Spray Foam vs. Wet-Applied Cellulose
Hello,
Reposting this question from last night at the suggestion of others. I apparently ended up on the wrong posting page during my first run at this! 🙂
……
I’ve just stumbled onto this site and signed up for a trial as what I’ve read so far seems perfectly aligned with our project.
My wife & I have begun restoration of a Victorian, pre 1911, three story in Syracuse, NY. She is documenting the project on YouTube as “The Grand Lady – Syracuse”.
We suffered a roofing company failure several months ago which resulted in the loss of one side of every original interior lath-plaster cavity and of all lath-plaster on the exterior walls. This due to complete saturation of the house interior, top to bottom in a heavy rain event with most of the roof removed and inadequate temporary protection.
We had, prior to the house soaking roofing event, begun removal of all the exterior side in preparation for application of 1” exterior rigid foam board, seam taped then over-wrapped and seam taped with Tyvek Commercial wrap. 1×4” furring follows on the exterior up each stud line. Planned siding to be lap siding as rain screen, maintaining the plenum space for convection.
With the interior side of the exterior walls now opened to the 1” sheathing, we have opportunity to choose a better exterior insulation than the loose fiberglass which was water soaked in the roofing company failure. I had thought to use spray foam after the electrical and rough plumbing is completed. Tonight’s reading however, brought me to spray applied cellulose as another possibility, with perhaps some additional benefit. Of this however, I am not certain.
May I have some of your thoughts about the insulation choices to be made here? Our concerns are first longevity, safety, insulation value, air seal and noise control as two side face streets which are occasionally loud.
Spray foam or sprayed cellulose into 2×4” cavities with vapor retarder on the inside if using foam and no retarder if cellulose?
Thank you for your thoughts!
Jim & Lindsay
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Replies
Hi Jim,
One inch of exterior foam is thin for your climate. (See https://www.greenbuildingadvisor.com/article/calculating-the-minimum-thickness-of-rigid-foam-sheathing for more detail.)
If it were my house, I would instal cellulose, rock wool, or high-density fiberglass. In case you are considering foam for the roof line, you will want to avoid open-cell.
Thank you Steve!
Jim,
Your first priority is an effective air-barrier. if you are using the foam for that make sure to detail the edges and penetrations to maintain continuity.
Another approach to air-sealing would be to use a self-adhesive WRB instead of the Tyvek Commercial, and apply it directly to your existing sheathing, with the foam over that.
A third option is to detail your interior vapour-retarder as an air-barrier.
If you follow the advice on exterior foam thickness in the link Steve posted, I don't think it makes much difference what you use in the bays.
Good luck with your project.
Thank you Malcolm, Yes we are edge sealing all of the foam, then wrapping that with edge sealed Tyvek Commercial. That package will be further sealed at top, bottom and around all windows and doors.
1. Air seal
2. Use the correct amount of insulation in the correct place
3. Do things that don't have the potential to complicate your life - if you ever need to get in the wall, having to deal with fiberglass will be a mess. Not so with wet applied cellulose.
Thank you CL
1910 gut reno zone 5. Deja vu your project.
Here's the balance we struck for exterior wall treatment inside and out.
Cedar claps over 1/4" air gap over self adhered WRB over the old sheathing. Blueskin providing the water and air barrier with a vapor perm of 33(?). Air gap to promote drying to exterior / extend the life of the paint on the claps. Doing it again ... I'd use Hardie plank instead of the cedar.
Inside 2x4 and 2x6 exterior walls all are dense packed mineral wool with Membrain vapor retarder. Would have liked a thermal break somehow.
I was impressed re: how much wetting / drying we observed when we opened up the exterior walls, so we took care to provide robust water and air barrier with drying path to exterior.
We did not install out-sulation due to existing trim details.
Building Science Corps Deep Energy Retrofit guide was my go-to reference. The 4 control layers drove all the decisions ... Water, Air, Vapor, Thermal (in that priority order).
https://www.buildingscience.com/documents/guides-and-manuals/gm-mass-save-der-builder-guide/view
I'd put some flashing tape around the wires where they penetrate the Membrain material. The flashing tape will help to reinforce the Membraine to prevent tearing.
Bill
Yes, we did that just before the blueboard went up.
Thank you!
The way I see it before you can insulate you need a water resistant barrier and upgraded flashing.
The paint and siding did a good enough job of keeping out the liquid water when you walls are warm with a ton of air leaking thru the wall. The heat evaporated the water and the air flow carries it away before anything rots.
Walta
Thank you Walter, I agree completely.
Jim, please be careful with all the asbestos remediation you are doing. We had the same issues (10 asbestos wrapped ducts running up through the building) and had to hire a remediation company for removal. I see you still have the original pot belly furnace in the basement?
Yes, I intend to retain the old gravity furnace as a functional antique. Asbestos remediation here is permitted to the home owner. Due caution is being employed, with most asbestos removed properly and a bit encapsulated and retained on those ducts which will remain functional within the wall space.