minimum roof slope?

[BauTomTom]

Hi

Is there actually a minimum slope for one family houses?

i saw now a architect plan with only 3 degree and somehow it semas for me quite little.

Does the BS or SABS says something to this topping?

Tom

 

[msquared48]

For flat roofs, 1/4" in 12 is the minimum for any drainage.

As for the roofing material:

Shakes and Composition - 4:12 and higher... 3:12 is very questionable aid I would not use it.

Metal roofs: 1:12 and higher are common.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[MiketheEngineer]

As M^2 suggested.

Check w/ mfgs of the roofing material to be used for confirmation - otherwise your warranty will be "null & void" as they say.

 

[cvg]

my house has a flat roof. I can't emphasize enough, 1/4 inch in 12 inches is not recommended! Recommend more to avoid ponding and leakage...

 

[ToadJones]

Flat roofs work great in deserts.

 

[BauTomTom]

Hi guys

ooouu ja is true the material is important of course that you will need a bigger slop by a roofing tiles then by tar paper

in my case it is a corrugated iron roof sheeting

 

[hokie66]

You may find this Australian reference useful. For traditional corrugated steel roofing, 5 degrees or 1/12 is the recommended minimum.

http://www.lysaght.com/files/dmfile/CustomOrbCombinedSept2010.pdf

 

[csd72]

We have used 3 degrees and even 1 degree on steel roofed industrial sheds but you do need to do a ponding calculation to prove that the deflection will not exceed the slope.

This works where you do not have a risk of snow/ice dams but where you do then I would expect that the 1 in 12 stated above would be a more realistic minimum.

 

[hokie66]

Different roofing profiles will accommodate lesser slopes than the corrugated sheeting mentioned by BauTomTom. For a concealed fastener system, you can get down to 1 degree, but the other variable which must be considered is length of run. None of the Lysaght data I referenced is appropriate for snow and ice, and hail is also a problem.

 

[cvg]

flat roofs do not work that well in deserts, it rains here too. again, you are doing a disservice to the owner by designing to the minimum slope.

 

[MiketheEngineer]

Even steel roofing has minimums set by the mfg. Don't forget - it will have lap joints somewhere and I guarantee that sealant of any kind will eventually fail - may take 20 years - but it will fail!!

 

[csd72]

Yes, agreed, I forgot to mention that.

 

[a2mfk]

2:12 for composition shingles is the minimum in many US codes, which makes it the minimum for many residential roofs here since shingles are by far the most common roof covering..

I agree with the others recommendations also, the more slope the better with any roof, especially if you receive a lot of precipitation in your area.

 

[BauTomTom]

Hei guys

thanks a lot to everybody. You all gave me good ideas. I also found something very usefull for me. I found a book is called
"building constructions and graphic standards" from andre Grobbelaar

this is based on the BS and SABS code and applies here for the southern Africa. They have a table for the roof pitch.
so ja 5 degree is the minimum but the overlapping must be 250mm and sealed. I change the pitch rather to 10 degree now. This would mean sealed laps 150mm or 250mm unsealed.