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Rafter tails: protecting roof sheathing from water damage

pdadamery | Posted in General Questions on

Hi,

We’re building in central Virignia, Zone 4. We are going to have exposed rafter tails. I’m sistering 2×6 tails onto 2×8 rafters–much like the attached detail I found on the web. I’m concerned about water getting between the T & G and the sheathing and causing problems beginning with the underside of the sheathing. Should I be wrapping the underside of the sheathing before I put it down and if so, what should I be using? House wrap, something like Grace Ice & Water Shield, drainable housewrap?  I’d appreciate any thoughts.

I’m note sure if it’s applicable, but we are just venting with gable vents, so negotiating soffit venting is not an issue.

Thanks,
Phil

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Replies

  1. Expert Member
    MALCOLM TAYLOR | | #1

    Phil,

    I wouldn't worry about your detail. The eaves-flashing will cover both the sheathing and t&g. There is no reason for water to get in between the two.

    Make sure to point that detail out to your roofers. They will need shorter fasteners for the first few courses so they don't come through the underside.

  2. GBA Editor
    Brian Pontolilo | | #2

    Hi Phil,

    I agree with Malcolm. That's a pretty common detail, with a few variations on how to execute it. Here's an example with lots of great details from FHB. It was done on a truss roof, but would work on a cut roof as well: Elegant Eaves for a Truss Roof

  3. Expert Member
    Peter Engle | | #3

    Phil,

    When Malcolm talks about "eaves flashing," that cean refer to several different products. In your area, Ice & Water Shield is probably not required by code, but it is still a good idea, and it will protect the sheathing in this area very well. You also want to make sure that the roofers use edge metal (drip edge) flashing that covers both the edge of the sheathing and the T&G. A drip edge with a small kickout to divert water into the gutter is best.

    One note about your attic: Check your local codes for ventilation. It can be difficult to meet the code requirements with just gable venting. You will need vents that provide a net free vent area 1/150 of the attic floor area.

  4. Seabornman | | #4

    I think it's wise to add a piece of trim to push your roof edge out just a little and to cover the edge of the t&g. It is important to protect the cut ends of the rafter tails. It will also straighten out that edge that can have a tendency to wander without support.

  5. pdadamery | | #5

    Thanks, everyone. Your responses are really helpful. Peter, I went back and double-checked on the gable venting and we'll be fine given the 1/150 ration. Thanks for jogging my memory on it.
    Phil

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