Insulating my garage, need advice

[Iamkar33m]

Hello all,

Here is the current situation in my garage:

North Wall, across from garage door (exterior wall): Un-insulated & open (bare 2x4's)

West Wall (shared with house): Drywalled & Insulated

East Wall (shared with neighbor): Drywalled & Insulated

Ceiling (exterior wall): Un-insulated & open (bare 2x8's)

I'm unhappy that the two exterior walls are un-insulated and bare, I am planning to fix that within the next few weeks. But first, I have some questions.

1) The garage is vented via a single roof turbine vent, how do I handle this if I want to close the wall the vent is attached to (ceiling).

2) How do I insulate a 2x8 ceiling? Do they make insulation that thick? Also what kind of insulation do I need to look for? I live in Orange County, CA, so I am primarily looking at keeping the summer heat out. I've never done insulation before.

3) I will be putting in electrical outlets in the north wall, do I do this before insulating or after insulating?

Aside from those questions, I'm a bit intimidated by selection of the insulation itself. I don't understand what the R- ratings are and how to narrow down to the right product for my job.

Any advice, direction is appreciated!

- Kareem

 

[Makoto]

1. I've got the same situation developing in my garage. The top will have a vent and I plan on either ducting the roof turbine to a vent in the ceiling (when I install it) or do that in addition to having a second vent in the attic to **** out the hot attic air (to keep the oven above my head from maikng the rest of the structure hot, still not sure if I need to do this).

2. not sure. ceiling insulation depends heavily on what i above it and your geographical location.

3. I would do the electrical work before the insulation just because working around insulation *****.

 

[sands35]

1) When you close off the ceiling, you will need some sort of soffit vent to allow air movement into the attic space.

2) Buy r30 rolls or batts in the appropriate width to fill the space between the rafters. R30 is sufficient for a temperate climate. You can put in more if you want. For a house with a conditioned environment, R40 or even r60 is common. But for a garage where wider temp swings are OK, less insulation is fine. Either kraft faced, or you will need to put up a vapor barrier (sheet plastic).

3) Before insulation

 

[Iamkar33m]

Thanks for the advice gents! Just to clarify, if you're looking at the picture I posted the plywood directly above the ceiling joists supports the garage roof. There's no "attic space" above the garage, it's just a flat (brick tiled) roof on top.

- Kareem

 

[Iamkar33m]

Ah ****... I just looked at the blueprints to the house. The ceiling joists are actually 2x10's. Maybe better for me (more space for insulation)?

 

[Zeke]

You could treat the turbine one of two ways: cap it off or duct it down to the new ceiling level. You might want to use it someday but some type of closing device would prevent any heat you've built up in the winter from escaping. I'd leave it open during the summer unless you put A/C in the garage.

You might be able to modify this to suit your needs:
http://www.amazon.com/dp/B000LONT44/?tag=atomicindus08-20

In fact, you could get that other piece and install it upside down under the whirlybird for your duct.

 

[sands35]

Ah ****... I just looked at the blueprints to the house. The ceiling joists are actually 2x10's. Maybe better for me (more space for insulation)?

Where do you live? I hope not in an area that snows with a flat roof!

I have zero experience with what the common practice is for a roof like that. It it more like a commercial building rood than a residential one.

R30 between the joists, air vent the sloped front to code? Plan calls for solid blocking at the eave, so that may be difficult.

(Edit, just saw SoCal)

 

[Iamkar33m]

sands35, snow is not a big issue in So. Cal. (unless hell freezes over) ;-)

I can't decide between R-30 and R-38 for the ceiling insulation. I think R-38 is going to compress about an inch, but for whatever reason it's cheaper per square foot than the R-30 (30 cents per square foot difference). But I know compressing insulation hurts the R- value, so I may just wind up doing the R-30 for maximum efficiency.

Any thoughts?

 

[Gerald O]

Compressing R38 only an inch is going to end up around R37.

 

[sands35]

It is a garage. Presumably, you don't need to have it conditioned like a house. Given the roof is flat and air venting won't happen anyway, I'd throw up on R38 and be done with it.

You will still want to have some way to inspect the roof / ceiling annually and address leaks before the rainy season.