There's nothing above the garage except an open floor, peaked roof attic. There's no wall in the attic that separates the garage from the rest of the house, so the thought is that insulating above the garage would help with heating and cooling the whole house. The house is, indeed, in a warmer climate. Thank you for the stats/figures. That helps!

I am going to make an assumption - the roof is vented. That would mean the attic is not conditioned and is vented directly to the outside.

So in the winter - it is cold and the insulation could help the garage stay warmer. In the summer, it can isolate the garage and make it a little cooler (not really by much).

That all being said, the garage is not conditioned so it typically is not insulated. This is particularly true in warm climates because it does wind up trapping car heat and can make the garage warmer. So it is not usually recommended. The attic does cool down at night and would help the garage shed heat.

As someone who favors going way above code, I would still not insulate above a garage in a warmer climate. In the frigid north, I would insulate the garage completely.

YES, the builder cheaped out because it wasn't in the code. They do that allllllll the time to put more money in their pockets. It's disgusting!!!! I hate to say but GC's on here KNOW this!

I've never seen an insulated garage, so I wouldn't say this is just cheaping out. You just don't tend to insulate unconditioned spaces.

That being said, if you live in a place with a substantial summer heat, the insulation can make a big difference. I have both a three car garage and an airplane hangar next to it. The hangar was heated (but not air conditioned) so I had it spray foamed with the rest of the house. The difference in the summer between the uninsulated garage and the insulated hangar is staggering.

Note, however, I don't think it's going to accomplish your goal. All you're doing is isolating the garage from the attic. They're both still unconditioned spaces and if your goal is to keep the house warm, putting more insulation on the common wall between the house and the garage/garage attic would do more than dumping insulation in over the garage.

Ron - is it also a function of cars in the space as opposed to a plane? Not that planes don't get hot but relative to the size and also frequency of use. 3 cars brings in a lot of heat. I think you are probably right (regarding insulating) but the car heat makes it more dramatic. Also foam is not batts so also making it more significant than the OP's situation.

jewel-

Insulation of any kind weighs very little relative to the load bearing capability of the sheetrock and the joists supporting them, whether the joists are on 16" or 24" centers. I have a new-ish house that has 6" thick walls everywhere and the 2X6 wall studs are on 24" centers, as are the ceiling joists in the living space and the garage. My garage is not insulated (neither the walls nor the ceiling). But the building envelope of my house is fully insulated. Cars coming onto the garage do not add significant heat, at least in the sense that they significantly alter the thermodynamics of the garage space. Garages are not typically insulated, at least in temperate climates, but if they are used for purposes other than housing cars (like being used for shops), it isn't a bad idea to insulate them. You can tell your husband that, whatever the reason your MIL's garage attic is not insulated, it has nothing to do with the spacing of the joists.

The best place for additional insulation would be the wall between the house and the garage. Adding foam insulation, and a layer of sheetrock there will keep the garage better isolated.

And make sure the house insulation extends over the intersection of house and garage by a foot or so.

" the builder cheaped out because it wasn't in the code" insulating a space that is not required by code and doesn't have people living in it is not "cheaping out". It's called following code and contract. If they had done it, someone would be griping about contractors doing things that aren'e needed just to gouge money from the client.

I would recommend adding the insulation. Blown in fiberglass is probably the best option. We are located in Connecticut and always fully insulate our garages. It definitely helps to keep them above freezing in the winter and cooler in the summer.

Nope, it has nothing to do with cars or the plane in there or not.

Didn't say anything about batts. I quoted weights and bearing for loose insulation (though it probably won't make any difference). The bigger issue than the insulation technology is that the spray foam is typically added to the inside of the roof here, making both the garage and the attic notably cooler in the summer.

YES, the builder cheaped out because it wasn't in the code. They do that allllllll the time to put more money in their pockets. It's disgusting!!!! I hate to say but GC's on here KNOW this!

Robin once again you're blowing smoke and running your mouth when you don't know what you're talking about. In a warmer climate it isn't common to insulate the attic space above the garage. My garage in SW FL is not insulated and I don't know any that are unless there's a room above it.

The only thing disgusting is your constant berating of builders.

If they had done it, someone would be griping about contractors doing things that aren'e needed just to gouge money from the client.

Yes most likely it would be Robin griping about them gouging money.

It probably depends on the location of the house. When I had a new home built in central Texas they did not insulate the exterior garage walls or ceiling of the garage (with unconditioned attic above), In fact, the exterior garage walls were required to have two ventilation grills to let the heat out of the garage. Some folks also put ventilation grills from the garage into the attic so that the heat from cars would exhaust faster when you parked in the garage and shut the doors.

During the building process I insulated the exterior walls, and planned to go back later and insulate the floor in the attic above, but never got around to it. It never seemed to be worth the trouble.

Bruce

The only reason to insulate anything is to prevent heat transfer. That’s what insulation does. That also translates to outside heat transferring into a garage in a hot climate, as well as inside heat transferring out in a cold climate.

Code already requires house walls of the garage be insulated, and the ceiling if there is habitable space above. That is sufficient if that is the only use plans for the garage. If you want to put in a window AC and turn it into a craft studio, you definitely want to insulate all walls and ceiling. Otherwise you are asking for mold issues.