Math Help

busterb · 01-04-2006, 11:15 AM

on slopes not less than 1/4" per horizontal foot. How much drop would that be in 25 feet? Would it be 25 times .25? 6.25 inches? If so the roof someone is trying to sell me is not recommended by this web site Here

Beestie · 01-04-2006, 11:29 AM

Think of it as a 1" drop per four feet of run. For guesstimates, there are six "four-feet runs" in 25' so make it a six inch drop. For precision, add the 1/4" for the extra foot (25 - 6*4 = 1) for a precise answer of 6-1/4"

1/4" per foot is basically flat. That's also, as I recall, the minimum slope for drain pipes making it the bare minimum angle to encourage the flow of water.

I assume you are not using shingles since the min rise to run for shingles is 3:12 (3 inches per foot).

What is the roofing material?

xoxoxoBruce · 01-04-2006, 11:48 AM

They're looking for positive drainage which they define as

Quote:

Positive Drainage: The drainage condition of a roof where all water is gone from the roof surface within forty-eight hours of precipitation during normal drying conditions.

So no low spots for puddles are allowed.
At least Modified Bitumen would be melted down and form a continuous cover unlike shingles which have to have more slope.

busterb · 01-04-2006, 12:14 PM

Looks like the answer is 25 times .25 for 61/4 or 6.25. What is the roofing material?
It's in link above thanks.

xoxoxoBruce · 01-04-2006, 03:56 PM

They're showing 3 different materials in that link, Buster.

Beestie · 01-04-2006, 06:06 PM

Quote:

Originally Posted by xoxoxoBruce

They're showing 3 different materials in that link, Buster.

Nor does it explain why what he is being "sold" falls short of what is being recommended. I'll see your

and raise you one

busterb · 01-04-2006, 07:28 PM

My bad all he put on bid was Modified Bitumen. So that's what lead me to look around.
A roofer, I'm not.

Elspode · 01-05-2006, 02:54 PM

I was in roofing for almost 14 years, Buster...what, specifically, are your questions on this roofing issue? The water evaporation within 48 hours thing is a stipulation for the sake of the warranty. Basically, you need enough slope to ensure that all standing water will drain off in that time. In reroofing situations, that is nearly impossible without replacing the substrate, because original roofing substrates sag unevenly over time, and you get "potholes" where the water will stand. 1/4" per foot average structural slope will *not* typically drain an older roof, but you can have a tapered insulation system installed to fix that. It greatly adds to the cost, though.

I assume you have some flat roofing involved, here, if you are looking at Mod Bit?

01-04-2006, 11:15 AM	#1
busterb NSABFD Join Date: Jul 2004 Location: MS. usa Posts: 3,908	Math Help on slopes not less than 1/4" per horizontal foot. How much drop would that be in 25 feet? Would it be 25 times .25? 6.25 inches? If so the roof someone is trying to sell me is not recommended by this web site Here __________________ I've haven't left very deep footprints in the sands of time. But, boy I've left a bunch.

01-04-2006, 11:29 AM	#2
Beestie -◊\|≡·∙■·∙≡\|◊- Join Date: Feb 2003 Location: Parts unknown. Posts: 4,081	Think of it as a 1" drop per four feet of run. For guesstimates, there are six "four-feet runs" in 25' so make it a six inch drop. For precision, add the 1/4" for the extra foot (25 - 6*4 = 1) for a precise answer of 6-1/4" 1/4" per foot is basically flat. That's also, as I recall, the minimum slope for drain pipes making it the bare minimum angle to encourage the flow of water. I assume you are not using shingles since the min rise to run for shingles is 3:12 (3 inches per foot). What is the roofing material? __________________ ♠ ♥ ♣ ♦

01-04-2006, 12:14 PM	#4
busterb NSABFD Join Date: Jul 2004 Location: MS. usa Posts: 3,908	Looks like the answer is 25 times .25 for 61/4 or 6.25. What is the roofing material? It's in link above thanks. __________________ I've haven't left very deep footprints in the sands of time. But, boy I've left a bunch.

01-04-2006, 03:56 PM	#5
xoxoxoBruce The future is unwritten Join Date: Oct 2002 Posts: 71,105	They're showing 3 different materials in that link, Buster. __________________ The descent of man ~ Nixon, Friedman, Reagan, Trump.

01-04-2006, 07:28 PM	#7
busterb NSABFD Join Date: Jul 2004 Location: MS. usa Posts: 3,908	My bad all he put on bid was Modified Bitumen. So that's what lead me to look around. A roofer, I'm not. __________________ I've haven't left very deep footprints in the sands of time. But, boy I've left a bunch.

01-05-2006, 02:54 PM	#8
Elspode When Do I Get Virtual Unreality? Join Date: Dec 2002 Location: Raytown, Missouri Posts: 12,719	I was in roofing for almost 14 years, Buster...what, specifically, are your questions on this roofing issue? The water evaporation within 48 hours thing is a stipulation for the sake of the warranty. Basically, you need enough slope to ensure that all standing water will drain off in that time. In reroofing situations, that is nearly impossible without replacing the substrate, because original roofing substrates sag unevenly over time, and you get "potholes" where the water will stand. 1/4" per foot average structural slope will not typically drain an older roof, but you can have a tapered insulation system installed to fix that. It greatly adds to the cost, though. I assume you have some flat roofing involved, here, if you are looking at Mod Bit? __________________ "To those of you who are wearing ties, I think my dad would appreciate it if you took them off." - Robert Moog

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