View Full Version : OT: Installation of Insulation in Shop

Paul Alciatore
10-11-2011, 03:05 PM
Well, it is for my shop so not completely OT.

Anyway, I am converting my garage into a shop and I want to add insulation to keep the heating and AC (I am in south Texas so AC is not optional) bills down. Anyway, I am removing the cheap paneling from the outside walls and plan to add the staple in insulation before replacing the paneling. I have already partially removed one sheet to be sure there was no sheet rock and there wasn't any so the job should be fairly easy.

My question is which way should the insulation face. I believe I installed some years ago in a new shop I was building and I installed if from the inside, with the paper backing (vapor barrier) to the inside of the wall. Is this the best/correct way to do this in a southern climate?

Slightly related question: At the same time, I also plan to add a vent in the same exterior wall in a small utility room off the garage which has my gas water heater and will serve as storage for the shop as well as a location for my grinders and air compressor. It will be a straight vent, no fan. Where should this vent be located on the wall; high near ceiling, low near the floor, or in between? Methane is about 1/2 the molecular weight of the principal components of air, oxygen of nitrogen, so it should tend to rise in the room. But are there other considerations? Where do building codes say a vent should be?

10-11-2011, 03:14 PM
Vapor barrier goes on the inside. i.e., always towards the climate controlled space.

10-11-2011, 03:25 PM
Paul, when your installing faced insulation, (paper or foil faced) the faced side should face the interior of the building.
For the vent in your storage room, install it high on the wall to the exterior and consider installing a vent close to floor level to the interior of your shop for improved ventilation for your compressor.
You may want install a removable panel on the exterior vent that would allow you to close/adjust the vent in the winter, or when your not going to be working in your shop for a while. (vacations, etc.)

10-11-2011, 03:34 PM
Vapor barrier always faces the "warm" side of the wall, i.e. where the condensation is going to occur when warm air meets cold material. Having said that, the paper backing on your insulation isn't vapor barrior, it's a facing that can act as a vapor retarder. True vapor barrier is usually a plastic film and normally isn't installed in residential construction, at least not in the South.

In your case, the paper faces inward.

10-11-2011, 04:56 PM
Vapor barrier goes on the warm side which in the far South is the OUTSIDE.


Vent should be above the heater. When in doubt, read and follow the manufacturer's directions.


uncle pete
10-11-2011, 06:47 PM
I wasn't aware that paper backed insullation was still avalible. At least I haven't seen any in western Canada lately. Even with paper backed insullation I'd still use a 6 mil plastic vapour barrier. Or I wouldn't bother with the paper backed insullation at all and just buy the normal insullation. Your using both heat and A/C. Your shop temperature would rarely match the outside air temps. So the vapour barrier goes to the heated/cooled side. Other than the small ammount of extra time involved, A 6 mil vapour barrier is dirt cheap to buy for materials cost. Once the inside wall surface is up and finished then that's sure not the time to think "Ya know I should have............" A 6 mil vapour barrier can only help. To me it makes logical sense to just do it. In your location you may find due to humidity that rust is a problem. A smaller cheap dehumidifier might be required so anything you can do now to seal the shop as much as possible would be well worthwhile.

Edited to add, Google "R-2000" It's mostly about interior living spaces but there's some real good information about how to properly seal off any space to prevent high energy costs for heating or cooling and also how to do it and not have problems with moisture within the walls. It takes a fair ammount of extra work but if your not planning to sell in the near future it's well worth it IMO.


10-11-2011, 07:46 PM

If your budget will stand it, I strongly recommend spray foam. Fiberglass is OK at controlling radiant heat, but it's nearly worthless for controlling air infiltration. In Beaumont, you want to keep all of that expensive cool, dry air in the building. Batts won't do that. Spray foam will insulate AND seal air leaks.

