Proper way to insulat the raftersin my shop

[CJC5151]

hello ,

I have just moved into a new house. More room in the house and great school system for the wife and kids and a 32 ft deep 40 ft wide garage with 10ft ceiling for dad. Im really excited but the shop is unfinished and un insulated. The ceiling joists are 32" on center, which is weird to me but here lies my dilema. While I will eventually fill in the missing joists and drywall the ceiling, I cant see affording that expense with the new mortgage. I live in the chicago region and have plans (and budget) to insulat the shop and finish the walls. Can i just put bat insulation between the rafters (which are 16"oc) or will that present a problem by not allowing the roof to breath properly. Please help I am getting started this weekend. thanks for all you future advice

[Vic]

OK..really quick..you can get away with installing your batt insulation over a 4-6 mil plastic (vapor barrier) stapled to the bottom of the truss joists. Tape the seams and tape the vapor barrier to the adjacent walls. Although, I HATE fiberglass insulation in an attic, it's better than nothing. You'll be able to sheetrock at a later date right over the vapor barrier. Buy caulk and air seal everything you can possibly think of.

[Chester]

CJ -

Please make your question again? I am confused about what you are asking. I did this in my shop recently and may have some suggestions to share.

Chester

[CJC5151]

CJ -

Please make your question again? I am confused about what you are asking. I did this in my shop recently and may have some suggestions to share.

Chester

What I am looking to do is leave my ceiling open and just put insulation bats inbetween the rafters. I guess it would be the same method as insulating a cathedral ceiling right?

[Vic]

What I am looking to do is leave my ceiling open and just put insulation bats inbetween the rafters. I guess it would be the same method as insulating a cathedral ceiling right?

Oh gotcha. Yes, you can do that. There is a lot of controversy surrounding whether a cathedral ceiling needs to be ventilated. It's usually done with soffit vents going to a ridge vent and using a plastic tray that allow air to moves up the length. But, the same response will apply. But, you WILL be conditioning a much larger space.

[leebo]

Don't worry about letting the roof "breeth". These days this idea is not the ideal thought. Heck, when they spray foam they spray the roof solid.

A question....why fill in the rafters? Was the roof structure inspected?

As Vic said, you can just put down a vapor barrier and go to town. Rather than just stapling though I would put down some strapping to help with the weight. If ya go batts I would suggest r-30 un-batted depending on the price. You also can blow in the insulation with cellulose. It's a snap to do with two people.

[leebo]

Edit.....ahhh

So I took awhile typing.

[Chester]

Don't worry about letting the roof "breeth". These days this idea is not the ideal thought. Heck, when they spray foam they spray the roof solid.

A question....why fill in the rafters? Was the roof structure inspected?

As Vic said, you can just put down a vapor barrier and go to town. Rather than just stapling though I would put down some strapping to help with the weight. If ya go batts I would suggest r-30 un-batted depending on the price. You also can blow in the insulation with cellulose. It's a snap to do with two people.

I understand now. You want to insulate the rafters right under the roof sheeting. I did have my builder's license at one time and things may have changed ... but ... if you are using any kind of air-trapping insulation (fiberglass, cellulose, rock-wool, etc.), I think that you will need to have those Styrofoam spacers between the insulation and the roof sheeting and ridge-venting. This allows for an air gap for ventilation and (I believe) that the biggest benefit of this will be to your roof shingles. How this is affected with full-cavity sprayed foam, I am not sure.

Chester

[leebo]

I myself would want to insulte at the rooms celling so you don't heat unused space. Treat it just as an attic. To my knowledge it is not recommend to insulate the rafters at the roof ridge anymore. This changes with closed cell as they recommend doing the entire house and make it 100% airtight. This is alot like woodworking Ten different people have twelve different ways....and they'll all work.

Any way we can see a photo of the space?

[leebo]

Here's two examples, you pick you're favorite.

http://www.applegateinsulation.com/Product-Info/Technical-Pages/249234.aspx

http://www.inspectapedia.com/interiors/Insulate_Cathedral_Ceilings.htm

[Dyami Plotke]

My 2 cents,

I would stay away from fiberglass bat insulation. Though the R-value to $ ratio is ok, the average bat insulation job only provides about half the stated R-value due to compression & air leakage.

The fist question to ask is should it be vented? This depends. If you plan to keep the ceiling cathedraled, then no, it should not be. In that case the exhaust vent at the top would let out all the conditioned air.

Under the no insulation strategy I would begin by sealing all voids & points of air leakage with Great Stuff spray foam (the gun applicator makes it much easier to install & the window & door greatstuff doesn't expand quite so much). This air sealing will most likely have a bigger impact than the insulation & be much cheaper.

Once it is air sealed I would insulate with rigid polyisocyanurate foam. It can be obtained at any good roofing or building supply company. A 3.3" layer will provide R-20. It comes in 4x8 sheets and can be cut very easily with a Festool foam blade in any jig saw.

Cut the foam to fit between the rafters and seal around it with more great stuff.

That will provide a wonderfully insulated ceiling.

If you must vent, let me know and I can describe that process. For know I'm done typing on the phone.

