# Insulation question



## VERMA071 (Dec 14, 2021)

Hello everyone,

we recently have a situation in our office where a contractor was advised to use Batt insulation (R-15) and rigid insulation (R-4) on an exterior 4" stud exterior wall.
Instead of having an OSB/ Plywood sheathing as a rigid  board attached on the outside of the studs, contractor cut that rigid board and added that inside the stud bays. this has reduced the depth required for the insulation and thereby compromised the r-value of insulation. Is there any way to correct this situation from inside as exterior is already finished? we advised him to add 2x2 on the inside in front of 2x4 but he is saying it will create further issues for plumbing and electrical work. Any advice?
Thank you.


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## classicT (Dec 14, 2021)

Per your energy code, what is the required insulation value? I am guessing that it is probably R-21 w/ intermediate framing?

Suggest that you contact the local AHJ on this one...


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## VERMA071 (Dec 14, 2021)

classicT said:


> Per your energy code, what is the required insulation value? I am guessing that it is probably R-21 w/ intermediate framing?
> 
> Suggest that you contact the local AHJ on this one...


Its R-19 for the wall. AHJ is asking a letter from Architect saying R-value is not going to be reduced but we think that by compressing the insulation to accommodate in the studs, its R-value will be affected.


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## classicT (Dec 14, 2021)

VERMA071 said:


> Its R-19 for the wall. AHJ is asking a letter from Architect saying R-value is not going to be reduced but we think that by compressing the insulation to accommodate in the studs, its R-value will be affected.


You are correct, the R-value will be reduced.


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## bill1952 (Dec 14, 2021)

You dont say how much cavity depth was reduced but if I assume 1/2", probably the R15 batt is providing R13 in 3" depth.  It's R11 in a 2x3 walk. https://www.google.com/url?sa=t&sou...IQFnoECAQQAQ&usg=AOvVaw2I5A9SQXDOGIz29xDqar05
1/2" of foam under drywall?


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## mtlogcabin (Dec 14, 2021)

A complete  ASHRAE report not just a letter from the architect should be required by the AHJ

N1101.3 (R101.5.1) Compliance materials.
The building official shall be permitted to approve specific computer software, worksheets, compliance manuals and other similar materials that meet the intent of this chapter.


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## e hilton (Dec 14, 2021)

VERMA071 said:


> Instead of having an OSB/ Plywood sheathing as a rigid  board attached on the outside of the studs, contractor cut that rigid board and added that inside the stud bays.


I think you need to evaluate the installation of the sheathing.  It’s supposed to span across multiple studs to provide racking resistance, sounds like the way he installed it … it’s not performing that function.


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## tmurray (Dec 14, 2021)

VERMA071 said:


> Hello everyone,
> 
> we recently have a situation in our office where a contractor was advised to use Batt insulation (R-15) and rigid insulation (R-4) on an exterior 4" stud exterior wall.
> Instead of having an OSB/ Plywood sheathing as a rigid  board attached on the outside of the studs, contractor cut that rigid board and added that inside the stud bays. this has reduced the depth required for the insulation and thereby compromised the r-value of insulation. Is there any way to correct this situation from inside as exterior is already finished? we advised him to add 2x2 on the inside in front of 2x4 but he is saying it will create further issues for plumbing and electrical work. Any advice?
> Thank you.



It sure will create issues with the plumbing and electrical, but without removing the exterior siding and installing the rigid insulation the way he was directed, I don't see another solution. 

We'll maybe some form of performance option.


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## Rick18071 (Dec 14, 2021)

There are other ways to insulate besides fiberglass that could fit.


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## Joe.B (Dec 14, 2021)

Maybe a higher quality batt that is meant to fit a 3" space and still provide the minimum R value? Does it exist? I don't know, I suspect you could get there with rockwool


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## ICE (Dec 14, 2021)

The insulation was supposed to span over the stud to eliminate a thermal bridge.  Now the 1/2" insulation is in the stud bay......The lost depth in the stud bay for the batt insulation is negligible.  So you might be getting R18 instead of R19.


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## Keystone (Dec 14, 2021)

First, verify exterior sheathing is in place, whatever the AHJ approved or will approve.

Fix 1. Pull the material out of the bays and spray foam.

Fix 2. Pull the foam board out of the bay, place your cavity insulation, R15 or whatever it is, use unfaced insulation.  Then place the foam board over the face of the interior studs and tape all seams with approved tape. Finally wallboard with extended fasteners. Use electrical box extensions or adjust boxes up front.  Plumbing can remain untouched, electrical, minor adjustment. 

No matter which route, you’ll need AHJ approval....


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## bill1952 (Dec 14, 2021)

ICE said:


> The insulation was supposed to span over the stud to eliminate a thermal bridge.  Now the 1/2" insulation is in the stud bay......The lost depth in the stud bay for the batt insulation is negligible.  So you might be getting R18 instead of R19.


I believe what was built was 2x4 studs with the 1/2" osb or ply sheathing somehow inset between studs and 1" (?) R4 foam continuous across studs.  I think the wall bracing has to be addressed but 1/2" R2 foam on inside should safely get the R19, better because it's continuous on both sides.


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## north star (Dec 15, 2021)

*$ ~ $ ~ $

VERMA071,*
*
Have you considered Cellulose Fiber Insulation ( CFI )*
*being blown in to the wall cavities , and afterwards,
...covering the walls with some type of plastic air barrier ?




$ ~ $ ~ $*


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## steveray (Dec 15, 2021)

If continuous insulation is not required, then it could work...The insulation manufacturers sometimes have a table of "compressed" values...




You might get there with a slightly reduced value if you run it through Res-check....The most OC says you can squish there R15 is to 2.5" and you get R11


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## Robert (Dec 16, 2021)

If metal studs, then Ice is correct in that the thermal bridging is an issue if the insulation is not on the exterior.


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