Home Improvement Expert Danny Lipford

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How to Insulate the Crawl Space Under Your Home


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,


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13 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,
    You should use a material that allows air to go through, such as landscape fabric, to prevent moisture build up. Or use spring rods every few feet that are made for such a purpose.
    Thank you for your interest!

  6. walter gregory Says:
    August 4th, 2014 at 2:27 am

    1st things people always ask me the rotation of ceiling fan in winter and summer.I tell them that in the winter time the ceiling fan rotation standing under it while looking straight up at the fan the blades should be going in a ccw direction and in summer the blades shouold be cw while being directly under fan and looking up.People really have an issue being able to decide rotation because they see videos like on youtube and some people are looking at the fan in a direction that communicates to certain people a different angle or look and it confuses people on the exact rotation.I am correct aren’t i?Please respond so i can ensure people i have told them correctly.And on the floor insulation r11(rolled batts) the paper is suppose to be on the bottom side. Is this correct like you do on a wall inside of your house?I have other questions but i will do them in another subject line later.Thank you so much for a response…A loyal customer!!

  7. Official Comment:

    Ben Erickson Says:
    August 9th, 2014 at 9:42 pm

    Hi Walter,
    When looking up, ceiling fans should turn counterclockwise in summer and clockwise in winter. See our article on How to Use a Paddle Ceiling Fan Properly at http://www.todayshomeowner.com/using-ceiling-fans-properly/ to find out more. On insulation, the paper should always face toward the heated (interior) of your house. So under a floor the paper would face up, in the attic down, and in walls toward the inside.

  8. Ray Patterson Says:
    October 28th, 2014 at 5:25 am

    Is it wrong to block crawl space vents in the winter. My house is in Roxboro,N.C.

  9. Ann Marlow Says:
    November 10th, 2014 at 10:59 pm

    Hi Danny I am confused my house is on piers built 1955 I have plastic laid on ground but want to insulate because I have hardwood floors an can feel drafts I have rugs on most floors but still cold will insulation help faced or unfaced I need a budget friendly solution thank you lela ann Marlow I miss your show every week see you when football goes way I live in saraland al 36571

  10. james Says:
    November 14th, 2014 at 1:37 pm

    Has anyone have any comments on the yea or nay of spraying the concrete blocks on the inside to improve insulating the craw space. can you forget about the batten insulating between the floor joist

  11. stuart windley Says:
    January 11th, 2015 at 9:47 am

    I had professional house movers come out and inspect my 1928 house crawl space and this is what they told me: ( they are excellent and I have known them for a long time) If your home sets low to the ground on original foundation, it is best NOT to put insulation under the house!!The insulation will hold in the moisture and rot out your subfloor etc.They said many home owners make this mistake and it ruins their foundations in older homes.

    Recommendations for older homes:
    1. remove any insulation that you have placed under the house
    2. seal underneath with plastic
    3. install one or two humidifiers as needed
    4. Must have gutters on home that work well to keep any additional water from getting under house

    Your home should last for many years without any additional destruction to the sub floor or joist.

  12. Jim Marhevka Says:
    February 5th, 2015 at 2:45 am

    After installing the insulation, 6mil plastic on the dirt floor of a 5′ dirt filled crawl space, I read an article that said to put 6 mil plastic over the ceiling insulation as well. Is this okay to do as well for added protection

  13. Official Comment:

    Ben Erickson Says:
    February 5th, 2015 at 8:40 am

    Hi Jim,
    I’m not sure what you mean by ceiling insulation. If you’re referring to putting plastic sheeting over the bottom of the floor joists in the crawlspace, you shouldn’t as it will act as a vapor barrier and trap moisture from the house in the floor joists. If you want to put something on the bottom of the joists to hold the insulation in place, use chicken wire, landscape fabric, or housewrap so any water vapor from inside the house can escape. If you’re referring to insulation in an attic, you shouldn’t put plastic sheeting over the top of it either for the same reason.

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