is it worth insulating a ceiling with can lights?

[Vintage Veloce]

OK, so the electrical is in. 20 can lights in the ceiling.
My trusses have 6" bottom cord/joist with an attic space above. The roof has radiant barrier OSB. Then the attic space below that. There will be a 3/4" plywood floor in the attic, and below that the 6" gab for the bottom truss cord/joist and then the garage ceiling drywall.
The ceiling can lights are shallow, IC air-tite led cans. There will be a 20W LED light in each can. I'm going to try and get the drywall guys to cut the holes properly so the rubber seal on the cans mate with the drywall ceiling, but I expect that to have some gaps because those guys tend to be sloppy
The attic floor, 3/4 plywood, is also likely to have some small gaps for wiring, edges under the roof slope, etc.
And the stairway opening is likely to not seal perfectly.
The walls and garage door are insulated, that was easy and cheap.
Oh, and I am in San Diego.
I intend to put a mini-split for heat and A/C in the garage.
So... it it worth trying to insulate the ceiling of the garage? (I'm not talking about the roof, I'm talking about below the attic floor). I'm thinking given our relatively mid climate, A/C will be the most important. And cold air sinks...
I suspect my effort is best spend on trying to get the ceiling as airtight as possible around the cans and stairway, and skipping the ceiling insulation. Getting that well installed around the 20 can lights and stairway will be a mess...
C

 

[DC73]

If you're going to heat and cool the space, it's definitely worth insulating and air sealing. The payback is fairly quick if you can do both yourself and is justifiable if you have to pay to have it done.

You can blow in cellulose or fiberglass insulation and HD or Lowe's will loan you the blowing machine. Easy to do if you have someone to help load the machine. I like cellulose myself. It's a better insulation than fiberglass but it can be a bit messy to blow as it creates quite a bit of dust.

DC

 

[Vintage Veloce]

I am thinking, "blown in" might be the easiest to get closely filled around the can lights.

But I'm also thinking the priority is sealing the gaps 1st, and if that can't be done well, perhaps insulation isn't worth the effort...?

C

 

[Jess]

Insulation is always good. If the light enclosures are rated for installation in an insulated ceiling, then pretty much whatever insulation you can get in there will be fine. If the lights are not rated for installation in insulation, some work will be required.

 

[wssix99]

If you are going to heat and cool the space, then the general answer would be do both!

If you aren't going to insulate the garage doors or the slab, then I'd think you'd get minimal return on insulating the ceiling.

What is your plan for HVAC in the space and insulation of the other surfaces?

One thing I've learned in my new attached (highly insulated and sealed) garage is that the space gets horribly hot and humid in the summer - even when its 70 degrees and nice outside. The heat and humidity coming off the engines of the cars turns the place in to a swat lodge!!! I only have heat right now, but may have to invest in a mini split for AC because its so oppressive. It feels like the garage is 20 degrees warmer than the outside at times. (Because its a heated garage and we are up north, I built it to trap heat - and it works well! Opening the doors doesn't help much...)

 

[Falcon67]

Don't count on the can seal - when the drywall is done, get a bucket of Duct Sealer and hand putty the edges of the cans to the drywall. Seal it up. And yes, insulate. Even skimpy R-13 makes a BIG difference.

 

[jdsac]

If the ply floor isn't in yet, and you can access the can locations from above- have the drywall guys use a circle cutter instead of a jab saw for the cutouts, then install your cans from above. If they do it that way, there should be less than 1/8" around the cans when installed, easy to caulk from below. You could even wait to install the cans until the texture is done- they seem so always spray some in the cans...

 

[benjamintmiller]

Can lights are an energy disaster.

I make sure to buy ones rated for direct insulation contact, seal all around them with foam on top, and thoroughly cover them with blown in insulation.

They STILL stick out like a sore thumb on a thermal camera.

 

[NUTTSGT]

If the space is going to be closed in, most definitely insulate now, it'll be a PITA later.

 

[DC73]

But I'm also thinking the priority is sealing the gaps 1st, and if that can't be done well, perhaps insulation isn't worth the effort...?

C

You need to do both but if you can only do one, insulation is the first choice. Air sealing is very important with fiberglass insulation as one of the weaknesses of fiberglass is its inability to stop air flow. Cellulose is much better at stopping air flow but it still makes sense to air seal.

Remember, heat gets transferred by one of three methods: Conduction, convection, and radiation.

Insulation blocks heat transfer due to conduction and is the first priority. Insulation gets you the most improvement in energy savings and comfort levels.

Air sealing stops heat transfer through convection (air movement). This is second priority to insulation but if you can do the work yourself, it's a very good bang for the buck.

Radiant barriers work to block heat transfer due to radiation and are the third priority after insulation and air sealing. But, the incremental gain from adding them and the high cost means they almost never payback (unless you get free materials and can do the work yourself).

DC



DC

 

[jetnow1]

Blown in cellulose will act as a pretty good air sealer if you dense pack it, and it has a better insulation value than fiberglass when air moves across it. Fiberglass loses a large
proportion of its r value with as little as a 4mph breeze across or thru it.

 

[wssix99]

Blown in cellulose will act as a pretty good air sealer if you dense pack it, and it has a better insulation value than fiberglass when air moves across it. Fiberglass loses a large
proportion of its r value with as little as a 4mph breeze across or thru it.

Wow. Do you have technical references for this?

BTW - I heard Vitamin C also escapes from orange juice once it sits in a glass, also.

 

[DC73]

Wow. Do you have technical references for this?

