# Garage Insulation



## Windows on Wash (Aug 30, 2011)

Boomer,

Are the wall batts that you priced out in fiberglass high density? 

If the fiberglass you are pricing out is high density, then R-Value is R-Value at that point. 

The mineral wool is more dense in a normal comparative and will therefore be far less subject to convection and the resultant R-Value downgrade. If you get the wall airtight (i.e. seal the backside of the outside wall and use ADA - Airtight Drywall Approach), the performance should be the same once installed in the wall. 

Mineral wool is much better when it comes to resistance to moisture and durability in the presence of moisture.

Soundproofing is moot in terms of difference is comparing similar quality levels of either. 

How big a space is the garage and how much will you be using it in a semi-conditioned (i.e. workshop) capacity? 

I would normally opt for the loose fill blown in cellulose as it is easier and cheaper to put more in. Be sure to air seal the top plates of the garage in the attic and depending on your location and the amount of moisture that is going to be percolating into the garage, look into some vapor retarder application on the ceiling prior to the insulation.


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## JA Boomer (Sep 25, 2014)

Windows on Wash said:


> Boomer,
> 
> Are the wall batts that you priced out in fiberglass high density?


These are the products I have priced out:

http://www.homedepot.ca/product/roxul-comfortbatt-r14-for-2x4-studs-16-in-on-centre/900116

http://www.homedepot.ca/product/roxul-comfortbatt-r22-for-2x6-studs-24-in-on-centre/900119

http://www.homedepot.ca/product/r-1...on-15-inch-x-47-inch-x-35-inch-783-sq-/905969

http://www.homedepot.ca/product/r-2...on-spacesaver-23-inch-x-47-inch-x-6-in/905973

http://www.homedepot.ca/product/r-3...on-24-inch-x-48-inch-x-95-inch-64-sq-f/925600



Windows on Wash said:


> If the fiberglass you are pricing out is high density, then R-Value is R-Value at that point.


Not quite sure what you mean here, can you elaborate?



Windows on Wash said:


> The mineral wool is more dense in a normal comparative and will therefore be far less subject to convection and the resultant R-Value downgrade. If you get the wall airtight (i.e. seal the backside of the outside wall and use ADA - Airtight Drywall Approach), the performance should be the same once installed in the wall.


The garage has 45 year old building wrap and stucco on the exterior, and yes I plan on installing vapour barrier on the interior between the drywall and insulation.



Windows on Wash said:


> How big a space is the garage and how much will you be using it in a semi-conditioned (i.e. workshop) capacity?


The garage is 26' wide by 19' long. It has a natural gas heater. The garage will be used as my workshop, parking for one truck, storage, and as a shed for garden tools. It will likely be unheated during the summer months and kept at 5 degrees Celsius in the winter for freeze protection and jacked up when I'm working in there.

I live in Calgary, Alberta, Canada for reference.



Windows on Wash said:


> I would normally opt for the loose fill blown in cellulose as it is easier and cheaper to put more in. Be sure to air seal the top plates of the garage in the attic and depending on your location and the amount of moisture that is going to be percolating into the garage, look into some vapor retarder application on the ceiling prior to the insulation.


I hadn't thought about blown-in insulation, as for myself to insulate the attic portion will only be a few hundred dollars. I assumed blown-in would costs more simply because of the labour to do it. I am not planning on leaving an attic hatch in the ceiling so I'm not sure I'd want to go that route.

I'm leaning towards the mineral wool, as I hear mostly good things. The primary advantage for me would be that it's easy to cut and place as there are a lot of non standard (less than 16" OC studs) in the walls.

My concern was about the health hazards of the mineral wool, but I see fiberglass insulation has the same listing on the MSDS: Class 3 - not classifiable as to it's carcinogenic effects on humans, but carcinogenic to animals in high doses.

My girlfriend wasn't familiar to mineral wool and wanted to make sure it wasn't the next asbestos so I've done more research than I would have otherwise.


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## 78Vette (Nov 25, 2009)

JA Boomer said:


> These are the products I have priced out:
> 
> http://www.homedepot.ca/product/roxul-comfortbatt-r14-for-2x4-studs-16-in-on-centre/900116
> 
> ...


I'd reconsider not having a attic hatch in the ceiling. Never know when you'll want to run extra wires for additional recepticals/ phone/ alarm or stereo......or add more insulation.
I used rockwool in my 2x6 walls and had r50 blown in the attic at a bargain cash price. Whatever you end up using, should be installed with the use of a mask anyway.


