FOIL FACED VS FIBER FACED POLYISO

[nh-dan]

Does anyone know if there is a huge difference between foil faced polyiso and fiber faced polyiso? There is a recycle insulation place offering big discounts on the fiber faced. I would be using it on my roof and walls. The only thing I have been able to find is that tape does not stick to the fiber as well. Other than that the R value should be the same, but I worry about possible vapor transmission through the felt vs the foil.

Roof construction will be 2x8 boards, ice and water shield, 6" of insulation (3) 2" layers staggered and taped, vertical strapping to hold down the insulation, horizontal strapping, metal roofing.

Wall construction will be zip siding taped and nail holes sealed, 4" of insulation (2) 2" layers staggered and taped, horizontal strapping to hold up the insulation, horizontal siding.

Any help would be appreciated
Dan

[mike_belben]

@Don P don what is the name of your buddy there northeast materials expert guy.. Mark something?  Hes a building materials wizard/ consultant .. Id ask him. 

[Don P]

  buildingscience.com, Joe Lstiburek

I'd go for the used, either tape or leave a ~3/8" gap between pieces and sprayfoam the gaps.

There was a conversation about heat stroke in the last week or so and how long it takes to recover. I was a kid working during the summer for my Dad. We were putting foil faced foam on a roof on a hot bright day. I woke up in the basement with chills, they had gotten me down but I have no memory of it. For about a decade hot bright sun was a recipe for a pounder. Be careful with foil faced this time of year it's tanning you from both sides.

[Ljohnsaw]

Roof construction will be 2x8 boards, ice and water shield, 6" of insulation (3) 2" layers staggered and taped, vertical strapping to hold down the insulation, horizontal strapping, metal roofing

I'm doing the same except the inspector made a note on my plans (don't have them handy at the moment) that I *think* he said the ice & water shield is on top of the insulation - or maybe it was something else for fire protection...  My plan also shows felt on the roof boards under the insulation.  That way, if a knot happens to fall out, I won't see white insulation.  My thinking is that *if* moisture gets below the insulation, it won't get to the wood.  Comments?

[Don P]

This one was 2x6 T&G roof decking, tarpaper, 5" polyiso with seams staggered, 2x4's vertically forming a vent channel, 5/8" ply, tarpaper and shingles. IIRC that was an 18/12, we called it a rain splitter  :D



 

[Ljohnsaw]

Don,
Was that snow country?  How much (snow load)?  What kind of ridge vent did you use?  That would be called a "cold roof"?  I'm just going to have 1x4 battens vertically then horizontal on top with the metal roof attached to that.  I'm thinking that is still a cold roof, correct?

I am planning on using EPS.  I had some free polyiso that I used at my old ranch for the well house.  We'd get below freezing a few nights in the winter.  Anyhow, carpenter ants loved it.  I went in one day when the pump was acting up (probably been a couple years on its own) and there were huge piles of polyiso dust everywhere.  So, EPS for me on the cabin!

[Don P]

Not really "snow country" we have a 25psf snow load.
I would call that a cold roof. With cold air flow under the roofing/ over the insulation yes, I'd consider yours to be a cold roof. I didn't do the shingles, I'm trying to remember, thinking it had shinglevent on it but not sure with that pitch, It may have been cobra or one of the shingle over mesh types. It's interesting to hear different experiences, I've had ant troubles in EPS and can't think of any in polyiso. The common denominator with ants is usually water getting in.

[Bruno of NH]

The foam with the felt is made for roof applications under edpm .
I wouldn't see why you can't use it.
Like Don says leave a gap and spray foam it.

[nh-dan]

Thanks for all the comments and suggestions. I think I'll be going with the felt, and spraying foam in the gaps.

I'm also thinking about putting a single layer of 1/2 foil faced on top of the felt.

Dan