# Second story overhang soffits



## bcemail (Sep 18, 2010)

Posted over in building, but thought it might actually be more of an insulation question. Been trying to chase down some HVAC ducts sweating, and after removing some ceiling was able to see inside the soffits. These don't run into the attic, we have a gambrel roof but this is on "end" of the house.

In the first picture, you can see the between the brick and the plywood a bit of the vinyl soffit peeking through. Obviously not very well sealed. The bedroom above the area is always colder in the winter, as are the rooms on the first floor. Probably will be pulling off more of the ceiling, but wasn't sure if it was easier to tackle from inside or outside. Any ideas on what should be done? There is some insulation behind the brick on the wall, from what I've seen some foil covered rigid board and then fiberglass batts between the studs on the wall.

Thanks!


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## Dave Sal (Dec 20, 2012)

Here's a link to Building Science Corporation. They have tons of articles and papers explaining the proper way to build. This is a search page and I searched for "condensation on HVAC duct" and came up with the four papers at the bottom. You could probably play around with the search terms and come up with something better. 



https://www.buildingscience.com/document-search?term=&field_doc_topic_tid=All&type[]=7


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## XSleeper (Sep 23, 2007)

In cantilevered construction, that entire area in your first photo should be insulated. IMO you want 2" of rigid foam against the rim and on top of your plywood soffit, the rest can be filled with fiberglass.


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## bcemail (Sep 18, 2010)

Dave Sal said:


> Here's a link to Building Science Corporation. They have tons of articles and papers explaining the proper way to build. This is a search page and I searched for "condensation on HVAC duct" and came up with the four papers at the bottom. You could probably play around with the search terms and come up with something better.
> 
> 
> 
> https://www.buildingscience.com/document-search?term=&field_doc_topic_tid=All&type[]=7


Thanks for the link, lots of good info on that site!


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## bcemail (Sep 18, 2010)

XSleeper said:


> In cantilevered construction, that entire area in your first photo should be insulated. IMO you want 2" of rigid foam against the rim and on top of your plywood soffit, the rest can be filled with fiberglass.


OK, that is similar to some searches I found. I'll do rigid foam on the "bottom" (on top of the plywood on the soffit) and against the rim joist, spray foam the edges/gaps, then fill with FG. Some searches showed rigid foam on the underside of the upper story sub-floor, but I couldn't figure out if that applied in my situation. I figured the rim joist and soffit were the main problems.

Guess I have my weekend project.
Thanks!


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## bcemail (Sep 18, 2010)

XSleeper said:


> In cantilevered construction, that entire area in your first photo should be insulated. IMO you want 2" of rigid foam against the rim and on top of your plywood soffit, the rest can be filled with fiberglass.



Would this be the right product on top of the rigid? Since the joists area 2x10 this would fill it up in one layer right?
 https://www.lowes.com/pd/Owens-Cor...th-Sound-Barrier-15-in-W-x-25-ft-L/1000373567

Thanks!


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## XSleeper (Sep 23, 2007)

That would work but it would be slightly compressed. After you put in 2" of foam, you will be left with 7 1/2". For some reason 2x8 insulation is often hard to find.


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## Nealtw (Jun 22, 2017)

It should be filled with insulation and have solid blocking over the lower wall.


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## bcemail (Sep 18, 2010)

XSleeper said:


> That would work but it would be slightly compressed. After you put in 2" of foam, you will be left with 7 1/2". For some reason 2x8 insulation is often hard to find.



Forgot about that. Maybe do 1.5" foam, then I'd have about 8" so compressed about an inch? Will that reduce effectiveness much?


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## bcemail (Sep 18, 2010)

Nealtw said:


> It should be filled with insulation and have solid blocking over the lower wall.



Interesting, hadn't thought about that. Is that for insulation efficiency, or fire prevention? I'll be working from the inside so would need to seal the edges from there? Also can't really do anything about the base plate for the upstairs. Thanks!


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## Nealtw (Jun 22, 2017)

bcemail said:


> Interesting, hadn't thought about that. Is that for insulation efficiency, or fire prevention? I'll be working from the inside so would need to seal the edges from there? Also can't really do anything about the base plate for the upstairs. Thanks!


How far is it out from the interior of the wall you are working with and how much room do you have the ceiling open?


