Subfloor repair in Bellingham, from the crawlspace up

What subfloor work costs in Bellingham

Subfloor repair in Bellingham runs $5.50 to $13.20 per square foot. Moisture mitigation on a concrete slab runs $880 to $2,750 for the project. Between those two numbers sits almost everything that happens under a finish floor in Whatcom County.

The spread is wide because the work is not one thing. Pulling one sheet of water damaged sheathing in a hall bath and screwing down a fresh panel sits at the bottom. Cutting out sheathing across a kitchen, sistering four joists, adding blocking, and laying new ground cover in the crawlspace underneath sits at the top.

Access moves the price as much as area does. A 24 by 30 inch crawl hatch tucked behind a water heater turns a two day job into a four day job, because every sheet of plywood and every 2x8 has to go through that hole one at a time, and every bucket of wet debris has to come back out the same way.

Height above grade matters too. A crawlspace with 30 inches of clearance is workable. One with 16 inches means a crew on their backs with short tools, and that shows up in labor hours.

If the damage is limited to a few boards and the framing under them is sound, you are in floor repair territory instead, which runs $330 to $1,650 per project. The difference between those two line items is whether the structure is doing its job.

Ask for subfloor scope as its own line with its own unit price. On our subfloor and moisture page it is quoted separately for exactly that reason. It should never be folded into the flooring number, because nobody knows how much bad sheathing is under a floor until the floor is off.

Bellingham subfloor and moisture pricing, plus what goes back on top

Access drives the number more than area does, and a tight crawl hatch or 16 inches of clearance can add days to the same square footage.

Why floors fail here and not in Spokane

Bellingham gets a little over 36 inches of rain a year, and it does not arrive in summer downpours. November averages 5.43 inches, December 4.88, January 4.84. Whatcom County sits in climate zone 4C, the marine zone, which means cool, damp, and rarely cold enough for long enough to dry anything out.

That is the whole problem under the house.

A vented crawlspace here breathes humid air for eight or nine months of the year, and bare soil underneath keeps feeding moisture into that air. Wood decay fungi need wood above its fiber saturation point, which averages around 30 percent moisture content, before serious rot starts. Well dried framing usually sits at or below 20 percent. That gap is your entire margin of safety, and a torn ground cover plus a downspout dumping against the stem wall can close it in one wet season.

Temperature decides how fast it goes. Decay slows below about 50 degrees and above about 95, and Bellingham spends most of spring and fall sitting right in the band where fungi grow best, with the humidity to match.

Washington amends the residential code for under floor spaces, and the numbers are worth knowing before you accept a bid. The state requires at least 1 square foot of net ventilation opening for every 300 square feet of crawlspace. That drops to 1 square foot per 1,500 when the ground is covered with an approved Class I vapor retarder. The ground cover itself is spelled out: six mil black polyethylene or approved equal, lapped 6 inches minimum at the joints, run out to the foundation wall.

Most crawlspaces we open in the older Bellingham neighborhoods have plastic down there somewhere. Far fewer have plastic that is still continuous, still lapped, and still tight to the stem wall after twenty years of pest control techs, cable installers, and insulation crews crawling across it.

The other local factor is age. Plenty of housing in Columbia, York, the Lettered Streets, and Fairhaven predates 1978, which brings the EPA renovation, repair and painting rule into any job that disturbs painted trim.

Reading your floor for what is underneath it

You can learn most of what a crew will find before anyone opens a wall. It takes a flashlight, socks, and twenty minutes.

Cupping and crowning

Cupped boards have high edges and low centers. That means the underside of the board is wetter than the top, and moisture is coming from below. Crowning is the reverse, high centers and low edges, and it usually shows up after someone sanded a cupped floor flat before it finished drying.

Soft spots you can feel

Walk every room in socks and pay attention to where the floor moves under your weight. A spot that gives near a toilet, a dishwasher, a fridge water line, or an exterior threshold is a sheathing problem until proven otherwise. Mark it with tape so you can show a crew instead of describing it.

Gaps that never close

Seasonal gapping in solid wood is normal here, opening in February and closing by August. Gaps that open and stay open, or gaps that appear in one room and nowhere else, point at a moisture gradient in the subfloor rather than a humidity swing in the house.

Cracks that line up

A crack running straight across several tiles in one direction is telling you where a joist runs, or where two panels of sheathing meet. Random cracks in scattered tiles are more often a setting bed or a bond problem.

Fastener heads and telegraphing

Nail heads pushing up through carpet or vinyl mean the sheathing is lifting off the joist and settling back down every time someone walks over it. That movement is what eventually breaks a glue line, a grout joint, or a click lock.

Smell

Open the crawl hatch and breathe. Musty air under a house is fungal growth reporting itself.

The moisture numbers that decide the job

Before anything comes out, the readings get taken. On a wood subfloor that means a moisture meter used in a grid across the room, because one reading in one corner tells you nothing about the wet corner you did not check.

