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Extending gables to make overhang for foam

user-669103 | Posted in Green Building Techniques on

In a few weeks I start the reroofing and while reroofing I will extend out the gable ends of two roofs so that I have enough overhang to fit 4″ of XP on the outside of the walls below.

One extension will be limited to 5 or 6″, and the other can be anything I like (probably 16″).

There are two ways that I know of to extend the gable:
Both are illustrated here:

1) Barge rafters (which attach blocks to the end rafter and build out).
2) Lookout rafters (which notch the existing end rafter to fit a 2″x6″ or 2″x4″ to extend out the roof)

Is one method accepted as better than the other?

My current plan is to use belt, braces, and a piece of string (at least for the 16″ extension).
That is to say, make a lookout rafter, but fit the blocking too, with the blocks fitted with steel hangers on the old end rafter, and spaced between the lookouts.

Also for the lookout, is it best practice to bring the lookout in one additional rafter?

Also if using lookouts because the existing end rafter has been notched and weakened, should one sister a smaller rafter to it (i.e. if existing is 2×6 sister a 2×4). The rational is that the smaller sister won’t have to be notched and strengthens the weakened rafter.

I do have a professional roofer to do this, but I am working very closely with him (50% of roofers weren’t interested in this job).

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  1. GBA Editor
    Martin Holladay | | #1

    The book to which you link points out that the lookout method is preferred to the blocking method for overhangs over 12 inches; in other words, the lookout method is stronger.

    There is a third method — using blocking that extends back as far as the lookouts in the illustration. The last existing rafter is eliminated, and the gable wall plate supports the middle of the pieces of blocking, which are 16 inches o.c., running from eave to ridge. This method is very strong but not suited to retrofits.

    It sounds like you're on the right track. Good luck.

  2. matt9923 | | #2

    I am planning to add 2-4” of exterior foam to a home without any gable overhang. My thought is to pad it out with 2x and wrap it with flashing. The roof is only a few years old, so to tear into it to extend the rakes 4” is a hard sell and will be hard to match.
    Any thoughts on this aproach? I have searched everywhere with no real answers or pictures.

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