How to Insulate your Crawlspace and Keep your Toes a Little Warmer.
Posted: Sunday, January 17, 2010
by Dan Bossenbroek
Just Green Homes
You may not realize it, but hundreds of dollars might be slipping out from under your feet every year. Adding R-19 insulation to a 400 square foot crawlspace could save you $125 a year on your heating bills and pay for itself in about a year. With an investment of a few hours this energy saving home improvement project will save you money and your toes from getting so cold.
Second, figure out if your crawl space is vented to the outside or deemed heated by the building code. Vents are typically 8" tall by 16" wide and are placed equally around the perimeter.
If your crawlspace is vented, you need to seal the vents. First close the vents if it's possible, then cut a piece of rigid insulation, treated plywood, or aluminum flashing to fit snugly into the opening. Next seal the crack around this with caulk or foam insulation in order to make an air tight seal.
The main enemy of crawlspaces is moisture so every step must be taken to keep moisture out. Cut strips of 6 mil plastic sheeting one foot wider than the crawlspaces walls are tall. Staple the edge of the plastic sheeting to the sill plate around the entire perimeter of the crawlspace. Overlap the sheets by 6" and tape all of the joints. Now you have a dry surface for the insulation to rest against.
The next step is to install the insulation on the walls of your crawlspace. Kraft faced fiberglass batt insulation works great in this application. If you purchase the batts to fit between the floor joists, it will be easier to install in vertical strips, but then you will be left with 1 " gaps between the pieces below the floor structure. Or you can add wood framing or cut strips of insulation to fit, but that's a lot of work. If you install the insulation horizontally, you will need to cut slits in the insulation so that it will fit around the floor joists. Staple the insulation to the wood joists to hold it in place.
Most crawl spaces will need two horizontal rows of 22 " wide batts. Use duct tape to secure the lower row to the upper row.
Once the insulation is in place, you will want to seal all of the seams between the insulation. Duct tape will fit the bill here. Installing the insulation in long horizontal strips will help reduce the amount of seams that you will need to seal.
You will also want to seal the joint between the batt insulation and the floor joists and sub-floor. If your house is fairly new and everything down there is fairly clean you could use more duct tape. However, if your house is fairly new the crawl space is probably already insulated. So, if things are a bit dirty in your crawl space a good product to use to seal these cracks is foam insulation. Spray a small bead between the paper and the joists and floor above. Wait for an hour or two and then return to seal any remaining gaps.
Next you should cover the entire floor with a plastic sheeting vapor barrier. If you won't need to go into your crawl space very often then 4 mil plastic sheeting will work, but 6 mil is recommended. Now that your crawl space is heated, you want to keep any unwanted moisture out. Overlap the joints of the plastic 6" and tape all the joints. Tape the joints between the plastic and the insulation as well.
Your crawlspace will now be heated, but there is no need to dump a bunch of extra air down there. So it's a great idea to seal all of the joints in the ducts in the crawlspace. One might think that this would be the perfect use for duct tape, but I have found that aluminum tape works much better. It sticks much better and lasts much longer than duct tape. It is a bit more expensive, but you might want to use it everywhere in this project instead of duct tape. The one drawback if aluminum tape is that it will tear and puncture easier than duct tape, so a little more care must be used when installing it.
Since your crawlspace is now heated, the floor above it should be considerably warmer as well, and thus will be much more comfortable to walk around on in the winter.
Dan Bossenbroek is a registered architect and has been incorporating energy conservation design strategies into his projects for over seventeen years. He has extensive experience in residential design, is a Leadership in Energy and Environmental Design Accredited Professional (LEED AP) and his area of expertise is high performance buildings and sustainable design. Furthermore, he is an avid do-it-yourselfer having renovated several older homes. For energy saving products and home improvement advice he recommends www.justgreenhomes.net
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Top-level comments on this article: (5 total)This is some very good advice, Dan. We did this in the house we were renting (spent 4 years there), and saved almost $400 a year.Richard,I don't expect to save quite that much since mine is only 400 s.f., but I'm expecting to save at least $125. Besides, the floor seems a bit warmer too.great! You'll see a difference pronto!
Dan,Thank you great article! good information.Jose,Glad that you liked it.
Some good ideas especially with energy prices going up and up each month! MarijoMarijo,You're not kidding - my electric rate has gone up 25% in the last two years and water has gone up 27%. Thankfully my natural gas rate came back down last year it was up 26%.
Hi Dan. Great money-saving advice. Informative and well-written. Thank you for sharing this to us. All the best to you and yours, ~Nenita~Nenita,Thanks for the comments and kind words. Take care! Dan
Great money-saving advice. Very informative and well-written. Thanks for sharing this. All the best to you and yours, ~Nenita~
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