R-13 Vs. R-15 Insulation..need help

[Johnnyy Johnson]

I'm turning my garage into a extra living room. It's connected to the house by a hallway. I used R-38 for the ceiling and I have 2x4 walls. would R-15 be worth the added expense over R-13. R-15 cost almost 50 % more. Garage is 24 X 24'.

House was built in 1982 and has R-13 everwhere else.

Thanks
Johnny

[Lee Schierer]

You don't indicate what part of the world you live in, but in my experience, more is better for insulation. The cost of energy is unlikely to go down and every bit of insulation will help keep your HVAC costs down. Adding more later will cost 2 to 3 times as much as adding it now.

[Sam Layton]

Hi Johnny,

When I remodeled my house and built my shop, I used R-15 insulation. I wanted the most insulation I could get into a 2x4 wall. I can't tell you how it would be with R-13, but the R-15 does a good job. My shop is about 27 X 28 and the R-15 insulation does a very good job. I would have installed a higher R value, however in 2 x 4 walls, R-15 was the highest R value that would fit.

Sam

[Roy Harding]

Depends upon where you are.

I have R20 in my walls (2 X 6 walls), and R40 in my ceilings - but I live in a fairly cold climate (Northern BC - right next door to southern Alaska).

Generally, you will recover your initial outlay fairly quickly by reduced heating bills - OR, depending upon where you live, reduced air conditioning bills.

As someone else mentioned, it's easier and cheaper to install insulation now, rather than later - after the interior is all finished.

[Kevin Bourque]

I would install the R-13, and then install a layer of T&G 1" foam insulation board over top of it. It gives you the same R value as if you installed R-15 in the first place, but more importantly it stops the air cold infiltration that sneaks between the stud and the insulation batts, so even though its a combined R-15 the actual value is much higher. As an added benefit the foam board stiffens the drywall, and it also makes the room more soundproof.

[David Weaver]

I'd vote for Kevin's method. I'd never thought of it before but a contractor did just that on an attached room renovation in my house and I'm shocked how well the insulation in the room is. He did that on the ceiling (which is just 6" of space to the roof, it's a porch converted to a sunroom) and in the walls and cut the foam very accurately and taped the insulation to stud joints all of the way around. Even though it's a sunroom, it's better than the rest of the house now as the sun is mostly overhead and doesn't come directly through the windows.

[Doug Ladendorf]

I like the idea of adding 1" foam insulation board over top. However, I would be concerned about hanging cabinets, wood storage shelves and other heavy objects on my walls without over-stressing the screws or other fasteners. Have you had any issues with this Kevin?
Doug

[Lee Schierer]

I would install the R-13, and then install a layer of T&G 1" foam insulation board over top of it. It gives you the same R value as if you installed R-15 in the first place, but more importantly it stops the air cold infiltration that sneaks between the stud and the insulation batts, so even though its a combined R-15 the actual value is much higher. As an added benefit the foam board stiffens the drywall, and it also makes the room more soundproof.

Most foam insulation requires drywall or other fire resistant covering to meet building codes. Foam board is also likely to cost 50% more than his R15 insulation will.

[Kevin Bourque]

I wouldn't use drywall screws since they are too brittle, but any screws designed for hanging cabinets should work fine.

[Benoit Rochon]

You could also invest a little bit more (price vary by region) and have a type-2 closed cell polyurethane spray foam installed. The once I have in my basement is R6 per inch, so you could get R18, plus it provides an air-tight and vapor-tight barrier.

Some experiments have shown that only 1.5 inch of spray foam insulate better than a full R15 of regular fiberglass insulation because there is less chance of small gaps in the installation.

[Kevin Bourque]

I assumed he'd be rocking the walls and ceiling.... and cost is no issue when it's someone elses moolah.:D