Is there an optimum house roof pitch to withstand strong winds?

Question

I'm considering a metal hip roof for a new build with a rectangular footprint (no valleys) and the wider sides will face north and south.

There doesn't seem to be much of a consensus among home builders on the internet, except perhaps a recommendation for moderately pitched roofs in the range 4/12 (18.43 degrees) to 6/12 (26.57 degrees). Some home builder website suggestions include 15 to 20, 25, or 30 degrees for the best roof pitch to withstand strong winds. Wikipedia (https://en.wikipedia.org/wiki/Hip_roof) mentions an angle greater than 35 degrees is necessary for hurricane regions.

Answer 1

0.6° or 1% (1:100 slope) (normally considered "flat" but you need some slope for water to run off) would be "best" for winds (least exposed area to wind pressure) and indeed you'll find plenty of flat concrete roofs in the tropical hurricane belt.

Flat roofs are less than ideal on other considerations - as with most things, you have trade-offs.

Answer 2

Structural engineers base their calculations on the “exposed side” of a building. That is to say, the higher the roof, the stronger the building (material and connections) need to be.

Also, most roofing manufacturers require additional membrane protection under metal roofing or shingles when the roof slope is less than 4:12.

Also, buildings less than 3:1 in length to width can use the standard structural values for wood and steel. When you exceed those dimensions you need to use different values and provide additional connections to transfer the loads to the groud, such as blocking all edges of wall sheathing, diagonal bracing, etc. (See IBC Table 2305.2.3)

Likewise, special requirements are required around large windows and doors, especially if there’s more than one window or door on the short side.

Answer 3

I am not an expert but the optimum pitch to minimize uplift (for a single storey dwelling with a hip roof) would likely be around 20 degrees (e.g. https://link.springer.com/article/10.1007/s40091-019-0227-3 ; http://web.mit.edu/parmstr/Public/NRCan/CanBldgDigests/cbd068_e.html). A steeper slope like the 35 degrees suggested in the Wikipedia webpage might be useful in hurricane regions but elsewhere the additional expense may not be justifiable. Also, wind uplift pressure generally increases with angles greater than 45 degrees and with angles smaller than 20 degrees. A flat roof (<10 degrees) would experience the greatest suction effect but as Ecnerwal, Lee Sam and crip659 point out a roof's resistance to being torn off also depends on building materials and other structural factors.