2 Layers of Plywood on the roof ?

[Sam Morris]

Has anyone ever seen this before ?? This roof has the the first layer of plywood sheathing, a layer of shingles, a layer of plywood and the top layer of shingles (in this area 2 layers of shingles is acceptable) I have near seen this in 18 yrs. with 2 layers of plywood, How would you report this, call out a licensed roof to cover myself, but the roof looked OK a far as life is concerned. Thank you for your insight


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[Jerry Peck]

This roof has the the first layer of plywood sheathing, a layer of shingles, a layer of plywood and the top layer of shingles (in this area 2 layers of shingles is acceptable)

Sam, the reason for the limitation of 2 layers of roofing shingles is weight. The trusses/roof framing are not designed for the additional weight of a 3rd layer of shingles.

The second layer of plywood adds that additional weight.

Additionally, how is that second layer of plywood fastened in place? A) To the shingles below? B) To the first layer of plywood below? C) To the trusses or roofing framing below?

Neither A) nor B) are correct.

Option C) may ... may ... may be correct ... with the appropriate fasteners (sufficient in size and long enough for proper embedment into the supporting framing. But then there is the question of 'how many nails are too many into the framing'?

The only solution for your protection is to refer to a structural to provide a signed and sealed engineer's letter stating what needs to be done. "What needs to be done" leaves it to the engineer to state "nothing needs to be done", which would be crazy, but engineers have their own rules, all you can do is to write it up as have engineer provide a signed and sealed engineer's letter.

Then it is up to the eningeer.

[Sam Morris]

Yes that makes seen to me, 2 layers of shingles is acceptable here, but not 2 layers of sheathing.

[david shapiro]

The dual issues of load-bearing capacity and securement look mighty similar to structure-related questions involved in adjudging the safety of adding roof-mounted PV arrays.