# Commercial roofing replacement vs retrofit question



## gjam (Feb 3, 2015)

Hello all,
My name is Gene and i am very glad to have found this resource. I am sorry to join and then right away ask a question but i could use some advice with this. 

I have a question about a built-up tar and gravel roof. The customer has had 3 roofing companies quote a job to replace his tar/gravel roof with a membrane roof. The quotes were $9600, $12000 and $32000. He has contacted me to see if these numbers are credible for his 3444 sf roof. Obviously something is wrong with the $32000 quote but the other 2 seem on target for this area (South Carolina). The contractors stated they would remove the top layer of loose gravel then lay underlayment then the membrane. Pretty standard replacement.

This will fix the customer's leaky roof but he posed a question to me and i am not sure i can answer it as i have not done anything like this before. He wants to know if the gravel can be scraped off, screw sleepers or purlins on top of whats left, then attach corrugated metal roofing over that. Now we would definitely have to get an engineer to sign off on the load but it is hard for me to believe the load would be much different once the rock are removed. 

Assuming the loads are within spec. is this a reasonable solution. He believes the cost would be much less with this option. There is a small crown to the building so water would flow off the sides. Has any one done this and if so was the cost that much less than a membrane. also is the life of the metal roof drastically superior to the membrane (it would seem to me that it would be). Is venting easily done without adding some sort custom truss which would increase the cost and probably negate the cost advantages?

Other information that may or may not be helpful. this is a single story building, probably dates to the 1940-50s. It was once the maintenance shop for a textile mill. Concrete block construction with brick veneer. currently in use as a wood shop with the tools strategically placed to avoid the leaks.

I appreciate you reading and look forward to any information you guys may have.
Gene


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## roofermann (Jul 7, 2012)

Other than the load question, what will the pitch be? Few metal roof system will work on something that is under 2/12. And corrugated panels with exposed fasteners is NOT one of them.:thumbup:


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## 1985gt (Dec 21, 2010)

Actually the $9600 quote is way off remember you get what you pay for. That is less the $300 a square, even for a recover that is way low. The $12000 is pretty low too, at around $350 per square, I don't know if I would even touch it. While the $32,000 might seem high that is less then $950 per square. Clearly the bids are not apples to apples in one way or another.


Now lets look at the metal option. Slope will be a big deal, some standing seam panels will go down to 1:12.


Lets assume this roof is a 40' X 80' 3400 sq ft.

Each panel is 21' long and since we are using the exposed fastener metal it is 36" wide. 

You need 26.6 panels for each side. So we round up for extra 27 per side plus 2 extra. So 56 panels btw I would order a couple of extra so 58.

58 Exposed fastener panels at 20' long

You also need trim.

80' + waste of drip edge
160' + waste of rake metal
80' Of ridge. 

320' of J channel

And screws! we will say 30 per panel + trim (i'm just throwing a number out here as you may need more screws) 1740 screws for just the panels.


Material list

58 Ea 21' long panels @ 53.20 Ea $3085.60
80' Drip edge @ 9.39 Per 10' $75.12 
160' Rake metal @ 26.59 Per 10' $425.44 
80' Ridge @ 62.91 per 10' $503.28
320' J channel @ 10.19 Per 10' $326.08
2000 screws @ 16.99 Per 500 $67.96

160' Foam Closures @5.99 Per 12' $ 83.86

+ 1920' Of 1x4's @ 3.29 per 10' $631.68
2000 wood screws @95.14 $95.14

Materials $5294.15 = 155 per square for material only.

Now if someone was to do it I'll do it the easy way ,

Materials X3 = total job cost.

$15882.45 or 467.XX per square.

No it wont last as long as a proper roof either.


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## roofermann (Jul 7, 2012)

Awesome answer, Sgt.:thumbup:


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## gjam (Feb 3, 2015)

*Thank you guys.*

those responses were exactly what i was hoping for. Thank you for the advice. Bottom line is the building owner wants to be dry but underestimated the costs of the reroof when he decided to buy. Based on the info here. the metal roof is not a viable option and i will advise him to do it right and suck up the costs if possible. Thank you again!
Gene


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## 1985gt (Dec 21, 2010)

I should clarify my self a bit. I absolutely love metal roofing, I really enjoy copper and have done some built in gutters ect with it. I think standing seam metal is really good in the right application. Even exposed fastener metal roofing has it's place, we have done a number of them on our local parks department picnic shelters and storage sheds where if there is a leak it isn't the end of the world. 

Now on a building that had expensive machinery in it I would consider a standing seam if the slope was right, but they often are more expensive then other methods. 

Now in this case if I was bidding the job and looking at a budget minded solution I would suggest removing the rock, installing a coverboard (1/2" HD ISO) and then installing a Rhino bond TPO system. It is a non penetrating mechanically attached system. This of course assuming it is a metal or wood deck. Now if it's concrete, Tecktum or Gyp deck I would scrape the gravel, mop a coverboard and something like a 2 ply SBS or another 3 ply and gravel.

Good luck on your project and remember, cheaper is generally never a good option. It's cheap for a reason.


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## 1985gt (Dec 21, 2010)

I also should have added in my original post, those prices were taken from the Menards web site, price always varies!


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