Insulating Floor

[KennyG]

I just volunteered to help with a project, insulating a floor. I haven't actually seen it yet, but I understand it is a typical joist construction over a crawl space. A family room add on that wasn't insulated when it was built. I've never done this before, but I understand we should have a good vapor barrier down on the ground. It seems to me that we should use unfaced insulation, and not have a vapor barrier under the insulation. Is that correct? Any ideas on the easiest way to hold the insulation in place?

 

[s219]

In my house, they used faced insulation batts with the paper up against the underside of the floor (so you see the raw fiberglass from the crawl space). Wire insulation supports were used to hold the batts in place. There is a heavy plastic sheet on the dirt floor of the crawl space.

 

[Shutesbury]

insulating floor of mudroom on footings

 

[JD 4520]

Those are separate matters. You do need a heavy dark plastic for ground cover. Several important reasons but to keep any moisture to the ground and not being absorbed above. Next, insulation can be done a number of ways with or without facing paper bit needs to be secured to perform its intended purpose. Often times it doesn't have any facing so a type of support is used from wire to string to plastic holders. Hope that helps.

 

[BIG DOOLEY]

I used small nails and wire.did a 12x12 room.
what a pain!
I eventually put 2 layers of 2" styrofoam (4" total) around the inside perimeter of our entire crawl space.
That made a huge difference.
crawl space is warm and floors are warm.
it may be easier to try the walls of the crawl space ?

 

[lutt]

I have heard of people using heavy chicken wire fence,not had any expierance with it myself. Dont know how long it would last. I had thought about doing it to my rent house,but have mixed emotions about it. Mostly concerned with moisture. LUTT

 

[SHORT KID]

I would first make sure there is sufficent drainage in the crawl space, and that it is fairly level. Next cover the dirt with heavy plastic,wall to wall then cover the plastic with fine stone about 4 inches deep. Then if you are still cold use styrofoam on side walls. A lot of people use chicken wire to hold up insulation but the wire stays pushed up between the joists will be sufficent as long the moisture is contained. Make sure all vents and doors or windows are sealed in the winter, and vent in the summer. The area I live in has many crawl spaces under the vacation homes and I repaired many including replacing main beams and supports because of moisture. The crawl space will stay about 40 degrees in the cold of winter as long as there is no air infiltration.

 

[BeezFun]

I just volunteered to help with a project, insulating a floor. I haven't actually seen it yet, but I understand it is a typical joist construction over a crawl space. A family room add on that wasn't insulated when it was built. I've never done this before, but I understand we should have a good vapor barrier down on the ground. It seems to me that we should use unfaced insulation, and not have a vapor barrier under the insulation. Is that correct? Any ideas on the easiest way to hold the insulation in place?

Yes, you have the right approach. I would use 15mil plastic on the ground and if you can tape the seams. More overlap the better. If there's pea gravel down there, throw some on top of the plastic around the edges to keep it tight against the wall. They make plastic "wires" now to hold up the insulation, they won't rust like the metal ones but either work fine. You're correct, don't get any facing on the insulation and if you do, face it up toward the living space. You might also think about using foam board to insulate the joist cavities around the perimeter. I cut them about 1/2" small and foam them in around the edges. That holds them snug and shuts out the air. That's the place where most air intrusion comes from because the sill doesn't fit the foundation properly and the base of the siding isn't sealed against the outside of foundation.

 

[KennyG]

Lots of good info. Thanks everyone.

 

[Qapla]

Don't know if this would help or if it is available in your area, but it should be available on the Internet.

Under Mobile Homes they use a moisture inhibiting, fiber laced paper type product that holds the insulation in the floor. This material is very hard to tear and will last as long 20, 30 or more years. It is designed specifically for holding fiber type insulation in flooring with the underside of the floor being exposed to the ground.