NotAPro

8" CMU walls

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hello,

by default, the CBS walls in CA have 1.5" studs and drywall on the interior of the wall.

 

What is the 1.5" thickness based on?  Are they using a 2x4 as a furring strip?  Or 2x2 strip or Two 1x2 furring strips stacked?

 

I understand it could mean any of those, but what exactly is the proper way to frame CMU walls? (to achieve the 1.5" thickness as shown in the CBS walls in the program)

 

 

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Confront and decide is my advice. If it is not what you want, change it to something you do like and want.

 

DJP

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hi David,

what would be the most cost effective method in furring the CMU walls?

 

Using 2"x2" furring strips it would be 1.5" thick (actual size) plus 1/5" drywall so the walls would be 2" from the face of the CMU.  The 2x2 furring strips seem to be inexpensive at $1.75 each and wold allow enough space for electrical outlets.

 

Is this the most cost effective way to frame the CMU?

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And what about just using 1"x2" furring strips with 1/2" drywall.. would there be enough space for electrical outlets? The 1"x2" furring strips are 3/4" thick actual size as you know.. so 3/4" plus 1/2" drywall is 1.25".. but I think the electrical boxes are 1.5" thick...

 

Any thoughts?

Obviously the 1"x2" furring strips are half as thick and half the price.. but will the electrical fit?

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The wall needs to be designed around your requirements, not some default wall Chief provided.

 

Where will insulation go in this wall?

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@Solver,

that is part of my question.. what would be the most cost effective method .. including the insulation?

 

Insulation inside of the CMU cavities?

or would it have to be behind the drywall?

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I can't help, but there is plenty of info available online. You need to understand any code requirements, as well as a bit of building science to start.

 

Cost effective depends on many factors. Local cost of materials, local labor force, speed of construction etc. Not something easily answered on a forum.

 

https://buildingscience.com/

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@Solver,

which are the most common methods of insulation CMU perimeter walls

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Lumber cost is the least of the issues. 

Personally I would use 1/2"-1" space between the CMU and a 2x4 framed wall with 1/2" drywall.  The wall would need a vapor barrier and be insulated with a minimum of R-13 batts (requires 3-1/2" minimum).

 

That's IMO a minimum requirement for habitable space - but you really need to talk to the local building dept.

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19 hours ago, NotAPro said:

@Solver,

which are the most common methods of insulation CMU perimeter walls

I would suggest building a relationship with builders in your area, who can give you the best advice on how they price their wall assemblies.  Also look into the building codes and learn a lot about local practices.  For any given application in my region, there can be many various solutions to meet code requirements for structure, sound control, fire separation, insulation, moisture/vapor/air barriers and seismic activity.  And in my province there are varying requirements for various regions, so this changes when I do work outside my region.  All of this needs to be taken into account to determine the most cost effective assembly for the application.  I don't even try to determine that myself, I rely on builder feedback.  Until you can understand the requirements of the building codes as they apply to your region, you will be shooting in the dark.

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Well if you are talking inches you might be in the Unites States.

You local climate will likely drive the decision as to the wall components.

 

Here in Florida 8" CMU block is common and we use a 1x2 furring system with insulation on between the furring strips.

If the Energy Audit (needed for every permit) requires more insulation to pass code a core fill insulation can be added to the cells of the block.

 

 

 

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