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Extending rafter tails

GOLDENBOY's picture

I am actually faced with two jobs where clients want to extend rafter tails.  The attached file shows a deck with a shed roof.  In order to reduce rain getting on the deck, client wants to add length to rafters.


The rafters are birdsmouthed an bear on a beam.  Is there a ratio for acceptable cantilever? 


For example overhangs on gable end of roofs are usually framed with lookout rafters.  The overhang is equal or smaller than the length of rafter inside the wall. 


Any thoughts on how to make this work appreciated. 

(post #78842, reply #1 of 8)

Tried to attach a pdf.  Here goes again!

(post #78842, reply #2 of 8)

Maybe no one has ever tried this before.  No info coming in.


Thanks in advance for any help.

(post #78842, reply #5 of 8)

Two in for every one out is the rule my engineer will stamp when we do ornamental rafter tails.

(post #78842, reply #3 of 8)

I'd follow the 2:1 ratio.  2ft in for every 1ft out.  So if your extension were to go 3 ft from the top plate I'd have 6 ft inside.  Seems a bit excessive but you don't want it sagging.  Might be able to get by with as little as 1:1 if you don't have a snow load.  2:1 will pretty much have no call backs for being weak. 


How you going to attach them?  Is the ceiling open?  You ought to be able to slide them in with the fascia removed but... how you going to attach them to the adjacent rafter?  You might be tempted to let them fit tight in the opening but any load on the extended tail will try to lift the roof deck, and will eventually be successful in removing the decking. 

(post #78842, reply #4 of 8)

Maybe sandwich two tails on existing rafter?  Clamp, if possible, and through bolt? Just a suggestion, I don't think you would need the 2:1 with this.

(post #78842, reply #6 of 8)

If you are looking to make long extensions you might want to consider a second plate with birdsmouth seats on the extensions and knee braces from the porch posts to hold that up. Where are you located-Think about snow load on those tails.

(post #78842, reply #7 of 8)

Thanks, guys.  I will go with the 2:1 ratio.  Access or attaching the new tails to existing rafters is not a problem. 


Yes snow us a consideration.  3.8kPa (80lbf/sf) 


How to attach?  Thru bolting seems like a lot of work.  Also I find bolts just split the wood in situations like this, unless there are lots of bolts. 


I'm thinking PL premium and nails.  Clamp before nailing.  Any thoughts?

(post #78842, reply #8 of 8)

Nails & glue would be how a cantilever deck on a house would be done so shouldn't be an issue with rafter tail extensions.  Clamping would make it better to ensure good glue adhesion & tight nailing. 


80lbs/sqft. Yikes!