Daughtering Vs Sistering Rafters

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Old 10-31-2007, 05:28 AM   #1
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Daughtering Vs Sistering Rafters

Hi... I'm talking with someone about an attic conversion, and the existing rafters are randomly spaced (around 24" OC) 2x6's. It's an old house.

They must be brought up to at least 2x8 -- and I am wondering how other people have done this. I see two ways - to sister on 2x8's or better, or to "daughter" ripped strips or 2x3's on the flat to add another 1-1/2 inches.

To daughter on strips, I think a nail is necessary every 8 to 12 inches, to prevent any buckling or shifting of the new piece against the old, to provide the beam strength.

Sistering could be a little hard to fit the rafter in place -- although I think you really don't need to extend all the way to the ends to add the 2x8 beam strength, as long as the old beam ends are solid, could hold it back 4 inches from each end if necessary. Also, maybe to hold it down from the roof sheathing by an inch would be helpful, because of protruding nails.

Any experienced opinions, or just thoughts on it?
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Old 10-31-2007, 06:07 AM   #2
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Re: Daughtering Vs Sistering Rafters

I don't believe the daughtering will help any. I've always gone the sister route. If I find the rafters are not over the studs, I put new rafters over the studs. ( Believe me, I've seen quite a few of those in the 19th. centur houses in Va.)

And I have held sisters below the decking when necessary, but it isn't my favored way. But it will work.

BTW- Wouldn't 1x6's between the existing be code. You'd have rafters every 12". But, wouldn't help any sags!


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Old 10-31-2007, 06:34 AM   #3
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Re: Daughtering Vs Sistering Rafters

I'm with Tinner, sisters. Firring is mostly cosmetic. Most of those deals we are out to isolate the new floor joist from the old ceiling as well, so I've cut the rafters short enough to allow sliding in a 2X at each end. one on the plate, that will raise the floor joist, and one at the ridge--if she even has a ridge. PITA but it has worked. End nippers and a Dremmel are the best I know for all those f***in nails.
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Old 10-31-2007, 06:50 AM   #4
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Re: Daughtering Vs Sistering Rafters

Because it's sometimes difficult to tell stability and age I stay away from daughtering ........I just go ahead and stick to doing sisters.
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Old 10-31-2007, 06:20 PM   #5
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Re: Daughtering Vs Sistering Rafters

I've seen some obvious big splits in old framing including rafters. Especially common in old floor joists that were pocketed in with a notched out bottom half. Anything like that I would repair in the rafters as well as daughtering, but from my experience with lamination I still feel like daughtering does add almost the same strength as the full solid width of wood -- given enough fastening strength to the old.

In terms of cosmetics, we would strap out the ceiling horizontally, shimming as required to plane it out.

If I were to sister, I still think it would be fine to hold it out from the sheathing an inch, to avoid that experience with the end nips. Ouch! My hand is cramping just to think about it!

Thanks for the opinions.
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Old 10-31-2007, 06:38 PM   #6
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Re: Daughtering Vs Sistering Rafters

This daughtering is not nearly as strong as the sistering. Are these rafters sagged or is the extra space for better insulation?
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Old 11-02-2007, 12:52 AM   #7
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Re: Daughtering Vs Sistering Rafters

2x4 plus 2x4 does not = 2x8. your not talking about laminating, a nail every 8 or 12 inches is not going to give you the kind of strength you get in a laminated glulam. The only way to gain the strength that you need is maybe lots of glue and biscut joint it every 4 inches but what for? sister it
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Old 11-02-2007, 05:11 AM   #8
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Re: Daughtering Vs Sistering Rafters

We did on old home once that we furred out with 2X4's flat on the existing rafters....and we drilled and screwed them, rather the nails, because of the age of the old wood. Worked great, and that is "daughtering", although that wasn't the intent at the time.
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Old 11-02-2007, 05:57 AM   #9
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Re: Daughtering Vs Sistering Rafters

Neo's got it, including the block at either end to relieve pressure at the center of the ceiling in the room below. The only downside is the transition from floor heights, which may be around half of a step.
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Old 11-02-2007, 12:44 PM   #10
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Re: Daughtering Vs Sistering Rafters

If the intent is not structural but to add insulation and get a smooth/level nailing surface, I'd do firring strips of 2x 18" OC. You get 1) better insulation isolation, and 2) a consistant nailing surface for sheetrock or whatever. 24" OC would mean 5/8 rock and if they're randomly spaced... uggh.


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