Insulation, Radiant and Vapor Barriers - basic insulation question re: garage

I've got a garage that I am planning to drywall, wondering if I should insulate the walls. Only ine wall is shared with the interior. The room is not heated directly; that is to say there is no register in the room...it relies on heat from the adjacent rooms. Also, the washer/dryer hookups are in this wall, so it can get noisy at times.

Should I insulate this wall? The garage is not heated, but if it would help with holding heat into the adjacent room, and knock down some of the noise, it may be worth it. Should the other three walls, that don't share the interior, be insualated? The temperature is not a concern in the garage, so no issues there.

Thanks all !

Walls and ceiling that are common to interior living space and the garage are required to be insulated by building code. It's easy to go ahead and insulate remaining walls. Insulating from heat and cold is always a good idea. Fire-rated 5/8" gypsum board is required on the wall adjacent to the living spaces. Fire-rated caulk should be used around any penetrations, such as electrical outlets and switches, in those walls. Insulated, metal, fire-rated door with a good weather seal is recommended if door leads into living space.

Thanks. Is there any benefit to insulating the remaining non-common walls? The garage is not a heated space so no heat 'loss' will occur if the walls are not insulated. I guess it depends on how you want to look at it.

And is there something other than regular insulation I could use on the common wall to help knock down some of the noise?

5/8" fire-rated gypsum has much better sound deadening qualities than regular dry wall. Insulation of other walls in garage will help with insulating out the cold and heat.

great. Isn't all 5/8" considered 'fire-rated'?

All gypsum board is fire rated to one degree or another. It is the board thickness and method of application that gives the wall a specific fire rating.

Under most codes, 5/8" with taped joints will give you enough for a separation between the garage and a living area. This is for wood studs. Steel studs may have a different (greater?) gypsum board thickness required.

The separation between the garage and living area must be complete to the roof and include a fire rated door.

If you have a concrete block wall between the garage and the living area, normally gypsum board is not required.

Dick

Unless you're going to insulate the walls AND the ceiling, AND seal and insulate the door opening, you're not going to gain anything. The adjacent room should be insulated by the wall between it and the garage already.
(my 2 cents)

got it. The common wall is not insulated as of right now. So I will do that and rock it with 5/8" and be done with it.

I was thinking about doing the same, insulating my garage, but if this wouldn't help because the garage door isn't insulated is there really any benefit.

exactly. Too many areas for air to come it. I'm going to insulate the common wall, and then insulate the stud cavity where the dryer vent goes to the outside. Don't want condensate to build up in there.

I was thinking about doing the same, insulating my garage, but if this wouldn't help because the garage door isn't insulated is there really any benefit.Even an uninsulated garage door will have some resistance to heat.

R-values are related linerally; a single sheet of glass is equivilent to R-1. 19 sheets of glass would be equvilent to R-19 insulation. Drywall and siding each add a small bit as well.

Assuming a 20x20' (for easy math) 2-car garage with unfinished space above and 2 walls exposed and two 8x7' garage doors and ignoring loss through the slab, you would have appx 720 square feet of exterior surface, 112 of which are garage doors.

Insulating every exterior wall with R-13 and leaving the uninsulated doors is roughly equivilent to about R4.5. Insulating all the exterior walls with R-30 would only increase this to about 5.5. Replacing those doors with even just cheap R4 insulated doors with R13 in the walls and ceiling would give you about R10 overall. (The same calculation applies to energy efficient replacement windows- going from R2 to R4 in a big window can make a huge difference to a room!)

You can calculate the warm air leakage through your insulated house walls and find out how warm your garage will be. In the house I'm building, my garage will be about 1/3 the difference between outside and inside- EG, if it's 40F outside and 70F in my house, it will be about 50F in my garage.

Some backgound on real insulation values.

You have to be careful when start tossing around the advertised R-values. From a practical and technical standpoint, they do not accurately recognize the actual insulating value of the assembly or structure. Because of this, most detailed calculations are not very realistic despite the decimal points.

There are several reasons for this:

1. The tests are conducted in a laboratory in a "guarded hot box" that provides a standardized method for testing under steady state conditions. The real world is subjected to daily and annual dynamic conditions.These results are obviously skewed toward the lightweight materials that show up well under steady conditions, but the real insulation benefits of lightweight construction are significantly decreased on an annual or dynamic basis.

2. The tests do not recognize any pressure differential between the two side of the wall being tested. Many assemblies are actually far superior to other with the same "indicated" insulation level.

3. The tests are for a material and NOT for a wall. A "R19" wall with fiberglass does not actuall have an R19 insulation value. Because the the thermal "short circuiting" of the framing members and plates the real insulation is reduced to something below what people think they are getting. Depending on the stud spacing, a 6" wood frame wall (wall only - not plates, etc.) the R-value is between about R15 and R17. For a steel stud wall, the difference between the insulation value and the steady state value for the wall is up to 40%. - For dynamic conditions, the differences or losses are even greater.

4. When insulating with rigid insulation, the effects of the framing thermal "short circuiting" do not exist due to the complete thermal break.

There is well documented information on these points that is available for those that need to make realistic accurate heat loss calculations. There are also factors increasing the real R-value that can be applied to heavier building materials that are based on the actual climate and type of wall. These increases in the real R-value do not exist for lightweight construction.

Some of the commonly used programs (model J, etc.) reflect some of these effects, but they are also masked by the factors thrown in to make the input simple and account for the differences in construction practices and quality.

Calculating average R-values for a structure is also dangerous because is can be as erroneous as assuming parallel heat flow. The stud short circuiting is an example that you cannot use an average R-value and get an accurate answer.

The R-value concept is a quick and easy way to advertise and insulation level for a meterial by itself. The test is easy to run and is cheap. The dynamic tests are more difficult and take a better knowledge of the subject to use (not for amateurs).

Dick