My $.02

10-11-2011, 08:23 PM
The paper goes to the inside. The paper tabs do not staple to the front surface of the 2x4s in the wall. Push the insulation down enough to stable the tabs to the sides of the 2x4. You don't want paper or stables on the edge of the 2x4 when you cover the wall it will be all wavy and weird with paper and stables under it.

Before you put in the insulation you need to look at the outside wall covering. What do you have? If the wind blows will it leak? If it leaks air the insulation is not working.

One more thing. If you have termites in TX I would put some type of termite protection on the 2x4 boards in the wall, at least the bottom 4 ft and the board along the bottom on the cement floor or cement blocks. I change my own motor oil and mix it 50/50 with kerosene then paint all the board with it. It keeps termites and carpenter ants away. About once a year I pour the oil/kerosene mix on the floor along the wall and push it under the board with a rubber squeege. If you have any wood ash from a stove pour it outside along the foundation.

My shop lost a lot of heat and AC through the large metal door. I covered the door with 2" thick styrofoam I bought at Lowe's. That made a world of different in heating and cooling my shop. It is easy to hand cut with a hacksaw blade then press the pieces in place on the door panels. A tiny 10k BTU air condition will cool my 24'x30' shop and the small wood buring box stove from TSC will heat it in the winter.

I got all of my styrofoam insulation free from furniture store dumpsters. The foam pads, paper pads, bubble wrap from furniture store dumpsters makes great wall and ceiling insulation too and its free.

10-11-2011, 08:47 PM
Re: Fiberglass is useless to control air infiltration.,,,,,,,,,,,,,,,,,,,,,,,

Without a vapour barrier YES!!

BUT,,,,,, It is never installed without a vapour barrier!!!!!!!!!!!!!!!

The barrier is just that, a barrier to stop the infiltration of air movement which gives the fiberglass it,s R value.

10-11-2011, 10:03 PM
It's often installed without a barrier.... in ceilings for example. Also, where's the "barrier" for blown-in insulation. Well... Taped sheet rock primed with PVA and at least 2 coats of PVC paint are an excellent air and vapor barrier. I have a study somewhere that shows it to be about the same as 6 mil plastic sheet,

As for which side the paper goes - well... it depends whether you are mainly heating or cooling... In many places the "warm side" switches around summer/winter.

10-11-2011, 10:32 PM
Re: Fiberglass is useless to control air infiltration.,,,,,,,,,,,,,,,,,,,,,,,

Without a vapour barrier YES!!

BUT,,,,,, It is never installed without a vapour barrier!!!!!!!!!!!!!!!

The barrier is just that, a barrier to stop the infiltration of air movement which gives the fiberglass it,s R value.

Some high humidity geographical locations it is again code rules to use plastic in walls, ceilings and floors it blocks moisture in as well as blocking moisture out. If you block moisture in you get mold. Heavy brown paper works great for blocking wind inside walls and it lets moisture mass through. You have to lookout for termites and ants they will eat paper too. There is a ton of 3/4" and 1" sheet styrofoam in furniture store dumpsters cut it to fit between the wall studs and press it in place it makes a great wind block and insulation too. Dumpster diving will be slow it may take 6 months to find enough styrofoam but Lowe's sells 3/4" thin 4'x8' sheets too.

10-11-2011, 10:51 PM
From what I've 'learned', the vapor barrier goes on the warm-in-winter side. It also makes sense that it should go on the side which has the highest average moisture content. For climates which require heating for more days than air conditioning, it would be the inside. I don't know about south Texas- it's likely to be the opposite there. I think SteveF is probably right-

The idea is to keep moisture out of the insulation, and out of the structure. There never will be a 'best side' at all times of the year, just averages where moisture is mostly on one side or the other.

