I have crawlspace with an earth floor. it is approx. 24" from the ground to the floor joist. I have 6 mil poly on the ground. I have vents that will be opened in the summer and closed during the winter. There are no heating or a/c ductwork in the crawlspace and the water lines are insulated to keep condensation from being a problem. What is the thought on installing insulation between the joist and if so what is the best type of insulation to use to keep it from keep insulation from hanging down over a period of time.


When I've done this in the past, I've put in fiberglass between the floor joists, and then covered it with sheets of extruded polystyrene insulation board (XPS) to add a bit more R value and keep it in place. If you're worried about critters chewing around, you can do the same thing with thin plywood or fiberglass reinforced plastic panels.

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    R-19 is required in Maryland, it may be different in batalor's area. Nice touch with the foam board, it keeps the area clean, although his needed access is minimal. I have the joist sections of my home insulated, built in 1989. The insulation is installed with the paper side to the floor, fiberglass exposed. I used wire supports to hold it in place, still holds today. I have had need to go into the crawlspace and run updated wiring from time to time and removing the wire supports came in handy for access of the floor from below. Please pardon my embellishment of your answer with more options.
    – Jack
    Apr 27 '14 at 3:19
  • @Jack - Not a problem at all, nice embellishment.
    – Comintern
    Apr 27 '14 at 3:28
  • @Jack, good comments . What are your thoughts on no insulation if the crawlspace vents are closed up in the winter. I am in eastern Virginia
    – bat1
    Apr 27 '14 at 17:39
  • I'd still insulate. Keep in mind that you insulate against heat transfer, so floor insulation will also help your A/C in the summer.
    – Comintern
    Apr 27 '14 at 17:54
  • Comintern is spot on, insulate. In our area, (I am near Annapolis) code requires R-19 for floors. For what its worth, there is debate on whether foundation vents do any good or not. I could see their purpose in a damp crawlspace. I know it is not part of the question, just part of your situation, I thought I would throw it out there anyway. In homes I have built, the crawlspace walls have been insulated with 2 lb spray foam. Any other kind I would worry about a handy insect path to your wood. Just getting that out there too.
    – Jack
    Apr 27 '14 at 19:54

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