crawl space air seal

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Improve indoor air quality by air sealing your crawl space

It’s important to make sure that the crawl space is sealed from the rest of the home. The reason for this is that often the air quality in the crawl space is poor compared to the air inside the home. If the crawl space contains many gaps, spaces or channels that communicate with the home, air will move back and forth between the two spaces which will introduce air of lower quality into your home.

areas of crawl space to air seal

Seal the floor above an unconditioned basement or crawlspace to prevent air leaks, and make sure the floor insulation fully covers the subfloor to create a barrier. Seal all gaps and holes in the subfloor with caulk or foam. Also, seal the rim joists to prevent air leakage. Install insulation in the floor joist bays without any misalignments, compressions, gaps, or spaces. Use supports to ensure the insulation stays in contact with the air barrier above, such as metal supports for batt insulation or netting for blown insulation.

Sub-floor Penetrations

A simple way to seal your crawl space is to address the areas of your sub-floor that have holes for pipes, electrical wires, and air ducts. Even small, undetectable gaps can allow air to pass through. To address this, you can purchase a Spray Foam Starter Kit from a DIY store and use it to seal these penetrations. You may need to adjust the position of wires and ducts to access the specific areas needing sealing, but applying spray foam will effectively seal the gaps for an extended period.

Rim Joists

The engineers at suggest that every home with a crawl space or basement should insulate and seal their rim joist. If you have a block foundation or a concrete foundation, it's likely that you have a rim joist. The issue is that rim joists are often uninsulated, leading to condensation and mold formation. Insulating the rim joist can help address this. Sealing the rim joists with foam board or spray foam can prevent thermal transfer and stop low-quality air from the crawl space from entering the house. It's another important area to seal to prevent air from passing from the crawl space into the home.


Many modern homes have central heating and cooling systems, with HVAC equipment often located in the crawl space alongside ducts. If these ducts are not properly sealed, low-quality air from the crawl space can enter the living areas, impacting the air quality where your family spends time. In addition, unsealed ducts lead to air leakage, causing the loss of conditioned, high-quality air from your home into the crawl space. It's estimated that as much as 25% of the high-quality air from your home is lost through gaps in the ductwork into the crawl space. You can easily seal your ductwork using duct sealing tape, available in our DIY store. This industrial-grade high-quality seal tape is designed specifically for sealing ductwork and offers long-lasting results.

why do you need a sealed crawl space?

Floors make up a significant portion of a building’s structure. If the air barrier and insulation system have flaws, heat can escape through floors above unconditioned basements or vented crawlspaces, leading to cold floors and higher heating costs. Heat loss in floors can be due to conduction losses, air leakage, and misalignment of the air barrier and thermal barrier. To prevent these heat losses, the insulation layer in the floor should be continuous and aligned with the air barrier. When basements or crawlspaces are uninsulated, the subfloor serves as the air barrier, and any openings in the subfloor must be sealed.

why work with us?

over 25 years experience

Serving Seattle for 25+ years with expertise and professionalism. Our experienced team, led by founder Jo, has been dedicated to delivering quality craftsmanship and friendly customer service to all his customers for almost two decades.

10-year warranty on insulation workmanship

All of our work is backed by a 10-year transferable warranty on insulation workmanship and a 2-year transferable warranty on mold remediation, sump pump, and French drain install workmanship (if applicable to the bid scope of work). Included in our warranty is one free complimentary courtesy check.

insured, bonded, and licensed

Providing licensed, bonded, and insured services for your insulation needs. Trust our expertise and commitment to quality work. It is important to choose a contractor who is licensed, bonded, and insured because this ensures we know how to do our job properly and can protect ourselves against any potential mistakes.

owner run company

Owning a business can be tough, but also incredibly rewarding. Experience the advantage of talking directly to the owner of our business, Jo, who started installing insulation at the young age of 10. Jo, the founder of the company, has firsthand experience in the insulation industry since childhood.

5 star customer reviews

Experience a customer-focused company that prioritizes your wants and needs. Customer interactions are our primary means of creating true customer relationships and building our brand.

free same-day estimates

Providing customers with fast, free, virtual, and same-day quotes will give you a starting point for your home improvement project.

insulation co. service areas

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air seal crawl space

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