It would seem quite appropriate that in areas of high average humidity the insulation itself should be impermeable to moisture. In other words, a closed cell foam would be a better answer than batts. And then further, when you're calculating the difference in cost of heating vs air-conditioning, you can settle on a thickness for the foam insulation. It might be cheap enough to cool the inside, even with only 1-1/2 inches of foam. It may not be cost-effective in the northern climes to have to heat the inside with only that amount of foam, however. If it's 0 outside and you want 70 inside, that's a 70 degree difference that your heater has to maintain. If it's 110 outside, and you want 70 inside, that's only a 40 degree difference for your air conditioner to deal with. You'd have to do some math to find the break-even time, when you factor the cost of the insulation vs the cost of running the air-conditioner.

I just priced some foam a week or two ago- it was an eye-opener.

Even with foam, I'd still use a vapor barrier. Best advice on this might come from a local building inspector.

10-12-2011, 11:17 AM
Vapor barriers are not needed with closed cell foam as it is does not pass water vapor. Open cell foams will pass water vapor but so slowly that they also don't need a vapor barrier.

Vapor barriers aren't used in ceilings because the vapor passes into a vented attic space. Close off those vents and you will get condensation and mold on the rafters and roof deck and your life will suck. Insulation blown into wall cavities is typically dense packed cellulose. The physics of the vapor transmission is different from fiberglass in that the water vapor will get absorbed into the first cellulose fibers and not pass all the way to the cold outside wall.

Gary's idea of using foam boards is good and works better than fiberglass if you put enough boards in. My choice is one or more layers of 2" XPS boards (the pink boards at Home Depot) cut 3/4" too short and too narrow which leaves a 3/8" gap around the outside then foamed into place with Great Stuff.

Unfortunately all foam choices are expensive. If you are going to use batts, make sure the outside sheathing is tightly nailed against the framing to make a wall cavity that doesn't leak. If it looks like it might leak, put some caulk around the inside of the framing. Otherwise you get air blowing through the fiberglass which significantly reduces its insulation ability (see "wind washing").

Paul - I hope you read that DOE web page I linked because all the people who said the paper goes on the inside in Beaumont are incorrect. Contact your local building inspectors as they may tell you not to install one at all.


Paul Alciatore
10-13-2011, 02:41 PM
Mucho thanks to al for the informative replies. I was under the impression that all rolled fiberglass insulation incorporated a vapor barrier in the paper backing, but apparently not. I will install it paper side out to be sure, but apparently the vapor barrier, if there is one, belongs on the outside here. I certainly don't want to create a situation where mold will build up. I will find out if there is an existing vapor barrier when I get the first sheet of paneling off the wall, perhaps tonight if I can complete a few "honey dos" first. Imagine thinking that a hot water faucet should actually dispense water. I mean, what the heck, the cold side works and it ain't like we are in Alaska.

10-13-2011, 03:21 PM
Paul, you're getting a lot of bad advise here.

The paper goes on the inside, period. It's NOT a vapor barrier. In Texas, you don't need a vapor barrier. There's not enough of a temp difference between the exterior and interior to cause significant condensation.

Also, the paper gets stapled to the front of the framing, not the side. Not enough thickness to make a difference when the wall is finished.

10-13-2011, 03:48 PM
<sigh> Yes, he is getting a lot of bad advise.


From the web site:

Batts and rolls are available in widths suited to standard spacing of wall studs, and attic or floor joists. Continuous rolls can be hand-cut and trimmed to fit. They are available with or without facings. Manufacturers often attach a facing (such as kraft paper, foil-kraft paper, or vinyl) to act as a vapor barrier and/or air barrier. Batts with a special flame-resistant facing are available in various widths for basement walls where the insulation will be left exposed. A facing also helps facilitate fastening during installation. However, it's recommended that you use unfaced batts if you're reinsulating over existing insulation.


10-13-2011, 04:39 PM
No, you're confusing kraft paper with kraft paper that contains a vapor barrier. Kraft paper by itself is not a vapor barrier.

But, as I noted, it's irrelevant. Vapor barriers are not needed in Texas, the paper is purely to prevent air infiltration.