Double Stud Walls?

My 2400 sq. ft. barn/workshop was constructed with 2x4 exterior walls and without insulation. To make the area usable more often I was considering installing an HVAC system. I was thinking of adding another wall inside to allow for more insulation but don't want to get carried away with all of the double wall constructs used today in homes. Our weather in NW Arizona is fairly mild and this after all is only a workshop. The biggest problem with respect to heat loss is the high sloped ceilings that reach about 30 ft. with about half of the shop having an open mezzanine. I could go crazy with insulating the walls but most of the loss will be in the ceiling. So, do you think it reasonable to construct an additional wall using just 2x4s or even 2x3s. Is it necessary to stagger the studs with those on the existing wall?

You could certainly increase the wall depth to allow for greater than R15 insulation using traditional fiberglas, but you could also use closed cell spray foam to get substantial (R-19 to R-23 or so) in the 3.5" cavity currently present. The same goes for the ceiling. This material also adds a lot of stiffness to the structure. Compare the cost of the extra wall depth plus traditional insulation at R15 vs spray foam with no structural changes and higher R-values.

And if you do choose to add wall depth, staggering would make it more complicated and thus, more expensive, to insulate.

You are correct that your greatest heat loss is up so unless that is addressed first anything you do on the walls would be an effort in futility, IMHO. That being said...One possible solution might be to install 2" of EPS (Expanded Poly Styrene...just don't call the "green" police ;)) foam over your existing studs and hold in place with 1x4 strapping screwed into the studs. Apply drywall or other over the strapping. Same could perhaps be used on the ceiling depending on your situation. EPS is semi vapor permeable (as opposed to XPS, eXpanded Poly Styrene, which is not) which would help mitigate condensation issues caused by indoor/outdoor temperature differentials. IIRC EPS will give you about R4-R4.5 per inch. Tape the joints will help keep air leakage to a minimum. Air leakage would be your next largest source of heat loss/gain behind the conductive and radiant heat loss/gains through the ceiling.

I'm no construction expert, but I've heard of two reasons for double walls with staggered walls -- sound isolation & thermal insulation. It doesn't sound like sound isolation is a significant concern. In well insulated 2x4 or 2x6 walls, IR scans show significant heat conduction through the studs. Double walls with woven (or sprayed) insulation almost eliminate the loss through the studs. However, with the foam-board solutions available today, I would expect a foam-board layer inside or outside would be as effective & not reduce your square footage like a staggered-stud double-wall would.

My Shop is 1750 sq ft, and the ceiling goes from 12 ft, to 17 or 18 ft down the center of the shop. I have a gas heater hanging from the ceiling. In addition, I installed 3 ceiling fans down the center of my shop to circulate the heat down.

Sam

Considering the high ceiling in barns, designed to store hay, think I would look at a suspended ceiling. You hang the framework using wall angle around the edges, and then support the framework with wires attached to the framing. They sell R30 batts to fit the suspended ceiling, so you put up a few tiles, then a few batts, and work your way across the ceiling. You can also buy troffer lights that fit in place of a tile so your ceiling is flat.

Since you have an open mezzanine, I would just insulate the 2x4 walls and insulate the ceiling, if it is not already insulated. If you don't insulate your ceiling, it won't really matter what you do with your walls. Your weather in Kingman is not unlike mine in Escondido, Ca. and I find that I can work comfortable the entire year. I put in 3-1/2" of wall insulation and 6" of ceiling insulation. Sometimes in the summer when the temps get up to 100 or so, I might turn on the room AC. But usually if I just wear walking shorts and a T-shirt and run the overhead fans, I'll be fine. In the winter, the shop seldom gets below about 45. I sometimes will set up an electric radiant heater and run it for a couple of hours if I'm going to be out there for a while.

My answer might be different if you were planning on working out there 40 -50 hours a week.

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Originally Posted by Steve Mathews

My 2400 sq. ft. barn/workshop was constructed with 2x4 exterior walls and without insulation. To make the area usable more often I was considering installing an HVAC system. I was thinking of adding another wall inside to allow for more insulation but don't want to get carried away with all of the double wall constructs used today in homes. Our weather in NW Arizona is fairly mild and this after all is only a workshop. The biggest problem with respect to heat loss is the high sloped ceilings that reach about 30 ft. with about half of the shop having an open mezzanine. I could go crazy with insulating the walls but most of the loss will be in the ceiling. So, do you think it reasonable to construct an additional wall using just 2x4s or even 2x3s. Is it necessary to stagger the studs with those on the existing wall?

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