View Full Version : Super thick walls (how efficient) ???

05-31-2008, 08:25 AM
Well maybe not super thick. It's looking like I need to expand my machine shop already. I have a stack of rough cut 2X8" I can make the walls out of.
8 inches of insulation should make this part of the shack pretty warm in the winter you'd think.
Anyone else here gone that route?

05-31-2008, 09:12 AM
Wood has a R value of about 1.125. A 2"x8 is 1.5"x7.25" so each of your studs will have a R value of 8.156 so you should put your studs on 2'0" centers. Because the R value of the stud is much less than the insulation, the fewer studs you use the better. I have 8" walls in my office, two rows of 2"x4"on 2'0" centers, one inside and one outside and stagered so the plates are the only places that wood runs from inside to outside. I also have a sheet of foam insulation. All in all, I have R 33 walls. The trouble is the windows are R3 (most windows are less) Gary P. Hansen

05-31-2008, 09:18 AM
I built my garage with six inch walls. When I finally insulated it last year I bought the super thick batts of fiberglass and pulled them in half thickness, then fluffed them up when installing. You can save a lot of money on insulation by doing that and it doesn't reduce the effectivness. The object of glass wool insulation is to reduce air convection currents. Glass itself is a lousy insulator but glass wool traps the air in place and air is a good insulator.

I have found that I can now keep the garage shop comfortable even at -20 without a heater in the garage. I have a port cut in the wall to the basement where the natural gas heater is and a small fan circulates warm air from that room into the garage. Below the fan is another port at floor level which is the cold air return. It's screened to keep out mice and bugs. Both ports have a flap that can be closed.

The difference between a standard 2x4 stud wall and a 6 inch wall is big. Going thicker is better but you rapidly reach a point of diminshing returns. If you insulate with fiberglass just use six inch batts and fluff them before installing by slightly pulling them apart.

05-31-2008, 09:28 AM
Ok.. thanks...so it'll be worth it then.
BTW.. these are rough cut 2X8 so they are a full 8" wide.
I'd planned on 2 foot centers. That's what I did with the other side of my shop.. used 2X6 on 2' centers.
Was hard to tell with that though... the rest of the shop is 2X4 walls. It's very hard to heat. Of course the old roll up garage door is probably -10 R value :D
Even the cost of getting free wood is getting out of hand now. And the time spent this past winter was more than I'd like.
Anything I build new here now will be aimed towards efficiency.
Evan... good tip on spreading the fiber batts. Sounds like just using the 6 inch thick ones will work witht he 8" walls.

05-31-2008, 10:11 AM
Another tip that most people don't know: You can add R3 to any wall or ceiling by adding a layer of aluminum foil. You put it on the inside of the insulation along with the vapor barrier. A single layer of aluminum foil acts as a radiant heat reflector in both directions and is equal to R3.

Also, my new roof on the my house is the lightest color shingles I could find.

I did a little analysis by taking a picture when the main roof was done but not the garage so I have a picture of both roofing shingles under the exact same lighting on a sunny day.


On the left the histogram shows that about 80 percent of the energy in all colors is reflected, that's everything to the left of the peaks. That's the new roof and should reduce heat gain in the summer and heat loss in the winter. A reflective surface reflects on both sides even if one side is in total contact with something else. Emissivity is exactly proportional to absorption so a low absorber is also a low radiator.

The old roof on the right absorbs and emits over half the energy that falls on it. Based on this difference I will have a more comfortable house in summer, a cheaper house to heat in winter and it will reflect enough incident solar radiation back into space that it is equivalent to reducing our carbon footprint by about 5% annually. Not a bad deal as I needed a new roof anyway.

