I was looking at a friend’s remodel/addition a few days ago and was surprised to see that the plans called for 6" walls (2 x 6 studs instead of 2 x4). The existing house is 2 stories, but the addition is only one story, nothing above it. When I asked why, he said the architect had told him it’s now code that ALL residential building requires 6" walls, no matter what.
I was surprised. Is this true? I tried googling, but no fu for me today!
Building codes vary significantly between jurisdictions. 2x6 framing may be required for structural reasons but the more likely explanation is that it is required for better insulation. It’s certainly not universally required; there is plenty of 2x4 construction going on still.
:smack: I did not even think about insulation. I think you’re right. The code* is now R19 for walls, whereas it used to be R13. So unless you want to go to rigid insulation, 6" walls are going to be needed.
*California uses the International Building Code.
The two additions on my house have 6 inch walls for the R19 insulation.
Building codes are modified for specific areas. Like many hotels in Hawaii do not even have any doors! There would be no reason to require 6" insulation in Hawaii.
But in Alaska, even thicker than 6" might be good idea.
Anyway check with your local building inspector. Your local codes may be different from national codes.
That’s “International” like the baseball “International League”
Most insulation has an R-value of about 3.0-4.0 per inch, whether that’s fiberglass, cellulose, rock wool, cotton, or open-cell spray foam. That limits you to about R-14 in a 2x4 wall. Closed-cell spray foam or rigid foam is about double the R-value per inch so you can get the insulation you need into a 2x4 wall but closed-cell is the most expensive so the economics seem to favor just going with 2x6 construction.
Any foam is a much better performing system than batts or blown-in, even at lower R-values, because it seals all potential vectors for air leakage. Wet-sprayed blown-in systems like cellulose or cotton are the next best, as they also seal air better than batts. You just need to be careful in open cavities like around rim joists or in soffits because while the insulation can hold itself up for a few weeks unrestrained, it will eventually fall out place if not behind drywall or a plastic sheet. Fiberglass of any sort is the worst performer, but also the cheapest.
Another factor that’s cropping up with tightened energy codes is that pretty much nowhere in the US allows anything less than R-38 roof insulation, though there are some exceptions for small areas and certain eave details that allow full-depth insulation all the way to the wall, and then only in certain jurisdictions. That means that unless you go to the closed-cell foam, if you have a flat roof or stick-framed vaulted ceiling you need to use 2x12 joists/rafters in order to get the required insulation depth. In more harsh climates that require R-49 it’s even more difficult. I recently finished up a historic renovation project which is still finalizing LEED Gold certification, and the existing roof joists are only 2x10. Since the building is from the 19th century they’re 2" x 9 1/2" to 9 3/4" but that’s still not enough, so we did 2 1/2" of closed-cell foam plus fiberglass batts to get R-47 without the cost of all-foam but still achieving a good air seal. The rim joists and a few other areas were also foamed, but the walls were just furred in with 2x4s and blown cellulose was used. Despite having only R-14 in the walls, the better air seal from the cellulose and turning the studs sideways to minimize thermal bridging, along with foaming the rim joists and the extra R-value in the ceiling allowed the building to pass even the more stringent energy model guidelines recently introduced for LEED projects, though it was registered under the older system.
Yeah, one or two storey single family residential buildings are structurally fine with 2x4’s … 2x6’s for the exterior walls are required for the extra insulation.
What’s R-14 etc? In the UK all our codes are in U-values.
You can get a higher R value by using spray foam insulation. A 2x4 spray foamed wall should be meet any building code’s insulation requirements. Mike Holmes builds in Canada and uses spray foam on nearly every job. Spray foam is popular because a separate vapor barrier isn’t needed. Mike’s known for exceeding code in his framing and construction. I don’t recall him using 2x6 studded walls.
But, whatever the local code requires is what matters. A builder has to do whatever is necessary to pass the inspections and clear the permits.
Here in Ohio, all occupied buildings must pass the REScheck. I designed and built an addition on my home about ten years ago and went through the process. It is pass/fail, either the software gives you a passing grade, or you have to go back and change something. There are two basic methods to pass.
You can build to spec. If every criteria in the construction is met, then the house automatically passes. This may specify R19 walls, R30 ceilings, R13 floors, overall R values for doors, shading coefficients for windows, 90% furnaces, windows only a certain percentage of wall area, etc. It’s pretty thorough, windows on north and south walls are factored differently, for instance.
You can pick and choose. If you are deficient in one item or area, then you can exceed the specs in another and still pass. It all comes down to energy use per square foot.
I went the latter way since although I was only building half of the home, the whole house had to pass. I barely made it, I had to add floor insulation in the original part of the home to pass.
On the other hand, no one came out and checked any of it.
Dennis
R-30 where I live in CA.
Yeah, in CA we go through what is called Title-24 (energy audit) that you have to submit with your building plans. But in my experience, no one ever bothers to make sure no change are made-- that is, added window, larger windows, added skylights, etc. Insulation inspection is standard, but to a large extent the T24 is a paperwork exercise.
When the kitchen in my 1909-built house was remodeled, we put 2x2’s on top of the 2x4 studs, specifically to provide enough room for more insulation.
[When we were doing that, we tore out the old ‘insulation’ (1/4" of shredded newspapers between tarpapers) before installing new 6" insulation bats. We finished removing the old stuff that night, and went to bed, planning to install the new insulation the next day. This was on the North wall, on a windy January day in Minnesota – the high temperature that day was -19ºF (-28C), dropping to -26ºF (-32C) overnight. I think the poor furnace kept running all night long!]
But of course, R-values are useful for air conditioning insulation too. Sometimes you want to keep the heat outside, especially if electricity is expensive.
R-19 is pretty standard for walls in Alaska. The only exception from the norm I ever saw was that in Fairbanks and other places of extreme cold, the ceilings required R-42.