Can I insulate over my friends attached garage while I'm doing the rest of the house? She has her w/d hookup out there and I think it would be a lot more comfortable year around if I did. There was never any over that section and I suspect it was done by the builder just to save money.

I see you have kind of a double post going here. Where do you live, what's your climate?

We live in western Oregon. I have added insulation to the entire house for her with the exception of over the garage, but I want to insulate over the garage as I think it will tend to even out the highs and lows in temperature for as she is out there year around doing laundry. It can be as hot as 100 in the summer and we had two weeks of snow this winter.
It is an unheated area with one garage door and one man door going out to the back yard. Would this cause any problems to the house?

So is it the actual garage that you want to insulate or a room above an uninsulated garage? I see no reason not too but it still will be cold out there, just not bone chilling.Can you add some heat for her

Heating a garage can be tricky. Id the garage is heated then a vapor barrier is facing the inside of the garage, If it's a heated room above the garage then the vapor barrier is facing the underside of that floor. They way to cover this in both ways is to use spray foam on the ceiling,

YouTube - Holmes on Homes Cold Bonus Room above Garage