# Making an external wall thicker?



## north (Jul 9, 2009)

This house is early 1970's 2x4 construction with crawl space, block foundation - very typical. It's in the upper midwest so in the coldest months it costs a fortune to heat the place due in part to the walls only being 3 1/2 thick. I need to install new siding anyway so what I'm proposing to do is to make the walls thicker from the outside and either install 30r batts in front of the old r13 or remove the r13 and install r36 batts. 

I'm primarily concerned with how to build out the depth of the studs to accommodate this extra insulation but also how to cram as much r value in the walls as possible. 

As I see it I could do one of two things:

1) place 2x10s in front of the studs then sandwich the 2x10 and existing stud between two pieces of ply or 1x6. This seems to be the strongest method but I'm concerned about the extra weight and it's effect on the house - don't want the walls to crack or bow outwards. I'll be using fiber cement siding.

2) use 2x4s with 6" of 2x4 at the top and bottom to form an elongated C shape. Use ply on both sides to clamp this C in place and attach to existing studs. - seems there would be less weight to this due to the hollow section in the middle but not as strong as 1)

I could dig concrete footings to support this build out from the existing wall if need be, I just need to be sure I'm not doing to compromise the structural integrity of the house.

Any advice would be greatly appreciated!


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## neolitic (Apr 20, 2006)

north said:


> This house is early 1970's 2x4 construction with crawl space, block foundation - very typical. It's in the upper midwest so in the coldest months it costs a fortune to heat the place due in part to the walls only being 3 1/2 thick. I need to install new siding anyway so what I'm proposing to do is to make the walls thicker from the outside and either install 30r batts in front of the old r13 or remove the r13 and install r36 batts.
> 
> I'm primarily concerned with how to build out the depth of the studs to accommodate this extra insulation but also how to cram as much r value in the walls as possible.
> 
> ...


My advice is seal it well
and spend your money increasing
the attic insulation.
Heat rises, most of your heat loss
is through the ceiling, not the walls.
Even with last year's energy prices,
your return on investment in the wall
schemes you have presented will be
20 years or more down the road.


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## JumboJack (Aug 14, 2007)

How about a layer of rigid insulation.


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## WarnerConstInc. (Jan 30, 2008)

Spray foam icyecelenenene, you know what I mean.


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## bob_cntrctr (Jan 30, 2008)

JumboJack said:


> How about a layer of rigid insulation.


Yep, check out this article - scroll down to the Siding section 2/3 of the way down the page.

http://www.homeenergy.org/archive/hem.dis.anl.gov/eehem/96/961110.html


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## mics_54 (Oct 28, 2008)

> How about a layer of rigid insulation.


:thumbsup:


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## bob_cntrctr (Jan 30, 2008)

mics_54 said:


> :thumbsup:


 
"Location: Sterling ,Alaska" - if you're gonna take insulating advice from anyone, I'm thinking a guy from Alaska's a good bet!


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## IaContractor (Jul 3, 2009)

Add 1" of ridged insulation to the exterior and then side over that. Add blown in insulation to the attic to at least an R40

You lose most heat through your roof, windows and the multiple air leaks throughout your house, not your walls. 

What are your windows like?


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## naptown CR (Feb 20, 2009)

neolitic said:


> My advice is seal it well
> and spend your money increasing
> the attic insulation.
> Heat rises, most of your heat loss
> ...


 This and an adequate sealing of infiltration is the ticket
I could not have expressed this better than Neo


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## mics_54 (Oct 28, 2008)

I agree that infiltration and ceiling insulation is important but neither of these issues was presented as a problem. We don't have any idea what the current insulation in the ceiling is given the information offered in the original post. We also do not know that the OP hasn't already addressed inflitration at windows, doors, ceiling fixtures or electrical boxes. What we do know is that the OP is replacing the siding on his exterior walls and that the walls are 2x4 construction. We also know with 2x4 construction that his r13 is in actuality nearer an r7 given the abundance of wood members in a given wall section causing thermal bridging. 
Given that the siding is coming off now, it's a no-brainer to add some insulation to the exterior if he is concerned about wall insulation values. 1" of foam would increase his existing values by 7 (approx). adding an additional 1-2 inches of insulation certainly would not be a waste of money. 
A note of caution...if you don't have a vapor barrier in the proper place now...be careful not to create one at the exterior of the wall.


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## PA woodbutcher (Mar 29, 2007)

Jeez, what happened to this guy? He could sure use a contractor:laughing: Sounds like he willing to spend a pisspot full of money that he doesn't need to.

You get a lot of those 1 post wonders here in the remodeling section don't you


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## neolitic (Apr 20, 2006)

PA woodbutcher said:


> Jeez, what happened to this guy? He could sure use a contractor:laughing: Sounds like he willing to spend a pisspot full of money that he doesn't need to.
> 
> You get a lot of those 1 post wonders here in the remodeling section don't you


Sure do. :whistling
If any of these guys ever did 
the math to find out what the
pay back is on retro fitting 
super thick walls they would...


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## north (Jul 9, 2009)

I'm gonna go with rigid insulation and wrapping the house tight to minimize air infiltration. Do you think it would be worth running some thin furring strips between the rigid foam and the new siding (concrete fiber) to make sure any moisture that works it's way back there can evaporate?

I totally understand the need for attic insulation but this house has no access to the attic and a very shallow pitch to the roof and is only vented at the ridge which might cause problems.

All your help is appreciated!


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## neolitic (Apr 20, 2006)

Ridgid foam on the ceilings,
covered with drywall, will pay back
a whole lot sooner, and 
make less of a mess.
2¢


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## jkesterson (Sep 13, 2009)

Here is what we have done in New England to old houses. We are using a new system on these old wooden sided farm homes called Tru-Brix. It is brick siding using real brick which has been sliced in half. They fit on to steel rails without using any glue. Once on the rail they are there permanently. There is over 300 styles of brick to choose from and you get a 50-year warranty with them. Nice, huh?


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