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Hello: Newbie here. I am perplexed by all the different types of insulation and roofing that would be best for this particular building. Any help appreciated. Here is what I am up against: When I was a kid, now 62, my father owned a commercial building, 2400 sq ft, in a small Midwest town in which we lived. He later gave it to the city which later sold it to a small business. Neither the city nor the small business took care of the building. The small business is located in another small town and was just using it for occasional storage and a delivery point for customers. After my wife died of cancer the small business had stopped using the building so I bought the building for my kids from the small business. The roof leaked and even ruined a portion of the first floor. The moisture had ruined all of the drywall and ceiling tile from the basement to the first floor ceiling. There is and was no insulation in the building at all, anywhere. The building was built before the turn of the century, about 1890. It was a single story building with a high roof. The roof rafters are supported by being placed directly into the brick side walls. It is 30 feet wide by 80 feet long. It also has a lengthwise dividing brick wall that goes from the basement foundation to the roof and provides roof span support. The building is sandwiched between two other buildings so it’s only exposed on the front, back and of course the roof. The biggest problem with the building is the roof. It is the older style commercial roof with a single slope of about 7 degrees from front to back. These types of roofs tend to leak if you do not keep up with the maintenance. We have now stopped all the roof leaks. After gutting the building we decided there was enough room to have shops on the first floor and have 2 apartments on the second floor that would each run about 700 sq ft. We studded out the first floor and after installing the second floor joists and ply there is 10 ½ feet to the rafters which slopes down to 7 feet at the back of the proposed apartments. A major point is I have paid for all of it so far with cash and do not want to go into debt to finish the building. A major corporation in a nearby large city redid its roof. We managed to salvage a very large amount of the closed cell foam 2 foot x 8 foot sheets of ridged insulation that is 2 inches thick. We have so much of it there is enough to do a single layer on the exterior walls and possibly a triple layer in the rafters. Each sheet is supposed to be R10. The problem I face, and my question here, is how to best do the rafter insulation. The rafters run perpendicular to the slope. I do not have enough room for ventilation of the rafters. We are planning on cutting the rigid closed cell foam insulation and installing it between the rafters. Then cover it with 7 mil plastic before drywalling the ceiling. I am worried that any roof leak could do a lot of damage before it is found by this method. Or long term undetected damage could cause the needed replacement of the entire roof. I have thought I might also cover the roof with metal roofing. Does any of this sound feasible? Thanks for your attention John
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Regardless of the foam (which I like), placing that vapor retarder is going to make location of a roof leak difficult to say the least. If you are worried about moisture and condensation, you will need to use it. I know that it can get pretty chilly in parts of Iowa so placing it on the warm side of the structure is proper. If you are moving your insulation layer to the underside of the deck and placing the vapor retarder on the roof side of the drywall, there is really not need for ventilation if the vapor retarder is complete and unbroken. If you go vented on the roof, you insulation layer should be on the attic side of the drywall ceiling and don't install a vapor retarder if you ventilate the attic space.
An informed customer is the Best Customer!
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