[CJC5151]

thanks for all your wonderful advice. But all as im trying to do is make the garage workable in the harsh chicago winter. I just bought the place so money is a little tight and i need to do it in the most cost effective way, but that being said, i have know knowlege in insulation and i dont want to cause problems in the future. thanks for all you info, ill let you know how it goes and post some pics when i get the shop done

[Vic]

thanks for all your wonderful advice. But all as im trying to do is make the garage workable in the harsh chicago winter. I just bought the place so money is a little tight and i need to do it in the most cost effective way, but that being said, i have know knowlege in insulation and i dont want to cause problems in the future. thanks for all you info, ill let you know how it goes and post some pics when i get the shop done

Air sealing is your biggest bang for the buck. Attention to detail is extremely important. Get ALL the gaps!!

[leebo]

I 100% agree here with Vic. Air sealing is the most help for least cash.

5 cans of foam, 3 tubes of caulking sets ya back around $40. Add a space heater and you'll be fine.

Is the garage attached to the house?

[Chester]

Here's a question ... how much difference does it make to insulate under the floor of an upstairs shop ... when the lower level is unheated?

Chester

PS - The floor is 3/4" plywood

[leebo]

I'd say it would vary from case to case.....just to me depends on what's under the shop. If the area below the shop is 100% unused space then I would insulate the space first by air-sealing it. Any spot where's there a hole....foam it up. Next take R-19 and put it in between the floor joists with the barrier facing up. Lastly you'll want to fully insulate the rim-joist to keep any air from the outside from coming in.

With that said....I wouldn't do any of it!

If there's ANY pipes or a water heater down there you'll have to fully insulate them or you will have problems with them freezing. If you've got any heating or ac ductwork running down there, you'll want to insulate them as the air would become cooled as it ran through it.

In several short words....it's just not worth the effort for the little you'll gain. I would air seal any open holes going in between the spaces with some foam, and use a roll or two of batt to insulate the rim-joists(depends on how big your space is) and call it good. The work in my mind to make the lower level a full "cold zone" just doesn't justify to added expense.

[Rutabagared]

thanks for all your wonderful advice. But all as im trying to do is make the garage workable in the harsh chicago winter. I just bought the place so money is a little tight and i need to do it in the most cost effective way, but that being said, i have know knowlege in insulation and i dont want to cause problems in the future. thanks for all you info, ill let you know how it goes and post some pics when i get the shop done

CJC5151,

After sealing the air leaks, I'd go with fiberglass R30, especially if you're on a budget. You can usually get this at one of the big box stores for about $10 for a 16" wide X 25' roll, unfaced. I would lay it on top of, and perpendicular to the ceiling joists (why heat the extra space to the rafters?). This will do an excellent job of holding the heat in for a few hundred dollars. When time and budget permits, you can add faced insulation in the joist cavities before finishing the ceiling. I did this in my shop and am very satisfied with the results. Good luck!

Joe

[nateswoodworks]

If money is your main concern and not so much the cathedral ceiling that treating it like a main space with an attic is the way to go. It will be less space to cover, easier to do, and allow for more storage space. Just seal air leaks (outlets and light fixtures being the primary areas) and put bats of the highest r# suggested that you can afford, especially in the ceiling, between the rafters and studs and cover it with poly. On the ceiling I would go with 2 layers of poly going in different directions.

One thing to keep in mind is that since you want to insulate the whole shop and sheath the walls now is that you need to make sure you have something to attach the sheathing to around the perimeter on the ceiling when the time comes. Depends on how it is framed you should be able to add a 2x2 on the gable ends even with the bottom of your rafters allowing you a spot to affix the ceiling when that day comes. You do need to figure this out before any insulating happens because you want the poly to completely wrap the whole area. When I built my shop here in Mn. I did it just the way you are doing it now and put the ceiling on hold, honestly when the time came I wish I would have just done it right away because of having to remove all the lights, DC, door tracks and so on that get added through time. Just thought I would mention it. If you need any more advice send me a message and I will be more than happy to help anyway I can.

Have fun trying to keep warm,

Nate

[Vic]

Nates procedure is spot on. I would add that you do air sealing inside along the studs where the siding breaks and also along the bottom and top plate. The latter two areas are prone to the most leakage from air outside. And yes, I would just go rent a lift and do the ceiling now. It's a major PITA after the fact. Nate, what do you do for a living. I don't run into too many people that know the importance of air sealing.

[jimmykx250]

CJC5151-

Welcome to the wonderful chicago area! Yes the winters are long and cold but this in my opinion is a great place to live. I do agree with nates procedure as well air leaks are a big part of the problem when it comes to heating a space. I would also recomend keeping an eye on craigs list in the materials section especially for plywood and framing lumber it's amazing what you can find on there and usually at a substantial saving. Where about are you located if you not to far from the barrington area i could give you a hand.

[CJC5151]

CJC5151-

Welcome to the wonderful chicago area! Yes the winters are long and cold but this in my opinion is a great place to live. I do agree with nates procedure as well air leaks are a big part of the problem when it comes to heating a space. I would also recomend keeping an eye on craigs list in the materials section especially for plywood and framing lumber it's amazing what you can find on there and usually at a substantial saving. Where about are you located if you not to far from the barrington area i could give you a hand.

Jimmykx,

I agree it is a great place to live. Im a chicago fan in every way. But as you know if your a true chicago fan you have to b@%$h about the weather and the traffic and oh yah especially "Da" Bears". You are way up north im on the south side actually exit 1 in Indiana(Munster) Thanks for your advice though and Its nice to here from others in here from the greatest city in the world "Chitown" baby!

[CJC5151]

I 100% agree here with Vic. Air sealing is the most help for least cash.

5 cans of foam, 3 tubes of caulking sets ya back around $40. Add a space heater and you'll be fine.

Is the garage attached to the house?

no its free standing