2x6 Birds Mouth and a Collar Tie Question


Old 04-10-12, 11:10 AM
Thread Starter
Join Date: Mar 2004
Location: Southern NJ
Posts: 137
Question 2x6 Birds Mouth and a Collar Tie Question

Hi Everyone,

I'm building a carport onto the side of a detached garage. It will be 9 1/2 ft wide, 40 ft deep, and a roof with 3/12 slope. The plans have already been submitted and approved for using 2x6 rafters 16" OC. They will attach to a ledger board on the garage side and will rest on doubled 2x12's on the outward side. My question is whether or not it is ok to cut a birds mouth into a 2x6 rafter? It wouldn't be a very deep cut since it's only a 3/12 slope. And It will only have a 4 inch overhang because it is getting close to the neighboring property (once you add the fascia and gutters in). So is a birds mouth the way to go or should I use some kind of bracket?

A second but related question, the plan I submitted does not include collar ties but I'm wonder if I should include them. Again, the roof slope is relatively shallow so it won't be far from square anyway. But should I include collar ties periodically? If so, with what size lumber and at which spacing?

Thanks for your recommendations!
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Old 04-10-12, 07:35 PM
Join Date: Mar 2009
Location: WA
Posts: 1,167
If the approved plans don't call for rafter ties to meet up-lift requirements at the beam, just cut the birds-mouths, they will only be 7/8" deep at the plumb cut to seat the heel of the rafter on the bearing; Fig. 19; Troubleshooting Guide to Residential Construction - Google Books

I suggest shear hangers to keep the rafters tight to the ledger board with a heavy snow load; LUS/HUS Double Shear Joist Hangers

Collar ties are to prevent rafter peaks from blowing off in a high wind. The hangers above with nails below should meet local Code, ask them.

Old 04-11-12, 08:28 PM
Thread Starter
Join Date: Mar 2004
Location: Southern NJ
Posts: 137
Thanks Gary, the link is helpful and interesting! And that does answer my question about the birds mouth.

Maybe collar ties aren't the correct term for this. What I meant was a "level" board running from the outside edge of the beam/header to the garage in order to form a triangle. Maybe it isn't a collar tie because it's not on two pitched roofs. Nonetheless, I guess you're saying I don't need them.

Thanks for your help!

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