Advice on insulating a 600 sqft workshop
Hello everyone, this is my first post here at GBA 🙂 I am in Chicagoland so climate zone 5a for context on the coming information.
I have recently completed the shell of my new workshop, it is a 15’x40′ 2×6 framed building with 9′ high walls. It is on a 5″ thick concrete slab with a 12″ footing. The roof is 4/12 pitch with 2×6 rafters and joists at 16″ spacing, no ridge vent but 2 separate static vents. There is one 10′ x 8′ overhead door and one 3′ x 7′ man door which are both on the same wall (if that matters), no windows.
Now to the question, I am thoroughly stumped on the “correct” way insulate the building. This will be home to many very expensive machines which are primarily made of cast iron, so the top priority is to keep the air inside at least minimally conditioned so that the temperature of the machines never crosses over the dew point and causes condensation on them. Equally important to me is choosing building materials and installation methods that will last the life of the building (which is intended to be the remaining ~50 years of my life) or at least close to it. It seems like there is a huge amount of conflicting information out there based on who you’re talking to. Of course the spray foam guys say that closed cell spray foam is the only way to go, anything else is just wasting money. Then in other places I have read about how in cold climates it can crack and allow moisture intrusion leading to roof rot, plus there is conflicting studies that say it off-gases for months after install. This is all not even to mention the price of it since I have to hire a contractor to install it whereas any other product I could confidently do myself.
If I have neglected any important information please let me know. I would be extremely grateful for any advice from you fine folks!
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Replies
Air seal and set up the overhead door as best as possible.
I cannot see the expense of spray foam
I am not anti foam, but one way of balancing insulation values is money.
A shop need not be heated to 68 degrees 24/7.
To protect the contents of the shop one need only keep it from going through the dew point.
If you insulated the slab edge and filled the stud bays with fluffy stuff, the energy [money] required for this will be minimal.
I live in a warmer part of zone 5 and and am shocked how little my 40+ year old R13 insulated garage varies. I run the heat in like February on the regular, and obviously when I am working there. Even with its substandard insulation, it is like turn the heat on this afternoon it will carry it for the week.
I am not trying to discourage insulating well, but IMHO R19ish walls and as much as you feel like piling in the attic space, you will spend little on heating the space if you use a sensible strategy.
TO me this is the fundamental difference between a shop and the house. If you wake up in the house and it is 55 degrees at 3AM, hey something is wrong. In the shop, who cares no one is there.
Thank you for the input, I was thinking of doing mineral wool insulation in the walls and blown cellulose into the attic but then I got nervous that I was missing something. One addition is that I am planning on using plywood as the wall material, so I'm wondering if there's some additional requirement for a vapor retarder since that will not be taped and painted to seal the seams like you would with gypsum board.
Trainwreck,
Can you describe the foundation a bit more. Is the slab insulated? Does it have poly below? How is it protected against frost-heave?
Hi Malcolm,
To my understanding it is a simple 5" slab on compacted gravel with a 12" x 12" footing around the outside. Unfortunately for me I hired a GC to build the structure up to the point it is at now (and I am generally unhappy with the work done to this point which is why I'm taking over myself now) and I was not present for the pour so I would have to get in touch with the GC to find out the specifics. I have attached the relevant page from the plans at hand that were submitted and approved by planning and development, but it is sparse on details.
I can get in contact with the GC to try and find out if it is important to the conversation!
Trainwreck,
If there is no poly under the slab you may have moisture issues with things you leave on the floor, and possibly humidity issues in the space. You may want to coat the slab with a vapour-retarding finish.
How much heat you will be losing through the slab influences how much insulation it makes sense to add to the walls or roof. You will need slab-edge insulation to limit heat lose through the thickened footings. Depending on the frost depth where you are you may need to extend that out as wing insulation to keep the foundation from moving.
Do you have any specifics you'd be willing to share? According to table R403.3(1) it would seem that I am looking for 1.5" of vertical rigid foam insulation, and there is no requirement for horizontal insulation. Does that sound correct to you? Would you be able to give me any suggestions for specific products at least to get me started?
Trainwreck,
This article describes both how to insulate the exterior of the foundation, and how to protect it against pests.
https://www.greenbuildingadvisor.com/article/how-to-insulate-a-basement-wall
You don't need an interior vapour-barrier (the plywood will act as one) but you do need a good air-barrier somewhere on your walls, and ceiling. For the walls, taping the exterior sheathing is probably the easiest. For the ceiling that's probably poly above whatever you are using as a finished surface.
I'm still bit uncertain about your foundation and frost heave. If your footings don't go down below frost depth in your climate, you need to protect them with insulation. This guide shows how:
https://www.homeinnovation.com/~/media/Files/Reports/Revised-Builders-Guide-to-Frost-Protected-Shallow-Foundations.pdf
Hi Malcom, I'm not sure why the site won't let me reply to your latest response so I am replying to this one. Thank you for the documents, they are very helpful. My exterior sheathing is already covered by the siding so unfortunately taping that is not an option for me. The building was wrapped with house wrap before being sided, but I do not believe that is an adequate air barrier and in fact is intentionally NOT an air barrier. Does that mean that before insulating I should be looking to seal the inside of the sheathing?
I am more than a little disappointed in the GC that I hired to do the first part of this project between all of the things that have come up in this post. I do not know what if anything was done regarding the FPSF, so it looks like I will be needing to excavate around the foundation to install the vertical insulation and wing insulation. R403.3(1) seems to imply that I would not require wing insulation but at the same time it is probably better to be safe than sorry when it comes to the foundation of the building.
Trainwreck,
Yes you need an air barrier. Your best bet is either poly if you are never going to use air conditioning there, or variable-perm membrane.
Do confirm whether you need wing insulation. That's a lot of work if not necessary.
If there is no perimeter insulation, get out the pickaxe and fix it. Really valuable to isolate the slab.
I would insulate right across the door aperture
It is huge in a intermittently heated shop to have the foundation insulated. It turns the floor from cold slab wicking heat out of the building to a storage medium for heat.
I have a dehumidifier in my garage because it has no poly and gets humid, even though I have a minisplit, I need it in cold weather
Sorry, not sure what you mean by "insulate right across the door aperture."
I also plan to keep a dehumidifier in there, cheaper to run that than to resurface a 1000 pound milling machine table!
exterior foam, all around the foundation if there isn't already foam. including where the door is
Perfect thanks for the clarification. Yes the biggest take away for me from this post is that I need to use 1.5 or 2" of rigid foam attached to the foundation the entire perimeter of the building. The last outstanding question I have is whether I need to put some kind of vapor retarder between the studs and plywood wall panels I plan to put up since unlike gypsum board plywood will not be taped at the seams.
In my opinion spray foam marketing has wrongly convinced most people that it is the best answer for every insulation problem. The way I see it spray foam does two things well one is it packs more R of insulation in fewer inches of space while sealing air leaks while being the most expensive least green and riskiest way to buy an R of insulation. Seems to me you have room for cheap fluffy insulation in your well sealed building.
Just to be 100% clear insulation alone will not be able to keep your machines safe from condensation.
To keep them safe you need to condition the air in your shop mostly by heating the air in the shop so the machines in the shop do not get very cold and cooling and drying the shop air when the weather warms suddenly after a long cold spell.
Yes, insulation is a good thing and will lower the cost of heating and cooling the shop.
This sensor seems interesting for your goal.
https://www.instrumart.com/products/43009/ee-ee046-condensation-monitor
Walta
A standalone dehumidifier is also a high efficiency space heater. So I would run a dehumidifier first and augment with heating as necessary.