Insulation Situation Advice

[bowhuntr311]

Well the more I think about it the more I start to question it....

I would like to try to insulate my shop this fall and Ive ran into a snag. I did scissor trusses for the first 6 trusses to accomadate a full height door in the center. No big deal there. Then I did bonus room trusses for the rest. Bonus room is 8foot wide and then I added another 3 feet of "flooring" on the outside of the wall so I can store more stuff.
Bottom cord is only 2x8 and I planned on leaving the bonus room cold storage. I live in Northern Minnesota and they recommend atleast an R49 attic insulation. How can I get the most R-value into that 2x8 area.

Thanks.

 

[DC73]

Closed cell spray foam has about a 6.5 R-value per inch which will get you close. You could put a layer of foam insulation board under the 2x8 to be over R49.

If you have enough overhead room, you might could sister additional lumber under the 2x8s to increase the size of the cavity for insulation.

Mineral wool, cellulose, and fiberglass all come in somewhere around R4 per inch and so will not even get you close to what you need.

DC

 

[bowhuntr311]

So a call to the guy that built it led me to a few options.

Spray foam the entire cavity below the floor.
Lift the floor and add some height.
Drop the ceiling as mentioned above.
Insulate with blow in or batts for what there and end up with R30.

A call to local insulator and I figured itll be about $2300 just to do the section where the room is. Not what I wanted to spend but seems like the long run I will be the happiest with.

 

[haugy]

I'll answer your question with another question for maybe others to chime in.

Could he put refelective foil up as the vapor barrier and then put fiberglass batts up on top of that? They staple into place easily and you can get creative with it.

 

[Crazy68Dart]

I'm not sure what your plans are for the garage, but you could just do R30 and leave it a that... it is still insulated, certainly better than no insulation, but not as much as the recommendation. You might spend some more in heating, again, all depends on if you plan on living out there, or use it as a hobby shop.

I wanted to get as much as I could as well, but I ended up with R30 as well with 2x8 lower chords in my attic section.

 

[bowhuntr311]

Well since I posted this last I spoke with 4 insulation contractors and several other friends that bend nails for a living. The general consensus is to insulate the section with fiberglass batts and dont worry about heat loss. Almost all of them said I'd lose more heat through/around doors and windows than I would through an R30 ceiling.

 

[Huntmaster86]

compare cellulose to batts before you pull the trigger. cellulose is faster and not ichy when installing, a little more exp in my area but i think its easier. I blew 18" in the top of my garage and dense packed it under my bonus room.

 

[DC73]

Almost all of them said I'd lose more heat through/around doors and windows than I would through an R30 ceiling.

You'll lose that heat through and around doors and windows regardless of how much insulation you put up above. There is enough difference between R30 and R49 that it will eventually pay for itself in energy savings. The higher your energy costs, the quicker the payback. If that's not important, R30 might be enough for reasonable comfort.

DC

 

[bowhuntr311]

The higher your energy costs, the quicker the payback. If that's not important, R30 might be enough for reasonable comfort.

I burn wood in an outdoor boiler. The wood only cost some chainsaw gas and man energy to get it from the back of property to the front, so it'll take a long time to ever justify $1000 in wood.



Thanks everyone for the advice.

 

[ForceFed70]

While R30 isn't ideal, even in Canada they only did houses to R20 back in the 60's. Today code is R40 minimum in the attic, with many choosing to go R60. The recommended minimum of R49 surprises me.

I'd be very tempted to go with rockwool insulation and see if you can stuff about R35 in there and call it a day. Especially if you're like me and only heat the garage while you are out there working - and even then, I only heat to about 60-65*.

Also - remember you need only do this for the section under your room. The whole rest of the attic can be insulated more. I have a room above my shop and that's what I did. My bottom cord was 2x10 (larger room/shop). The entire attic got 10" of rockwool for ~R40 which took up the whole 2x10 cavity. Then I added another 6" of blown-in insulation to either side of the room to bring the sides up to R60. The way I look at it... heat that leaks past the R40 insulation just goes to warm up my attic room a little.

Spray foam would do the job, but it's not cheap at all. You'll likely never see an ROI vs R35 rockwool.