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Community and Q&A

Hanging common rafters from top plates vs double bird’s mouth

kbentley57 | Posted in Energy Efficiency and Durability on


I’m nearing the completion for the planning of a 10’8″ x 13’4″ monoslope shed, and I have a question concerning the roof.  With the tall side being 10′, and the short side being 8′, I’m planning for a low-slope snap lock metal roof, with 2’x8′ rafters spaced 16″ OC.  The framing will be 2’x’6, with 7/16 Zip sheathing, 2″ rigid insulation, and James Hardie siding.

Is there a mechanical difference between hanging rafters from the inner dimensions of the walls, with ridge rafter strong ties, vs having a longer rafter for complete overhangs, with two bird’s mouths cut in?  I know that span/load is only calculated by clear span, and this method would allow me a short list of benefits if there are no issues.

(1)  Purchasing shorter lumber / less waste
(2)  Easier material handling and transport
(3)  A reduced number of hurricane straps that I was planning on using anyway
(4)  Lower roof line for a constant outer dimension maximum height
(5)  Ease of full-envelope insulation with eaves made of smaller lumber on insulated roof detail

A penny for your thoughts?

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  1. Expert Member
    Akos | | #1

    Either one works just as well. It all depends on how much overhang you need and how you'll construct it. Generally it is easiest to build overhangs with the rafter tails, thus the bird's mouth.

    I've done roofs with hangers where there were no overhangs. In that case the hanger install is much simpler. Just watch your hanger heights otherwise the roof deck won't sit flat over the top plate.

    1. kbentley57 | | #2

      Thanks Akos.

      I've got that detail yet to work out, good catch.

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