.S. Environmental Protection Agency’s mold guidance, still the standing reference when he checked it in December 2025, puts the ceiling at 60 percent relative humidity indoors and calls 30 to 50 percent the comfortable band. A collection sitting at 74 percent is not in a gray area. One thing belongs here without any hedging: do not climb a wet or moss-covered cedar roof to look for yourself, because moss-covered shakes are slick as glass and a fall off a split-level costs far more than a warped slipcase. Use binoculars from the driveway, or pay someone who works up there with a harness.
Shaded North Slopes Rot Cedar From Underneath
Second-growth firs on the north side of that lot mean the slope sees maybe two hours of weak sun in December. Cedar dries from both faces or it does not really dry at all. The 28-year-old north slope was carrying moss thick enough to hold water for days after the rain quit, and the underside of those shakes had nowhere to give the moisture back, because a re-roof sometime in the late 1990s had laid a solid deck and a non-breathable underlayment straight over the original spaced boards. So the deck stayed damp, the shake butts stayed damp, and the vapor that could not escape upward loaded into the room below instead. Call it twelve years of that slow loading. Honestly, closer to eighteen once you count how long that second layer had been sealing the whole assembly in. The ceiling never leaked because there was no single hole to leak through, just a slope that held water instead of shedding it.
Old Shake Roofs Breathed More Than Sealed Ones
The original 1970s job was crude by current standards and better in exactly one way: skip sheathing left an air gap under every course, so a shake that got soaked on top could still dry from the bottom. Ten and fifteen years ago the common answer around here was to go over the top with solid plywood and a synthetic underlayment, which sheds bulk water beautifully and traps vapor just as well. Cedar work today goes back to breathing on purpose, with a ventilated mat or spaced sheathing under the shakes, real intake at the eave, continuous exhaust at the ridge, and stainless fasteners so nothing bleeds. Same material, opposite result for the room underneath.
One Issaquah cedar roof, before and after. An example scenario rather than a spec sheet.
| Layer | The 28-Year-Old Assembly | What The Replacement Changes |
| Shake grade | Mixed grade, moss held on the shaded slope | Premium edge-grain cedar that cups less through wet and dry cycles |
| Underlayment | Non-breathable synthetic over a later solid deck | Breathable underlayment sized for a vented cedar assembly |
| Decking | Original skip sheathing buried under plywood | Ventilated mat restoring an air gap beneath every course |
| Intake ventilation | Soffit vents packed shut behind old insulation | Clear continuous intake along the eave |
| Exhaust ventilation | Two box vents crowded near one gable | Continuous ridge exhaust across the full slope |
What Replacement Week And The First Season Looked Like
Tear-off ran two days and the new assembly went on over the next three, which is an ordinary week on a slope that size. By day three the deck was open and the staining under the old underlayment was obvious from the room below. The collection came out of the room first and went to a neighbor’s spare bedroom, and in my book that part is not optional. Within the first week after the ridge exhaust went in, the hygrometer dropped into the high fifties and stayed. By month three it read between 44 and 52 percent on normal days, helped along by the crew pulling back the insulation that had been choking the soffit intake, which did as much work as anything nailed to the roof. The first full wet season is the honest test, and through that one nothing on the shelves moved. Two long boxes that had already curled stayed curled, because cardboard does not remember what it used to be.
The damp sheathing and the rusty stained insulation at the eave were not painted, sealed or coated over. The EPA’s mold cleanup guidance for homes advises calling a professional experienced in cleaning and fixing buildings damaged by contaminated water, rather than closing up a wet assembly and hoping it dries on its own. On a deck that has been holding moisture for the better part of two decades, that is the line worth holding.
Protect The Room Under The Roof First
Anyone storing paper, cardboard or sealed plastic under a shaded slope should own a hygrometer before they own an opinion about their roof. A week of readings costs about the price of a comic and tells you whether the covering belongs on the suspect list at all. Readings that stay above 60 percent through a wet stretch point somewhere, and a clean ceiling does not clear the roof of anything.
Most of the roofing companies Issaquah WA homeowners call will glance at that ceiling, find nothing, and move along to the gutters. Bring them the numbers instead, and ask specifically about deck preparation and ventilation on a cedar job rather than about the shakes alone. The collection is the whole reason any of this matters, and it will tell you the roof is wrong months before the drywall ever does.
