More Q&A Spotlight
Eric Nash is renovating a kitchen with “old school” 2×4 walls. He’s gutting the room, but not touching the outside of the house. He’d like to present the homeowners with some options for increasing the R-value of the exterior walls while making a better air seal.
Here’s his plan: fill the stud bays with cellulose, add 1 1/2 in. of rigid foam insulation on the inside, then a layer of 1/2-in. plywood on which to hang cabinets, and, finally, 1/2-in. drywall.
How about that? he asks in a Q&A post at Green Building Advisor.
Is plywood necessary to hang cabinets?
Anyone who’s installed kitchen cabinets knows how reassuring it is to have solid material in the walls to catch mounting screws. That’s what the layer of plywood beneath the drywall would accomplish.
But is 1/2-in. plywood enough?
Robert Riversong doesn’t think so. “If it’s only the cabinets you’re concerned about, I would forgo the plywood, install appropriate blocking and use 3-in. cabinet screws,” he writes. “I would rather have cabinets secured to framing than to 1/2-in. plywood.
“You’ll have to move the electrical boxes inward or use deep box extensions,” he adds. “For that, I’ve used plywood pieces attached to sides of studs to attach the boxes.”
David Meiland wouldn’t bother with continuous layer of plywood, either. “But,” he adds, “I might run a 2×4 across the wall at the top of the uppers, interrupting the foam. Tape the 2×4 to the foam.”
Andy Ault, however, favors the plywood route. In fact, it’s standard operating procedure for his crew when they build wine cellars.
“The only difference being that we step up to 3/4-in. ply to increase our holding power,” Ault writes. “Granted, those racking systems have many more points of…
Weekly Newsletter
Get building science and energy efficiency advice, plus special offers, in your inbox.
This article is only available to GBA Prime Members
Sign up for a free trial and get instant access to this article as well as GBA’s complete library of premium articles and construction details.
Start Free TrialAlready a member? Log in
22 Comments
wall blocking
on commercial projects, we've utilized sheet metal strapping in lieu of blocking. i don't know how feasible that is for residential projects, but this was for labs and exams.
Dew Point Analisys
Scott,
In many cases and specially in the colder climates, adding interior insulation to a wall can move the Dew Point of the wall away from the sheathing, to the inside. To mitigate this, you must do a wall dew point analysis, as you probably need to add some exterior insulation or develop a good seal and drying application and techniques for that wall.
What about french cleats?
What about french cleats? Fast, easy, and effective.
Have you considered a strap wall?
You have the opportunity here to increase the wall thickness for insulation, eliminate most of the thermal bridging and give yourself solid blocking in one step. Simply install horizontal 2x2 or 2x4 strapping on the studs at 24" O.C. (or at the appropriate height for the cabinet attachments). This will give a 5" cavity for insulation. Since you're in the northeast you should probably have the vapor impermeable surface on the outside of the wall. You could use closed cell foam there, thick enough to keep the dew point away from the inside of it. Then fill the rest of the cavity with cellulose or other insulation. It should be pretty easy to reach about R-30 with this system.
Interior Rigid Insulation
In the discussion above, different types of wall cavity insulations and rigid insulations, but no discussion about sprayed-in-place foam. We typically use closed cell foam insulation. How should that be included in this discussion?
Isn't Mr. Riversong
Isn't Mr. Riversong suggesting expanded polystyrene rather than extruded? Isn't extruded polystyrene vapor impermeable?
Response to Patrick
Patrick,
1. In his original comment on the Q&A page, Robert Riversong recommended the use of XPS (extruded polystyrene) because it is more permeable than foil-faced polyisocyanurate.
2. XPS is not vapor-impermeable. The permeance of 1 inch of XPS varies from 0.4 to 1.2 perm.
3. Foil-faced polyiso is much less permeable; 1 inch of foil-faced polyiso has a permeance of 0.05 perm.
Inside foam layer
To give Eric some confidence in his proposal to add foam inside the studs, I can report that for my house (built 30 years ago in Connecticut) I have had no vapor problems with a similar sequence of construction.
Back then, it was the generally accepted theory that you should have a permeability gradient from inside to outside. You intended to keep moisture inside the structure and out of the wall with a good interior vapor barrier, and any moisture that did enter the the wall would dry to the outside.
In our exterior walls, we placed R19 fiberglass batts in the 2x6 stud bays. To the inside of the studs we applied two, inch-thick layers of foil-faced iso foam (joints staggered), with the inner layer's joints taped. We applied 5/4" wood strapping over the foam as a nail base for the two layers of 5/8" gypsum board that were the interior finish. (Two layers of gypsum were installed to provide "distributed thermal mass" to minimize temperature swings from the effect of lots of south-facing glass.)
The exterior side of the studs received plywood sheathing and cedar clapboards - this was prior to the advent of Tyvek.
The foil on the foam provides a good vapor retarder. There are indeed four (4) vapor barriers in the wall (on the faces of the two foam boards) but in my opinion, the fear of multiple vapor barriers is overblown. The dewpoint is inside the foam, in any case, if moisture should escape into the wall.
same problem different approach
We have run into this problem as well. The building is an old 2X4 (real 2x4s as it was built in the early 50s). As an added twist, the walls run out from top to bottom and are not plumb. Here's what we have done from the outside in.