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## JA Boomer (Sep 25, 2014)

78Vette said:


> I'd reconsider not having a attic hatch in the ceiling. Never know when you'll want to run extra wires for additional recepticals/ phone/ alarm or stereo......or add more insulation.
> I used rockwool in my 2x6 walls and had r50 blown in the attic at a bargain cash price. Whatever you end up using, should be installed with the use of a mask anyway.


Well I just finished redoing the entire electrical. Put in 7 indoor and 1 outdoor receptacles, 6 flush mount lights, and 2 florescents over my work bench. I can't see a need to ever run additional wiring up there. Plus the roof slope isn't great, and with all the trusses up there it would be super hard to crawl around.

Is R22 acceptable for attic insulation? I installed 3 soffit vents and 2 roof vents in the fall, so it should have good ventilation.


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## 78Vette (Nov 25, 2009)

since you're heating it, R50 is what I recommend


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## Davejss (May 14, 2012)

You can look up the energy code and R-values for your region. If you are planning on using it as living space then you'll have to do it to code. If not, then do as you wish.


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## Gary in WA (Mar 11, 2009)

WoW---- you made this statement; "Are the wall batts that you priced out in fiberglass high density?" * Why?* JA Boomer listed the insulation in his opening post.... "Fiberglass (Owens Corning) with R14 walls and R20 attic at $654
Fiberglass (Owens Corning) with R14 walls and R31 attic at $805" The R-values are listed; just equate them for density.... clue; http://www.diychatroom.com/f98/biggest-loser-fiberglass-insulation-90438/

Rock wool would be my choice. They do make an encapsulated FG batt- no itches. And, rock wool does absorb water to lose R-value- eg.; in a rainscreen application; http://www.google.com/url?sa=t&source=web&cd=36&ved=0CDYQFjAFOB4&url=http%3A%2F%2Fwww.dow.com%2Fscripts%2Flitorder.asp%3Ffilepath%3Dstyrofoam%2Fpdfs%2Fnoreg%2F179-04569.pdf&rct=j&q=XPS%20in%20wall%20cavity%20vs.%20outside%20wall&ei=gRHtTbbvFZGWsgP2rOnZDQ&usg=AFQjCNEN_j-wXM2AA2UNU07zZTmsW6TAjQ&cad=rja

The attic access is required per code for fire safety, your choice in a detached non-living space as said already. Only three soffit vents may not wash every rafter bay... unheated (mostly), no problem, keep in mind the moisture from heat source if in same room. Is there a vapor barrier poly under the slab.... or at least seal (waterproof) the slab on surface from capillary wicking.

Gary
PS If money is no problem, insulate it well. Otherwise; http://www.buildings.com/ArticleDetails/tabid/3321/ArticleID/6061/Default.aspx


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## JA Boomer (Sep 25, 2014)

I'm appreciating the feedback on this topic, thanks everyone. I'm pretty sold on the Roxul product at this point. Today I found out that it was Holmes approved (the Canadians will know what I mean. I'm sure they're many opinions of the man, but I trust his word when he endorses a product.



78Vette said:


> since you're heating it, R50 is what I recommend


Here's my problem. The trusses are 2x4 construction. I can easily buy R22 5.5" thick mineral wool insulation. Granted I can get R31 and even R40 fiberglass insulation, but I like to keep things consistent (walls will be Roxul). So the only way for me to get higher than R22 in my roof, is by blowing in insulation, or carefully laying a few layers of batts (which is pretty impracticle given the volume constraints of the garage attic space.

Putting anything greater than 5.5" batts in between the rafters is probably a waste of time, as the heat transfer from the rafters themselves and into the open attic is the biggest problem.

I figure the R22 in the attic is greater than the R14 the walls will be, so as long as they're losing less heat then the walls, who cares? Yes, I know heat rises, but still, it's just the garage, and I don't want to go crazy on the budget for this project. Am I crazy?



Davejss said:


> You can look up the energy code and R-values for your region. If you are planning on using it as living space then you'll have to do it to code. If not, then do as you wish.





Gary in WA said:


> The attic access is required per code for fire safety, your choice in a detached non-living space as said already. Only three soffit vents may not wash every rafter bay... unheated (mostly), no problem, keep in mind the moisture from heat source if in same room. Is there a vapor barrier poly under the slab.... or at least seal (waterproof) the slab on surface from capillary wicking.
> [/url]


Apparently in Alberta minimum code is R40 in the attic. Are you both saying the R40 and an attic access are NOT required if it's not a living space such as a garage?


