Rigid insulation vs. Fiberglass

cbc58 · February 02, 2012, 05:19:13 PM

Are there any issues with putting rigid foam insulation in the walls instead of fiberglass bats?

I was reading somewhere that there may be something that has to do with moisture getting trapped between the foam and the sheathing - causing the sheathing to deteriorate faster because the wall can't breathe as well. When you do spray foam (or get SIP's) there is no air gap... but with the rigid panels I can see where there may be. Was going to go (from inside out) sheet rock - vapor barrier - insulation - sheathing - felt paper- siding.

Reason I ask is someone has a bunch of commercial panels for sale and they are 2.75" / R19. Was thinking of putting it in 2x4 walls. Anyone looked into rigid insulation?

MountainDon · February 02, 2012, 07:06:40 PM

Hmmm. I just think that cutting, fitting, then getting it sealed properly is more work than I want to take on myself.

February 02, 2012, 09:27:59 PM

What about cutting them ~1" undersized and sealing them with a good bead of sprayfoam?

cbc58 · February 03, 2012, 08:07:35 AM

I could do that and was going to seal them if I went that route... but became concerned about possible moisture buildup. I guess that they will work fine if everything is sealed tight. Was hoping someone here has been through the process of weighing rigid vs. fiberglass. The extra labor might not be worth it as Mtn Don pointed out.

Squirl · February 03, 2012, 09:25:37 AM

I did some, but it was scrap packaging Styrofoam. The cutting and placing was not worth the aggravation. After an hour I got maybe one stud bay done. Then I looked up and realized I could have done half the shed in fiberglass in the same amount of time for $10 a roll. The cost of spray foam sealing really adds up.

Is the siding or roofing already on? Rigid foam is more effective on the outside of studs. Faster, easier, and because you don't get the extra stud heat loss of 3.5 inch studs spaced 16" O/C, more energy efficient.

February 03, 2012, 10:18:53 AM

siding and roofing not on. was looking at doing some thin rigid insulation on the outside as you mention.. in addition to fiberglass.

years ago I met a builder who built high energy efficient homes and he showed me how he sided a house so that there was actually a gap of a half inch or so between the sheathing and the siding (using furring strips) which created an air envelope... anyone done or researched that type of construction?

MountainDon · February 03, 2012, 10:45:31 AM

Works good with vertical furring screwed through the foam into the studs. Use structural rated screws not deck screws. If the final layer of foam has reflective foil you can pickup a little extra "rated R value" from heat going into the house in summer. I have some polyios foil faced foam I'm planning on using when I get around to my window and siding project here at home.

Yankeesouth · February 03, 2012, 12:00:54 PM

I did exactly what you are talking about doing with my cabin. I got 2" rigid for 4 x 8 sheets pennies and used it instead of insulation batts. 4 buddies, couple cases of beer and we had living room, two bedroons, loft, and kitchen done in about 2 hours. Panels were cut to fit between stids then I spray foamed the gaps. I did it for two reasons one to eliminate critters, ants, etc....from nesting and the second my cabin is OLD and was balloon framed therefore that's about all I could get to fit. Thus far it seems to be working. That was over 2 years ago. One thing....the rigid butts directly to the exterior wood slat walls, no exterior sheathing or siding , therefore there is considerable air movement. I'm not concerned about moisture.

SouthernTier · February 03, 2012, 12:27:53 PM

The thinking about where condensation may occur inside the walls is a good thing to think about.

I've read this book:

http://www.amazon.com/designing-comfortable-efficient-environmentally-responsible/dp/0975512714/ref=sr_1_1?s=books&ie=UTF8&qid=1328289767&sr=1-1

and it has a lot of good (though fairly technical) discussion about this. It looks as various combinations of insulations, moisture and vapor barriers and tells how you can predict whether you will have condensation within the walls for different climates. It shows how to estimage the temperature gradient from inside the house to the outside of the house and where the due point falls, and whether moisture is driven to that point. Highly recommended.

