Studded wall and insulation question

[tbz]

So, I have a situation, asked to come in and review a site, it's an indoor archery range for a private club, being built by the membership, all volunteers.

PreFab Metal building with 2x4 wood studded walls spaced away from the metal framework, on 24" C/L for Rockwool batts, the batts they are looking to use are the R-23 5.5" deep.

So, 3.5" stud with 5.5 batts, there is enough room depth wise, but part of the batt will go 2" past the 2x4 wood stud.

What's your thoughts on this?

 

[Joe.B]

2x4 wood studded walls spaced away from the metal framework,

Structurally independent? Sounds fine to me if so.

 

[RLGA]

They will not get R-23 (are you sure it is not R-21?). When blanket insulation is compressed, it loses its R-value and will be somewhere around R-15/17 (https://insulationinstitute.org/wp-content/uploads/2016/08/Compressed_R_values.pdf). If they need the R-23 for energy code compliance, then they need to use 2x6 studs.

 

[Joe.B]

When blanket insulation is compressed, it loses its R-value

there is enough room depth wise, but part of the batt will go 2" past the 2x4 wood stud.

I didn't get the impression that would be an issue, but it is somewhat vague. I got the impression that there are basically two structurally independent systems, but not yet confirmed by @tbz

 

[Keystone]

Can you place R15 Rockwool batts, 3.5” within cavity and then use R10 foam board offer the face to achieve the min wall R value?

 

[Keystone]

They will not get R-23 (are you sure it is not R-21?). When blanket insulation is compressed, it loses its R-value and will be somewhere around R-15/17 (https://insulationinstitute.org/wp-content/uploads/2016/08/Compressed_R_values.pdf). If they need the R-23 for energy code compliance, then they need to use 2x6 studs.

I believe what it meant, Rockwool 5.5” depth equals R23. The wall assembly sounds as if it’s a stand off so no insulation compression will occur, if that is accurate

 

[tbz]

Thanks everyone,

• yes, the metal building is its own structure,
• the wood studs are structurally independent and there is 7" from face of stud to metal
• The Rockwool #169094 is advertised as R23 x W23 x h47 x d5.5, and the bags say R23 not R21, so I am guessing they are R23 by label.
• The building is not going to be heated above 55, I believe in the winter and the 2 bathrooms will be separate heating on their own.
• Just an enclosed metal building with targets on one end and people standing on the other end.
• I am not sure why we didn't leave it as a dirt floor and call it a storage building but say la vee.

 

[Jay Smith]

If this is to meet the prescriptive value of R-20 for wood framed walls, I don’t think it complies without 2x6 studs. There will be a gap between the insulation batts. What would meet the requirement appears to be R-13 insulation between 2x4 studs and R-3.8 continuous insulation. That‘s sort of a technicality, though, since not much R-value is lost by not having 2 more inches of wood in the gap.

 

[bill1952]

The space behind the batts - 7" cavity with 5 1/2" batts - will also reduce the insulation effectiveness, probably more than the 2" stud gap.

 

[steveray]

Tom....As long as you are using "cavity" for the insulation it is fine sticking out...Think 2x4 roof trusses with R49 batts....same same....

 

[Tim Mailloux]

I might be concerned by the 1.5" gap between the inside face of the metal siding and back side of the insulation. There is a chance you get some condensation in this space leading to mold issues as that water will have no way to escape. Might be wise to have a dew point analysis performed on the wall assembly.

I may also be over thinking this and its not an issue at all.