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Ragwrite 09-17-2013 06:10 PM

Dormer without rafter sistering?
Thanks all for a great forum. I'm hoping to add a small gable window dormer to a finished attic so it can be deemed a bedroom for resale purposes. House was not built to code (no clue how they got it past county inspectors...) so it's an iffy proposition, I think.

Downsides - 2x6 upstairs floor joists (:eek:) w/ 16 inch spacing so I can't set the dormer on these, no way to set dormer front wall over exterior bearing wall (has to set back a few feet due to a partition half wall upstairs), rafters are 16 feet long on a 7/12 pitch (hip roof, structural ridge), upstairs is all finished and has the half wall so sistering rafters would be very difficult.

Upsides - rafters are 2x8, I only need to cut ONE rafter for a small window (maybe 28x36 window or something close), dormer will be small because of the 40 inch high half wall it doesn't need to go floor to ceiling, part of the dormer area is above a first floor interior bearing wall.

The big question - can I safely cut one rafter and set a small dormer bearing entirely on the 2x8 rafters without sistering additional rafters? Front wall would be about 6 feet from rafter heels, side walls directly over existing single rafters 32 inches apart.

Any advice would be much appreciated. Many thanks for your consideration!

oh'mike 09-17-2013 06:15 PM

I've seen that done on cape cods---and the result was a sagging roof--so NO don't try that----sorry----

joecaption 09-17-2013 06:20 PM

If you do not mind a sagging roof, skip the most important part of sistering.
I've seen the outcome and it's not pretty. I have a customer that's been trying to sell a house for 4 years, no one wants it because of the sagging where the dormers are.

Ragwrite 09-17-2013 06:34 PM

oh' mike and joecaption - thank you both for the replies. Sounds like I would be headed for trouble. Do you think just sistering 2x8 rafters at this length/pitch would do the trick if I could find a way to get them in there?

oh'mike 09-17-2013 06:48 PM

That should do it--along with the rest of the proper roof framing for a dog house---I've got several old books that show the framing---you should be able to get a framing book at the library----

This is not advanced carpentry---but must be done correctly--valley rafters are needed to create the opening and support the connections.

joecaption 09-17-2013 06:55 PM

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