Garage Ceiling/Roof Insulation

[teal95]

Now that it's finally starting to be above zero I want to insulate the ceiling in my garage (bought the house last October). The issue is that the trusses are fabricated from 2x4's so I can only get 3.5" of insulation and I know I want more than that. The roof is somewhere around 12/12 and it has an attic with an OSB floor. I'm looking for input on my plan. I'm planning to put craft faced insulation on the bottom of the trusses and then unfaced under the roof. I will also have to put the vent trays under the upper layer of insulation. This will give me 2 layers of 3.5" fiberglass which is more than what I would get if the trusses were 2x6. I was trying to figure out how i would cover the garage ceiling as I want to keep the weight down as I'm concerned with the trusses only being 2x4. My wife suggested that we repurpose the paneling that is the entire basement (and I really hate). Paint it white and it's good to go. Of course I need to finish my wiring first (currently only has a couple of outlets and lights).

Comments?

steve

 

[GYPSY400]

Since you are crammed for insulation space in the upper attic I would recommend spray foam up there.. If you only have 4" of space to work with, that will give you the most R value per inch..
You could also make the attic a cold zone, and just insulate the ceiling


Sent from my iPhone using Tapatalk

 

[teal95]

I want to do both as I don't think the 3.5" that I can get in the ceiling will be enough.

 

[Scott H in Wheaton]

Will you be heating the attic space?
If not, there is no reason to insulate the rafters, and actually it is not recommended due to trapping summer heat in the shingles and shortening their life.

Unheated attics are supposed to have the floor insulated, not the ceiling (roof).

 

[Scott H in Wheaton]

What Zone are you in? Meaning where are you located?

3.5" in the bottom of the trusses along with paneling, drywall, or plywood will provide a pretty decent heat barrier. That's what is in a lot of residential walls.

 

[Steevo]

What is on top of the 2x4 truss chords that limits you to 3.5" of insulation there?

 

[teal95]

I'm west of Detroit. This has been a bad winter and I've spent a lot of time running in and out of the garage doing remodel projects for the house.

I know I need the vent trays against the roof if I insulate up there. The attic has a floor so I can't put more than the thickness of the 2x4's in the ceiling. The idea is to insulate the roof also to get the extra thickness. I realize some is better than none, I just want more.

steve

 

[LB-1911]

I'm west of Detroit. This has been a bad winter and I've spent a lot of time running in and out of the garage doing remodel projects for the house.

I know I need the vent trays against the roof if I insulate up there.

The attic has a floor so I can't put more than the thickness of the 2x4's in the ceiling.

The idea is to insulate the roof also to get the extra thickness. I realize some is better than none, I just want more.

steve

Who installed the floor in your "attic" and what is the thickness of the flooring material?

 

[J Persons]

My trusses are 2X4's so I have the same problem as you do. My plan is to add a 2X2 to the bottom of the rafter to effectively give me 6" of width. This will allow bats of R-11, which is 3½" to be installed between the rafters, and also provide an air space for roof ventilation between the roof deck and the insulation. The air space should void the requirement for vent trays. If you wanted thicker insulation, simply install a 2X4 on edge on the bottom edge of the rafter.

 

[Zeke]

What you're creating is a dual zone. If you don't heat the attic after the insulation is installed it will do nothing to keep the lower zone warmer. When placing the trays in the roof bays you make the 3.5 problem worse.

For heat gain (and a tiny bit of heat loss), you could put foil on the underside of the roof. And you can use attic fans.

You say you are concerned about weight on the ceiling. To that end, do you use the attic space for storage? If not at all or only a little, you could put rigid insulation on the top of the OSB. For storage platforms use the paneling over that. Not much of a walking surface but you'll figure a way.

On the underside of the ceiling truss what is the overall height to the floor? You could run some furring strips parallel on the bottom chords. That will allow you to increase the R value to R-19. Combined with some rigid foam at prox R-4 per inch of thickness, you could get a serious barrier. Or R-13 with 2" of foam for prox R-20.

 

[Kevin54]

What is on top of the 2x4 truss chords that limits you to 3.5" of insulation there?

He has a floor on it.