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## Windows on Wash (Aug 30, 2011)

Gary in WA said:


> WoW---- you made this statement; "Are the wall batts that you priced out in fiberglass high density?" * Why?* JA Boomer listed the insulation in his opening post.... "Fiberglass (Owens Corning) with R14 walls and R20 attic at $654
> Fiberglass (Owens Corning) with R14 walls and R31 attic at $805" The R-values are listed; just equate them for density.... clue; http://www.diychatroom.com/f98/biggest-loser-fiberglass-insulation-90438/
> 
> Rock wool would be my choice. They do make an encapsulated FG batt- no itches. And, rock wool does absorb water to lose R-value- eg.; in a rainscreen application;


I didn't cross reference it with the R-Value. I was somewhat asking the question to highlight the difference to the poster so that he could make the connection between the two. 

I like mineral wood as well but I am just pointing out that it is not a magical substrate nor will it provide some amazing level of performance over good fiberglass if the wall is tight and well constructed. 

Thanks for the rest of the links and that thread (Fiberglass - Biggest Loser) should be required reading for everyone posting a question in the insulation forums. 

:thumbsup:


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## ddawg16 (Aug 15, 2011)

Out of curiosity.....have you tried getting a quote from a insulation company? When I did my house (addition), when I compared my cost of just the raw material vs paying someone to do it....it cost me maybe $400....and this was a 2-story addition of about 1100 sq ft.

At $400 and all that itching? Who do I make the check out to?

They were done in one day. And cleaned up.

I am the ultimate DIY'r....but some things are best farmed out. This is one of them.

You have already saved yourself a ton of money doing your own wiring. I think it's ok to splurge a little in this case.


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## Gary in WA (Mar 11, 2009)

"I didn't cross reference it with the R-Value. I was somewhat asking the question to highlight the difference to the poster so that he could make the connection between the two."- --- I doubt the average poster would understand density/convective loops. My point was his first post listed the density; R-20 is low, R-30 is also, no reason for you to even ask: "Are the wall batts that you priced out in fiberglass high density?", unless you are not familiar with the correlation, just repeating my answers on this forum as no one else has mentioned it before me until now. That it something I thought of and researched for the links to prove my answers. Same as the value/cost of insulation.... and FB on rim joists, FB on cantilevers, FB on crawlers, FB /house wrap on knee walls, cellulose/house wrap on loose-fill, ADA (air-tight drywall), etc. that are now in your standard answers. Most of that is common knowledge and acceptable; save the first two mentioned. Something I adjust to when viewing, though; even my exact same links... then my respect drops at each occurrence. 

On a better note; 
"Here's my problem. The trusses are 2x4 construction. I can easily buy R22 5.5" thick mineral wool insulation. Granted I can get R31 and even R40 fiberglass insulation, but I like to keep things consistent (walls will be Roxul). So the only way for me to get higher than R22 in my roof, is by blowing in insulation, or carefully laying a few layers of batts (which is pretty impracticle given the volume constraints of the garage attic space.

Putting anything greater than 5.5" batts in between the rafters is probably a waste of time, as the heat transfer from the rafters themselves and into the open attic is the biggest problem.

I figure the R22 in the attic is greater than the R14 the walls will be, so as long as they're losing less heat then the walls, who cares? Yes, I know heat rises, but still, it's just the garage, and I don't want to go crazy on the budget for this project. Am I crazy?' ------------------------------ 


Check with your local AHJ for the minimum insulation in an outbuilding. Add some rigid FB to the joist bottoms; thick enough to act as a vapor barrier for your location, along with batts- leaving the 2" air space for ventilation. Add chutes continuously with the reduced air space of the chute as second choice. R-10 XPS/R-14 batt will stop about 97% of the heat loss at ceiling- including the thermal break at wood joists. Add the FB scraps (after cutting ceiling FB to break on joists for total area coverage) flat over the wall plates at the reduced clearance. 
Warm air rises, heat radiates to cold areas/object- all around. Less heat will go up through the ceiling than out the doors/window in your garage- notice the 6" insulation in attic- the air movement will get you; https://www.masonryinstitute.org/pdf/805.pdf

Gary


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## JA Boomer (Sep 25, 2014)

Gary in WA said:


> Putting anything greater than 5.5" batts in between the rafters is probably a waste of time, as the heat transfer from the rafters themselves and into the open attic is the biggest problem.
> 
> Check with your local AHJ for the minimum insulation in an outbuilding. Add some rigid FB to the joist bottoms; thick enough to act as a vapor barrier for your location, along with batts- leaving the 2" air space for ventilation. Add chutes continuously with the reduced air space of the chute as second choice. R-10 XPS/R-14 batt will stop about 97% of the heat loss at ceiling- including the thermal break at wood joists. Add the FB scraps (after cutting ceiling FB to break on joists for total area coverage) flat over the wall plates at the reduced clearance.
> Warm air rises, heat radiates to cold areas/object- all around. Less heat will go up through the ceiling than out the doors/window in your garage- notice the 6" insulation in attic- the air movement will get you; https://www.masonryinstitute.org/pdf/805.pdf
> ...


