That method came into popular use in the late seventies. Some locales still depend on it even to the point of pushing it via building codes in spite of the fact that since then, much better ways of adding insualtion and quality to the house have been developed, including spray foam such as Corbond and breaking the thermal bridging with foam sheets over fibreglas.

The originators of 2x6 style framing sold us on the idea of changing to 24" OC instead of 16" OC to keep total lumber cost similar but other drawbacks exist with such wide spacing of studs, such as wavy walls.

Most knowledgeable builders understand there is no cost to benefit ratio by using 2x6s over 2x4s. None.

In fact, using 2x4s can be cheaper AND more efficient as far as insulation goes.

First, if one uses 2x6s one not only increases the cost to insulate, one also increases the cost in windows and doors sicne jambs must be ordered or constructed to fit a 2x6 rather than a 2x4 wall.

Second, 2x6s may add an increase in depth for and to include a 'thicker' insulation but this insulation alone will not insulate a home 'better' than a 2x4 wall with proper treatment...

Here is how most 'pros' do it:

-Construct 2x4 walls. (There is no less structural difference between that and 2x6) construction...

-Add 1 " of foam insulation on the outside of the house. This creates a thermal barrier that increases the insulating factor much mor greatly than simply increases the wall dimensions to 2x6. This also decreases the chance for condensation to form in walls. Eliminates the need for housewrap, builder paper, or other secondary weather barrier beneath siding.

- Eliminates the need for another and more costly 'backer' beneath vinyl siding...

Only 2x4 construction for me...with 1" foam insulation over sheathing on the outside. Compressed R-13 on the inside.

Thanks for the info, guys. Homebuild, I have read that 2x6 walls allow for an R value of 21. As far as I know, 1" foam typically has an R value of ~5. When you say that 2x4 walls with 1" of foam on the outside "increases the insulating factor much mor greatly than simply increases the wall dimensions to 2x6," is that simply because the exterior foam is contiguous, as opposed to the batt insulation which is broken up by the studs? By rough calculation, 10% of the wall by length would be un-insulated with 16" OC construction, so that R21 with the 2x6 would average out to more like R19, all things being equal.

Exterior foam creates a thermal barrier between the studs and the external environment.

Not only does that create a warmer house than using batt insulation alone, it greatly lessens condensation problems is walls.

The reason is that by insulating the sheathing over studs, you can usually keep the stud spaces above the dew point so that condensation will not occur.

Foam exterior sheathing also eliminates convection currents within stud spaces for more uniform insulating tempertaures. This also reduces the potential for condensation.

Condensation in fiberglass reduces the ability of fiberglass to insulate.

Therefore foam over studs is much more effective than just fiberglass between studs alone.

But in all fairness, you could get a greater insulating factor using 2x6s with exterior foam compared to 2x4s with exterior foam, but the cost to benefit ratio may still not be there.

Thanks for taking the time to explain this to me in so much detail, Homebuild. When the time comes to build my new house, I'm certainly consider this method.

Good info.

My wife likes 2x6 walls, it gives the window area more room for her cat to sit and look out the window

M C

Screen room | Garden room | Outdoor room | http://www.HomeLivingSpaces.com | Do-it- Yourself

How is this accomplished? We are building a home with 1/2" OSB, and if we add 1" of foam, then our hardiplank siding will stick out beyond the edge of the brick ledge trim at the outside perimter of the windows. Can you get a deeper brickledge?

Also, if you use foam instead of a house wrap, do you install the foam 1st and the windows second? Would this not cause the windows to be nailed into foam causing an unstable nailing surface since the foam may get futher compressed with time?

It is possible to nail window flanges over the foam if you are careful not to nail too deep and compress. Some builders use a wood shim directly behind the window flange.

If you are using brickmold on the windowsfor acasing, the load is spread out enough to not compress the foam. Brickmold is for bricks though. a Casing is better for Hardi, IMO.

In warm climates it is best to add this faom on the exterior, but in cold climates, it is best to use it on the interior side of the wall

Excellence is its own reward!

If you do not plan to use a house wrap over the foam it is also a good idea to tape the joints between the foam panels to prevent air infiltration through the cracks between the panels.

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