Crawlspace Vent Covers
Crawlspace vent covers are custom-cut closed-cell rigid foam blocks with a foam-tape perimeter seal, strapped or magnetically held against the exterior face of each foundation vent on a vented Seattle crawlspace — installed in November, removed in March, labeled and stored for next season — from $150 for a standard 4-vent kit with spring removal included. The seasonal pattern is the building-science correct fix — permanent vent closure traps summer humidity and grows mold within two to three years, which is why we will not do it. The kitchen floor that is unwalkable in socks from November through February, the bedroom over the crawlspace whose carpet feels like a refrigerator deck in January, the cold air you can feel coming up through the floor registers in winter — foundation vents are open to outside air year-round by design, because the crawlspace needs to dry through summer (Washington State Energy Code WSEC R408).
Service
What Do Seasonal Crawlspace Vent Covers Include?
Seasonal crawlspace vent covers are custom-cut closed-cell rigid foam blocks (1.5 to 2 inches thick polyisocyanurate or extruded polystyrene) with a perimeter foam-tape seal, held against the exterior face of each foundation vent by stainless-steel strap or rare-earth magnets, installed on a documented November-to-March schedule with labeled off-season storage and a spring vent-screen inspection, from $150 for a 4-vent kit to $300 for an 8-vent kit. A typical Pacific Northwest home built on a vented crawlspace has 4 to 8 foundation vents around the perimeter, each 16 inches wide by 6 to 8 inches tall, opening through the concrete or block foundation wall. They are required by code for warm-season ventilation — the crawlspace needs to dry through summer or the framing under the floor absorbs ground moisture and grows mold. Seasonal covers solve both problems by closing the vents from November to March and reopening them April through October. The work below covers the kit we install, the seasonal rotation, and the comparison against permanent encapsulation.
Standard Vent Cover — Custom-Sized Foam Insert
Each cover is a closed-cell rigid foam block (typically 1.5 to 2 inches thick polyisocyanurate or extruded polystyrene), cut to fit the specific dimensions of your vent opening with a perimeter foam-tape seal that compresses against the exterior face of the foundation. Cover is held in place with either a stainless-steel strap anchored to two foundation screws (preferred for high-wind exposure) or rare-earth magnets on a metal foundation-vent frame (faster to install and remove). The cover seats against the exterior face of the foundation, not into the vent opening — so the vent screen behind it stays clean and free of debris.
Site Measurement on Every Install
Foundation vent openings are not standardized — even in tract homes, vent sizes can vary by an inch or two between builders, between sides of the same house, and between original construction and any later vent replacements. We measure each vent on the install visit and cut covers to fit each opening individually. No universal kit — every cover is sized to its specific opening. We label each cover with its location (FRONT-NORTH-1, SIDE-WEST-2) for easy re-installation next season.
Foam-Tape Perimeter Seal
The foam-tape strip around the perimeter of each cover compresses against the exterior face of the foundation when the cover is strapped or magnetically held in place. This is the actual air seal — the rigid foam blocks heat transfer through the opening, the foam tape blocks the air leak around the edges. We use 1/4-inch closed-cell polyethylene tape that compresses to seal a foundation face that is rarely perfectly flat.
Storage Between Seasons
Covers are removed in late March or early April when the dry-out period begins, labeled and packed into a single storage container, and stored either in our shop or at a client-designated location (a garage corner, a basement shelf). The next October we deliver and re-install per the labels. Storage in our shop is $30 per cover per year and includes the round-trip delivery. Client-stored covers are free.
Seasonal Schedule — November On, March Off
The standard Seattle schedule is install around November 1 (when daytime highs drop below 55 degrees and the heating system is running daily) and remove around March 15 to April 1 (when daytime highs hit 55 degrees consistently and the warm-season drying needs to begin). Exact dates depend on the year's weather; we set reminders for both visits and confirm timing with the homeowner the week before. Customers who travel can leave the covers on for an extra two weeks; we will not leave them on into May.
