6 Succefull Methods to Insulate Your Crawlspace
Crawlspace insulation is the application process of thermal protection materials in the underfloor space beneath a building. Crawlspace insulation helps to reduce heat transfer, control moisture intrusion, and improve energy efficiency in the structure above.
Crawlspace insulation can be done using foam and fiberglass batts mainly. In order to have a successful crawlspace insulation, you should follow these 6 successful methods.
- Insulate crawlspace walls
- Seal and insulate the rim joists in the crawlspace
- Install insulated crawlspace doors
- Add crwlspace floor insulation
- Encapsulation of the crawlspace
- Insulate crawlspace ceiling
1. Insulate Crawlspace Walls
Crawlspace wall insulation is a method of applying a thermal barrier directly to the interior sides of foundation walls to reduce heat loss and moisture intrusion in the subfloor area.
Insulating crawlspace walls is one of the most effective ways to stabilize temperatures in the underfloor space while preventing common moisture-related issues. We often use materials like rigid foam boards (XPS and EPS), spray foam insulation, and polyurethane panels, which resist moisture absorption and provide a high R-value per inch crawlspace. Each of these wall insulation material reduces thermal transmission and serves as a protective lining against damp air and condensation in the crawlspace.
Crawlspace wall insulation helps to reduce the energy bills, block moisture intrusion, improve indoor air quality, protect plumbing lines, and boost HVAC efficiency. Aqviz experts always recommend wall insulation when dealing with vented crawlspaces in colder regions, especially if the crawlspace floor remains uninsulated.
2. Seal and Insulate the Rim Joists in Crawlspace
crawlspace rim joist insulation is the process of sealing and insulating the horizontal framing member that caps the ends of floor joists where they meet the foundation wall in the crawlspace or subfloor cavity.
Unsealed rim joists cause to serious heat loss, air infiltration, and condensation problems in the crawlspace. Hence the rim joist area is a notorious weak point in the crawlspace thermal barrier. It often allows unconditioned outdoor air and moisture to creep into the plenum space, which can lead to mold, wood rot, and energy inefficiency in the crawlspace. So we highly recommend you to seal gaps with closed-cell spray foam or caulking combined with rigid foam panels, depending on the joist configuration and material exposure.
Sealing and insulating rim joists helps to prevent cold air draft from entering the underfloor space, stops moisture vapor from condensing on cold wood surfaces, improves energy efficiency by closing off a high-loss zone, strengthens the building envelope at a critical transition point, and enhances comfort in floors above by minimizing temperature swings.
3. Install Insulated Crawlspace Doors
Insulated crawlspace doors are access panels or entry doors equipped with thermal protection and moisture-resistant sealing to minimize air leakage and temperature loss in the crawlspace or underfloor access point.
Uninsulated crawlspace doors can become a major source of thermal bridging and moisture intrusion, especially in homes with otherwise well-insulated subfloor areas. Standard wooden or unsealed metal access doors often allow unconditioned air, pests, and humidity to enter the cavity space, weakening the overall crawlspace energy barrier. So we recommend replacing or upgrading to doors made with rigid foam core, vinyl-clad insulated panels, or pre-fabricated composite doors with integrated gaskets.
Installing an insulated crawlspace doors seals off the outside air, reduces the humdity level, protect pipes and ductworks from temprature extrems, block pest infestation and support overal crawlspace encapsualtion. Aqviz experts always recommend for the best results, to install insulated doors with compression latches, weather stripping, and water-resistant frames. Every door acts as part of the larger thermal envelope, so even small upgrades like this have a big impact on maintaining crawlspace stability and performance.
4. Add Crawlspace Floor Insulation
Crawlspace floor insulation is the installation of a thermal barrier directly over the ground surface or concrete slab of the crawlspace to reduce heat transfer, dampness, and energy loss in the underfloor zone.
Insulating the crawlspace floor is essential in cold or mixed climate. You can use materials like rigid foam board (XPS, EPS), closed-cell spray foam, or a thermal blanket with vapor barrier backing for the crawlspaces. These materials help reduce ground heat loss, resist moisture migration, and prevent soil-originated radon gases from infiltrating the subfloor cavity. For vented crawlspaces, the insulation sits above a sealed vapor barrier, while in conditioned crawlspaces, it complements wall insulation.
Adding crawlspace floor insulation reduces upward heat loss into the building’s structure, controls ground moisture, minimizing dampness and mold, increases floor comfort in living areas above, enhances air quality by reducing soil vapor entry and improves HVAC efficiency by maintaining stable subfloor conditions.
5. Encapsulation of the Crawlspace
Crawlspace encapsulation is the process of fully sealing the subfloor cavity with a moisture-proof liner, vapor barrier, and optional insulation components to create a controlled, dry, and energy-efficient environment beneath the home.