05-31-2008, 01:10 PM
Torker and the group...I can well imagine that you need as much R value as you can get in the cold climate that you live in. I have been very impressed with the insulative qualities of American Polysteel ICF concrete forms. When I built my shop building on our retirement property I put up a 40x60 metal warehouse building. The building is a staging area for all our stuff from the old house as well as a residence while we build a new house. Here in north Arkansas there are severe storms, some with tornadoes, as was recently illustrated by the twisters that wrecked Gassville and Cherokee Village. I wanted to make the bedroom and bathroom a tornado shelter. After studying the FEMA booklet on storm shelters I chose the Polysteel type. The forms are the ps 4000 which are 2'x4'x1' wide. They are essentially a wire cage with 3" of styrofoam on each side with a 6" cavity down the middle. My safe room is 20'x14' with a 10' ceiling. At the time I bought them the price was not bad and I built the room for about $4000 including the concrete and the rental of a pumper. The real surprise was the insullation factor. I put a small passthrough for a small window air conditioner and when I started running it in June of '05, I could keep the room at 68* in the hottest weather and the a/c unit just idled. This is a 4000 btu, 110vac unit, the kind you usually have to run wide open to stay at 80*. The materials are a little expensive up front but the payback is pretty quick in fuel costs. It has been a very comfortable living area and I hope to be able to build an entire house out of it some time soon.

Back to your original subject, foam might help out with insullating your walls. They have a spray on expanding foam now that does not have the chemical smell or fire problems that the old stuff did. best of luck with your expansion.

05-31-2008, 01:39 PM
Go for the thick walls you won't regret it.

05-31-2008, 03:30 PM
Thick walls are nice. I have a post-frame shop. The walls are 6" thick with 2x stringers on the outside for the steel to screw to and same in the inside to screw the OSB walls to. As such, there is 6" of insulation with an air gap about 1-3/4" thick on either side.

I would tell you, however, that you should be sure not to dismiss roof insulation as you may loose more there than the walls. I had shredded fiberglass blown in. I believe that 13" of it makes R-34 as I recall. However, our climate here in Illinois is not quite as cold as up there, so I don't know what is considered standard.


Bruce Griffing
05-31-2008, 04:43 PM
I built a timber frame house with stress skin panels when I lived in upstate New York. Low e windows and R40 roof. I think the stress skin panels were R36, but I am not sure. It was also very well sealed. The result was year around comfort. No cold spots. Easy to heat and cool. In your case, I would consider ripping the x8's down to x4's and using staggered studs.

Forrest Addy
05-31-2008, 06:51 PM
I don't know if this is germane or not but when my Uncle Buck built a house in Fairbanks, AK on Nine Mile Road he built the walls two feet thick - actually two studded walls separated by two feet of batt insulation. It was a big three bedtoom rambler with all the amenities but from the outside it looked like a fortress because of the tiny windows and at every window the thickness of the walls was disgused as a window seat. The outside doors were more air locks. All in all it was an arctic house but expensive to build. He said he heated the whole house on five cords of wood per year. Pretty good for -40F nights 100 days per year. Insulating really works.

There's a point of diminishing returns when if comes to the first cost of insulation and the annual cost of heating/cooling. The trick is to strike the best balance.

If you have the material already and a need to heat the space it would make sense to build the walls as thick as practicable and insulate them.

05-31-2008, 10:13 PM
A vapor barrier is a good idea,warm is good,warm and dry is better IMHO.

Lot of folks here building with ICS foam blocks,the ones you stack and pack with rebar and then pour concrete in.R-33,wind proof,fire proof and dead quiet.

Also seeing a lot of spray in two part foam.Stuff works great on the bottom of metal roofing.

05-31-2008, 10:39 PM
Hmmm Yes I've seen the staggered studwalls before and they do work. I'd kinda like to stay with the full width 8" studs as this is a shop and it'd be nice to have really strong walls as well.
Darin... that spray foam.. is this a DIY product? I can get that done commercially but it's pricey.
Evan.. interesting data on the roof colour. All my roof material will be metal...galvanized most likely.

05-31-2008, 10:53 PM
Darin... that spray foam.. is this a DIY product? I can get that done commercially but it's pricey.

Russ,yes here you can get it in kit form from the local distributor.Comes in two canisters that look like 15gallon propane cans.Here if you buy the foam they loan you the gun and hoses to shoot it.Last I used was 2 years ago and the kit cost $185 before prices started really going up.It was enough to cover about 200sq ft of quanset hut type building metal 1" deep.It made a big difference in the heat transfer and noise in the building,plus it dries with a slick skin that takes paint good.It's about the only way to insulate the underside of a purlin/rafter metal roof.

Here is one mfg,the stuff I got was different brand 1/2 the price,but still fire rated.