All old sheathing (fireboard) was removed. New GP Bluwood was installed. All connections (every stud and both plates) were caulked with high quality polyurethane caulk (Sika 15LM). OSB seams were taped with 6" Vycor so as to prevent air infiltration. Housewrap was installed with plastic cap nails. We also replaced all blocking with a 16G galvanized metal strap from Simpson. It is much stronger and eliminates the bulk of thermal bridging given off by blocking.
Inside, we have to build new walls and bring them back to level to hang the kitchen cabinets. Because the first wall has no block, we have uninterrupted insulation, so we can run electrical, plumbing and additional blocking in the interior 2X4 wall to hang cabinets. Plus, it gives us an opportunity to get more insulation in. We may use wool batts, or if the budget allows we may go to closed cell spray.
I must admit that this only works when you have the interior room to build an additional 2X3 or 2X4 non load bearing wall. In this project, room is limited, and the homeowner didn't want to give much up, but it was the only workable option and will benefit them in the long run. Double stud walls are something that me and my crew have been turning towards lately in new build as well beacuse of their cost vs benefit.
An elegant solution to this
An elegant solution to this problem might be to use Dow Wallmate (routed for 1x3 furring and available in 1.5 and 2" thick 2x8 panels) and set the furring strips horizontally. It is XPS, and if the furring is properly anchored to the studs, they will provide anchorage for the wall cabinets... mostly. Some layout considerations may be needed, or additional pin rails to back of wall cabs may need to be added.
Field Mods on XPS (or any iso based foam)
TC - You mentioned routing the XPS. The problem with field modifications on XPS which involve high-speed power tools (routing, drilling, saws, etc.) is the significant health-hazard created by the isocyanate off gassing.
When XPS foams are created (in the factory or in the field) the cure process is an exothermic reaction between the two components. This is when the foams are the most unstable and the most dangerous. When you use a high-speed tool on the cured board products, it heats the product back up to the point of recreating the exothermic reaction causing isocyanate laden vapors. in addition, the dust created by the tool becomes respirable and that is a known carcinogen once in the lungs. This is why NIOSH, OSHA, and the EPA have all issued Safe Work Practice guidelines against that type of work.
Granted, you may only be making a few small grooves in a limited amount of board product, but when multiple agencies all come down with the same recommendation, it probably bears paying attention to. So even if one was still determined to do it, I would definitely say that it should be done outdoors and with a cartridge-style respirator at minimum. But I'd avoid the option completely if it was my health or that of my workers.
Response to Andy Ault
Andy,
You misunderstand. Dow Wallmate is routed out in a Dow factory. When you buy it, the routing has already been done.
Pre-Routed XPS
Martin,
Got it. Just looked at the product site (guess I should've done that first, huh?)
Then the issue with that product (in my mind) goes right back to the plywood vs. blocking vs. french cleat question. Specifically, the pre-done slots are 24" on center. The likelihood that your cabinet layout would fall onto that wide of a gap is dicey.
I suppose you could specifically design your cabinets to meet that, but you'd have to have a pretty flexible client willing to accept sizes or spacing they may not initially want. Otherwise, you're right back to having to bridge the furring strips somehow to ensure available solid connection points which defeats the benefits of the pre-routed board. (But I do see where it makes great sense for hanging gyp board in a basement.)
Alternatives for Solid Brick Thermal Retrofit
Here in Toronto we have many old solid brick houses needing retrofit.
Up until recently I've put against the inner face of double-brick walls either 15 lb felt (moisture protection in unlikely event driving rain penetrated the inner wythe), or housewrap (to stop windwash from vertical stack effect or cracks in mortar joints) or XPS against inside of empty brick wall, then filled up remaining space with Roxul out to 2 x 4 stud walls inset to whatever depth of insulation the client wanted, and put a conventional super-six vapour barrier sealed from ceiling to bottom-plate only.
However when I checked with Harold Orr, the grandfather of super-insulated housing & chain-saw retrofit in Canada, on the various above design choices, he recommended skipping everything but the Roxul between brick and inner stud-face, and extending the vapour barrier by making joist-bay wide tabs of Super-six to meet up with ceiling one floor down. These tabs can be cut & fastened with considerable effort if the floor is opened up and the inside of brick is regular enough, though it's often not the case, & would be nice to have two-part polyurethane foam with hose to complete vapour-seals rather than messing with acoustic sealant & 1 x cleats to complete those tabs.
Mr Orr also noted that putting boardstock against brick is a bad idea, as any gaps between brick & foam board can lead to accelerated heat loss, as in the Canadian maritimes there was once a government grant program he reviewed, that put EPS board behind basement walls which actually accelerated heat loss, as convection currents around the board stripped heat out faster than if board was left out altogether. Plus there's the additional cost of using XPS and the intransigence of XPS manufacturers to find alternative blowing agents that aren't super-GHG's. I usually set frame walls in toward the brick face for ~ 1/2" extra compression of Roxul & at same time plumb up over out-of-plumb brick face with new interior wall.
