A client is having a new roof installed and in the process will abandon the passive pancake vents currently in place and replace those with a ridge vent. Can the roof sheathing be cut out that contains the hole for the passive vent and replace that with a new piece of sheathing without a hole. Can that new piece of sheathing span from one rafter to the next or must it span more than two rafters?
If its going to only span the area that the hole was in, it’ll need supported underneath, otherwise your going to fall through when you step on it. 3/4 overlap on a rafter isn’t going to hold the weight up.
Yeah, well after asking the question I did find that “OSB by Design by the Structural Board Association” does say that all panels must be continuous across 2 or more spans which would be 3 rafters.
Yes Mike,
A rectangular piece of sheathing is cut out slightly bigger than the hole to be patched and solid blocking is added at right angles to the rafters and nailed. Somewhat like lader framming that we see on overhangs.
A new piece of sheathing is then nailed on all four sides and well supported.
When it is a small hole like a vent, one slides a piece of furring through the hole and screws it through the sheathing on both sides and then a plug is set in and screwed to the furring underneath.
Hope this helps. 
Exactly, Marcel…have done it many times with no problems.
OK, that seems to make the most sense even though it doesn’t quite comply with the OSB Design Guide I referenced. The rest of the story is that the client (not my client btw but rather another local inspector’s) is an ‘engineer’ of some persuasion and is adamant that the new sheathing span 3 or more rafters. The roofer was planning to use the blocking method but the client wouldn’t hear of it. No big deal and not really an inspection issue…just another example of me and the other inspector wanting to know the best and/or most industry accepted practice in this case. Thanks.
Yep, what the senior member from Maine said 
In reality spanning 3 rafters is much stronger, but it ain’t going to be done like that
Regards
Gerry
Also supposed to be a minimum width of 24 inches to achieve span rating. How often do you see those narrow strips at the ridge that someone stepped through?
A lot of the vent patches I see just have a piece of sheet metal nailed over the hole.
Nothing to add. Marcel, as usual, got it right.
There goes a couple more trade secrets.
Anyone have any documentation showing sheet metal repair is not permitted?
Thanks
How not to patch a vent pipe or hole in the roof sheathing.
Read the above posts for industry standards.