The International Cessna^® 170 Association

I'm researching insulating my 40'X50' shop. The shop came with the house when we bought the place. Without insulation it is an oven in the summer and an icebox in the winter. Summertime high temperatures are in the high 90's and wintertime lows are 20's-30's. It's a Miracle Truss steel building similar to the one pictured below. It has 2X6 purlins. There seem to be as many different insulation options as there are websites touting each one. One I'm considering is this one. I get an occasional leak around the nail(s) that attach the tin to the purlins. If I use fiberglass I'm concerned about that getting damp. Also don't want mice nesting in the fiberglass. Thoughts?

Foam it .

Not certain about your "nails"... My hangar uses tec-screws with neoprene washers which leak-proof it (as long as they're installed correctly using the proper tool {tec-screw-gun} without excessive torque.)
You should seal those leakers before insulating, regardless of what you use. 50-year silicone should do it if you're unwilling to replace the fasteners.

I don't know about foaming on top of existing fiberglass, but if the process can be done (ask the installers). You might also consider "flocking" to improve the fire-code of your bldg as it also covers the structural steel. You may find a reduction in insurance premiums and/or fire-codification.

gahorn wrote:Not certain about your "nails"... My hangar uses tec-screws with neoprene washers which leak-proof it (as long as they're installed correctly using the proper tool {tec-screw-gun} without excessive torque.)
You should seal those leakers before insulating, regardless of what you use. 50-year silicone should do it if you're unwilling to replace the fasteners.

I don't know about foaming on top of existing fiberglass, but if the process can be done (ask the installers).

George,
The picture which I stole from the internet above may have been misleading. My shop has no insulation--just bare tin. I like the tec-screw with washer idea. Thanks. The nails holding down the roofing do have a rubber washer under them but every year it seems I have to add sealant to one or two new "leakers". The rubber washers are rock hard and don't do a thing if the nail loosens.

I'm with George, get rid of the nails, they will be a problem forever. Replace them with the screws, hopefully before the 2x6 purlins have rotted around the nail holes, and the problem is solved. It will be a big job but worth it and easier than re-caulking the nail heads every couple of years as the nails back-out. Hopefully all the nail holes are on the ridges and not in the valleys.

Then foam it with polyurethane, not soy-based. Decide on thickness according to your climate, ask the foam contractor for guidance. Even a couple of inches will make a huge difference in radiated heat and is an almost perfect vapor barrier, no condensation. Adding thickness later on can be done if you need more later. There is even a fire retardant paint additive that can be added to latex paint and sprayed on.

The insulation in the link you provided is for insulating the building before the sheet metal is installed, would be difficult after the sheet metal is on. Condensation can still form between that insulation and the sheet metal, leading to problems.

Locally we have a company that does spray insulation of different kinds. Check your local for any type spray.

John

hilltop170 wrote:Then foam it with polyurethane, not soy-based.

What's the advantage to polyurethane foam?

hilltop170 wrote:The insulation in the link you provided is for insulating the building before the sheet metal is installed, would be difficult after the sheet metal is on. Condensation can still form between that insulation and the sheet metal, leading to problems.

If you go to the bottom of that link they show adding the sheet insulation to an existing building. I wonder how well the sprayed foam works against radiant heat? I guess what I'll try first is the sprayed foam insulation. If that is inadequate I'll add the sheet stuff as pictured below. Thanks for the advice, it's much appreciated.

I think it will be difficult, if not impossible, to add the sheets on top of foam. (Foam results in an uneven surface.) I can imagine the reverse being easier.