Flat Roof Replacement for a Shop Building

Shop owners trade re-roof stories. February 17, 2011

We have an 18,000 SF building with several CNC routers, beam saw, edgebander and all the stuff it takes to do panel processing. Business has been off for the past 2 years, but it is starting to pick up... thank goodness. I own the building personally, which I lease to my business.

For the past several years we have needed to replace the roof. We have leaks everywhere, including right over a $100,000 machining center. For the past year or so we have had to tarp everything in the shop every night. When it rains we spend the next morning mopping and tossing out damaged material that did not get covered well enough.

I am planning to borrow the money personally and re-pay myself from the company over the next 10 or 15 years. We have received bids from several different companies which all have a different type of roof system they recommend. I am sure that others in our industry have had to replace a large flat roof before. Does anyone have suggestions on the best solution? So far the bids have ranged from a low of $85,000 to over $150,000. The lowest bid so far is from a company rated as A+ with the BBB and the highest bid was from a company not even listed with the BBB.

Forum Responses
(Business and Management Forum)
From contributor A:
Please explain what type of roof system you presently have. Do you have a lot of penetrations? What are the dimensions? Your low bid is $4.72/sq ft, which would probably come close to buying you an IB Products membrane roof in the town where I live.

Standing-seam metal would be my first choice if it were possible to use. IB Products would be my first choice for membrane-type material.

I'd suggest you stay away from any coating (such as elastomeric), any product that requires periodic coating (such as polyurethane foam), anything hot-mopped, anything EPDM (it shrinks something like 2% per year), and the stuff we used to call rolled roofing.

Keep in mind that it is extremely difficult to find a roof leak on membrane-type systems.
If any part of your present roof system is waterlogged, you likely have a mold/moisture problem that needs to be properly dealt with.

From contributor T:
I did a roof replacement on the building I own last year. 5000 square feet. This was a total rehab of an unoccupied 42' X 120' block building. The old roof was hot tar/membrane on 1/2" ply on 2x6' S spanning 20ft (think trampoline), 40 yrs. old, to each steel girder beam spanning the 40 ft width of the building. This was all demoed. We looked at sky for a week. New steel joists with new galvanized decking were welded in place to the beams.

We cut out for 8 new Velux 2' x4' double insulated skylights at $350 each. I shop made 12" high curbs from doubled up 3/4" exterior ply and secured these to the steel deck. I feel the cost of these skylights is well worth it. The lights are not even turned on most days.

On the roof deck - a 4" thick tapered iso-foam system was secured down. Tapered to a new internal roof drain system. On top of this is a Carlisle Membrane system glued down to the foam, up around the skylight curbs, and up the exterior parapet walls, new metal cap on top of the parapet wall (nice blue).

I tapped every one of my resources - the commercial builders I know, the steel guy (I did his kitchen 5 years ago), the local architects I deal with, the web for info. Don't put too much stock in BBB ratings - you pay money to belong to that club.

Just like somebody buying work from us, check out their past jobs with the building owners. My roof guy gave me a list of 10 local ones, reputation, how long they been around, etc.

I am very happy with the way it turned out and plan on being my own tenant soon. Great to pay yourself rent! This is my retirement plan.

From contributor S:
Contributor A has a point about mold and stuff. When you look for somebody, also find the person who did the rehab or demo - good problem solving skills. Stripping the roof would also eliminate problems in the future. Where I live, all commercial buildings with flat roofs get rolled rubber membrane. Hot in the summer and 5' of snow on it in the winter. It would not be a bad idea to take the worst spot on the roof and open it up carefully and see what you find for a mess under it. Then you and the roofer know what to expect so you're not in the middle of the job and say uh-oh, what now? Open up the roof and seal back up with a 5 gallon bucket of tar for the time being.

From contributor L:
It might be worth considering changing the pitch so the water would run off better. We’ve got a 1/12 metal roof - so far, so good. Oldest part was built in '87. In the newer part of the building I had double layer fiberglass panels put in for lighting. One 27" x 120" panel/1000 square feet of floor. I wish I had done double that. We wouldn't need any lights then, at least on most days. The natural light is really nice and diffused. Disadvantage of metal building is the limitation on how thick the fiberglass insulation can be (4"), at least with this particular manufacturer.

From contributor C:
Skylights do let in light. In one part of my building, where the skylights are, I usually do not need to turn the lights on during the day. In another part, where there are no skylights, the lights must be turned on to work.

Now, the downside. The skylights do let in a lot of heat when the sun is shining on them. Mine are a single layer of corrugated fiberglass (in a metal roof), so maybe that is not good enough. The metal roof does have R11 insulation under it, which does a surprisingly good job. Not great, but good.

Using an infrared thermometer, I have noticed a large difference in temperature between the skylight and under the metal roof. That skylight can get very hot. So, the extra heat is bad in the summer, and runs the electric bill up (AC runs a lot). But the light is nice and the heat isn't really a problem the rest of the year. My shop is located in FL, so your mileage may vary for your local climate.