Practicality of 2x8 walls

Posted by David Bonnell on February 1, 2007, 10:02 am

Out of curiosity (I live in a cold-ish climate, so thicker walls
strike me as a good idea)

Does anyone do home construction using 2x8 (or two 2x4s)? I haven't
seen anything like this locally, but that doesn't necessarily mean it
doesn't exist.

Despite a material cost increase (and larger external footprint
required for the same internal square footage), wouldn't the increase
in R-value offset the additional cost over time?

Alternately, assuming 2x6 exterior walls, are any homes constructed
with additional EPS/XPS insulation on the outside of the wall?

Posted by Bob Morrison on February 1, 2007, 10:22 am

In a previous post David Bonnell wrote...

> Out of curiosity (I live in a cold-ish climate, so thicker walls
> strike me as a good idea)
>
> Does anyone do home construction using 2x8 (or two 2x4s)? I haven't
> seen anything like this locally, but that doesn't necessarily mean it
> doesn't exist.
>
> Despite a material cost increase (and larger external footprint
> required for the same internal square footage), wouldn't the increase
> in R-value offset the additional cost over time?
>
> Alternately, assuming 2x6 exterior walls, are any homes constructed
> with additional EPS/XPS insulation on the outside of the wall?
>

Finding single batt insulation to fill a 2X8 space will be difficult. You
would need to install two sets of batts.

If energy efficiency is your paramount consideration, then you might want
to look at Structural Insulated Panels (SIPS) as your method of
construction. Another method gaining favor in some areas is Insulated
Concrete Forms (ICF) for the whole house (not just the foundations).

--
Bob Morrison, PE, SE
R L Morrison Engineering Co
Structural & Civil Engineering
Poulsbo WA
bob at rlmorrisonengr dot com

Posted by Steve Barker on February 1, 2007, 3:56 pm

Sprayed in place cellulose would be better in any case anyway. Would work
perfectly in this case.

--
Steve Barker

> Finding single batt insulation to fill a 2X8 space will be difficult. You
> would need to install two sets of batts.

> Bob Morrison, PE, SE
> R L Morrison Engineering Co
> Structural & Civil Engineering
> Poulsbo WA
> bob at rlmorrisonengr dot com

Posted by Michael Bulatovich on February 1, 2007, 10:24 am

> Out of curiosity (I live in a cold-ish climate, so thicker walls
> strike me as a good idea)

Only when thicker = warmer. Thicker for thicker's sake is a stylistic
concern. I'm not saying that's a bad reason...just making a distinction.

> Does anyone do home construction using 2x8 (or two 2x4s)? I haven't
> seen anything like this locally, but that doesn't necessarily mean it
> doesn't exist.

I've done it in places where the walls were very tall, but not typically.

> Despite a material cost increase (and larger external footprint
> required for the same internal square footage), wouldn't the increase
> in R-value offset the additional cost over time?

Yes, but that's a 'present value of money' question. Maybe Pat has something
to say about ROI, etc.

> Alternately, assuming 2x6 exterior walls, are any homes constructed
> with additional EPS/XPS insulation on the outside of the wall?

Ever heard of EIFS?
--

MichaelB
www.michaelbulatovich.ca

Posted by DT on February 1, 2007, 1:02 pm

>Alternately, assuming 2x6 exterior walls, are any homes constructed
>with additional EPS/XPS insulation on the outside of the wall?

Absolutely. Even with 2x6 studs, the studs represent a significant loss of
insulating value compared to the cavities. Adding a continuous layer of
insulation over the entire structure improves the performance of the whole
system. I like Tuff-R, which has the highest R value combined with the lowest
cost per sheet (in my area, Northern Ohio).

--
Dennis

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