Exterior wall insulation help
I recently replaced a window on the exterior wall of my 1960 house. The wall is half concrete, half 2×4 construction. I framed in the window with 2×6 with the intention of furring out the rest of the wall to improve insulation.
I have attached rigid foamboard to the concrete. I will be furring out the walls so that I can put in fibreglass insulation for 2×6 walls.
The outside of the house has shiplap sheathing nailed to the studs, a layer of building paper on top of the sheathing and cedar siding directly on top of the building paper. How do i properly insulate this exterior wall?
I live in Vancouver British Columbia area. Thank you
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Replies
B.C. Bud,
Q. "The outside of the house has shiplap sheathing nailed to the studs, a layer of building paper on top of the sheathing and cedar siding directly on top of the building paper. How do I properly insulate this exterior wall?"
A. It's possible to insulate this wall with a wide variety of insulation materials. If installed properly, any of the following materials will work: cellulose, mineral wool, fiberglass, open-cell spray foam, or closed-cell spray foam.
What should you choose? It depends on your R-value goal and your budget.
In all cases, you need to pay close attention to airtightness -- especially considering the leaky exterior. (Board sheathing is usually leakier than OSB or plywood sheathing.) If you choose to install spray foam insulation, the spray foam insulation will do a good job of air sealing. You may want to consider the flash-and-batt approach. For more information, see "Flash-and-Batt Insulation."
With fluffy types of insulation (and no spray foam), you'll have to caulk the major cracks in your sheathing before you insulate, and that's time-consuming. You'll probably also need to install your interior drywall in an airtight manner (which means investing in airtight electrical boxes).
Finally, if a high R-value is your goal, you may want to consider the installation of interior rigid foam. For more information on this approach, see "Walls With Interior Rigid Foam."
My budget won't allow for spray foaming. Is there any other options? Could i staple building paper to the shiplap or even tyvek (i have leftovers)?
B.C.,
Q. "My budget won't allow for spray foaming."
A. Then you should buy a case or two of good caulk.
Q. "Are there any other options? Could I staple building paper to the shiplap or even Tyvek?"
A. Yes, you could, but (a) building paper isn't a good air barrier, and (b) Tyvek isn't an air barrier unless you tape all the seams -- which means taping the Tyvek-to-Tyvek seams as well as the Tyvek-to-wood-framing seams. That's labor-intensive and expensive -- so it might be cheaper to buy one or two spray foam kits (the two-component kits available at lumberyards).
Is there a certain brand or type you would recommend? I don't want to purchase the wrong type of foam. I guess I would spray vertically along the studs and horizontally into each seam of the shiplap?
Thank you for your help
B.C. Bud,
There is no inexpensive way to air seal this type of sheathing from the interior. How you proceed depends on your energy performance goal and your budget.
If you want a good air seal, and you have more time than money, I suppose you could try to caulk every seam with a high-quality caulk.
If you can scrape together enough money, you can use the flash-and-batt approach -- either with two-component spray foam kits (all brands are similar) or with a spray foam contractor's help. In most cases, hiring a spray foam contractor for a flash-and-batt job is cheaper than buying several kits for a DIY approach.
If you don't have enough money or time for either of these approaches, you can slip narrow rectangles of asphalt felt into each stud bay and call it good enough. You'll have more air leakage with this approach, but it will be cheap.
In addition to a case or two of caulk, you should invest in a commercial grade foam-in-a-can system and gun. Hilti makes a pretty good one. You will save money over buying lots of cans of Great stuff, and get a better job, too. A god rule of thumb is that joints less than 1/4" should be caulked, but wider than that should be foamed. Like Martin said, this approach takes a long time and success is not guaranteed. If you do it yourself very carefully, it can be done.
When furring out the 2" to accommodate batts designed for 2x6 framing consider using Bonfigliioli strips made of 1" or 1.25" (if you can find it) foil faced polyiso and 1x furring rather than solid wood. With R6 on the framing it cuts the framing fraction's losses by more than half compared to solid wood. See:
https://www.finehomebuilding.com/membership/pdf/9750/021250059.pdf
It's dead-easy to cut precise 1.5" wide strips of foil faced polyiso using a 3-5" wide steel wallboard taping knife sharpened on it's edges and a straight edge:
https://www.finehomebuilding.com/2009/01/29/theres-a-better-way-cutting-rigid-insulation
Could I use a combination of foam board and fiberglass insulation? I have already purchased the fiberglass ( 2x6 type) and find foam board very easy to work with. Example: a 1/2 layer of foam board against the ship lap and the 2x6 fiberglass on top of that?
B.C.,
Q. "Could I use a combination of foam board and fiberglass insulation? Example: a 1/2-inch layer of foam board against the ship lap and the 2x6 fiberglass on top of that?"
A. Yes, in your relatively mild climate zone, that approach will work. (Any GBA readers in colder climates, however, should realize that thicker rigid foam would be needed in a cold climate.)