What kind of insulation

[PipeDown]

I want to insulate the bottom of the floor (inside crawlspace). The problem is the floor joists are nowhere near 16" on center. My single story 1000SF house is built on a deck like subfloor. It is made up of 4x8 beams running the length of the house set 4 feet apart with 2x8 tongue and grooved planks set perpendicular. The result is a thick solid floor with few beams underneith.

To put it another way, the floor joists are 4 feet apart and the crawlspace access is a 2'x2" hole in the closet floor.

I was considering 4x8 sheets of solid core insulating panels cut in half the long way but this would be expensive and would not have as good R value as fiberglass. I would need to double or triple up on them to get the same R

Has anyone seen a product that sounds like it would work well here or am I stuck using 16" wide rolls and stapling in strips to the underside of the subfloor instead of the joists. This is not ideal because it would compress the edges of the insulation.

Do you think installing paper faced insulation with the paper up so I can staple through it is a good solution?

Fortunately, I am in northern CA and the climate is mild.

[roger61611]

Is the ROI there to warrant the expense ?

[Jeff]

One possibility. Put nails in the beams every two feet, leaving enough space between the heads and beams to wrap a loop of steel wire. Run two 23 wide insulation rolls between the beams and use the wire to hold in place, i.e. the insulation is resting on wires. Kind of a PITA to do this way, but might work.

[RicodJour]

The rigid insulation is the way to go - if you've determined that the potential energy savings and increase in comfort is worth the expense and effort. Since your climate is mild, 2" rigid insulation should be fine. Go with polyisocyanurate insulation (~R14 for 2") if you feel it's worth the money, extruded polystyrene (~R8 for 2") if not.

Since your floor is so thick you can just screw the boards in place with some of those pancake plates that they use for EIFS and use some expanding foam to fill in the gaps.

As an alternative, and not necessarily a great one, you could suspend

2x3s on 16" centers between the existing joists, then staple up fiberglass batts or use those wire press fit hangers. R

[mm]

This would compress tthe middle of the insulation. :( I don't know how bad that would be, but as bad as t he edges.

48 is 3 times 16. I would think you could tie the stuff up with strings wrapped around occasional nails or something, and after all three bats of insulation are up, nail a wood strip to hold things in place. Or soemthing like that.

Remove NOPSAM to email me. Please let me know if you have posted also.

[George E. Cawthon]

That type of construction is a standard type called post and beam. I would consider insulating the walls of the crawl space rather than the floor.

The paper should be toward the warm side, i.e. for the floor it would be directly against the subfloor. I would use 24" wide fiberglass so two widths would fit between the beams and just staple it to the floor. You might need to compress the sides a bit that is ok. It will be a messy job, but with the paper facing against the floor it should go up fairly well.

However, you will still need some type of material to support the fiberglass as it would eventually pull away from the paper. A very wide mesh or netting with holes at least 1" square and better

2" square could be used. Nylon might be preferred but most anything will do. Check what is available and cheapest in your area. Don't forget to cover the dirt floor of the crawlspace with 4-6 mil plastic if not already covered.

[Michael Daly]

Since there is no constraint on thickness, you could use expanded polystyrene foam (beadboard) that's thicker. Why pay for a high- priced insulation that's volume efficient when you can just go with thicker and cheaper insulation?

Mike

[Goedjn]

Either staple chickenwire to the bottom of the beams, and stuff insulation on top of that, or buy canisters of spray-on-foam and squirt insulation in place.

[PipeDown]

This definately is a concern too. This is my second winter in the house so I will be able to more accurately estimate my energy needs from my gas bills now.

[PipeDown]

Thanks everyone. It looks like solid core is the most practical solution from an installation standpoint. I just need to study the price a little more to see if it is really worthwhile (and find just the right material locally). I may insulate under one bedroom at first to see if it makes any difference. I might be able to get a good price from a packing materials company for foam core like material.

Another Idea that came to me was to string up nylon mesh (or similar) and fill it with packing popcorn as I get it leftover from shipments at work. Filling may be gradual but might cost nothing.

[RicodJour]

Tyvek instead of mesh/wire. The rigid is an easier installation, the peanuts are free. I wouldn't want to be the one stuffing peanuts into something over my head while I was lying on my back.

R

[PipeDown]

I was thinking shop vac in reverse to blow it in like blown in insulation. Just a concept but moot since I probably only can get the peanuts in modist sized batches.