Best Insulation For Vented Crawl Space

Jul 25, 2018

Best insulation for vented crawl space can help turn them into energy efficient crawl spaces, when combined with air sealing and moisture control. Crawl space insulation types depend on whether you have a ventilated or unventilated crawl space. Most crawl spaces are vented, as to prevent moisture issues – which is why the majority of building codes require vents in the first place. However, there are contractors and other building professionals who recognize that unventilated crawl spaces might be the better option for homes that are using proper drainage and moisture control techniques.

Ventilated crawl spaces can be an absolute magnet for cold and moisture under your floorboards, resulting in uncomfortably chilly floors, and, in some cases, even an unpleasant odor. With nothing underneath the ground to prevent heating loss, a great deal of warmth can escape through your crawl space. The best insulation for vented crawl space is a new breakthrough in insulation technology.

Best Insulation For Vented Crawl Space

In some cases excess moisture can be introduced through the same vents intended to relieve moisture. This can be especially problematic during summer months in warm humid climates. Regulated by the ground, crawlspace temperatures can be 20 degrees or more below the outdoor temperature.

As warm humid outside air comes in, it cools to the crawlspace temperature. Since the ability of air to hold moisture decreases as its temperature decreases, the moisture in the air condensates onto the cooler surfaces in the crawlspace. You may notice drops of water on the underside of the floor, joists, supports or even on the ground. The vents intended to relieve moisture are actually causing this problem and if left unaddressed will result in mold, rot, or other damage.

For many years, the standard way to build a crawl space involved venting the crawl space walls and installing fiberglass batt insulation between joists in the crawl space. The widespread availability of fiberglass insulation, along with its low cost, went along well with the other economies of crawl space construction.

Ventilated or Not Ventilated?

That is the question. Originally it was assumed that if suitably ventilated, these subsurface areas would remain moisture-free. However, in the winter, cold air can make things rather drafty and during the summer humid air can make this open space pretty muggy with no way to remove the moisture. Therefore, oddly enough, ventilated crawl spaces are the most energy efficient. When ventilated, everything is sealed and there’s no chance for moisture buildup or drafts. So you may want to first think about sealing up this space beforehand to make the project a bit easier and to make the final result more effective.

Crawl Space Insulation

There are a few things to keep in mind before beginning the project. First of all, are you ready to do this yourself? If you have to seal up the area, it may be best to hire a crawlspace encapsulation contractor. But if you’re taking it on yourself, make sure to wear long sleeves, gloves, and protective eye gear to keep safe. Here are some other things to consider beforehand:


The benefit of ventilated areas is that you’ll only have to worry about the foundation walls and therefore won’t spend as much money or time on labor. However, if left open to the exterior air, you’ll want to mount crawl space insulation into the sub-floor cavities as well.


Batt insulation with an R-value of 10 (unventilated) to 20 (ventilated) will do the trick since it’s cheap and easy to use, though rigid foam board works. And always use vapor barrier and lay down a ground-sheet to prevent rising moisture from below.


If your pipes and other ductwork are located within the house, you won’t have any worries. But if they’re exposed underneath, you’ll want to wrap them separately in crawl space insulation in order to prevent freezing or unnecessary heat loss.


Whether ventilated or not, you’ll always want to make things air tight. Seal up any air gaps leading into the home to avoid seepage and drafts. Also, you may want to install an access door within the home or make sure it is tightly sealed on the exterior.

Some of the benefits of best insulation for vented crawl space

> Stay dryer than open crawl spaces
> Protect pipes from freezing
> Require less insulation than open-air crawl spaces (since the area of the perimeter walls is less than the area of the crawl space ceiling)
> Bring ducts within the conditioned envelope of the home — an improvement that usually results in energy savings compared to open-air crawl spaces.

Best insulation for vented crawl space can be designed and constructed as mini-basements, as part of the house, and within the conditioned space. When crawlspaces are included within the thermal enclosure, home inspectors should make sure they are insulated and air sealed on their perimeters and should have a continuous sealed ground cover.

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In cold climates or in very low energy-consuming buildings, installing insulation below on the floor of the crawlspace is also recommended. When crawlspace floors and walls are air sealed and insulated, the temperature and humidity conditions inside the crawlspace become stable and are essentially identical to the rest of the interior of the building.

If it is not possible to treat the crawlspace as a part of the house, such as in flood zones, coastal areas, or in dry climates where it is not necessary, it is important to construct the house such that the crawlspace is isolated from the house, i.e., outside of the home’s thermal boundary. Home inspectors should keep in mind that homes with uninsulated and unsealed crawlspaces should be treated like homes built on piers, with thorough air sealing of the floor and floor joists, and insulation installed on the underside of the floor in full contact with the floor.

Look here to know more in detail about Installing Insulation In Crawl Space Under House

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