The National Wood Flooring Association asks for 20 test locations per 1,000 square feet on a wood subfloor, and 40 readings per 1,000 square feet on the flooring itself. The acceptance numbers matter more than the count. Strip flooring narrower than 3 inches can go down with no more than 4 percent difference between the flooring and the subfloor. Plank 3 inches and wider tightens that to 2 percent.

That 2 percent is why wide plank jobs get delayed here. A 7 inch white oak plank set over a subfloor reading three points high will cup, and no amount of installer skill prevents it.

Sheathing thickness is set by joist spacing, worth checking before anyone quotes hardwood. NWFA calls for 5/8 inch CDX plywood at 16 inch on center, and 3/4 inch plywood or OSB at 19.2 inch.

Concrete is a completely different test. ASTM F2170 uses probes set into holes drilled to 40 percent of slab depth where the slab can only dry upward, or 20 percent where it can dry from both faces. The standard calls for three test locations in the first 1,000 square feet, plus one more for each additional 1,000, with probes placed within 3 feet of exterior walls and wherever a surface meter flags a wet area. Readings come after the hole equilibrates, generally about 24 hours later.

The older calcium chloride method, ASTM F1869, measures vapor coming off the surface across 60 to 72 hours. It reads roughly the top half inch of slab and nothing deeper, which is why most flooring manufacturers now write their warranty against the in situ relative humidity number instead.

When a slab reads over what the flooring manufacturer allows, mitigation is the answer. A two part resin membrane meeting ASTM F3010 has to test at 0.1 perms or less for water vapor permeance and pull off at 200 psi or better, with the failure happening inside the concrete rather than at the bond line. Ask for that test data. Sheet products such as Schluter DITRA and MAPEI Mapeguard handle uncoupling and vapor management under tile, and liquid applied systems such as Koster VAP I 2000 handle it under resilient flooring. That scope is the $880 to $2,750 line on your estimate.

Joists, deflection, and how flat is flat enough

Tile is the least forgiving material in the house, so it sets the standard everything else is judged against. The Tile Council of North America puts the accepted minimum floor rigidity at L/360, measured before any underlayment goes down. Tile still fails on floors stiffer than that under some conditions, which is why a good setter looks at joist span, species, and spacing rather than trusting a rule of thumb.

Sistering is how a sagging or partly rotted joist gets help. Done properly, the sister runs full length from bearing to bearing, matches the depth of the original, and gets fastened in a staggered pattern roughly every 12 to 16 inches with structural screws or through bolts, kept at least 1.5 inches off the top and bottom edges so the fasteners do not compromise the joist. Common nails alone do not develop the connection.

Where only a section of joist is bad, a partial sister has to extend well past the damage, commonly a third to half the span, and it still has to land on solid material at both ends.

Some of this is not our call. If the bearing itself has failed, if a post has sunk, or if the sag traces back to a beam or a foundation problem, that is an engineering question and it gets answered by an engineer before we quote a repair.

Flatness gets checked with a straightedge, not by eye. For flooring installed with fasteners 1.5 inches and longer, the tolerance is 1/4 inch in 10 feet or 3/16 inch in 6 feet. Thinner material with shorter fasteners tightens to 3/16 inch in 10 feet or 1/8 inch in 6 feet. High spots get ground down, low spots get filled with patching compound, and it gets rechecked before a single board goes in.

That tolerance is also why a floor that looks fine to you fails an installer's straightedge. It is a measured number, and it is the one the manufacturer will ask for if you ever file a claim.

Where squeaks come from and what actually stops them

A squeak is two surfaces moving against each other. Finding which two is the entire job.

The causes we find, roughly in order of how often they show up:

• Fastener withdrawal. Framing lumber dries down toward 6 to 12 percent moisture content, shrinks, and the smooth shank nails that held the sheathing lose their grip. Ring shank nails and screws resist this. Smooth and coated nails do not.
• Uncrowned joists. If the framer did not set every crown the same direction, the sheathing bridges the high joists and leaves a gap over the low ones. Step on it and the panel drops onto the nail.
• Skipped or dried out subfloor adhesive. Gaps in the glue bead let a panel move up and down under load, which is why glue and screws both belong in a new subfloor.
• Missing blocking. Without blocking between joists, joists roll instead of transferring load, and the whole bay flexes together.
• Duct and pipe contact. A register boot cut tight to the sheathing rubs metal on wood every time someone crosses the room.

From below, in a crawlspace or basement, the fix is direct and permanent. Shims set in construction adhesive close the gap between joist and panel, screws driven up through the joist pull the panel down, and blocking stiffens the bay. Fasteners stay at least 3/8 inch off panel edges so they do not split out the tongue.

