Tacoma Crawl Space Questions

Most of Tacoma's hills sit on Alderwood-series glacial till with a hardpan 20 to 40 inches down. From December through April rain perches on it, one to three feet below the surface, which is the depth of a crawl space floor. By June the perched water is gone. A crawl space that behaves this way needs a drain and sump before any liner goes in; see moisture and mold.

Closing vents with nothing controlling the humidity is the fastest way to grow mold on the joists, because the crawl space air still carries ground moisture and now has nowhere to go. Vents get closed as part of encapsulation, together with a sealed liner, a dehumidifier or conditioned air, and the radon provision the state code attaches to an unvented crawl space.

A dry-looking crawl space floor in Tacoma is still giving off water vapor for most of the year, and the residential code requires 6-mil black polyethylene over the soil regardless. If the ground is bare or the old sheet is in pieces, a new barrier is the cheapest useful work in this trade.

Before, and it is priced as its own line. Rodent nests and droppings in the insulation and on the soil are bagged out under respirators, the framing is cleaned, and the entry points at the vents and rim are screened, all before a liner goes down. Sealing a fouled crawl space traps the smell under the plastic and leaves the entry points open. The cost guide carries the cleanup line.

Twelve to 20 mil, string-reinforced, is the range Tacoma encapsulations are built with. Six mil is the code minimum for a ground cover under an open-vented crawl space and is not an encapsulation liner. Twenty mil is the figure the national brands advertise with 25-year warranties; 12 mil reinforced is a reasonable floor for a sealed system.

Under WAC 51-51-0408 an unvented crawl space is permitted only with a continuous sealed Class I vapor retarder and a radon system built to Appendix AF, and WAC 51-51-60101 applies that appendix to unvented crawl spaces in every Washington county, Pierce included. Pierce County is in the EPA's lowest radon zone, and the EPA still advises testing every home.

Replacing a vapor barrier or insulation falls under the ordinary repairs Tacoma exempts from a permit; cutting or removing a beam or load-bearing post does not, and closing the vents brings in the unvented crawl space section of the code. Tacoma's Planning and Development Services confirms what a plan needs; in unincorporated Pierce County it is Planning and Public Works. Structural repair is the page where this comes up most.

About $6,000 to $14,000 for a typical 1,000 to 1,500 square foot crawl space, or roughly $4 to $10 per square foot, with small dry crawl spaces from about $4,500 and large or wet ones up to about $18,000. Drainage, rodent cleanup, and structural repair are added lines. The cost guide has every range.

Tacoma Power pays $750 toward crawl space floor insulation, up to $2,250 across floor, attic, and walls, when the existing floor insulation is R-11 or less, the new installation reaches R-30, the home is electrically heated and served by Tacoma Power, and a participating contractor does the work. It does not cover the liner, drainage, or cleanup.

Standard policies generally exclude groundwater seepage and gradual moisture damage as maintenance, so a crawl space that is wet every winter is an out-of-pocket repair. A sudden event, a burst supply line for instance, may be covered. Read the policy's water exclusions and ask the agent; the contractor's inspection report is what a claim would need.

A reinforced liner with taped seams, fastened to the wall, is advertised by the national brands with 25-year warranties and lasts as long as nobody tears it. The dehumidifier is the component that wears out and gets replaced. A 6-mil vapor barrier under a house that gets regular service visits usually needs replacing within a decade.