Insulating floor of attic truss

[jawmaw]

I am building a 24x40 garage with attic trusses. the bottom cord is 2x8. The attic is for storage and will not be insulated at this time but the garage will be insulated and heated.

What type of insulation should i use for the ceiling? I only have 7.5 inches. I am going to install steel liner panels for the ceiling and drywall for the walls of the garage. I wanted to install the ceiling and insulate from above before I put down the decking in the attic for ease of hooking up and positioning my lights below.

Should I compress r-30 fiberglass or use cellulose for the ceiling? I intend to use cellulose for all other areas of the ceiling.

Thanks!

 

[NUTTSGT]

If you're insulating from above, blown in might be the easiest choice. Personally, I hate blown cellulose insulation.

I just redid the insulation in part of my garage ceiling like you're doing. I put fiberglass batts down and styrofoam in between the joists on top of the fiberglass. Once that was done, I put flooring down.

 

[jawmaw]

If I end up using cellulose in the part of the ceiling under the decking should I really pack it in there tight to minimize the settling or should it be loose?

 

[Elginz]

I used the fiberglass bats, R19 where the floor is, R38 else where.

 

[roscoe2000]

If I end up using cellulose in the part of the ceiling under the decking should I really pack it in there tight to minimize the settling or should it be loose?

No you should not pack it in, ideally the cellulose would be blow in and let it settle to the height need.

 

[40x60shop]

Hello fellow members
I have just registered with your forum and hope to obtain and share good ideas with you guys. Looks like a very informative site.
Best regards

 

[40x60shop]

Sorry guys, looks like I'm off to a good start, in the wrong post. This is all new to me. I just now found the introduction post of the forum.

 

[larry4406]

Assuming you have true attic trusses with an area for a floor, put 2" rips on the floor floor area to give you 2x10 in that area. Then you can go to R30 in the floor area as well as the attic spaces where you can either batt or blow.

 

[MagKarl]

Mine was done with batts before the drywall was put up.

 

[jawmaw]

Mine was done with batts before the drywall was put up.

What size batts did you use? I would like to get more than r19 but I would need to compress r30 2 inches.

 

[jawmaw]

Assuming you have true attic trusses with an area for a floor, put 2" rips on the floor floor area to give you 2x10 in that area. Then you can go to R30 in the floor area as well as the attic spaces where you can either batt or blow.

That seems like a lot of trouble ripping 2 inches and adding to the top of the bottom chord.

 

[jawmaw]

If you're insulating from above, blown in might be the easiest choice. Personally, I hate blown cellulose insulation.

I just redid the insulation in part of my garage ceiling like you're doing. I put fiberglass batts down and styrofoam in between the joists on top of the fiberglass. Once that was done, I put flooring down.

Why do you hate cellulose? I know it is dusty but I have read it outperforms FG.

 

[NUTTSGT]

Why do you hate cellulose? I know it is dusty but I have read it outperforms FG.

Because when it comes to overhaul after a house fire, it's a royal PITA. Every rekindle I have been on, with the exception of one being relit, had cellulose insulation in it.

 

[fastjohnny]

I would dense pack cellulose for air-sealing and R value.

 

[bczygan]

Foam.
Then a 2" layer of rigid foam boards below.

 

[Jlbc212]

Because when it comes to overhaul after a house fire, it's a royal PITA. Every rekindle I have been on, with the exception of one being relit, had cellulose insulation in it.

As a firefighter I tried to get the State Fire Marshall and the Consumer Product Safety Comission to ban the use of cellulose insulation. I had numerous fires where cellulose insulation in a ceiling or a wall was the first item ignited. The only way to avoid a rekindle is to remove all the insulation that has charring, which most often meant we had to pull open every ceiling and wall in the building. Sadly, the way fires get reported to the National Fire Incident Reporting System there's no good way to accurately track such fires. In addition, the production of cellulose insulation is a huge industry. Back in the late '70's the local natural gas distributor opened a facility to make cellulose insulation. On several weekends I remember responding as a firefighter to fires in trailers at their plant. The already processed, treated and packaged for shipment celloluse was smoldering inside the trailer - spontaneous combustion. The gas company wisely closed that facility.

 

[racerex]

I furred up my 2x8's with 2x3's.......giving me 10". I'm going with Owens Corning kraft faced R-30 insulation (9-1/2" thick).

 

[larry4406]

I furred up my 2x8's with 2x3's.......giving me 10". I'm going with Owens Corning kraft faced R-30 insulation (9-1/2" thick).

This.

 

[jawmaw]

Thanks for the ideas everyone. That is why I love this site.

 

[rburke65]

I have attic trusses and I am in Ohio. I cut 2 1/2" styrofoam and stuffed it between the trusses. I then had cellulose blown in the attic to fill the void. I think I have 2x10" bottom cords. Lined the ceiling with plastic vapor barrier and installed metal ceiling liner. Right or wrong......that's the way I did it.

 

[LaneRover]

When I insulate my garage I am going to go with Roxul 'rock wool' insulation. I find it easier to work with, it has a higher fire rating and it is my understanding that vermin don't like it either.

And compressing insulation reduces your R-value.

 

[jawmaw]

I would dense pack cellulose for air-sealing and R value.

How would you dense pack with a rented blower? It appears dense packing is done by a professional install due to the need for high pressure.

 

[jawmaw]

I have attic trusses and I am in Ohio. I cut 2 1/2" styrofoam and stuffed it between the trusses. I then had cellulose blown in the attic to fill the void. I think I have 2x10" bottom cords. Lined the ceiling with plastic vapor barrier and installed metal ceiling liner. Right or wrong......that's the way I did it.

What was your reason for using foam board and cellulose?

 

[ms fowler]

The insulation value depends on trapped and isolated pockets of air. Packing it in tightly REDUCES the R value. Watch when pros insulate a house---if they are doing it right, they will even cut out and remove a piece of insulation behind electrical boxes rather than compress it tightly.
Depth of the insulation is important; the higher the better.