From above, with finish flooring already down, the options narrow to screws driven through the floor and concealed, which works well under carpet and is a visible compromise on hardwood.

Powdered graphite and talc buy a few weeks of quiet. The movement causing the noise is still there.

How to read a subfloor bid

Start with registration. Washington requires contractors to register with the Department of Labor and Industries, post a bond, and carry liability insurance. A general contractor posts a $30,000 bond and a specialty contractor posts $15,000. Coverage has to be at least $200,000 public liability and $50,000 property damage, or $250,000 combined single limit. All of it is public, and the state's contractor verification tool will show you registration status, bond, insurance, and any suspensions before you sign anything.

Then read for these six items.

• A separate subfloor line with a unit price. Nobody can see under a floor before demolition. A bid that names a dollar figure per square foot for additional sheathing or per joist for additional framing protects you from renegotiating at the worst possible moment.
• Named moisture testing. Which test, how many locations, and what number the crew is holding to. A line that says we will check moisture is not a specification.
• Asbestos handling. Every remodel and demolition project in Whatcom County has to determine whether asbestos is present before work starts, enforced by the Northwest Clean Air Agency, which covers Whatcom, Skagit, Island, and San Juan counties. Nine by nine inch vinyl tile and black cut-back adhesive under an old kitchen floor are the usual candidates.
• Lead paint certification. If the house predates 1978 and the work disturbs painted baseboard or trim, the EPA renovation, repair and painting rule applies and the firm doing the work has to be certified for it.
• Disposal. Wet sheathing and rotted framing are heavy, and dump fees are real money. The bid should say who is hauling and who is paying.
• Change order language. Photographs of the discovered condition, a written price, and your signature before the extra work happens.

A bid that lands 30 percent under the others is usually missing the framing work, the ground cover, or the disposal. Read the exclusions page before you read the total.

Also ask what the crew does if they open the floor and find joists that are wet but not yet rotted. The right answer involves drying and measuring before anything gets rebuilt.

What you can do yourself and where to stop

A fair amount of this is homeowner work, and doing it yourself is a legitimate way to spend money on the parts that actually need a crew.

Laying fresh six mil black poly in an accessible crawlspace is a miserable Saturday and a genuine repair, provided you lap the seams at least 6 inches, run the sheet out to the foundation wall, and seal it around the piers instead of leaving holes. Buy more than you think you need. Overlap is cheap.

Screwing down a squeaky panel from underneath is homeowner work. So is pulling the insulation batts a previous owner stuffed into the crawl vents, trimming back the shrubs that are blocking them from outside, and extending the downspout that has been discharging two feet from the stem wall since the house was built.

Stop at anything that carries load.

Notching a joist for a pipe, sistering a beam, jacking a sagging girder, or replacing a rotted post has a failure mode that is not a squeak. If there is rot at a bearing point, if a floor has dropped more than it has flexed, or if there is standing water under the house, get a structural opinion before you buy lumber. The City of Bellingham Permit Center at (360) 778-8300 will tell you what needs a permit, and asking before demolition costs nothing.

The other hard stop is old flooring. If the tile you want to pull is vinyl from before the mid eighties, do not sand it, do not dry scrape it, and do not break it up. Get it tested first.

How the work runs and what you do after

A normal subfloor job runs in this order.

1. Moisture readings across the whole floor area, a straightedge check for flatness, and an inspection of the crawlspace or slab underneath.
2. An asbestos determination if the building or the existing flooring is old enough to warrant one.
3. Demolition of the finish floor and any failed sheathing, with the framing exposed and photographed.
4. Structural work, meaning sistering, blocking, and any post or beam corrections.
5. New sheathing, glued and screwed, with panel edges gapped per the manufacturer.
6. Ground cover in the crawlspace, or the mitigation membrane on a slab, plus drainage corrections outside.
7. Re-test, patch and flatten, then hand the floor to the flooring crew.

Timelines run 1 to 2 days for a crawlspace ground cover upgrade, 1 to 3 days for sistering depending on joist count and access, and 2 to 5 days for sheathing replacement of typical size. Slab mitigation is a day of application plus cure, and the cure is not negotiable no matter what the calendar says.

You can stay in the house for crawlspace work. You will hear it. For interior sheathing replacement, the room being worked is out of service for the duration and the rest of the house is normal.

After the crew leaves, the job becomes drainage. Most crawlspace moisture in Bellingham is surface water that never should have been near the building. Extend the downspouts past the foundation. Keep grade sloping away from the stem wall. Clear the vents in April and check them again in October, because that is when leaves and beauty bark find them.

Then look under the house once a year with a flashlight. You are looking for wet patches on the plastic, rust streaks running down duct straps, and framing that has gone dark or grown anything. Catching that in year one is a $330 to $1,650 floor repair. Catching it in year six is a subfloor replacement at $5.50 to $13.20 per square foot with new flooring on top of it.