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Old 08-18-2010, 10:27 PM   #1
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Old Building problems


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 itís 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 Ĺ 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

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Old 08-19-2010, 08:12 AM   #2
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So you patched the roof and did not replace it. That would be a mistake. Replace the roof with a membrane roof and you won't have any issues with the interior.
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Old 08-19-2010, 09:36 AM   #3
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If that were my building and I were going to do what you are doing, I would vent the roof by installing the styrofoam chases against the underside of the decking and vent the top and bottom ends of the roof. I am not a big fan of plastic sheeting on ceilings and walls as it can and sometimes will sweat and cause problems. JMHO
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Old 08-19-2010, 07:13 PM   #4
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The roof itself is the old hot tar type roof coating over tar paper. To replace it would be a major undertaking since it is about 4 inches thick and has old metal roofing in places buried in there too.

The leaks were so bad we had to fix them before we went any farther with the building. I called it patching but in reality we have redone the roof several times with tar. One day soon I would like to put new metal sheeting on it. Rubber membranes may sound like the a good solution but you can only get a 10 year warranty with them verses up to 50 years with metal roofing and the cost is the same.
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Old 08-20-2010, 06:03 AM   #5
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You need at least a 3/12 pitch for a metal roof, seven degrees won’t cut it.
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Old 08-20-2010, 08:32 AM   #6
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Q. What is the minimum roof slope for metal roofing?
A. Absolute Steel offers a wide variety of panel systems to meet a variety of slope requirements. Information regarding minimum slope requirements can be found on the specific technical Data Sheet for each product. Typically, metal panel systems can be applied to pitches of 1 : 12 or greater. Actual minimum slopes may be dependent upon roof geometry, substrate, and physical location of the project.

Low Slope Metal Roofs Provide Years of Low Cost, Low Maintenance Performance

Low slope metal roofs have been a preferred roof covering for commercial, institutional and industrial buildings for years because of their ability to protect against the elements, to allow water to drain away from the roof surface, and to keep building contents and occupants dry and comfortable.
Recently, building owners and architects have come to recognize and appreciate still other attributes of low slope metal roofs – their long service life, low life cycle cost, sustainability, recyclability, low maintenance requirements, light weight and resistance to wind.

The cost for metal sheet roofing is slightly less than rubber sheet.

My main concern is about insulating the ceiling. I am concerned about moisture barrier and moisture between the drywall and roof. Some people say to plastic the wals for sure yet some say to and some say not to plastic the ceiling. I assume it is a question of how the ceiling breathes and the moisture from inside escapes. This ceiling to roof would be unvented and closed. I have stacks upon stacks of used 2 ft x 8 ft x 2 inch thick closed cell foam we salvaged off a very large commercial building. I would like to place it 3 layers deep (R30) between the rafters and then cover it with 7 mil plastic. Then drywall.

Last edited by jake62; 08-20-2010 at 08:40 AM. Reason: added text
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