I sometimes wonder if solid brick walls, especially N & E facing, or sand-blasted walls (that doubles the effective surface area), will degrade faster after these interior retrofits, but have only ever heard of post-retrofit damage at grade due to absence of a damp-proof course in an 1880's era house.
One masonry science paper said that solid brick walls should have maximum 12% occlusion by mortar-droppings to allow for air-flow, and the last time I checked a solid brick wall while adding a steel lintel to support a fallen window-arch (built 1885, lime mortar) it looked more like 25% occlusion, and the wall looked slightly wavy from outside, so in that case I added very little insulation (the classic useless EPS between brick strapping before I knew any better, which makes for faintly smudged condensation lines on drywall over strapping once paint is a few years old, as we have in our own house).
closed cell spray foam?
Isn't sprayed in place closed cell foam a potential solution for this situation?
Response to Alice
Alice,
It's important to be cautious before you insulate the inside of a multi-wythe structural brick wall. If you insulate the interior (even with closed-cell spray polyurethane foam), you make the bricks colder.
Cold bricks stay wet. (Before the insulation was installed, the bricks stayed dry, because the interior heat leaked through the bricks.) Wet bricks deteriorate faster than dry bricks, especially in freezing climates.
A brick wall must be carefully evaluated by a knowledgable expert before it is insulated.
Closed cell spray foam on older concrete
How about foam on older structurally sound (thick, solid), but surface finish crumbling concrete?
Could a metal interior stud wall spaced to allow a continuous layer of closed cell foam sprayed directly on a concrete basement wall provide both surface stabilization, moisture control, and a good first insulation layer? Assuming it would be followed up by Roxul (or more foam) to fill out the studs to their face, covered by cement board and finish.
Would this work?
Response to Tim
Tim,
I don't see why not.
Response to Martin Holladay and caution on brick wall retrofits
Yours is the third cautionary comment (thanks!) I've heard on brick walls, and it would be great to have an article (or references) or longer comment on this topic, as my next job this week is a solid brick retrofit, this time on an upper story North facing wall in considerable shade from a neighboring house 4' away. Here in Canada the old "Canadian Mortgage and Housing" (CMHC) guide "Keeping the Heat In" http://oee.nrcan.gc.ca/residential/personal/heat/keeping-heat-in-toc.cfm?attr=4 says nothing specific on protecting solid brick walls. Two engineers teaching home inspection courses said they wouldn't worry that much about insulating from the inside, however one green architect did recommend leaving the strapping cavity uninsulated to help protect brick.
Which solid brick walls would you say may be less likely to be at issue?
Walls showing foundation settlement or deflection, sandblasted, spalled, shaded, very old brick fired at lower temperature, substandard flashing & seals, or known to have unusual point sources of moisture in any form from either inside or out might be of concern.
I've seen some brick walls damaged for no apparent reason, one West-facing third story (5' from next house) where there was no leaking parapet or adjacent chimney, yet a sizable field was spalled. Other than that from anecdotal evidence I've only found one case of brick damage attributed to retrofitting, and that was at grade with no damp-proof course & very old brick from 1885.
There are many houses in Canada that had 2 x 4 walls built inside of solid brick starting in the 1970's, so there should be no shortage of sites to survey.
Response to Peter
Peter,
Read more on the topic here:
https://www.greenbuildingadvisor.com/blogs/dept/building-science/insulation-retrofits-old-masonry-buildings-building-science-podcast
Insulation of wall
I see about as many opinions as I see posts. The original question it seems was best way to upgrade the insulation and hang cabinets. Were I to be looking at a project like that I would suggest 3" of closed cell foam for an R-21 with it also being a good moisture barrier and adds structural strength to the wall. All the other types I have heard lack one thing and that is going in as a liquid and expanding to give it an airtight seal.
The mositure part I saw about being behind brick moulding being that I am not real familiar with that type but if you stop heat loss and excessive moisture coming out of the thermal envelope it seems like it would help the bricks.
As far as hanging cabinets a 3/4 ply is best for that and gives alot of options for down the road and makes hanging nick nacks up real easy.
I forgot to say although not an expert but I have been doing carpentry for qyite some time and also own an insulation company.
Fire Stopping?
While not a huge issue, as a kitchen might not have a wall over 10 ' in either direction, it could, and thus require fire blocking under some codes.
Installing foam btw studs and (inside) wall board creates a potential for some / all of it burning or melting out, contributing to fire and smoke and leaving a cavities to spread fire and smoke as well as reducing structural integrity, especially with cabinets installed. Finally, while foam won't support combustion, if exposed to the heat typically generated in building fires, it can melt or evaporate in part and that can burn creating huge amounts of toxic smoke. Then there's the chemical outgassing and moisture retention and embedded carbon..... Which is all a long way around to just use high density rock wool suitable for fire blocking, and be on the safe side of all the above. I admit, I can't easily get it where my folks live, and resort to high density fiberglass, but I can get rock wool where I live.
Russell Higgins AIA
Roughdesigns
Log in or become a member to post a comment.
Sign up Log in