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## bcemail (Sep 18, 2010)

Nealtw said:


> How far is it out from the interior of the wall you are working with and how much room do you have the ceiling open?



It goes out about 24" from the wall and the joists are 2x10s.


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## Nealtw (Jun 22, 2017)

bcemail said:


> It goes out about 24" from the wall and the joists are 2x10s.


 It is going to be tricky to get insulation out there.
Here they don't bother with the lower plywood outside just vinyl soffet.


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## XSleeper (Sep 23, 2007)

The thinking with putting at least 2" of foam on the _exterior_ side is to put enough r value between the cold exterior and the heated side so that the inside surface of the foam stays warm enough to never sweat. Most problems with condensation and frost occur in the winter.

But there are various schools of thought. And if its compressed slightly I dont know that it will matter too much. Yes it decreases r value _slightly_. If you can find 7 1/2", use it. If not, use the 9 1/2".


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## bcemail (Sep 18, 2010)

XSleeper said:


> The thinking with putting at least 2" of foam on the _exterior_ side is to put enough r value between the cold exterior and the heated side so that the inside surface of the foam stays warm enough to never sweat. Most problems with condensation and frost occur in the winter.
> 
> But there are various schools of thought. And if its compressed slightly I dont know that it will matter too much. Yes it decreases r value _slightly_. If you can find 7 1/2", use it. If not, use the 9 1/2".



Sounds good. I don't see 7.5" online so it's either 9" or 6.25". I guess I could double up the foam board or use 2" with 1" on top which would leave me about 6.25-6.5". 
Like you said might not make much of a difference. I'm coming from R-0 after all. 
For the little gaps between the plywood and vinyl soffit (I can see a bit of daylight) does that need to be caulked or will the foam board seal it? I was going to spray foam the inside on the top of the foam board where it meets the joists. 
Thanks again for all the help


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## XSleeper (Sep 23, 2007)

Generally you just cut the foam board to fit as tight as you can, then seal the edges after its in.

If you foam it first, you can potentially create a mess if the foam doesnt quite fit and you have to take it back out to recut it. Foam all over everything.


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## bcemail (Sep 18, 2010)

XSleeper said:


> Generally you just cut the foam board to fit as tight as you can, then seal the edges after its in.
> 
> If you foam it first, you can potentially create a mess if the foam doesnt quite fit and you have to take it back out to recut it. Foam all over everything.



That makes sense, I'll go with that method. Reading online sounds like compressing won't really be a problem and at least I'll make sure it's completely filled


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## XSleeper (Sep 23, 2007)

Cutting the foam on a table saw is the way to go, if you've got one. Just dont cut your hands off.


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## bcemail (Sep 18, 2010)

XSleeper said:


> Cutting the foam on a table saw is the way to go, if you've got one. Just dont cut your hands off.



Table saw is working really well. 
Also decided to check the soffit on the side of the house too. Not an energy expert but guessing this isn't ideal...


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## Nealtw (Jun 22, 2017)

bcemail said:


> Table saw is working really well.
> Also decided to check the soffit on the side of the house too. Not an energy expert but guessing this isn't ideal...


 If this is roof overhang, you would not expect insulation there. There should be vents there to allow air over the insulation in the attic.


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## XSleeper (Sep 23, 2007)

Nealtw is correct. You have 2 different situations. Your first photos are a cantilever. It needs to be insulated. Your last photos are of the soffit and rafter tails... which do not get insulated. Styrofoam chutes can be installed between the rafters and then you insulate between the top plate and the chute. This allows air to ventilate the attic while allowing for maximum insulation. The chutes should be long enough to extend above your R-49 attic insulation.


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## Dave Sal (Dec 20, 2012)

My house has plywood soffits like yours, except mine had no venting at all when I bought it. I had to cut each hole for the soffit vents on both the lower and upper levels. I think I have about 20 soffit vents on each level so that was a lot of cutting. Once I was done the attic breathed so much better and with the addition of extra insulation, would stay just a few degrees above the ambient air temps. A bonus was no more icicles in winter. 

Make sure you have adequate soffit ventilation.
https://todayshomeowner.com/adding-soffit-vents/


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## bcemail (Sep 18, 2010)

Nealtw said:


> If this is roof overhang, you would not expect insulation there. There should be vents there to allow air over the insulation in the attic.



