 |
 |
 |
 |
 |
 |
|
 |
 |
 |
 |
 |
||
Roof Decking
All roofing materials must be installed over sound roof decking per Building Codes and manufacturer's Installation Specifications/Instructions and Roofing Manufacturers Associations' Installation Manuals/Handbooks.
As an example: From the Asphalt roofing manufacturers Association
(ARMA) Residential Asphalt Roofing Manual
Design and Application Methods 2014 Edition "The
underlying structure should provide a rigid deck surface. It
should not sag, shift, or deflect under the weight of roofing
materials, the worker installing materials, or the snow or rain
loads the roof may have to support."
See
https://www.asphaltroofing.org/arma-publications/
When replacing an existing roof covering many Contractors simply remove the existing roof covering and then install the new underlayment and the new roof covering without paying any attention to the poor roof decking. (See Slide Show below as an example of what we have found in the past.)
The proper installation of roof decking made of Plywood or OSB sheathing panels per Building Codes and/or the APA - The Engineered Wood Association is:
- All sheets of Plywood or OSB used as roof decking must be installed over a minimum of two spans between roof trusses/rafters or in other words be nailed to a minimum of three roof trusses/rafters.
- The roof sheathing panel used as stated above, "must be thick enough to provide a rigid roof deck surface. It should not sag, shift, or deflect under the weight of roofing materials, the worker installing materials, or the snow or rain loads the roof may have to support."
- All sheets of Plywood or OSB used as roof decking must be a minimum of 24" wide going up the roof slope.
- There should be a gap of approximately 1/8" (about the thickness of an 8d nail shaft) left between all edges of Plywood or OSB used for roof decking.
- Nail the roof sheathing panels with minimum 8d nails placed a minimum of 6" o.c. at the supported ends/edges of the panel and 12" o.c. at intermediate supports. Recommend nailing the middle of the panel first before nailing the bottom and top edges and both ends of the roof sheathing panel.
- Drive the nails flush with the surface of the roof sheathing panel - no over driven nails, under driven nails and/or nails drive crooked.
- Make sure that the underside of the roof decking is properly vented equal to or better than the Building Codes require.
See the APA - The Engineered Wood Association web site: https://www.apawood.org and their video at: https://www.apawood.org/roofs
Visit our
Roof Inspection Services
web page
and the many other web
pages throughout this website to find
answers to your roofing questions and
solutions to your roofing problems.
Page Revised/Updated 2/27/2023