quick ceiling insulation question

[UncleJoe]

I am insulating the ceiling in the shop and redoing the lighting and will hang sheet rock. It has always been an open ceiling until now.

What is the current thinking about the right way to do this. I have kraft faced insulation which is 23 inches wide to fit between the trusses bottoms. Is it considered a good idea to add a layer of poly film stapled the the ceiling joists before putting up the sheet rock or is that old school, new school or waste of time school??

I will only be in this shop for a maximum of the next 5 years, if that information makes any difference.

 

[mobetta]

a well sealed vapor barrier will make a huge difference in air mitigation, deffinatly worth the few bucks and an hour or so of time.

 

[LIVELY]

vapor barrier--yes

 

[28HopUp]

I'm in a similar situation with the OP in terms of looking to insulate my garage ceiling (over a 2-car attached garage).

a well sealed vapor barrier will make a huge difference in air mitigation, deffinatly worth the few bucks and an hour or so of time.

My ceiling is already drywalled (2 layers). I had considered blown-in insulation, but should I be concerned about not having a vapor barrier if I do that? Am I not considering an obvious alternative here? The garage is not currently heated, but at some point I want to install an electric Dayton G73 heater.

EDIT: sorry for the hijacking, but it's somewhat related to the OP's question

 

[Kevin54]

I'm in a similar situation with the OP in terms of looking to insulate my garage ceiling (over a 2-car attached garage).



My ceiling is already drywalled (2 layers). I had considered blown-in insulation, but should I be concerned about not having a vapor barrier if I do that? Am I not considering an obvious alternative here? The garage is not currently heated, but at some point I want to install an electric Dayton G73 heater.

EDIT: sorry for the hijacking, but it's somewhat related to the OP's question

A vapor barrier is not imperative, but when first building and before sheetrocking a lot of people want it. If you do not have it now, I would not worry about it and just go ahead and insulate as you see fit. The 2 layers of drywall plus paint should make a good enough vapor barrier in itself.

 

[Shocker]

I believe the kraft paper is vapor barrier.

 

[shanker]

yes...Kraft paper IS a form of Vapor Barrier...so if you're going to use plastic..do NOT use faced insulation as the plastic & the faced insulation will possibly create condensation if used in conjunction with eath other..

and according to Mike Holmes, use a 6mil at least and tape it good or all of it is pointless..

 

[fefarms]

You are in North Carolina, not North Dakota. You are talking about a garage, not a bathroom or kitchen. (Presumably) you have a ventilated attic, not a cathedral ceiling.

You do NOT need 6 mil poly. Leave that to the Canadians and other places with a "severe cold" climate. Even unfaced bats over drywall will be fine for you. I suggest you do some reading at buildingscience.com.

 

[fefarms]

I'm in a similar situation with the OP in terms of looking to insulate my garage ceiling (over a 2-car attached garage).



My ceiling is already drywalled (2 layers). I had considered blown-in insulation, but should I be concerned about not having a vapor barrier if I do that? Am I not considering an obvious alternative here? The garage is not currently heated, but at some point I want to install an electric Dayton G73 heater.

EDIT: sorry for the hijacking, but it's somewhat related to the OP's question

Go ahead and use the blown-in. It will work fine.

There is a difference between air barriers and vapor barriers. A layer of drywall which is carefully taped with all openings sealed is an effective air barrier, will stop loss of heat from air motion, and will also stop the transport of water vapor through air leakage. You don't need to augment a good drywall job with 6 mil poly.

Poly is intended to stop the diffusion of water vapor from a warm wet space to a cold dry space. Picture an upstairs bathroom with teenage girls taking long showers in North Dakota on a dry winter day with an outside temp of -40. Water vapor can diffuse through even well sealed drywall, but it takes a large difference in temperature and humidity to do it. A couple of coats of ordinary latex paint will cut vapor diffusion substantially, and you can even buy specialty vapor diffusionn paint if you want to cut it more.

But a garage generally doesn't have a major source of water vapor, nor is it kept all that warm compared to outside. And in Delaware, it isn't ever cold enough outside the garage to drive significant vapor diffusion from inside to outside.

In fact. in some cases poly can do more harm than good, especially if you air condition the space in summer. Now the hot humid air outside tries to drive the vapor inward. There are cases where drywall has developed mold inside the wall where poly has been inappropriately applied.

 

[TN_GARAGE]

Go ahead and use the blown-in. It will work fine.

I agree. Blown insulation is cheap, quick and pretty easy.