Insulating brick veneered walls
redmonte
| Posted in General Questions on
Hi, I wanted to know if foam or cellulose is the better option for my situation. I have 2×4 walls with fiber board (looks like celotex), air gap and one layer of brick. What should I be insulating the walls with if I want avoid moisture issues down the road. Border of climate zones 5/6 in the midwest. Ive read about the thermal bridging issues and why closed cell is considered a waste of money but open cell is not that much higher than cellulose. Thanks
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Search and download construction details
Replies
Redmonte,
I will give your question a bump. In the meantime, this thread may be helpful.
https://www.greenbuildingadvisor.com/question/insulating-a-brick-veneer-house
>" Ive read about the thermal bridging issues and why closed cell is considered a waste of money but open cell is not that much higher than cellulose. "
Open cell foam & cellulose may be comparable in cost, but not comparable in environmental consequences:
https://materialspalette.org/wp-content/uploads/2018/08/CSMP-Insulation_090919-01.png
(open cell foam has about half the CO2e impact of HFO blown closed cell foam at any given R value).
With fiberboard sheathing it won't be possible to dense-pack cellulose without bowing out the fiberboard (or even popping nails) but cellulose batts are an option. It may still be "worth it" to go with open cell foam despite a higher environmental cost for the ease of air sealing, since not many sealing agents will stick to fiberboard sheathing for the long term.
Be sure to lay a bead of polyurethane caulk on any doubled up framing, such as top plates, jack studs, window headers, etc, as well as where the bottom plate meets the subfloor. Spray foam insulation can only air seal inside the stud bays- and those framing seams have been proven to be much bigger air leaks than they might appear.
If you can give up an inch of interior space, putting an inch of foil faced polyiso over the interior side under the gypsum brings the assembly fully up to current IRC code. Foil faced polyiso is usually no more than 1lbs per cubic foot density, and blown with low impact hydrocarbon blowing agents, making it roughly half the impact per R as HFO blown closed cell spray foam. Foil facers are true vapor barriers, so it will impede drying toward the interior, but with a vented veneer cavity the drying capacity toward the exterior will be pretty good.
Thanks for that bit of information on inside foil-faced polyiso. I've been looking for answer to my fears of doing so because of reduced (or no) drying potential to the interior. Do you have any concerns about the overall drying potential to the exterior due to lower temperatures of the sheathing?
I thought about adding some rigid foam to the inside but I didnt because of all the added work and cost with furring out all the gang boxes and everything. I never thought about the cellulose blowing out the celotex. I will not be dense packing the cellulose, it would be stabilized cellulose blown into the walls, no drywall yet.
I just want to get an idea if the open cell foam would cause any moisture issues down the road with the walls. I definitely think the foam has much better air sealing properties. Should I be using vapor barrier primer if I use the open cell foam?