Where to put the EPS foam?

[Maverickv46]

If you have seen it, I am working through installation of 1 3/16 EPS foam in my 40 x 32 with 14ft ceilings. Right now I have completed the wall covering where we cut the foam to fit between the purlins and spray foamed the gaps.

To give context, this is phase 1 that the budget allows in order to make the space habitable for this winter. Next phase will be to stud the walls, add kraft face batts and a wall covering. The ceiling will get a covering and proper R60 batts as well, but that is not in the budget at this time.

Now the decision point is where to put the ceiling EPS. The way I see it, there are three options:

- Nail to the bottom of the trusses to make a "ceiling". Not the most conventional way, would seal up nicely for this winter and batts could be added on top. Downsides are the unusual stack distance for light receptacles (1 3/16 + 1/2" covering), and anything ceiling mounted would be squishing foam.

- Attach to the bottom of the roof deck, between the trusses and spray foam any gaps. Probably the most proper, but having soffits and a ridge vent will allow the cold winter air in the shop until the eventual fiberglass and ceiling.

- Finally, cut and fit to sit on the top of the bottom chord of the trusses. This would also create a good envelope, allows mostly whole sheets of foam, batts can still be added on top, and the ceiling covering can be attached to the bottom of the trusses like normal. This would be the most complicated method to cut around all of the truss members.


Reaching out to you guys to understand what might be the best option here and get some opinions. Please let me know if anything was not clear, and here are a few inspirational pics of the build thus far.

 

[Radix2]

What is the purpose of the ceiling eps? For the same money and work you could drywall or put metal liner on the ceiling and blow cellulose on top. Done and better insulation.

Don't get your version with the eps by the roof...if there is going to be vents, it needs to be above the eps.

 

[toyotadriver]

I assume that you don't plan to use the rafters for storage and I believe I understand that you plan to eventually put a ceiling in and insulated above it. If so, then I would install the sheet foam on the bottom of the rafters and create an insulated space in the shop and cold space above in the attic.

Your foam won't do a ton of insulation in your cold climate but it's WAY better than nothing. I did something similar for my shop (used XPS though) and then insulated with batts. Worked great. I did keep my rafters open for storage and used the XPS below the roof deck (1.5 inches between the purlins on the roof and another 1.5 inches on the underside).

If you create the cold space attic, I would not use batts. I would use blow in insulation, either fiberglass or cellulose but my choice would be cellulose. Blow in is likely cheaper and will be faster and much easier. It's also better at insulating than batts for the same rated R value.

 

[rburke65]

I cut and fitted EPS between my truss openings, covered with Visqueen and then installed a metal liner ceiling then my surface mounted 8'...4 lamp fixtures. Then I had a company come in and blow fiberglass insulation atop the EPS in the attic.

 

[Maverickv46]

The reason for the EPS is because I was able to source enough for the walls and ceilings plus a bunch of leftover for less than half of a ceiling and insulation would cost alone. This phase 1 plan should suffice for one season, and then will only add extra insulation and air flow reduction for a more traditional insulation setup.

 

[homebuilt burner]

I saw something different a while back maybe it would work for you. The guy had cut the eps into strips that fit between the trusses, then had laid 1x4's on top of the bottom truss 2x4. He fastened and foamed the eps between the trusses and to the bottom of the 1x4's. So the top of the eps was even with the top of the bottom of the 2x4 truss bottom. Advantages, you can blow in insulation on top of the eps. or you can roll fiberglass on top of the eps, this also allows you to run your wiring above any ceiling.

 

[Radix2]

The reason for the EPS is because I was able to source enough for the walls and ceilings plus a bunch of leftover for less than half of a ceiling and insulation would cost alone. This phase 1 plan should suffice for one season, and then will only add extra insulation and air flow reduction for a more traditional insulation setup.

Then I would just put it on the bottom of the trusses and add your ceiling below and insulation above when ready.

I don't think either the electrical box or squish are real problems. If you surface mount light you may not use boxes anyway. drywall will not squish eps foam and liner panels need a soft touch even driving into wood

 

[toyotadriver]

I just build a metal sided house and we covered the purlins with EPS rigid foam. We the screwed the metal right over the foam. Worked fine.

If you are going to have a metal ceiling, definitely attach the foam to the bottom of the rafters.

 

[Maverickv46]

I am going to snag some pictures this weekend to convey each concept I am going between and get a good visual. Have a motocross race, so we shall see if I fit it in

The idea of going in between the bottom chord and flush with the top is interesting to me. I do plan to use receptacles and plug in lights for the ceiling, so I will use elec boxes. Costco lights are cheap and hella bright. They are chain-able though, so with my three rows of lights I may only need a few receptacles.