Some manufacturers will allow overlays on flat roofs if no water is in the old roof as long as the roofs are separated by a recovery board (insulation board). May I scream here? Why are you replacing the roof if water didn't penetrate it? It's not broken so don't fix it.
When you overlay, you probably lose a lot of wind, weather, and longevity warranties.
Let's break it down. A residential roof costs anywhere from $1.60 per square foot up to $6.00 per foot for specialty metal roofs. Slate goes even higher but this is a rare roof. For a mean ( average and not my ex) price one might use $2.00, a little higher than what 30 year laminated roofs like Timberline cost. Flat roofs go for anywhere from $3.00 per square foot installed up to $7.00 for a whama jamma super roof. Let's average that at a respectable $5.00 per foot installed.
Composition roof removal is about $.30 per foot and there is anywhere from 10% to 20% less square feet of tear off than installed when we calculate residential roofs. Commercial roofs run about $0.50 per foot of removal. In both cases subsequent layers are removed at a lower cost of about 25% per layer.
Here's how one might figure a composition roof with x being the surface area:
$0.30x · (1.15x · $2.00)
For every foot of tear off you need $.30, and for install you need 15% more squares times $2.00.
For every $2.30 you spend installing the roof you'll need about $0.30 for a tear off, which gives you a better roof and a better looking roof. If you have a 30 square tear off you'll need almost 35 square for installed roofing. So if you spend $7,000.00 on installing your roof, you need only add $900.00 to make it look nice, last longer, and resist wind better.
Would you tear off all that roof, haul it to the dump, clean up all the pieces and put down $300.00 worth of felt for $900.00? Now you see why the Tinker Toy roofers want to overlay your roof. Quality is not worth it to them.
On flat roofs you may calculate as such:
$0.50x · $5.00x
For every $5.00 you spend on your new roof you'll need $0.50 to get a roof like the engineer who designed the system wanted. 10% not spent on the flat roof can make for a roof that is not just more easily damaged by hail or wind, but with a disease causing swamp that smells like the pit of hell.
If your building has 10,000 square feet, like a small shopping center and you need $50,000.00 to roof it, don't you think the $5,000.00 you need to make the job work like it is supposed to would be a small price to pay for a good roof.
Anyway, if you don't tear it off you have no idea what is under there. No excuses either. Don't let that penny pinch nerve destroy everything.
Jon Alan Wright
Jon Wright Roofing, Siding, and Windows
1915 Peters Rd., Suite 310
Irving, TX 75061
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