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TOPIC: Installation Process

Insulating a Shop Building

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I recently poured a slab for a 28 X 36 shop building. My plans are to use a 5/8" rigid foam board (R value 3.8) nailed over the horizontal purlins on the roof placed on 2' centers and covered with the metal roofing. The walls would be covered the same way with the insulation board nailed to horizontal 2X4's and covered with the metal roofing. The pitch on the roof is 3 in 12 - I will have no overhang, thus no soffits. I do not plan to put any gable vents either. Neither the ceiling nor the walls will be sealed. I am not very concerned about heat or cold as this shop will only be used occasionally (mostly for welding and working on farm equipment) when the weather is good. I live in the deep south (Mississippi) where we get no snow but a lot of humidity in the summer and moisture in the winter. I had one metal building that was built exactly like this one but had absolutely no insulation. At certain times it "rained" condensation and I would like to avoid that if possible. Will this 5/8" insulation board help or make the condensation problem worse? JT
Guest User

2/25/2004
If the insulation has a vapor barrier on the bottom side and the seams are all sealed, it will help the moisture situation. Otherwise, you could end up with moisture trapped between the insulation and the bottom of the roofing -- not a good situation.
Guest User

2/26/2004
I was also considering placing the rigid insulation between the roof and purlins but was worried about the roofing fastners crushing the insulation and not sealing. In our commercial steel building they used a plastic blanket insulation between the roof and purlins.We have had a couple of leaks over the years at the screws but you couldnt tell until the insulation started to sag. When we checked it was usually screws that backed out a bit or were not fully tightned. But on an uninsulated area we have never had a problem with screws leaking. Thats why I thought it would be better to put it on the bottom of the purlin and I figured the extra air space between the roof and insulation would provide extra insulation.(see post on insulation)I also considerded leaving the ribs open at the eave and ridge to allow some ventilation but am not sure that it would gain anything.It sounded like we were constructing similiar buildings. It seems like there are a lot of companies selling metal roofing but no good information on installing it (ie fastner placement,ventilation, etc.)
Guest User

2/27/2004
I am not entirely sure I am following the last few posts correctly. However, if you put the insulation between your roof trusses, leaving a gap at the top for at least 1" of vented airspace (plus the depth of the purlin), and then you install soffit and ridge vents, you should be a in good shape. I would still suggest, though, a vapor barrier on the bottom side of the insulation. You are correct in that there is a general lack of knowledge which the Metal Roofing Alliance, along with other associations as well as individual manufacturers, is trying to correct. In all cases, though, I do think that quality metal roofing manufacturers can give you good direction. If you're working with a manufacturer who doesn't have the answers, find a different manufacturer.
Guest User

2/29/2004
I jumped into this thread because it looks like we are building similiar buildings and I thought I would put in my opinion/experiance about putting the insulation between the metal roofing and wood purlin/truss. Not about the air space issue but more about the the fastner issue crushing the foam insulation and not sealing properly. Thats why I am considering putting the insulation on the bottom of the purlin, and still have not decided whether to ventilate that space between the insulation and metal roof or to seal it with foam closure's along the edge of the eave and ridge and make sure I use a rigid insulation with a vapor barrier.
Guest User

3/1/2004
Thanks for the ideas fellas. I too am a little concerned about the "cushion" the insulation board will make between the metal and the purlins. I put some 3/4" Owens Corning foam board on a small portable building that my wife uses for her crafts (I call it her craft crap house). When you tightened down the screws the foam and the 29ga metal would give enough to make a slight dimple. I am planning on using a 5/8" "R Board" made by Atlas roofing on the shop. The R value is about the same and it is a lot stiffer board than the foam. I tried some sample pieces and it seems to do ok but I'm not sure about the screws staying tight. I too thought about putting it directly to the trusses and between the purlins but that would be a bit of a pain. Greg, when are you starting on yours? JT
Guest User

3/1/2004
I hope to start within the next month. I just finished up my slab. I am using a steel truss designed for pole barns, it is a gable style truss and along the top it has pockets welded for 2x6's to be attached horizontally 2' o.c. As soon as I finish up a few other projects I am going to be able to start construction. So I have been working on a few of the details like the roof construction.
Guest User

