I am about to insulate my new 18x26 detached garage and I’m trying to decide between R-20 and R-24 batts for the walls. The cost difference is significant, the R-24 is almost double the cost of the R-20. R-24 is about 1$/sqft and the R-20 being around 0.50$/sqft. I am in Montreal so we definitely get some pretty cold temps in the winter. Will it be worthwhile to spend the additional money on the R-24 or will the difference in heating costs be so minimal that it would take decades to recoup the additional costs?
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Detached garage insulation
- Thread starter Mike_72
- Start date
I think it depends on how much you're out there, if you keep it fully heated or not , but a quick think seems the r-20 is the way to go . 5% more r value for double the cost seems out of line
Yeah, I was starting to lean toward R-20 also. Most of the time I will be keeping it around 10 degrees C during the winter. Bumping it up only when I’m going to be out there. I’m assuming the benefits of higher R value are diminished as the temperature delta becomes smaller.
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How are getting the is large variable in R value. The wall Cavity thickness is determined stud used.
Usually a Wall with:
2x4 construction gets 3.5” batt yielding about a R13
2x6 Construction gets 6” batt yielding about a R19
R13 is about .30 per square ft. R19 is .42 , R11 is .21 (US very rough estimate material only)
Is this spray foam insulation in quote in the OP ?
Putting R19 batt in 3.5” stud space does not work as far as R value.
Usually a Wall with:
2x4 construction gets 3.5” batt yielding about a R13
2x6 Construction gets 6” batt yielding about a R19
R13 is about .30 per square ft. R19 is .42 , R11 is .21 (US very rough estimate material only)
Is this spray foam insulation in quote in the OP ?
Putting R19 batt in 3.5” stud space does not work as far as R value.
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20 to 24 R-value is an increase of 20% not 5% - unless of course I don't understand how R-value gets calculated.
Do you have a lot or any windows? If so are they double or triple paned? Are the garage doors sealed well, are the garage doors insulated? Being a new garage I believe they most likely would be. Also, is the slab/foundation insulated around the edge?
What R-value are you putting in the ceiling?
Overall I think I would agree that the R20 is your better option. Especially if there are other things that you would need to improve upon. (hopefully being new nothing else needs help!)
Do you have a lot or any windows? If so are they double or triple paned? Are the garage doors sealed well, are the garage doors insulated? Being a new garage I believe they most likely would be. Also, is the slab/foundation insulated around the edge?
What R-value are you putting in the ceiling?
Overall I think I would agree that the R20 is your better option. Especially if there are other things that you would need to improve upon. (hopefully being new nothing else needs help!)
20 to 24 R-value is an increase of 20% not 5% - unless of course I don't understand how R-value gets calculated.
Do you have a lot or any windows? If so are they double or triple paned? Are the garage doors sealed well, are the garage doors insulated? Being a new garage I believe they most likely would be. Also, is the slab/foundation insulated around the edge?
What R-value are you putting in the ceiling?
Overall I think I would agree that the R20 is your better option. Especially if there are other things that you would need to improve upon. (hopefully being new nothing else needs help!)
2 3’x4’ double pane windows, 8x12 garage door R-10 sealed well. R10 Under slab and R10 around perimeter of slab with R10 skirt insulation out 2’ on all sides.
PhantomEB
Well-known member
Myself I wouldn’t cheap out on Insulation, especially if you gonna be there a while. I have R50 blown in the ceiling and T16 door out here in Calgary.
Myself I wouldn’t cheap out on Insulation, especially if you gonna be there a while. I have R50 blown in the ceiling and T16 door out here in Calgary.
I agree, I’ve decided to go with the R-24 in the walls. It’s not a huge shop and the difference in cost, although double the price of R-20 only comes to 300$ more.
How are getting the is large variable in R value. The wall Cavity thickness is determined stud used.
Usually a Wall with:
2x4 construction gets 3.5” batt yielding about a R13
2x6 Construction gets 6” batt yielding about a R19
R13 is about .30 per square ft. R19 is .42 , R11 is .21 (US very rough estimate material only)
Is this spray foam insulation in quote in the OP ?
Putting R19 batt in 3.5” stud space does not work as far as R value.
Johns Manville makes an R-24 Batt for 2x6 walls
dcg9381
Well-known member
I can't see spending double going R20 to R24 on WALLS. Most of the radiant heat gain (when cooling) and heat loss (when heating) is in the roof - at least in my climate. Focus your insulation spend on the roof first, walls second, windows third... Or minimize windows.. (Note, I know nothing about climates where you need insulated foundations)
20 to 24 R-value is an increase of 20% not 5% - unless of course I don't understand how R-value gets calculated.
...
brain fart!
Spend the extra money on making your building tight. Spray foam the seams or use caulking. I would take a tight building over a insulated drafty building any day. Fiberglass is nothing more then a super efficient air filter. I .in a fiberglass don't get me wrong, you just have to stop the air first.
Spend the extra money on making your building tight. Spray foam the seams or use caulking. I would take a tight building over a insulated drafty building any day. Fiberglass is nothing more then a super efficient air filter. I .in a fiberglass don't get me wrong, you just have to stop the air first.
I will certainly be paying attention to that as well. All the walls will be covered in 6 mil vapor barrier and taped, all of the outlets in installed in vapor barrier moulded boxes, doors and windows are well sealed. Any addition openings will be spray foamed.
I assume the r24 is mineral wool vs fiberglass at r20?
You potentially get some other benefits there as well.
It’s actually a higher density Fiberglass so unfortunately doesn’t have the benefits of mineral wool.
The stud cavity I am filling is 9’ so I’ll have 2 full 48” batts and a 12” section to fill the cavity. Is there any specific guidelines as far as what order to put them in? Should I be concerned if the joint in the exterior sheathing lines up with the joint of the insulation batts? I think this is probably another case of me overthinking things but always good to check!!
I think you're overthinking the joint issue , but, what you could do is on the next bay use the cut off (3') and lay a 48", then a 24" . that way all your seams are staggered.