Honest Comparison Against Permanent Encapsulation
Permanent crawlspace encapsulation — a sealed vapor barrier across the floor and up the walls, all vents permanently closed, often with a dehumidifier — is a larger project that addresses both the cold-air infiltration and the moisture issue together. It typically costs $4,000 to $12,000 depending on crawlspace size and requires a building-science assessment first. The right answer for some homes (especially those with chronic crawlspace moisture issues, radon concerns, or planned floor-system insulation upgrades). The wrong answer for homes that are otherwise dry — seasonal covers cost a few hundred dollars and address the cold-floor issue without the full encapsulation cost. We will route you to a crawlspace contractor for an encapsulation assessment if your situation calls for it.
How Seasonal Crawlspace Vent Covers Work
Six steps from the per-vent measurement to the spring removal — the actual sequence we follow on every seasonal foundation-vent cover install.
Foundation Vent Count and Site Measurement
Walk the foundation perimeter and count every dedicated ventilation opening — typically 4 to 8 rectangular vents at the top of the foundation wall on a vented Seattle crawlspace. Measure each opening individually (sizes can vary by an inch or two even within the same house) and note location for labeling.
Custom-Cut Foam Covers
Cut closed-cell rigid foam blocks (1.5 to 2 inches thick polyisocyanurate or extruded polystyrene) to the specific dimensions of each vent opening. Apply 1/4-inch closed-cell polyethylene foam-tape strip around the perimeter of every cover — this is the actual air seal against a foundation face that is rarely perfectly flat.
Label Each Cover by Location
Label every cover with its specific location (FRONT-NORTH-1, SIDE-WEST-2, BACK-SOUTH-3) so re-installation next October is fast and accurate. The cover that fits the front-north vent will not fit the back-south vent if dimensions varied by an inch — labeling avoids the wrong-cover-on-wrong-vent error that breaks the seal.
Strap or Magnetic Retention
Hold each cover against the exterior face of the foundation with either a stainless-steel strap anchored to two foundation screws (preferred for high-wind exposure) or rare-earth magnets on a metal foundation-vent frame. Cover seats against the exterior face, not into the opening — the vent screen behind it stays clean for the spring re-open.
Calendar the Install-Remove Schedule
Set reminders for the November install (when daytime highs drop below 55 degrees) and the March-to-April removal (when highs hit 55 consistently and the warm-season drying needs to begin). Homeowner gets a reminder text the week before each visit. Covers never left on into May — that is the building-science line we will not cross.
Spring Removal and Screen Inspection
Late March or early April we return, pull every cover, inspect the original foundation vent screen behind it (rust-through, tears, pest entry), replace failed screens at $40 per vent, and pack the covers into labeled storage for next October. The crawlspace dries through summer; the covers come back when the heating season starts.
Crawlspace Vent Cover Pricing
Final pricing depends on vent count, vent size, and whether storage between seasons is in our shop or at a client location. Spring removal is included on every install. Request a free estimate for an accurate quote.
Tell us the home age and the rough number of foundation vents — we will quote the seasonal kit.
Why Choose a Professional for Seasonal Crawlspace Vent Covers?
Crawlspace vent covers are one of the few weatherization fixes with seasonal building-science consequences — get it right and the cold floor goes away while the crawlspace stays dry. Get it wrong (covers left on year-round) and you trap summer humidity in the crawlspace, condense moisture on the joists, and grow mold inside two to three years. We have pulled out two homeowner-installed permanent vent closures that had grown visible mold on the subfloor. The right answer is custom-sized seasonal covers with a documented install-and-remove schedule — we keep the calendar, you keep the warm floor. The Energy Trust of Oregon and the Northwest Energy Efficiency Alliance both recommend this exact seasonal pattern for vented Pacific Northwest crawlspaces.
