Insulating balloon walls
High I am renovating a 1927 Dutch colonial with balloon wall construction. Th attic is finished but will be taken down to exposed walls and rafters. The exterior will be resided on the second level with Hardy board fibercement clapboards. The ground level is one layer of brick over wood sheathing. The roof will be replaced with an imitation slate product (DaVinci roof scrapes). All the windows were already replaced (Trim line) Aluminum clad wood thermopane windows. My question is about insulation. I will be cutting a ridge vent. Matching or exceeding its area with soffit vents and using standoffs to provide 2″ between the standoffs and sheathing for airflow. I would like to use closed cell sprayfoam on the ceiling down to where it meets the floor of the attic. Below this the first and second floor have intact plaster walls that I would like to fill completely through the top of the stud bay or by drilling holes from the interior. My concern is Condensation in the stud bay leading to wood rot or mold. I found a spray foam company that uses a foam with a shaving cream like consistency. Can you recommend a type of foam ? Closed(hopefully to get a vapor barrier) any other approach?
Thanks
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Replies
EH413,
First of all, can you tell us your name?
I don't know of any type of spray foam product that can be installed in balloon-framed walls from the top.
Your best bet is to insulate these walls with dense-packed cellulose. For more information on installing dense-packed insulation in the empty stud bays of an older home, see this article: How to Install Cellulose Insulation.
The shaving-cream crud is injection foam, which is injected at low pressure, then sets up. It's fairly vapor permeable, and it has a propensity to shrink over time leading to air leaks & thermal bypassing.
There are slow-rise polyurethane open cell "half pound pours" or slow rise closed cell polyurethane pour options, that can work, but the risk of blow-out is real if not done carefully. It's VERY expensive stuff too.
Since you are both re-siding and re-roofing, a lower cost lower risk option is to blow the walls full of cellulose, and install sufficient rigid foam (or rigid rock wool) over the sheathing for dew point control. In the roof, half-pound open cell foam on the underside of the roof deck, with enough rigid foam over the top of the roof deck for dew point control. The amount of exterior foam needed to limit moisture accumulation risk varies by both climate, and the R value of the vapor permeable insulation in the wall cavities or underside of the roof deck.
Making the cavity insulation vapor permeable and controlling condensation/adsorption with exterior insulation is more moisture safe than a closed cell pour, since it both limits the peak moisture accumulation from vapor diffusion drives, yet provides a reliable drying path. Closed cell foam cavity fill forces the sheathing to dry primarily to the exterior, which is OK as long as the siding is rainscreened and the exterior moisture drives are bounded (parameters that are location/climate specific.)
Thanks Martin and Dana. I'm located in Floral Park,NY. A small town on the edge of NY City. It sounds to me like you are both in agreement with dense packed cellulose. I guess my only other question would be how I can obtain a spec for the three insulating techniques to work together as a system? Would an energy audit be able to provide the specs for the products you suggested? I was considering a blowerdoor and infrared thermography test for befor and after comparisons. Would this be a logical way to go?
Thanks again for sharing your knowledge!
Eddie Hanna
Floral Park,NY
Eddie,
Q. "How I can obtain a spec for the three insulating techniques to work together as a system?"
A. If you want a formal written specification to use for bidding purposes, you should hire an architect to write the specification. That approach is common when soliciting bids for big construction projects, but it usually isn't done for residential insulation work.
As an alternative to creating a written specification for the work, you could interview insulation contractors until you find one you trust, and then write out a scope of work -- something less formal than a specification.
Long Island is entirely within US climate zone 4A, so it doesn't take much exterior foam for dew point control on 2x4 framing- a mere R2.5 minimum would be fine over 2x4/R13 cellulose, per IRC prescriptives. But to meet current IRC code for thermal performance you'd need 2x4/R13 + R5 continuous insulation. An inch of foil-faced polyisocyanurate would likely be the cheapest & greenest way of getting there.
https://up.codes/viewer/general/int_residential_code_2015/chapter/11/re-energy-efficiency#N1102.1.2
https://up.codes/viewer/general/int_residential_code_2015/chapter/7/wall-covering#R702.7.1
The roof would require a minimum of R15 above the roof deck for dew point control on R34 under the roof deck (to hit the total R49). If you have 2x8 rafters you'd only be able to get R30 rock wool batts or R27-R28 cellulose or open cell foam under the roof deck, so you'd really be looking at ~R20 above the roof deck to make it absolutely clear to the inspectors. By doing a bit of U-factor calculation analysis you could probably prove compliance on a U-factor basis with only R15 of continuous sheathing above the roof deck, R15 above the roof deck. Either way, putting 3-4" of RECLAIMED roofing polyiso above the roof deck is pretty cheap & easy. There are several building materials reclaimers trading used roofing polyiso that would deliver to the NYC area, eg:
https://newyork.craigslist.org/search/sss?query=rigid+insulation
https://newyork.craigslist.org/brk/mad/d/used-poly-iso-insulation/6213370658.html
https://newjersey.craigslist.org/mad/d/rigid-foam-insulation/6224645132.html
If you have 2x6 rafters it'll take a bit more foam above the roof deck, of course. With 2x10s you can use R30 fiberglass/cellulose/open cell foam between the rafters + 3" polyiso above the roof deck.
Thanks again !