Check out BuildingScience.com and/or GreenBuildingAdvisor.com. One or both will have an article or two showing that properly installed cellulose can be a better insulation than fiberglass and that fiberglass does indeed have issues if air is allowed to pass through it. Air sealing is important anyway but especially so when using fiberglass.

DC

 

[xyster101]

Insulation is a thing you do once and really only have one chance to do it right. If 3 years down the road you want to do it, the cost will be double due to having to opening things up.
Spend the money and do it now if you plan to cool/heat the space. Oh and there is never too much insulation. I put 8" of foam in my ceiling for a R-40. Northern NY here.

 

[Fixed]

Just make sure the cans are rated for use with insulation. Some **** blew insulation over the potlights in my parent's house, which weren't the right type for that, and it creates quite a fire hazard.

 

[barnee]

The garage ceiling doesn't have to be fire rated, does it? Is the drywall 5/8 type X?

 

[wssix99]

fiberglass does indeed have issues if air is allowed to pass through it. Air sealing is important anyway but especially so when using fiberglass.

My bad on that one. My eyes read the words and then my brain processed the language as air blowing over/across the insulation. Since the cans here are installed in drywall, I wasn't figuring how fast moving air could occur through this insulation.

Compressing loose fill insulation will not make it more efficient.

 

[tinmanwpk]

Usually, compressing loose fill insulation will make it less efficient. The air trapped in there helps in the overall R factor.

 

[DC73]

Compressing loose fill insulation will not make it more efficient.

Usually, compressing loose fill insulation will make it less efficient. The air trapped in there helps in the overall R factor.

Somewhat true of fiberglass. Not true of cellulose. Fiberglass traps air between the fibers to help control heat. You need to compress it to a certain point to get enough fiberglass to do the job but after that you hurt R-value by compressing it too much. That's why fiberglass batts come with instructions to not compress them as they've already been designed with optimum compression.

Cellulose does not operate like this. The cells in cellulose are the insulation medium and don't require air pockets. Cellulose can be compressed to offer additional r-value. Some builders dense pack cellulose into walls to get as much as possible in order to maximize the r-values.

I prefer cellulose over fiberglass but I really prefer mineral wool to both. It helps block sound, is fire resistant, and doesn't let air flow through like fiberglass.

DC

 

[wssix99]

ellulose does not operate like this. The cells in cellulose are the insulation medium and don't require air pockets.

True

Cellulose can be compressed to offer additional r-value.

Not True. If it was, why would we blow it in? We could just stuff compressed bricks of the stuff in our attic.

Some builders dense pack cellulose into walls to get as much as possible in order to maximize the r-values.

I think you may be confusing this with eliminating voids and spaces. (see below) Compressing the insulation changes its density and takes one away from the optimal state. (blown in)

http://www.jmhomeowner.com/insulation/install/blowninsulation.asp
http://www.hgtv.com/remodel/mechani...n-attics-installation-tips-and-best-practices

 

[DC73]

Not True. If it was, why would we blow it in? We could just stuff compressed bricks of the stuff in our attic.

You could just stuff compressed bricks into your attic and do very well but cost is a factor. Manufacturers don't make cellulose bricks or batts of proper size and installation would be a pain. Another weakness would be how to handle the gaps between the bricks.

I think you may be confusing this with eliminating voids and spaces. (see below) Compressing the insulation changes its density and takes one away from the optimal state. (blown in)

They blow cellulose into walls to eliminate voids. They dense pack cellulose to gain additional r-value. One dense pack method uses water as the blowing agent to help eliminate air pockets and more densely pack the insulation.

DC

 

[JimVonBaden]

As the owner of a garage with zero insulation in it, then added insulation to just the garage door, I say insulate everything to the best you can afford. No insulation means your garage will be hot and cold, and generally uncomfortable nearly always!

Just adding garage door insulation made a noticeable difference. Next I am blowing insulation into my ceiling. The walls may one day get blown in insulation, but that is a hassle due to the drywall and stud configuration.

 

[wssix99]

They blow cellulose into walls to eliminate voids. They dense pack cellulose to gain additional r-value.

The installers who do this are working to a plan.

This doesn't mean you can take X amount of cellulose insulation, compact it, and have it perform better. If you have 3" of insulation and compress it to 2", your R value per inch may go up, but your thickness has gone down and the overall result will be worse. The relationship is not linear. (This is why the cellulose manufacturers warn against settling for the blown-in stuff. As it settles, the overall performance drops.)

If one were to take 3" of this insulation, compress it to 2", and then add another 1" of the same stuff at the same density, then things would be better - but that's not the premise that was put forward here. Compressing any existing cellulose insulation without adding more on top of it will yield a negative result.

 

[DC73]

This doesn't mean you can take X amount of cellulose insulation, compact it, and have it perform better. If you have 3" of insulation and compress it to 2", your R value per inch may go up, but your thickness has gone down and the overall result will be worse.

Agreed. I should have been more clear that when compressing, you need to add more to completely fill the space. My contention was supposed to be that stuffing more cellulose into a given space results in a higher r-value.

Awhile back the Cellulose Insulation Manufacturers Association commissioned a study by Oak Ridge National Labs & R&D Services which showed that normal cellulose installations result in an r-value of 3.6 to 3.7 per inch while dense pack installations result in an r-value of 3.8 to 3.9 per inch. Not a lot of difference but it makes the point. They also concluded that installing to a density of more than 3.5 lbs per cubic foot in a wall cavity was not worth the additional r-value. They further concluded that the main advantage of dense packing was for the reduction in air infiltration rather than the increase in r-value.

This is why the cellulose manufacturers warn against settling for the blown-in stuff. As it settles, the overall performance drops.

Also agree. It's why installers factor settling into the over r-value calculation to determine how much product to blow.


DC