Spray vs Rigid Foam for Metal R-Panel Building

[CA_Tallguy]

Hi Folks -- I've been reading as many threads on insulation as I can but my head is spinning and I'm still very uncertain about how I should go about insulating a metal building. Part of the structure already exists as an RV cover, and it seems to be built pretty well. I am going to be expanding it and closing it up to make it into a shop with a small amount of living/mancave space.

Here's a pic of the building as it stands... (located in deep east Texas)


The main question I'm wrestling with at the moment is if I want to use spray foam or rigid foam insulation. (Or spray foam UNDER rigid foam!?) Either way, I'll probably use wood framing to close the building up (with more R-panel for siding/roofing) and will be pouring a concrete cap over a good chunk of the existing slab to raise it above grade a bit. Maybe french drains along some sides.

But I digress...

When I get to reading about sheathing a building with rigid foam, it sounds like it can get pretty complicated and labor intensive. I'm thinking 2 layers, maybe polyiso, that are staggered, and I'd put this under the roof and outer walls. Then it sounds like there are other components that can be a part of this, such as furring out a "rain screen" for airflow, installing insect screens, before the metal siding. Maybe vapor/radiant barriers in there somewhere. And maybe OSB or plywood sheathing under everything as a base. Whew!

It seems like this whole process with rigid foam would give me a pretty solid and reliable building that will better handle water penetration than simply going hog wild with spray foam on the inside of the metal. My big fear in spray foam would be tracking down any leaks that might arise (and I guess these r-panel buildings can be leak prone with their exposed fasteners and all).

But looking at all the different layers and watching videos on flashing and taping and other labor intensive stuff on rigid foam and vapor barriers and all that... won't all this stuff get to be just as expensive as spray foam?

Which end product is more attractive as well? The outcome is pretty different. spray foam gives you a nearly airtight building (in one day or so of installation). Furring out a rain screen over rigid foam gives you a much more complex building envelope (but is it better or worse than spray foam).

I would very much appreciate your wisdom and advice! Thanks in advance.

 

[Shadowdog500]

My current shop has 1" thermax rigid insulation installed under the metal and it works well. A shop that I rented 25 years ago had a spray on insulation on the walls and ceiling and it also worked well.

Since your building is partially built the spray stuff may work better for you.

Chris

 

[CA_Tallguy]

Thanks Chris - in your current building, is there any kind of vapor barrier and/or "rain screen" air gap between the insulation and the metal? Is there any OSB or other underlayment under the rigid foam?

In looking at the specs for this R-Panel metal that I believe that I have, it says that it is "self ventilating" so maybe I'm overthinking the plan to also use furring to create a wider air gap/rain screen.

With the existing part of my structure, the main thing that is already there is the roof. That area is about 27x31 feet (I'm expanding this to maybe 27x50). So there are not TOO many panels that would have to be removed if I decide to add the rigid foam underneath. The structure is new to me so I can't say how water-tight it is so that makes me a bit nervous to just go spraying foam up there.

If I get a more robust building with rigid foam and some airspace/rain screen, maybe some tyvek, etc.... I'm wondering if it is with the effort to go that route. Especially if there is some kind of barrier that handles screw/nail penetrations really well considering all the exposed fasteners on this type of building.

On the other hand, some people might argue that the foam is the more robust solution. There are a lot of posts raving about spray foam except for the cost. But my main hesitation is the penetrations and potential leaks from exposed fasteners that SEEM like they might be better handled by the rigid foam route. Need to know if my thinking is flawed here.

 

[over40pirate]

I also have a metal building (30 x 31) taht I am thinking of insulating.
Does your roof have trusses? Mine has them, and I am thinking of putting a ceiling under the horizontal lower chord of the trusses, and putting insulation on top of it. I'm in SW FK (hot and humid) and from what I understand, a vapor barrier is not needed.
For the walls, I was thinking of filling the space between the wall uprights (legs? studs?) with fiberglas insulation with 7/16 painted osb over it. 7/16 osb for ceiling also.
Another idea I had was to use rigid insulation. Cut panels to fit between the roof rafters. One idea was to someway secure the panels, so there is an air space between the roof and the reflective side of the panels. Have the lower edge of the panels flush with the rafters. Then put a second later of panels under the first, staggering seams. Screw these to the rafters. They would support the first layer.
Reflective (radiant) insulation needs an air space to work.
Never read of doing it this way, but who knows.
If you have rafters and put in a ceiling, it will be less space to ac, and you can pile on a lot of insulation.

 

[CA_Tallguy]

No, my building isn't really built with trusses. It's all 3x3 and 2x2 galvanized square tubing -- even the purlins. I'll probably be using wood to build out the walls.

But in any case, I kind of want to preserve the height in the shop as I'll be adding in a lift and just to have the vertical storage space. In the "living" area I will have a sleeping loft above a kitchenette and bathroom, and the loft will open over a small living room with a big screen TV and all that jazz.

Also I've been reading up on HVAC systems and other energy efficiency stuff and somewhere I read about it being good to have your heating and AC ducts within conditioned space and some builders are basically just sealing up the building so the whole interior is conditioned space.

It is pretty humid where I am in TX in the summers and I plan on keeping the whole building conditioned year round, even when not in use (of course not to the same degree). I just want to keep the moisture out of my stuff! Plus, I like messing around with solar and different energy technologies (I'm in a forest so I might do some wood burning and even wood gasification) and so it will be fun for me to mess around with different things.

I'm still quite confused about all the different ways you can build out the "skin" of a building. There are so many house wrap type barriers and even debate on using those vs. felt paper with it's 100 year track record. Then there are arguments on how much air and moisture/vapor needs to be able to move, if any, and from where to where so you don't end up with rot and mold in the walls.

I'm currently leaning heavily towards rigid foam and some kind of wrap (maybe just tar paper) along with a "rain screen" gap directly under the metal r-panel siding/roofing. That air/rain gap seems like it might do wonders when the sun is beating down on the building, plus it just seems like a really good fail-safe measure for any moisture inside the walls or leaks or blown-in moisture from outside. I'm still not sure if the felt paper/house wrap would go under or above/outside the rigid foam, and if I can also use batt or spray foam in the inside wall cavities under the rigid foam. I do think that I've read that closed cell spray foam forms a moisture barrier so you're not supposed to use that with another barrier (but open cell foam would probably be OK I guess).

And I won't even get into a radiant barrier right now! It all makes my head hurt.

 

[theoldwizard1]

Polyiso has the highest R-value per inch of any insulation so it is a good choice.

Most applications like yours would use metal panels with the polyiso already bonded to the panel. A double layer with staggered joints is the preferred method for best sealing, but I can not find nothing about attaching it to finished exterior metal panel.

If you are going to continue with the same metal panels, I would bite the bullet and go spray foam.

 

[DEnd]

First off I will say don't try to re-use your existing structure, you will not likely save much money. At least not by framing out the interior. Also since you are planning on adding electrical to the building you may need to have it inspected and meet code, that may be difficult with your existing structure, since it's not typical you will likely need engineered drawings.