Fitting 30" wide insulation into 24" rafters?

[ptgb]

Pricing out insulation for the garage. R-13 in the walls, 15" wide... no problem...$200 total for all the walls.

As far as the ceiling... 24" wide R-30 is completely outrageous at $40 per roll.

I can get 15" wide, R-30 for $11.87 per roll. Would there be any issues with stuffing two rolls side by side in the 24"OC rafters?


I figure I can do the ceiling about $250 cheaper by placing the 15" wide side-by-side as compared to the 24" wide stuff.

Any issues with mushing 30" wide in a 24" rafter width?

 

[Highbeam]

Is this an attic with a flat ceiling or rafters up against the roof deck?

 

[jhelrey]

Insulation works better being gently laid in between the rafters... No smashing, folding, etc.

 

[zmaxmotorsports]

Insulation works better being gently laid in between the rafters... No smashing, folding, etc.

thank you

 

[KPSquared]

why not trim the one batt? Compressing insulation is a bad idea. Pretty much kills the insulating value by eliminating the air space. Any way to blow in cellulose or fibreglass as opposed to batts?

 

[Falcon67]

Yes, the issue would be that you wasted your money. Better to buy R13 24" rolls and do it twice, or just pay the fee and get on with life.

 

[ptgb]

Yes, the issue would be that you wasted your money. Better to buy R13 24" rolls and do it twice, or just pay the fee and get on with life.

Not sure if everyone who responded is following exactly what I am talking about. I am talking about placing two 15" widths of rolled insulation side-by-side in the rafter space (24"). Picture an open book and the left side is one roll and the right is the other roll.

As the floor is clear I am just going to unroll the entire 25' length and cut it in half lengthwise. Then I can put a 15" wide up there and the now 7.5" wide up there butted next to it in the 24"OC rafter space.

The savings is significant... to the point that I can do the walls in R-13 for free! I don't feel it an issue of "just pay the fee" when there is a TON of money to be saved.

 

[nwav8tor]

What type of insulation are you planning to use? Is it faced or unfaced?

What you're proposing would certainly work if the insulation is unfaced and there is already a vapor barrier installed. If the faced insulation will be used as the vapor barrier, then not having the continuous facing (due to the lengthwise **** to **** edges) would be detrimental to the vapor barrier.

Paul

 

[JakeKohl]

Don't discount the notion of hiring it out. Having someone fully insulate my 2 story garage was only about $150 more than if I did the whole thing myself and paid box store prices for the materials....and it was done in 1.5 days. I got a premium product with the blown-in cellulose and a fast turnaround. It was well worth the tiny little bit of extra cash.

 

[St-rider]

Then I can put a 15" wide up there and the now 7.5" wide up there butted next to it in the 24"OC rafter space.

that's not as bad as:

... mushing 30" wide in a 24" rafter width?

30" wide insulation pushed into a 22.5" wide space is not good.

what size lumber is the bottom chord of your joist? 2x4? 2x6?

best would be to fill between the joists with a thickness matching the height of the chord then run the thickest insulation you want to purchase on top of that but going the opposite direction. (criss cross) to eliminate having the seams going all the way through.

a little extra spent now is worth a lot in the long run.

of course, like others have said, you could do blown in.

are you planning on putting a floor for storage up there?

 

[Falcon67]

Cutting one down the middle will work. As noted, you want it snug between the joists. The more you crush it, the less it works.

The R-30 price he quotes in the OP is R-30 unfaced. Kraft does drive the price up.

 

[Steevo]

Have you compared the price per square foot of your two-piece solution to the price per square foot to have the insulation company come out and just blow in R-30 (about 10-12") in the attic area?
When I looked into it, they were so close in price that it wasn't worth the price difference, and with all the cutting and fitting you are talking about doing, it would be even more work.

Blown-in also goes over the top of the ceiling joists, which provides a better insulating blanket up there, too.

 

[Highbeam]

I asked the question earlier but got no answer. It is foolish to install batts in an attic if it is possible to blow in.

 

[Falcon67]

I asked the question earlier but got no answer. It is foolish to install batts in an attic if it is possible to blow in.

If insulation dams are not present at the plates, then a combination of batt and blow would be a better idea. I just paid a guy big bucks to do an energy audit and the thermal camera showed just how poorly plain blown insulation with no controls does at the top plates.

 

[Kevin C]

Pricing out insulation for the garage. R-13 in the walls, 15" wide... no problem...$200 total for all the walls.

As far as the ceiling... 24" wide R-30 is completely outrageous at $40 per roll.

I can get 15" wide, R-30 for $11.87 per roll. Would there be any issues with stuffing two rolls side by side in the 24"OC rafters?


I figure I can do the ceiling about $250 cheaper by placing the 15" wide side-by-side as compared to the 24" wide stuff.

Any issues with mushing 30" wide in a 24" rafter width?

I noticed the same thing, the 15" wide R30 was way cheaper per SQ ft then the 24" wide. Stuffing 30" of insulation into a 24" space is going to be a problem. I have been cutting 24" bats in half to fit 12" OC center framing.

Much past 1" over seems to make for a poor fit.

The 15" stuff is so cheap that I could cut it down to 12", throw away the cut off piece and its still 50% cheaper per sq ft than the 24 in wide bats.

 

[jlckmj]

I also recommend getting a price from an insulation contractor. I had mine done for about $250 more than it would have cost me to do it myself. PLUS. they did a better job that I would have.

They did the walls, ceiling, vapor barrier, and caulked the cold seams in less than one day.
Jim