Crawlspace encapsulation transforms a musty, mold-prone void into a clean and insulated crawlspace. The encapsulation system includes sealing foundation vents, installing a 12 to 20 mil polyethylene vapor barrier over the ground and walls, taping all seams, and often adding rigid foam insulation to the walls and air-sealing any openings.
Crawlspace encapsulation helps to eliminate ground moisture and prevents condensation on surfaces, stops mold, mildew, and wood rot caused by trapped humidity, improve energy efficiency by creating a continuous thermal and air barrier, extend HVAC life by protecting ductwork and reducing air leaks and enhance indoor air quality by sealing off soil gases and allergens.
6. Insulate Crawlspace Ceiling
Crawlspace ceiling insulation is the installation of an insulating layer between the floor joists above the crawlspace to reduce heat transfer into the living space and improve the overall thermal performance of the home.
To insulate crawlspace ceiling, you can install fiberglass batts, mineral wool, or closed-cell spray foam between the joists of the subfloor area when the crawlspace is vented and unconditioned. This method helps isolate the living areas from temperature swings and damp air rising from the basement-like void. We’ve learned that using insulation with a vapor-resistant facing installed towards the warm side. For added protection, we secure the batts with wire supports or mesh netting to keep them from sagging or falling over time.
What is Crawlspace Insulation?
Crawlspace insulation is the application of thermal protection materials in the underfloor space beneath a building to reduce heat transfer, control moisture intrusion, and improve energy efficiency in the structure above.
To insulate the crawlspace you can use rigid foam boards, spray foam, fiberglass batts, and encapsulation-grade liners. Each type of insulation must be selected based on the climate, crawlspace condition, and structural design.
The R-value of crawlspace insulation represents its resistance to heat flow. Higher R-values offer better insulation performance. Here are typical R-values used in crawlspaces:
- Foam board (XPS): R-5 per inch
- Closed-cell spray foam: R-6.5 to R-7 per inch
- Fiberglass batts: R-3.7 per inch
- Mineral wool batts: R-4.0 to R-4.3 per inch
For cold climates, we often aim for R-19 to R-30 in the crawlspace ceiling, and R-10 to R-15 on walls. Choosing the right insulating layer based on local building codes and energy goals ensures that the crawlspace thermal barrier performs efficiently and durably.
Read More About: 6 Effective Ways to Boost Crawlspace Ventilation
What is Crawlspace Foam Insulation?
Crawlspace foam insulation is a method of applying spray-applied or rigid foam board materials to the surfaces of the crawlspace, such as walls, ceilings, and rim joists to create a high-performance thermal and moisture barrier. Foam insulation in crawlspaces offers the best combination of air sealing, moisture resistance, and thermal performance.
We commonly use two types: closed-cell spray foam, which expands into cracks and seals air leaks while delivering an R-value of R-6.5 to R-7 per inch, and rigid foam boards like extruded polystyrene (XPS) or polyisocyanurate, which offer durable, mold-resistant panels with R-5 to R-6.5 per inch. These materials don’t absorb moisture, making them ideal for damp subfloor areas and foundation walls.
What is Crawlspace Fiberglass Insulation?
Crawlspace fiberglass insulation is use of fiberglass batts or rolls installed between floor joists or on crawlspace walls to form a thermal barrier that reduces heat transfer and improves energy efficiency in the underfloor space.
Fiberglass crawlspace insulation is installed in moderate climates where controlling airflow and radiant heat is critical but full encapsulation may not be practical. Fiberglass batts typically provide an R-value of R-3.5 to R-4 per inch, and are often installed in thicknesses of R-19 to R-30 between ceiling joists in the crwlspace. We prefer kraft-faced fiberglass for ceiling applications, with the vapor barrier facing the heated space, while unfaced batts work well for sealed wall cavities when combined with a separate vapor barrier.
Can cork be used to Insulate the Crawlspace?
Yes, cork can be used for crawlspace insulation. But cork insulation is rarely used in crawlspaces due to its higher cost, limited availability, and lower R-value per inch compared to spray foam or rigid polystyrene. Cork insulation is a natural, renewable insulation material made from the bark of the cork oak tree, known for its thermal resistance, moisture resistance, and acoustic dampening properties.
We recommend cork in specific cases where eco-friendly building materials are required or where synthetic foams aren’t desired. If used, cork boards must be mechanically fastened and combined with a vapor barrier, especially on crawlspace walls or over concrete slabs, to ensure long-term durability in the underfloor cavity space.
Does Crawlspace Waterproofing Include Insulating the Crawlspace?
No, crawlspace waterproofing does not include insulation. Crawlspace waterproofing focuses on keeping water and moisture out of the crawlspace, while crawlspace insulation controls the temperature and energy efficiency of the home. Hence, crawlspace waterproofing does not include insulation.