February 03, 2012, 06:11:31 PM

I did the exact thing you are describing...got a great deal on the 2" foam panels and cut them to fit snugly between studs to a total depth of 4". Cut them snug and they work great. The labor and mess is incredible however. Fortunately, you only need to score the panel and "crack" it to make your cuts.
One other note, I did drill a small vent hole on the top and bottom of all my panels just to minimize any potential for the studs to sweat behind the panels. In the summer its like an ice box and the winter it takes nothing to heat. Also tossed 2" in the ceiling along with R30 fibreglass.

beckhamk · February 05, 2012, 09:03:12 AM

If you go the rigid foam, get yourself a sawza (Reciprocating Saw) to cut this stuff fast. We had purchase rigid foam 2-2.5 inches thick to sandwich between our window and door headers. I brought a steak nife as i didnt own the saw yet. boy did that take forever. Later we used some more rigid foam elsewhere and now i had the saw and it was a world of difference in cutting

. wish i has that saw earlier.

DirtyLittleSecret · February 07, 2012, 03:35:10 PM

A sharp razor blade and long edge makes a much cleaner job!

MWAndrus · February 07, 2012, 08:53:45 PM

A tablesaw works good too.

MountainDon · February 07, 2012, 09:01:49 PM

Any kind of a saw makes a lot of bit bits of foam that stick to everything you don't want then to stick to. Static electricity. My experience at least. Virtually no mess if you cut a line, using a metal straightedge (flat 1.5 x 0.125 aluminum), then "snap" the board to break it. Unfortunately the table saw does make the most precision of cuts. But I was vacuuming static clinging foam bits forever, it seemed. YMMV

February 09, 2012, 10:17:48 AM

Quote from: DirtyLittleSecret on February 03, 2012, 06:11:31 PM
I did the exact thing you are describing...got a great deal on the 2" foam panels and cut them to fit snugly between studs to a total depth of 4". Cut them snug and they work great. The labor and mess is incredible however. Fortunately, you only need to score the panel and "crack" it to make your cuts.
One other note, I did drill a small vent hole on the top and bottom of all my panels just to minimize any potential for the studs to sweat behind the panels. In the summer its like an ice box and the winter it takes nothing to heat. Also tossed 2" in the ceiling along with R30 fibreglass.

I am also doing the exact same thing except, I am sandwiching and gluing two panels between 2 layers of OSB, building my own sip panels, this will give me a r28.

Don_P · February 10, 2012, 05:44:26 AM

to the forum
Don't forget that the OSB/foam connection in a Structural insulated panel is part of the structure. That is nigh on impossible to attain in the field.

manonthemountain · February 10, 2012, 10:13:10 AM

Quote from: Don_P on February 10, 2012, 05:44:26 AM
to the forum
Don't forget that the OSB/foam connection in a Structural insulated panel is part of the structure. That is nigh on impossible to attain in the field.

Hi Don. The way that Sip panels are made is through lamination, all panels are glued and the pressed, its the same as any lamination. The way that I intend to do this in the field is to use construction adhesive between each layer, and then carriage bolts on the 2' center @ 12" on center to get my compression, The foam itself has structural integrity, and by adding the OSB to the outside layers you are gaining all the structural integrity you need.

Just have to make sure to use adhesive designed for foam, most adhesives will eat foam.

I worked for the studios for many years and we used foam and OSB all the time to create many forms and the structural integrity was awesome.

firefox · February 10, 2012, 07:50:07 PM

Would you please post the adheasives that you have used to bond the osb
to the foam.
Thank you!!!
Bruce

cbc58 · February 14, 2012, 10:13:52 AM

wonder if there would be any issues if you took two 1.5" panels and stacked them in - on on top of the other - to get double the R value. I know things would need to be tight but wondering if they should be glued/nailed/screwed together or just float on top on one another.

i am seeing a ton of rigid insulation come up for sale in my area and according to the sellers it is coming from commercial buildings and cold storage units that were damaged from a tornado about 8 months ago. guess insurance is covering the buildings and they are tearing down the old ones and scraping all the materials.

Erin · February 14, 2012, 12:03:44 PM

Something to remember is that SIPs are indeed structural. They are designed to be used with NO FRAMING system. That is, they are the structure. As such, one probably shouldn't create their own structural insulated panels.

A type of panel/curtain wall, on the other hand, is a similar creation with foam sandwiched between two pieces of plywood and/or drywall. They are then hung on a frame of some sort. Technically not SIPs, because they aren't structural, they are often referred to as SIPs...

MountainDon · February 14, 2012, 01:13:19 PM

Right Erin, I think it is safe to say you could make something that looks like a SIP. Then use that in a timber frame building the same way they build straw vale buildings here in NM. Firts the structural frame, then the infill. I don't think a little bit of construction adhesive installed by the owner building id going to come close to what a factory turns out.