Seasonal only — never permanent on a vented crawlspace
Permanent closure of crawlspace vents on a vented (un-encapsulated) crawlspace traps summer humidity, condenses moisture on the framing, and grows mold within two to three years. This is settled building science — every Pacific Northwest weatherization contractor, the Northwest Energy Efficiency Alliance, the Energy Trust of Oregon, and the Washington State Energy Code agree on this. We will not install covers that stay on year-round. If you want permanent vent closure, the right path is full crawlspace encapsulation, which we route to a specialty contractor.
Custom-cut per vent, not a universal kit
Foundation vent openings vary by 1 to 2 inches across vents even within the same house. We measure each vent on the install visit and cut a custom cover for each opening. Universal-fit covers leak around the edges where the dimension does not match — the gain is roughly half what a properly sized cover delivers. Custom cuts add 5 minutes per vent on the first install and pay back every season after that.
Labeled storage and a kept calendar
Each cover is labeled with its location (FRONT-NORTH-1, SIDE-WEST-2, BACK-SOUTH-3) so re-installation next October is fast. Covers stored in our shop come back to you with the same labels. We keep the install-and-remove calendar — you get a reminder text the week before each visit, no homeowner has to remember to call in November.
Vent screens get inspected when covers come off
Spring removal includes a quick inspection of the original foundation vent screen behind the cover — checking for rust-through, tears, or pest entry. Failed screens (more common on homes 30+ years old) get a $40 per-vent replacement so the screen is sound for the summer dry-out season. We will not put a cover back on next October over a screen that has pests using it.
Insured, background-checked, 30-day guarantee
Every Handis weatherization technician carries liability insurance and has cleared a background screening. If a cover loses its strap or magnetic hold, the foam-tape seal fails, or any cover detaches within 30 days because of our workmanship, we come back and fix it at no extra charge. Materials carry the manufacturer warranty — rigid foam is rated for 30+ years against R-value loss, foam tape is rated for 5+ years against UV and compression set.
Estimate
Tell us the home age, the rough square footage, the approximate count of foundation vents (or just say "I do not know" and we will count on the visit), and whether you have noticed cold floors over the crawlspace in winter — we will send back a clear estimate.
Customer Reviews
Recent crawlspace vent cover reviews from verified Seattle customers.
1992 split-level, 6 foundation vents around the perimeter. The kitchen floor was unwalkable in socks from November through February for the four years we had owned the house. Tech measured the vents, made custom covers, installed them in early November with magnetic retention. The kitchen floor is now the same temperature as the rest of the house. He came back in late March and pulled them, stored them for us, and re-installed this October. Best $300 we have spent on the house.
We had tried to seal the vents ourselves with foam from the hardware store two winters ago. Worked great until summer — the crawlspace grew mold and we had a remediation bill. This tech pulled the homemade plugs, made proper seasonal covers that strap on for winter only, and explained why permanent closure was the wrong answer. Wish we had called him first.
1955 rambler, 8 vents and the back two were partially overgrown with a hedge. Tech trimmed the hedge enough to access the vents, replaced two failed screens (the original galvanized had rusted through), and made covers for all 8 vents. The bedroom over the crawlspace is no longer freezing in January. Honest scope on the screen repair — pointed out the failure and quoted it separately.
He told me upfront that our home was a candidate for full encapsulation, not just seasonal covers — the crawlspace had standing water in two corners and the framing had visible moisture marks. Routed me to a crawlspace contractor for the encapsulation assessment. Could have just sold me $300 of seasonal covers and called it done. The encapsulation was the right answer for our situation.
First year we are using these — installed this November. The cold spot in the front of the house where the floor sits over the crawlspace is significantly better. Looking forward to seeing how it goes through January and February. Tech labeled every cover by location and gave me a printed schedule for the spring removal. Professional from start to finish.
Frequently Asked Questions
Common questions about seasonal crawlspace vent covers, foundation ventilation, and the difference between covers and encapsulation.