If the top of the trusses (against the bottom of the roof) are still open, I think I would have it foamed, and if you have a ceiling and floor, blow in some insulation. The combination of the foam and blow in out to keep you warm in the garage.

I'd like to ask though, if you have a 12:12 pitch, why do you only have 2x4 trusses? A truss with a pitch like that is usually a heavier truss to allow a room upstairs. You sure don't want to load the bottom chord down with any weight with it being a 2x4.

BTW....any pics of what you are dealing with?

 

[Zeke]

12:12 is steep but if the overall width isn't but 20' then not much of a room. More like a tunnel. I'll bet the trusses are normal web types with some OSB runners. Therefore no 'room' but some areas suitable for walking upright and storage as long as the OP doesn't mind stepping over bracing.

If that's the case, I can see placing some catwalks in the V's to traverse the attic allowing for above OSB insulation.

Keep it coming pal, we'll figure it out.

 

[bczygan]

You need to give us photos and measurements.

 

[wssix99]

I'm planning to put craft faced insulation on the bottom of the trusses

You don't want to do this as it will put act as a vapor barrier. You want moisture to escape through the attic.

IMO - this isn't a big deal to stick with 3.5". That's the same insulation you'd typically have in the walls. More heat will escape "up" during the winter but given the comment in your post about being ready to go now that its above 0, do you even have a heated garage? Are you doing this to keep cool in the summer?

 

[teal95]

I thought the whole idea was to keep the moisture in the "heated" area as if it gets in the unheated area it condenses.

It won't normally be heated but it's attached and I know from prior experience that the heat leakage from the house will generally keep the garage above freezing which keeps the cars melted off. I will occasionally run a kerosene heater in it (I know the risks and keep it far away from everything).

I'm working on getting lighting in the attic so I can get pictures that you can actually see something.

tanx for all the ideas,
steve

 

[wssix99]

There is debate over this kind of thing. Here's a decent article that goes in to some of this stuff: http://www.jlconline.com/insulation/q-a--ceiling-vapor-barrier---yes-or-no-.aspx

For non-climate controlled garage, I wouldn't want to trap any vapor inside. (A house might be something different.) With all the hot/cold cycles that a garage sees with the door opening and shutting, I'd be worried about getting condensation on the vapor barrier itself. (I've hear a lot of horror stories about vapor barriers in places where they entice mold to grow.)

 

[Falcon67]

FWIW - I have R-13 (3.5 ") in my shop attic. Even on the long cold weeks here below freezing the shop never got below high 40's. You might be surprised at how well a sealed ceiling (drywall, etc) and 3.5" of insulation will do.

 

[Kin Creed]

Putting any sort of insulation along the roof trusses seems like a waste of time and materials and will likely do bad things like trap warm air in the attic. You want the attic cold in the winter otherwise you are going to get ice dams. Even with vent trays.

I added roof vents to my garage to help keep the attic cool in the winter and have no ice dam issues at all. The insulation should all be in the ceiling... that's the only place to do it.

I agree 3.5" is fine for a garage. If you absolutely want more then pull the OSB off and stack it up in the ceiling or add more via rigid foam like Zeke said.

Good luck!

 

[J Persons]

Putting any sort of insulation along the roof trusses seems like a waste of time and materials and will likely do bad things like trap warm air in the attic. You want the attic cold in the winter otherwise you are going to get ice dams. Even with vent trays.

I added roof vents to my garage to help keep the attic cool in the winter and have no ice dam issues at all. The insulation should all be in the ceiling... that's the only place to do it.

I agree 3.5" is fine for a garage. If you absolutely want more then pull the OSB off and stack it up in the ceiling or add more via rigid foam like Zeke said.

Good luck!

This is fine for people living in the northern tier, but for those that live where the ambient temps are almost always above freezing, ice dams are unheard of here. I wanted the additional interior volume in my garage to help with dissipating vehicle exhaust. I'm also using three powered gable vents. At this time my garage is uninsulated and last summer, the temp under the roof deck was over 140º. At 10 feet up from the floor, it was 120º. How should I insulate the garage to avoid heat stroke this summer.

 

[Kin Creed]

The OP is in the northern tier so that's why I said to keep the attic cold.

If ice dams are not a concern then that's totally different and I should probably move to that place!