3/1/2004
The steel trusses should work well and go up fast for you. I thought about building the whole thing out of metal, using square or rectangular tubing and metal trusses. I've got a welding machine and would have gone that route if the cost weren't prohibitive. I am going to be building mine mostly by myself and using steel would have allowed me to work on it at my leisure not being affected by the weather. When framing with wood I don't like my framing to be exposed to rain and sun any more than necessary so there is a bit of urgency on getting it sealed up. Since I am framing with wood I guess I'll go ahead and use wooden trusses. After the posts about screws loosening up and roof leaks I am seriously considering ripping the insulation board to 2' X 8' and putting it between the purlins and directly onto the trusses. That will allow me to use thicker insulation board and to screw the metal directly to the purlins. For some reason I don't like the thought of sandwiching the insulation board between the trusses and the purlins - just my weird mind I guess. As far as the airspace created between the metal and the insulation, I don't know if this will help or hurt the condensation problem. I think if I can make it fairly airtight it will be ok. If warm air can get between there it may be a problem. I'm anxious to get started but the weather hasn't cooperated. We've had rain, rain and more rain. Good luck on your project. JT
Guest User

3/2/2004
My building is also going to be primarily wood (2x6 stud construction) just the trusses are steel. I found these at a farm show and it looks like it will be much faster and easier than wood trusses. I am definately concerned about the leaking issue at the screws so I will putting the insulation somewhere else. What type of insulation did you say you were going to use? And I think I am going to close up the edges with foam closures to bypass the condensation issue.
Guest User

3/2/2004
I plan to use R-Board, made by Atlas Roofing Corporation. Their 5/8" board has an R value of 3.7 and is a very stiff and rigid board that doesn't compress like the foam. 3.7 isn't much insulation but I don't need a lot. We don't get much cold weather in Mississippi and it is going to be hot in the summer insulated or not. I mostly want the insulation for the sweating problem - as I said we have a LOT of humidity. I looked at several manufacturers (Dow, Owens Corning, Georgia Pacific) and I like the R Board best. I am considering using your idea of putting the insulation board down over the rafters and the purlins over the top of that. I think the rigid board would be ok for that - the foam board I think would compress when you nailed or screwed the purlins down to the rafters. The Dow board and the Owens Corning board (both foam) comes in a tongue and groove which I really like. It makes the seams pretty much airtight. If you need websites for any of these I think I've still got them bookmarked. I had planned on taking vacation next week and get started but we've got more RAIN in the forecast. I ordered my metal yesterday supposedly just before a price increase. By the way, what part of the country do you live? JT
Guest User

3/3/2004
My thoughts were to put the insulation in after the roof was up. I thought I could just fill in the space between the trusses with the insulation board and attach it with both construction adhesive and some type of fastner (nail or screw) with a large washer. My trusses are set 12' apart so I figured I could just fill in that area using scaffolding and seal it where it meets the truss. I am located in north Florida, in the Gainesville area. So I have the same problem with heat and humidity.If you have the site for the Atlas product that would be great. Thanks
Guest User

3/3/2004
Greg, here is the link to the R Board: http://www.atlasroofing.com/residential/rboard.asp As you can see it comes in several thicknesses. I just noticed the 5/8" is 3.8 instead of 3.7 R value. Atlas also makes some other boards that you might like better. I am also planning on using it on the outside walls, which will be exposed on the inside. The facer on it looks like it would be pretty tough. Some of them (especially the foam boards) are very easily damaged. Their web site is a little hard to get around in but I think you can find what you need to know. That's interesting how you plan on putting your insulation board on the bottom side. That should be pretty easy with the wide truss spacing and some good scaffolding. That is the only part I'm not sure about at this point. Again, good luck with your project. If you have any questions you can e-mail me at [email protected] so we don't hog this forum. I haven't broken down and bought a digital camera yet but I plan on using one at work to take some pictures on the shop-in-progress(If I ever get started). If you would be interested I will email them to you and I certainly would be interested in seeing yours. JT
Guest User

3/3/2004
Greg, I lost your email addy but since we talked I have started my shop. I came up with a way of putting up the insulation that worked well for me. If you're still following this thread, Email me and I'll share it with you if you're interested. JT
Guest User

3/25/2004