# Insulate an eave soffit between 1st and 2nd floor?



## joefrompa (May 16, 2011)

Hi all,

I have a 1970s built 2-story colonial. On the rear and front of the house, the 2nd story extends out from the 1st story wall by about 24" and is about 20' long.

As far as I can tell, this soffit goes directly into the joists/subfloor below the 2nd story bedrooms/areas.

I'm planning on having my siding re-done, during which time they'd re-clad the soffits. I'm thinking about having them add a 1-2" hard-foam board before re-cladding to add an additional r-4 to r-8 value in that space.

Any thoughts on this? I can't seem to find any directly analogous situations anywhere online

Joe

P.s. These soffits are not accessible attic space, nor are they vented.


----------



## lukem (May 16, 2011)

Just put some batts in there...way cheaper and you'll get a lot more R value out of it.

My last house had the same thing, except the first floor was basement.  I tucked in batts so they were L shaped...covering the outside wall and bottom of the soffit where it extended beyond the wall.  I didn't have any moisture issues if that is what you are worried about.  Think about it...soffit generally vents to your attic...and that's never a problem for moisture.


----------



## lukem (May 16, 2011)

joefrompa said:
			
		

> P.s. These soffits are not accessible attic space, nor are they vented.



Even better.  Batts all the way.


----------



## joefrompa (May 16, 2011)

Ok, so I can rip off the soffits (painted plywood) before the siding people come out and shove up in there some thick batts  with a vapor barrier facing the outside? Or do I need vapor barrier, since they should be wrapping the soffit in tyvek before cladding it over.


----------



## lukem (May 16, 2011)

I can't tell you what local code is, or what the book says to do (take this advice as you get what you pay for), but I would think that Tyvec + soffit would provide plenty of protection  

This is all the walls in your house have, right?  And the rain/wind/snow hits them directly....the soffit however will rarely have a direct exposure (wind/rain rarely come from ground up, at least where I live).

I would pull down the existing soffit, batt it up, and let the contractor take it from there.  

I think it would also be prudent to call the contractor and tell them what you are up to.  They might have some better advice for your locality.


----------



## midwestcoast (May 17, 2011)

I'm a belt & suspenders kind of guy when it comes to insulation.  For something like this I figure you're (hopefully) only going to tear into it once so be sure to get plenty of insulation in there while you're at it.  In other words I'd probably put in batts and add 1" or 1 1/2" foam board on the bottom.  As well as getting a higher R-Value the foam would prevent the loss of R-value due to convection that occurs in fiberglass batts at very low temperatures.  I'd ask the contractor directly about using a vapor barrier with the Tyvek. Otherwise I'd pass on using one.
A really important detail here will be how well they seal the soffit to wall seams.  You don't want any air leakage there, soffits like that are a common source of major air leaks. Done well, the air sealing will be worth more than the insulation.


----------



## benjamin (May 17, 2011)

midwestcoast said:
			
		

> I'm a belt & suspenders kind of guy when it comes to insulation. For something like this I figure you're (hopefully) only going to tear into it once so be sure to get plenty of insulation in there while you're at it. In other words I'd probably put in batt and add 1" or 1 1/2" foam board on the bottom. As well as getting a higher R-Value* the foam would prevent the loss of R-value due to convection* that occurs in fiberglass batt at very low temperatures. I'd ask the contractor directly about using a vapor barrier with the Tyvek. Otherwise I'd pass on using one.
> A really important detail here will be how well they seal the soffit to wall seams. You don't want any air leakage there, soffits like that are a common source of major air leaks. Done well, the *air sealing will be worth more than the insulation.*



I'm with him.

Tear off some of the soffit to see what's there. Most likely there's nothing or just a batt stuffed in the joist space. You want to put foam in the space between the joists and the top plate of the wall and the floor sheathing above, caulked or foamed all the way around. If the second floor sheathing is boards instead of plywood then you want to cover that with foam also and caulk or foam it to the joists, other foam, and drywall and floor sheathing. 

Cut the foam loose and use expanding foam to seal it. Cut 8 3/4" x 14" for a 2x10 16"oc and it will go in easier and better with foam.  The foam on the inside forms the vapor barrier where is should be.  You can put batts outside the foam, but they don't add much.


----------



## Don2222 (May 19, 2011)

midwestcoast said:
			
		

> I'm a belt & suspenders kind of guy when it comes to insulation.  For something like this I figure you're (hopefully) only going to tear into it once so be sure to get plenty of insulation in there while you're at it.  In other words I'd probably put in batts and add 1" or 1 1/2" foam board on the bottom.  As well as getting a higher R-Value the foam would prevent the loss of R-value due to convection that occurs in fiberglass batts at very low temperatures.  I'd ask the contractor directly about using a vapor barrier with the Tyvek. Otherwise I'd pass on using one.
> A really important detail here will be how well they seal the soffit to wall seams.  You don't want any air leakage there, soffits like that are a common source of major air leaks. Done well, the air sealing will be worth more than the insulation.



Hello

I did the same in my 1st floor overhang except I put in Home Depot's Reflectix foil instead of the rigid foam insulation. Then I filled the cavity with 6" R19 batt fiberglass or you could use the 5.5" R23 Roxul for more benefit. See  http://www.roxul.com/residential/products/roxul+comfortbattâ„¢


The reason I used the foil:
Not only does it seal the cracks but it also keeps the radiant heat in the house during winter!

See foil specs
http://www.reflectixinc.com/


----------

