Friday, July 8, 2011

How to slope and vent a flat roof

The roof is built flat out of the roof joists that you can see in our earlier posts.  Once all the seismic and blocking has been installed we begin to slope the roof.  To create a slope we cut long tapered pieces of 2x4 and nail them to the rafters.  I like to have a minimum of 1/4" per foot of slope for a roof.  Any less and you will have puddles.  You can see this in these pictures; they are sandwiched on top of the rafters but under the 2x4 strapping.

This shot highlights the 1 1/2 " airspace needed for air ventilation

After the slope have been created we cross strap the roof for air ventilation using 2x4s on flat. They bend nicely when you stand on them while nailing them down. Finally, you sheet the roof using tongue and groove plywood and presto you are ready for the roofers.


  1. In any instance, ventilation is very important. Aside from the fact that it is not normal not to have it in our house or in any establishment, it also have a very good purpose.

  2. ronse massey developmentsAugust 1, 2011 at 5:37 PM

    I might have a great shot of what happens to a roof that wasn't vented.