Tstuds and exterior foam
I received a plan set today that calls for Tstuds as the framing and 2″ foam exterior continuous insulation. This doesn’t make sense to me as my impression of Tstuds is to get continuous insulation without exterior insulation. Wouldn’t it be better to use 2×6 framing and use the cost savings to make the exterior insulation thicker? Has anyone built or done modeling using both? (FYI this is in Northern Minnesota – Climate Zone 7)
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I've not built or modeled this, but the rudimentary math (for what that's worth) comes out something like:
Scenario 1— 2x6 T-studs, R-21 wall batt, 2" ext. EPS and 18% framing factor: whole wall R=28.3
Scenario 2—2x6 dimensional stud, R-21 wall batt, 2" EPS, 18% ff: whole wall R= 24.5
Scenario 3—2x6 dimensional stud, R-21 wall batt, 3" EPS, 18% ff: whole wall R= 28.6
Keep in mind this is a basic series/parallel heat flow calc, not a more complex model. Your realities may also differ from the inputs I used. But it might give a ballpark.
Might also be worth mentioning that some would consider 2" exterior insulation inadequate in climate zone 7 for condensation control reasons. You might be aware of and taking steps to mitigate those issues already, but just wanted to throw it out there.
I don't understand this new tstud thing. Solid wood is a better insulator. I also question the compressive and buckling strength of these new fangle studs. Less natural wood and more chemical products adding to more toxic materials in your wall assembly in your non breathing, tight house......more money to the tech giants rather than obtaining and renewing natural, free materials given to us from our environment.
Solid wood used for studs has a R-value of approx 1.4/inch so no it's not a better insulator. In fact it's a horrible insulator.
So I guess log cabins don't really cut it and should be made from foam from now on...
Log cabins have a lot of attributes, but insulation isn't one of them. They test out so poorly the proponents tried to invent a new metic "perceived heat" to help them meet codes..
Yes, because foam has the same structural properties as logs. It's only for the superior insulation value of wood that homes aren't built entirely out of foam.
Tom, wood is almost 100% responsible for that "Thermal Bridging" thing so many people are speaking of these days in residential construction. :)