Thanks Neal, hope that's correct in my situation. We have a gambrel roof and my last picture was of the "side" roof (other soffits in my earlier pictures were the "ends" of the house). These soffits lead into the ceiling space between the first and second floor where I'm having trouble with sweating ducts. I thought this edge of the roof would be isolated, which is how I thought agambrel worked. Do you still think they don't need to be blocked off? Tried to get another picture although it's dark out now. Thanks!


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## bcemail (Sep 18, 2010)

XSleeper said:


> Nealtw is correct. You have 2 different situations. Your first photos are a cantilever. It needs to be insulated. Your last photos are of the soffit and rafter tails... which do not get insulated. Styrofoam chutes can be installed between the rafters and then you insulate between the top plate and the chute. This allows air to ventilate the attic while allowing for maximum insulation. The chutes should be long enough to extend above your R-49 attic insulation.



So in this case the soffits lead into the space between first and second floor. Same ceiling space as the cantilever soffits too. Hope that makes sense. Basically when I stick my head in the ceiling I can see into the soffits on both sides of the house. And I did a quick check and the third side is the same way. Back of the house isn't cantilevered so don't need to worry about that at least.
Thanks!


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## Nealtw (Jun 22, 2017)

bcemail said:


> Thanks Neal, hope that's correct in my situation. We have a gambrel roof and my last picture was of the "side" roof (other soffits in my earlier pictures were the "ends" of the house). These soffits lead into the ceiling space between the first and second floor where I'm having trouble with sweating ducts. I thought this edge of the roof would be isolated, which is how I thought agambrel worked. Do you still think they don't need to be blocked off? Tried to get another picture although it's dark out now. Thanks!


 Sorry I forgot about gambrel roof. 

Is this how the house was built with my arrow pointing at the area in question?


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## bcemail (Sep 18, 2010)

Nealtw said:


> Sorry I forgot about gambrel roof.
> 
> Is this how the house was built with my arrow pointing at the area in question?



Yep that's correct. My last picture is in that area looking between the floor joists. I was expecting this area to be blocked off from the ceiling area somehow. I'm guessing the plywood I see is the subfloor? Again I was picturing the little wedge of area under that side of the roof isolated if that makes sense


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## Nealtw (Jun 22, 2017)

bcemail said:


> Yep that's correct. My last picture is in that area looking between the floor joists. I was expecting this area to be blocked off from the ceiling area somehow. I'm guessing the plywood I see is the subfloor? Again I was picturing the little wedge of area under that side of the roof isolated if that makes sense


I think for air sealing and fire stop, there should be 2 blocks. One above the wall and another under the wall with insulation between


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## bcemail (Sep 18, 2010)

Nealtw said:


> I think for air sealing and fire stop, there should be 2 blocks. One above the wall and another under the wall with insulation between



In that diagram, is the area over the soffit usually the same air space as the area behind the second floor wall? That's what I was picturing how a gambrel worked. But in ours the subfloor is there. 

Would there be a down side to insulating the same way as the cantilevered section? Foam and fiberglass filling the area from exterior of the soffit to just inside the exterior of the first floor wall?

I was going to try and do this area from the outside just to not have to pull down more ceiling but if that's not feasible I can just add some more drywall work to the project!
Thanks!


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## bcemail (Sep 18, 2010)

Also have some areas where there is some plumbing just inside the lower wall so might not be able to block and insulate further in. Here is a picture inside one of the soffits looking in


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## Nealtw (Jun 22, 2017)

bcemail said:


> In that diagram, is the area over the soffit usually the same air space as the area behind the second floor wall? That's what I was picturing how a gambrel worked. But in ours the subfloor is there.
> 
> Would there be a down side to insulating the same way as the cantilevered section? Foam and fiberglass filling the area from exterior of the soffit to just inside the exterior of the first floor wall?
> 
> ...


 I found diagrams on insulation that shows that it can be either wall that is insulated up stairs. 

If the inside wall is insulated, you will want to insulated the joist space inside.
If it is the outside wall you would insulate the over hang. 

Maybe you can cut a hole in the flooring above and get your phone in there for a picture or two to see what insulation you have.


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## Nealtw (Jun 22, 2017)

bcemail said:


> Also have some areas where there is some plumbing just inside the lower wall so might not be able to block and insulate further in. Here is a picture inside one of the soffits looking in


I think I would pass on the inner block just the block on the end and insulate either inside or outside that depending on the insulation up stairs.


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