Make Crawl Space Warm – DIY Energy Efficient Solutions

With winter just around the corner, it’s normal for homeowners to start thinking about the cold frigid weather and how that might affect pipes and monthly energy bills.

One area of the home that often gets overlooked is the crawl space. Many homeowners don’t even know how to take proper care of this space in their home.

I’m going to go over some of the ways that you can make your crawl space warmer during the winter.

Can I Heat My Crawl Space?

Heating a crawl space with a heating device such as a space heater or light bulb is not necessary, but more importantly, it could be dangerous. Placing any heating device in your crawl space that is unattended could be a fire hazard, not to mention it will cost a lot of money to keep running. It’s just not an effective way to prevent pipes from freezing. 

The most energy-efficient way to heat your crawl space is by ensuring that the crawl space is properly insulated. That includes making sure that you have sealed any gaps, cracks, or other potential ways for cold air to enter the crawl space.

One method that some homeowners use to add a little more heat to the crawl space is by installing or modifying existing ductwork from the HVAC system. This method could work for some people; however, my concern is that the HVAC system would begin adding extra moisture into the crawl space through condensation or leaking condensate drain lines.   

Crawl Space Insulation

Crawl space Insulation can help improve the homes overall energy efficiency by preserving the air quality, which in turn will reduce the energy costs. Without insulating the crawl space, heat and cool air will get lost through the floor, and other small holes and cracks.

There are two types of crawl spaces; ventilated and unventilated, each requiring a different kind of insulation. 

A ventilated crawl space is the traditional type that you would find in most homes, and also more ideal because the vents help remove access moisture in the air. In the case of a ventilated crawl space, fiberglass insulation can be used under the subfloor and between the floor joists. When using fiberglass insulation, remember to use a vapor barrier such as a plastic tarp to prevent moisture from attaching itself to the insulation. Over time that moisture could turn into a mold problem fairly quickly.

Unventilated crawl spaces generally use a dehumidifier, exhaust venting or an HVAC system to help control the humidity in the air. If you have an unventilated crawl space, then you will want to insulate the foundation walls only and not the sub-floor above. By insulating the walls, this will eliminate the need to separately insulate the heating ducts and water pipes.

As an extra line of defense, if your crawl space has a dirt floor, you can install a polyurethane vapor barrier that will cover the entire floor. Cover the vapor barrier with dirt after to help protect it from getting damaged.

Manufacturers will assign an R-value to the different thicknesses of insulation. The higher the R-value, the better the insulation works. To determine how much insulation you will need to buy, you can try using the insulation calculator found at Rockwool website.

How Do You Insulate an Unvented Crawl Space?

In an unvented crawl space, the general rule is to insulate the perimeter foundation walls from the inside of the crawl space.

To do so:

  1. First, start by insulating the perimeter joists between the floor joists. There are two types; the header joists and the stringer joists. Header joists are the ones that run across the ends of the floor joists, while the stringer joist run parallel to the floor joists.

  2. Measure and cut unfaced insulation and wedge it in between header joists. Try not to cut the pieces smaller than the space between the header joists. You want the pieces to sit in tight to block out the cold air.

  3. Once the header joists are insulated, you can now begin to insulate the walls below. To do so, use an insulation blanket that will be long enough to run down the wall with an additional 2 feet at the bottom that extends into the crawl space. Using furring strips, nail the insulation down along the wooden sill plate.

  4. Next, we can move onto insulating the stringer joists and walls. When it comes to the stringer joists, you have two options.

    Option 1: You can run the insulation blanket down from the sub-floor and straight down the wall.

    Option 2: You can cut unfaced insulation strips to wedge in between the sub-floor and sill plate, and then run the insulation blanket down the wall, using a  furring strip along with the sill plate.

    Whichever option you use, don’t forget to extend the insulation blanket an additional 2 feet out into the crawl space, and make sure the insulation is running next to one and other with no gaps between them.

  5. Next, using 2×4’s, anchor the insulation as close to the walls as you can.

  6. Last, use some duct tape to secure and seal up any cracks or small gaps between the strips of insulation blankets.

How Do You Insulate a Vented Crawl Space?

When insulating a vented crawl space, the underside of the sub-floor is what should be insulated. Look for insulation that has a vapor retarder built-in.

To do so:

  1. First, start by measuring the length and width of each cavity that you will be filling. Note, not all joists will be the same.

  2. Next, begin cutting long strips of insulation to snugly fit in between the floor joists, making sure to fill in any gaps completely. Even small gaps will allow cold air to pass through.

  3. When shoving the insulation up in between the floor joists, put the paper side up so that it is pressed up against the sub-floor above.

  4. Depending on which type of insulation you are using, on the bottom of the insulation or non-vapor retarder side, you might have some flanges that you can use to staple into the floor joists. If you do not have flanges, you can use an insulation support wire to secure the insulation in place. Support wire should be cut a little longer than the width of the joists so that they can be installed to hold the insulation in place.

  5. Any spot where you have ductwork exposed, insulation should be installed over the ductwork to prevent any heat loss. The same goes with any water pipes, make sure to install the insulation over the top of the pipes to help keep them from freezing.

  6. Use a wire mesh to prevent small animals from nesting within the insulation. Some people use chicken wire for this; however, small rodents can fit in between the holes. I would recommend a product like Yardgard which have smaller holes.  Amazon currently sells a 24-inch x 50-foot for $45 (click here for current price).

    Nail the wire mesh to the bottom side of the floor joists. Pull it nice and tight, and position the nails within 12 inches of one and other.

Should I Cover Crawl Space Vents in Winter?

In general, the answer to this question is. Yes, you do want to cover crawl space vents during the winter months. There are two main reasons why you should close the vents during the winter. The main reason is that you don’t want to allow snow to make its way in, or have the water lines freeze.

The second reason is that cold air will tend to hang around the lower part of the home, while the warm air rises to the upper floors. Although closing the vents alone won’t stop the cold air from finding its way in, it will help slow it down or at least prevent a more serious problem.

A good time to begin covering the vents is typically in October when the days begin to get shorter, and frost starts to occur overnight.

How Do You Cover Crawl Space Vents?

A very handy DIY way of covering crawl space vents for the winter is to use 2-inch foam insulation sheets and cut them to fit perfectly behind the vent covers. To do so, you have two options.

#1. – You can crawl inside of the crawl space with the pre-cut foam insulation, and wedge them into place. Since you want to fill the width of the wall, you will need to use 2 or 3 pieces of insulation. Once the insulation is in place, use a can of spray foam to fill in and around the foam insulation to close off any cracks and gaps.

#2. – If crawling inside of the crawl space is not an option, you can remove each vent cover on the exterior and wedge your foam insulation in from the outside. Once you have the first foam block wedged in, take your can of spray foam to seal up the cracks and gaps. Install another layer of foam behind that and once again spray foam any gaps and cracks closed. Once finished, put the vent cover back on.


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