attic air sealing low temp material?

[pybyr]

Hello all and Merry Christmas-

I have realized I have a serious need to do some air sealing in my attic.

House (roughly 1840s) was built with "plank lath" walls (even interior walls) in which what we'd call "studs" in modern times really are only spacers- and the plank lath is attached lath to lath at all corners of walls and ceilings.

Net result is that where there is no plaster (in the places where wall cavities meet each other or ceiling) there are all the openings from the hatchet cracks in the lath. Thus the wall cavity interiors of all the interior walls "duct" to the attic.

When I bought the house it had zero attic insulation, and I quickly put about 6 inches of blown cellulose in attic (know I need more but needed to be able to work up there for other things such as wiring).

I now realize that before adding any more insulation, I really need to "mud over" all the void-areas in the lath from the top side to air seal it so that my interior walls are not "ducting to the attic."

Of course it is now below freezing nearly all of the time, so simple things like old sheetrock compound or one-component foam won't cure

Appreciate suggestions on materials and methods to accomplish this in a simple and affordable way!

Thanks

 

[EatenByLimestone]

Plastic along the rafters will create a barrier that air can not pass through. This will allow you to get some heat in there so you can work. As for the air spaces drafting, fiberglass batts pushed into the cavities and then insulation blown in on top will stop that. You will still have convection currents in the walls though. If your house is baloon framed you may be able to just blow insulation right down into the cavity.

Matt

 

[woodgeek]

For open stud bays in stick buildings, a good approach is fiberglass batts stuffed into 11 gallon plastic kitchen bags. Specifically, I get R-11 or whatever unfaced FG, cut it into 16" long squares, put a batt in the bottom of a kitchen garbage bag (about the right dimensions), fold it over double, and stuff it in the hole. The doubling over makes enough pressure to hold it in place, the plastic bag keeps air from leaking through the batt (which might be a problem with Matt's suggestion depending on the rest of the install). Some folks like to use rigid foam pieces, sealed with foam or caulk--the bag method goes really fast and works well.

As seen on the DOE website.

 

[pybyr]

Thanks for the input- but these are _interior_ walls. Top of wall cavity is not "open" to attic in the normal sense one would envision- nothing resembling a stud bay- it's that there's no "plate" on top-

Entire interior second floors ceiling was done in plank lath (big random width 1/2 inch thick planks cut with hatchet and stretched to make linear openings for plaster to key into) then interior walls were attached to the floor and the ceiling plank lath.

No 2x plate on top, so vertical open space in wall connects to those voids in the ceiling lath where no plaster went because it is up above the interior wall.

No big void to put material down into. Interior walls' inside cavities are only about 2 inches thick- truly- as rough-cut 2x4s "flatwise" make up the spacing for the plank lath that comprises the interior walls. Completely opposite to modern construction, the plank lath is the only thing with much structural substance and the 2x "infill" only provides vertical orientation and rigidity.

Just lots and lots of little cracks where the walls meet the top floor ceiling's plank lath, and those many little voids are cumulatively adding up to substantial stack effect

Need to glop something (to use the technical term) in or over those many little cracks where the interior walls meet the ceiling plank lath, and the only way I can get to that is up in the attic.

 

[woodgeek]

Okay. I think I get it. I have sealed similar cracks (next to a top plate) with good silicone caulking (rated for attics). I do this in the winter, on sunny days, when my attic is a lot warmer than the outside. I tuck the insulation back over it when I'm done and figure it will be warm enough (under its blanket) to cure up ok (verified later). Of course, some FG sticks to the caulking, harmlessly.

Folks go back and forth about sprayfoam versus caulking for this app, I use caulking cause it goes faster, easier clean-up. I have a little brush I use to brush the crack thoroughly beforehand to remove loose dust to get good adhesion, and have never had a problem. Invest in a good respirator for this--the paper masks are not good enough.

 

[EatenByLimestone]

For cracks I'd just fill the small ones with plaster of paris if you want to stay traditional or drywall compound if you don't. Thicker ones I'd probably stuff fiberglass into as filler and then go with the compound or plaster.

Matt

 

[laynes69]

I did our mid 1800's Victorian with fireproof caulking (blue) and whatever aluminum flashing I had for our open cavities. All the cracks around the exterior walls at the top plates, I used expanding foam. I did this in the winter time and the foam set without any issues. Our attic is around 1200 sq ft and there was a ton of cracks and open voids. I used materials that would remain flexible and withstand the hot cold temps. I've checked everything I did and there's been no problems whatever. I bet we saved at least 20% by airsealing the attic. After that we put 12" of cellulose on top of the 3" that was there. It's been a huge improvement to say the least.

 

[benjamin]

Foam in a can works fine in cool weather, just store it in a warm place and add moisture if the house and attic are dry. It cures with moisture so the dryness of the air will slow the cure down as much as the temperature. But it will cure fine as long as the can is warm enough to get the foam to fill the cavity and keep from dropping through.

"Fill and Seal" only works upside down, "Great Stuff" works OK upright also, not that it matters for this application, so use Fill and seal.

If there wasn't any insulation in the way a spray foam contractor could do a great job on this, maybe get a leaf blower vac and move all the insulation to one side and then back?

 

[Don2222]

For open stud bays in stick buildings, a good approach is fiberglass batts stuffed into 11 gallon plastic kitchen bags. Specifically, I get R-11 or whatever unfaced FG, cut it into 16" long squares, put a batt in the bottom of a kitchen garbage bag (about the right dimensions), fold it over double, and stuff it in the hole. The doubling over makes enough pressure to hold it in place, the plastic bag keeps air from leaking through the batt (which might be a problem with Matt's suggestion depending on the rest of the install). Some folks like to use rigid foam pieces, sealed with foam or caulk--the bag method goes really fast and works well.

As seen on the DOE website.

Hello Woodgeek

That is a great idea with the FG and kitchen trash bag. I have seen FG encapsulated with the plastic at Home Depot. That is another way to go but the Kitchen Trash bag idea might save some bucks and work just as well!!

 

[woodgeek]

For open stud bays in stick buildings, a good approach is fiberglass batts stuffed into 11 gallon plastic kitchen bags. Specifically, I get R-11 or whatever unfaced FG, cut it into 16" long squares, put a batt in the bottom of a kitchen garbage bag (about the right dimensions), fold it over double, and stuff it in the hole. The doubling over makes enough pressure to hold it in place, the plastic bag keeps air from leaking through the batt (which might be a problem with Matt's suggestion depending on the rest of the install). Some folks like to use rigid foam pieces, sealed with foam or caulk--the bag method goes really fast and works well.

As seen on the DOE website.

Hello Woodgeek

That is a great idea with the FG and kitchen trash bag. I have seen FG encapsulated with the plastic at Home Depot. That is another way to go but the Kitchen Trash bag idea might save some bucks and work just as well!!

Thanks.
Its OT, but in the plastic encapsulated FG I have seen, the film was perforated to allow vapor migration and avoid having a cold vapor barrier.

On topic, I think the OP should use foam, since his gaps are large and there is little/no backing. This is prob time to invest in a gun and the bigger cans to speed up the job.