foam vs. fiber insulation

[a2rjh]

Hello all,

Looking for opinions on crawl space insulation. This is for an old rent house on block and pad foundation. I am considering either R13 or

1 1/2" rigid foam (vapor barrier on one side and radiant barrier on the other).

Fiber seems to have better cumulative R-value. However, I don't know if bugs and crawlies nesting in it will be an issue. I can get the 1

1/2 for about 10 dollars a piece. Fiber will let me do this incrementally as time allows.

Trying to get a feel on what is the better option.

thanks richard

[aemeijers]

Get it spray-foamed. You can probably take an energy credit (if I understand the IRS page correctly), and you can depreciate it on your taxes (schedule E) as a substantial improvement.

[Tony Hwang]

Hi, Fiber is out if there is a possibility of getting wet.

[Ed Pawlowski]

There is price and there is value. No way would I use fiber in a crawl space. Could be good rodent nesting. Spray foam is best for that, but foam board would be my next choice.

[ransley]

Foam board is easier to work with , not affected by moisture, no itch. Fiberglass looses R value as it gets colder near zero, filber glass irritates but there are types they say dont but they cost more. Foam should be easier to get an airtight seal between sheets. With gas prices going up I think foam will be alot more.

[Jim Elbrecht]

Second the spray foam. Your gain will be more noticeable in comfort than $$ saved--- but if you're renting, keeping those tenants for a second winter is a plus.

Fiberglass will last a couple years before critters make it useless. Rigid foam *could* be done with a whole lot of crawling in the dirt and sealing edges with great stuff. [ideally the rigid stuff would be placed between the joists with 1/2 dead air space between it and the floor-- edges 'caulked' with expanding foam-- a foil sheet in there would probably be a good idea, too.]

The spray foam will be most expensive-- but you can be doing something more productive for the days you would have spent crawling in the dirt.

Jim

[a2rjh]

Thanks folks,

Foam seems to be the favorite for this application. Yes, my intent is to keep a tenant as long as possible. Paying utility bills is another burden/factor.

Will leaving a dead space not cause a problem with moisture accumulation/condensation?

Again, thanks. Will go with foam.

richard

[ransley]

Google it,

[ransley]

Loosing r value as it gets colder is a fact and at zero might be

10-25% or more, if you read fiberglass manufactuers they admit it but say its minimal, if you read cellulose manufacturers thay will say 50%. Maybe or the US gov site will have the best info. Its documented, but the exact percentage and at what temp I dont know. For southern areas its not to relavent, but up north it is. Cellulose is supposed to settle more than fiberglass, but both do settle. Best is to over do it and take a higher standard, not your minimum code requirements. For my area Zone 5 is R35, but I did R100 and iy settled to R 90 about. Heat rises and doing an attic is actualy cheap in what you can save over time. foam seals out air, so it helps even more.

[aemeijers]

Okay, dumb question- what if you applied foam board below the joists, running it crossways. Hang it with those screwgun screws with the big washers, and tape the joints? Would the dead space between foam and subfloor cause problems, assuming the foam board was rated as a vapor barrier? That way it would go up pretty quick, and if you marked where any ducts or utility lines run, it would be pretty easy to get at them, later. Is there something obvious I am missing? I've seen detached garage ceilings done this way, to keep the vented attic from superheating the garage bay while it is closed up all day.

[ransley]

It would work and lower humidity in the house in summer by keeping it in the crawl space. Just butting the joints will seal most of the air. I wonder if just stuffing batts up in the rafters might not be best for a cost reason, fiberglass has to be cheaper. and it wont get any drafts or rel low temps that would disadvantage it. It has to be a cost decision I would guess. Unless the crawlspace is a swamp !

[larry moe 'n curly]

Do fire codes actually allow installing foam without covering it with something highly fire resistant? Should they allow it?

[Ed Pawlowski]

"larry moe 'n curly" wrote

Foam is made from modified materials that will not burn unless thee is another source of ignition present. Unlike a living space, there is no heater, etc. that will start a fire. Local codes can always vary though.

[ransley]

It may be code to cover it, I think its the fumes that will kill you if it burns. Fiberglass doesnt have that issue. I think.

[larry moe 'n curly]

Regular styrofoam is like that, and that's why I don't trust the term "self extinguishing" very much.

[aemeijers]

I thought the requirement to cover it was only within the living area, or around ignition sources? I'd love to hang a foam panel curtain from the sill plate in my abandoned barely-accessible garage bay in the basement, but nobody around here sells the fire-rated stuff. Don't wanna stud it out and finish it due to moisture problems, but I figured a foam curtain from the sill plate to a few inches above the slab (and well below grade) would would warm the space and the bedrooms above it, and still let me see any leaks as they occur. Remove a couple screws, and the panel could pop right off.

[Ed Pawlowski]

"aemeijers" wrote

ALL foam made for insulation and construction is made from "modified grade" material. It must meet the specifications or cannot be sold. I must be in compliance with ASTM C578 Typical specification:

1.01 INSULATION A. Foam-Control EPS in compliance with ASTM C578. B. Foam-Control EPS with flame spread of less than 25 and a smoke developed index of less than 450

[aemeijers]

So why do all the panels in the local Borg say they have to be covered with drywall? I thought that one flavor of foam panel (can never remember the name) had been blessed for uncovered installations?

I'm tempted to just buy the thickest foil-covered iso panels I can stand to pay for, and do it anyway, since there is pretty much no inspection out here. I'm just afraid I'd have to rip it all down at sale time though, and that stuff adds up fast.

[zek]

Fiberglas is considered poor for small currents that build up when there is a high temperature differential. I guess the orientation is also important. Cellular is better at blocking air flow, thus offering better r value. Rigid foam has no Air flow. I believe the thinner the glass fibers, the better r value. I liked when corning made the no itch fine fibers. Also best in speaker boxes.

Greg

[Ed Pawlowski]

"aemeijers" wrote

Foam will not support combustion on its own, but it will burn if others things around it are burning. Put a match to it and it burns. Take the match away, the fire goes out in seconds.

I'd probably do that.