Home Improvement Expert Danny Lipford

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How to Insulate the Crawl Space Under Your Home

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My house has a crawlspace under it, and the floors get very cold in winter. What is the best way to insulate a crawlspace on a budget? -Margaret

Hi Margaret,

Having a crawl space under your house can make your home colder in the winter than a house built on a concrete slab. Also, mold and mildew can be a problem in a crawl space, so you need to be sure to guard against that as well.

To make the floors in your home warmer, and prevent mold and mildew from forming in the crawl space, requires more than just insulation. Here’s how to go about reducing moisture and insulating a crawl space under your home:

  • Cover Ground: Start by removing any items stored under your house, as well as any construction debris, such as scraps of wood or broken bricks. Next, even out the dirt in the crawl space, and correct any problems you might have with water standing under your house by filling in any holes or depressions. Finally, cover the entire area under the house with a layer of 6-mil plastic sheeting. Overlap the sheets a foot or so, cut the plastic around piers, and run the plastic all the way to the foundation walls. As an added measure, you can tape the seams in the sheets together to keep the plastic in place.
  • Insulate Under Floor: Fiberglass insulation batts or rolls are the most economical and easiest DIY choice for insulating between the floor joist in a crawl space. The U.S. Department of Energy recommends R-11 (3½”) insulation under floors in warm climates and an R-25 (6” to 8”) in cold climates. Install the insulation with the paper vapor barrier facing up toward the heated living space, and make sure the insulation fits tightly between the joists. Hold the insulation in place from below using insulation support wires, or by stapling chicken wire to the bottom of the joists.
  • Enclose Foundation: If your foundation isn’t enclosed, fill the space between the exterior piers with bricks, concrete blocks, or lattice panels. To install brick or block walls, pour a concrete footing between each of the piers around the outside of the house, then lay bricks or blocks on the footing. Install foundation vents in the walls, so there is one-square-foot of vent space for every 150 square feet of crawl space. Another option is to make 2×4 frames from pressure treated wood to fit between the piers; then cover the outside with lattice, and staple landscape fabric on the inside to reduce (but not stop) air infiltration under the house.

Good luck with your project,

Danny

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5 Comments on “How to Insulate the Crawl Space Under Your Home”

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  1. Margaret Says:
    June 18th, 2012 at 11:32 am

    I have a new addition on my house. The footing walls in the addition have been insulated with spray foam. Now I have vapour barrier and rigid foam insulation to complete the ground. What order do they go down and should attach anything to the walls?

  2. Gary Janke Says:
    November 19th, 2012 at 11:34 am

    What is the Tennessee code for having paper backed vs no paper back Batt insulation inbetween joist up against flooring. I have heard the code changed to no paper backing due to moisture collection issues.

  3. Carl Roderick Says:
    December 6th, 2012 at 3:58 pm

    During a recent termite inspection, the agent mentioned that I have severe mold on the insulation and on the floor joists ( i had noticed it also during my last trip under the house). He recommened ripping out the insulation, treating the wood and laying down a new layer of 6 mil plastic. He also said not to bother replacing the insulation as it wasn’t cost effective. Is that right?, not to bother with insulation, it would cost an extra $2500 to replace.

  4. darryl Says:
    November 7th, 2013 at 2:32 pm

    I am insulating crawl space in Louisiana of a 1880′s house. House is 7 ft off of the ground. We are using batts. in the past I have used visquin and stabled it in between the joist to help hold the insulation in place. The contractor told me not to due this because it will cause moisture build up. I have done this in the past with no problem. I have had problems with chicken wire…it rust and is hard to work with if you need to get in to do work. The contractor wans to use a nylon cloth that looks like the material used under the bottom of chairs….Suggestions

  5. Official Comment:

    Ben Erickson Says:
    November 18th, 2013 at 9:27 am

    Hi Darryl,
    Your question about how to insulate your crawl space was answered in the second hour of our November 16th Today’s Homeowner radio show. You can listen to the show on our website at http://www.todayshomeowner.com/radio/2013/11/16/todays-homeowner-radio-show-for-november-16-2013/

    Thank you for your interest!

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