Minimum roof slope for steel framed warehouse building?

[clarke1973]

I am designing a very large (90m wide x 300m L) steel portal frame warehouse structure with roof pitch along the center. The building is located in the Middle East and the local building regulations have no guidelines on minimum roof slope for storm water drainage. normally I would consider 5 degrees to be reasonable but the Architect wants to go as low as 3 degrees to allow easier access. Does anyone have any advice on this? I couldn't find anything in the IBC although admittedly I did not have a very detailed look through it..

Thanks

 

[OHIOMatt]

The IBC minimum required roof slope is 1/4" in 12" which is about 1.2 degrees for a membrane roof. If you are using a metal panel roof, then you may need to go steeper. The code may still have a provision for hot mopped asphalt (but I cannot see this being used in the Middle East).

What kind of rain fall rates are you looking at?

 

[ajh1]

IBC limits metal roofing to 1/2:12 for lapped through-fastened panels and 1/4:12 for standing seam panels.

 

[clarke1973]

Thanks Matt. It will be lightweight metal deck roof on purlins. Have no idea of annual rain fall rates in Qatar but I know that when it does rain it is like a tropical rainstorm, but only rains 5 or 6 days per year.

 

[civeng80]

I designed and built many portal framed building in Australia with fairly low rainfall. 5 degs is considered a minimum for metal roof thats fixed by screws to purlins (corregated profile).
3 deg and actually down to 1.5 deg is satisfactory for deck with conceled fixing clips and shouldn't present any problems.

 

[hokie66]

The selection of roof slope has to go hand in hand with the selection of roofing profile. There are many steel roofing profiles, by a number of manufacturers. Before using a profile in a given application, advice should be sought from the manufacturer. Steel roofing is just a series of small valleys or gutters, and overtopping these gutters often causes leakage due to capillary action. Concealed fastener systems can accommodate lower slopes, but they also generally require steps at the ends of sheets. As well as consideration of slope, the length of run and the intensity of rainfall will determine if a given profile can carry the volume. Follow the manufacturer's recommendations.