I have to say .. I had trouble following and visualizing that. I assume rigid FB is rigid insulation boards? I'm not sure where the 2" air space is suppose to be?

My new and improved plan .. is to buy R32 Roxul, and place it in between the rafters as I had planned. But I am also going to cut 2" strips of Roxul to put on top of the bottom joist of the rafters, so that I will have 8" of uniform and continuous insulation, with 5.5" of insulation on top of each rafter joist in between the whole batts.

Here's another quandry. My garage doesn't have soffits, so I have low roof vents and high roof vents to provide ventilation. towards the sides of the roof where there's less then 8" of clearance from the ceiling, is it okay for the Roxul to butt up to the roof? Or should I leave a small air space, or simply staple baffles so the insulation itself won't be in contact with the roof?


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## JA Boomer (Sep 25, 2014)

JA Boomer said:


> I have to say .. I had trouble following and visualizing that. I assume rigid FB is rigid insulation boards? I'm not sure where the 2" air space is suppose to be?
> 
> My new and improved plan .. is to buy R32 Roxul, and place it in between the rafters as I had planned. But I am also going to cut 2" strips of Roxul to put on top of the bottom joist of the rafters, so that I will have 8" of uniform and continuous insulation, with 6.5" of insulation on top of each rafter joist in between the whole batts.
> 
> Here's another quandry. My garage doesn't have soffits, so I have low roof vents and high roof vents to provide ventilation. towards the sides of the roof where there's less then 8" of clearance from the ceiling, is it okay for the Roxul to butt up to the roof? Or should I leave a small air space, or simply staple baffles so the insulation itself won't be in contact with the roof?


Or if the mineral wool is too difficult to cut in 2" strips, I will put Extruded Polystyrene Rigid Insulation in between the whole batts above the rafter joists.


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## Gary in WA (Mar 11, 2009)

Because you have a low pitch roof angle, 2" air space under the roof sheathing is better than our code required minimum 1" air space. You can add rigid foam board to the bottom of the horizontal ceiling joists (eliminating thermal bridging of the wood) with cavity fill above that- up to some baffles made of rigid foam board as here- separating the air space from the cavity; www.buildingscience.com/documents/published-articles/pa-crash-course-in-roof-venting

Never let cavity insulation (other than rigid FB) abut a cold sheathing to transmit warm temps to cold roof- conduction loss of R-value.

Gary


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## JA Boomer (Sep 25, 2014)

Gary in WA said:


> Because you have a low pitch roof angle, 2" air space under the roof sheathing is better than our code required minimum 1" air space. You can add rigid foam board to the bottom of the horizontal ceiling joists (eliminating thermal bridging of the wood) with cavity fill above that- up to some baffles made of rigid foam board as here- separating the air space from the cavity; www.buildingscience.com/documents/published-articles/pa-crash-course-in-roof-venting
> 
> Never let cavity insulation (other than rigid FB) abut a cold sheathing to transmit warm temps to cold roof- conduction loss of R-value.
> 
> Gary


Interesting!

Unfortunately I can't use the rigid FB between the ceiling joists and drywall because I can't afford to lose any head room, as it's a pretty low ceiling.

Here's my next question. Should I leave a 1-2" space between the insulation and roof boards all the way to the roof edge? I was thinking of going right up against the roof boards at the very sides of the roof, but I think I could run into ice damming problems in the future. Better to be slightly less thermal efficient than causing other problems I suppose.


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## Windows on Wash (Aug 30, 2011)

You have to provide for unobstructed ventilation pathway. If the roof pitch is steep, the smaller gap is less worrisome, however, you really should have about a 2" continuous gap to allow for the space to vent.


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## JA Boomer (Sep 25, 2014)

Windows on Wash said:


> You have to provide for unobstructed ventilation pathway. If the roof pitch is steep, the smaller gap is less worrisome, however, you really should have about a 2" continuous gap to allow for the space to vent.


Even if that means the very edges of my garage will have almost no ceiling insulation???


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## Windows on Wash (Aug 30, 2011)

I think Gary referenced it earlier, when it was mentioned about putting rigid foam over the top of that outer top plate.

Caulk, foam, or otherwise seal that top plate connection against any air leakage. After that is completed put the highest R-value foam, rigid board, that you can in that location.

If you use something like a polyiso bored, you get the maximum R-value you can per inch at that location. Be sure to seal that phone where it connects to the framing into the attic floor as well.


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