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Under Your Home In Crawlspaces

Using AtticFoil™ radiant barrier in a crawlspace

Other than heat retention, there really is no added benefit to using a radiant barrier in a space that does not have a regular source of radiant heat.


That being said, using a radiant barrier foil in a crawlspace is beneficial if you are losing heat in the wintertime through the floor of the house into this crawlspace; if the heat is radiating across the air gap from the flooring to the ground outside, then AtticFoil™ can help reduce that heat loss. You would use AtticFoil™ Radiant Barrier in crawlspaces to help protect against heat loss from the floor above into the crawlspace.


If you do not have a vapor barrier in the crawlspace and it is open to the earth below, you can use AtticFoil™ Radiant Barrier Vapor Barrier to stop moisture and help retain heat in the floor above.


AtticFoil™ is tear-proof, so adding it to a crawlspace can help with critter control.


When installed with the proper air gap, AtticFoil™ Radiant Barrier will stop 97% of radiant heat loss from the floor above the crawlspace.


Converting Vented Crawlspaces to Sealed Crawlspaces

In the past it was common to build homes with ventilated crawlspaces, because it was thought that outside air would help control moisture problems in a crawlspace. While it is true that ventilation helps moisture dry out, it’s been found that in this environment this is not always the best practice.


Introducing warm air to a cool environment (or vice versa) creates the conditions necessary for condensation, which is typically the root of the problem in a damp, moldy crawlspace. To address this, we have seen the introduction of sealed crawlspaces and crawlspaces that utilize a vapor barrier in order to stop moisture from the ground from coming up into the home.


As a first option we recommend sealing the crawlspace and making it semi conditioned space. Doing this has many benefits, including controlling the humidity/moisture and the temperature of the crawlspace. However, sealing a crawlspace can be labor-intensive and costly. As an alternative, we recommend using radiant barrier technology to achieve similar results.


Using Radiant Barrier in Crawlspaces

If you are using a radiant barrier to help retain heat in the floor above the crawlspace, installation is simple. The simplest way to do it is to staple the radiant barrier foil across the bottom of the floor joists, creating a single reflective layer.


Ideally this works best when there is an air gap between the existing insulation in between the joists and the radiant barrier, but if there is not an air space there, it will still work since there will be an air space between the foil and the ground.


Because the application is below a conditioned space, you want to utilize both radiant barrier and traditional insulation. You can use foam board, spray foam or traditional batt insulation and a single layer of radiant barrier foil. Products like foil-fiberglass and bubble foil aren’t really best used in this application, since you need R-value and reflectivity. You will get the best return on your investment if you buy the radiant barrier and the traditional insulation separately and then combine them yourself. For more information about other foil products, see our article on False R-value claims of Bubble Foil and Fiberglass Foil products.


If you do not already have a vapor barrier in the crawlspace, then you should choose the AtticFoil™ SOLID Vapor Barrier Radiant Barrier product to get the double benefit of blocking moisture and retaining heat in the flooring. See some photos of radiant barrier in a crawlspace here.


If you do have a vapor barrier (e.g. plastic sheeting on the ground or some other waterproofing layer) then you should utilize the perforated AtticFoil™ Radiant Barrier foil for the installation.


Having two vapor barriers in the same assembly isn’t a good idea, and this article explains in more detail why not: Perforated Radiant Barrier Foil versus Solid/Vapor Barrier Radiant Barrier Foil.

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