Air sealing the ceiling-- question & photo of a unique area

[Propane_Poor]

Hi all,
We just put a new Blaze King Ashford 30.2 in our new living room addition (we knocked out the old exterior wall, and the new ceiling is about a foot higher. ) What you're seeing is the end of the rafter joists, sitting on a new beam, and obviously large gaps going into the old attic.

Given that the new ceiling is higher, I'm concerned this will be a major source of heat loss.

Any suggestions on how to air-seal something like this before we cover it in decorative planks? We'll insulate, but is there anything else that should be used after the insulation goes in?

 

[kennyp2339]

Best bet is to spray foam (mix of low & high expansion) foam all the little open cracks, you can take 1x3 and pad out the new sheet rock area and get foam board for in between the new 1x3 24” on center

 

[Propane_Poor]

Thanks-- interesting thoughts. I also wondered about just adding some R30 batts to the large gaps, and stapling + taping some left-over Tyvek across the entire span.

 

[EbS-P]

I would use foam board fastened/glued in place. Foam or caulk all seams/corners . Add batt insulation behind.

 

[DuaeGuttae]

We used to have a raised ranch home with part of the main/upper level cantilevered over the lower level. When we had an energy audit done, that proved to be a major source of heat loss and air infiltration. I do not know all the details, but I do remember that the person who remediated it for us had to cut out a long strip of our basement ceiling to get access. He then did use batt insulation in each cavity and cut foam board to fit in between the studs and sealed the edges with spray foam. Just like what @EbS-P just suggested. It’s nice that you can do all the work before you put the finishing in place.

 

[John Galt]

Batts won't air seal, neither will the tyvek. The foam board is the least expensive, cut it smaller than the opening and use canned expanding foam to seal/glue the edges in place. You can research "Rim Joist Insulation" that is a very similar approach. The 2 part spray foam sold in boxes at Home Depot would also work and be quicker, but you'll have to put in something as a backer to spray onto and that stuff is pretty expensive. Your biggest concern is moisture going into that area. The warm moist air will go into the attic and condense or frost on cold surfaces. Then mold, rot, and water stains will be a concern.

 

[begreen]

Staple some plastic up to cover the gap with the edges sealed with a flexible caulk.

 

[stoveliker]

I'd close the gap with plywood, then get in the attic and seal all the edges/seams. That can be done with a few cans of spray foam. Then insulate properly.

In fact, while up there, pull up all insulation and seal all seams where internal and external walls meet the attic. And silicone all electric penetrations (including the holes innthe top boards where power lines go down to outlets in your wall).

Then get insulation with a total r value of 45 or higher (I don't know what the common values are; I added r38 on top of the r19 that was in between the joists.)

 

[zrock]

i want to know who built that old roof 2x4 stacked ontop of a 2x2. Only way to do it properly is pull down the ceiling in the other room and fully insulate it

 

[Propane_Poor]

i want to know who built that old roof 2x4 stacked ontop of a 2x2. Only way to do it properly is pull down the ceiling in the other room and fully insulate it

Those might be for furring out the drywall. The whole old ceiling has a mix of batt insulation and blown in insulation, but adding more is definitely on my to do list.

BTW you would shake your head at how the rest of this 1950s/60s house was built. Foundation rests on a fieldstone cistern so they said "oh well" and stopped the foundation at about 2' below grade.... no wonder my floors are crooked. I guess at least it's still standing 70 years later, right? lol.

 

[Propane_Poor]

I'd close the gap with plywood, then get in the attic and seal all the edges/seams. That can be done with a few cans of spray foam. Then insulate properly.

In fact, while up there, pull up all insulation and seal all seams where internal and external walls meet the attic. And silicone all electric penetrations (including the holes innthe top boards where power lines go down to outlets in your wall).

Then get insulation with a total r value of 45 or higher (I don't know what the common values are; I added r38 on top of the r19 that was in between the joists.)

So do you use your attic? My joists in the new attic are 2x6 and we furred them out to 2x8 then put a plywood floor down for storage. I am guessing we'd need to rip that up, make it SUPER thick, then re-lay the plywood, in order to hit something like the ~r60 that you have.

 

[Propane_Poor]

Batts won't air seal, neither will the tyvek. The foam board is the least expensive, cut it smaller than the opening and use canned expanding foam to seal/glue the edges in place. You can research "Rim Joist Insulation" that is a very similar approach. The 2 part spray foam sold in boxes at Home Depot would also work and be quicker, but you'll have to put in something as a backer to spray onto and that stuff is pretty expensive. Your biggest concern is moisture going into that area. The warm moist air will go into the attic and condense or frost on cold surfaces. Then mold, rot, and water stains will be a concern.

Thank you. We have foam board and some extra batts on hand already so we'll put that to use.

 

[stoveliker]

So do you use your attic? My joists in the new attic are 2x6 and we furred them out to 2x8 then put a plywood floor down for storage. I am guessing we'd need to rip that up, make it SUPER thick, then re-lay the plywood, in order to hit something like the ~r60 that you have.

Yes, I made an elevated storage platform.
I had r19 batts between the joists. After pulling those out, sealing, adding them back, I added(unfaced) r38 on top, 90 deg rotated. It's less than a foot above the joists, I estimate.