Best way to build out 2x4 rafters?

I've got a portion of a roof built with 2x4 rafters. I'm trying to stuff R30 in the space with some airspace-savers underneath, which would normally warrant 2x10's instead. What would be the best way to build these 2x4's out to the depth I need for my insulation? Running 2x10's next to the 2x4's would be annoying, but is the only answer I can come up with. Any suggestions? Any possibility of getting away with 2x6's attached to the face of the 2x4's? Thanks for the advice!
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Rip lengths of 2x4 in half or purchase 2x2 or 2x3 stock and screw to 10" wide lengths of plywood or waferboard, screw the plywood to existing rafters. Nailing surface stays in the same plane.
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beecrofter wrote:

You beat me to it. This is the simplest solution. It is also the least expensive, easiest to install, and overall, gives a very good end product.
--
Robert Allison
Rimshot, Inc.
  Click to see the full signature.
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You could use truss plates or something similar to attach 2x6's. Or some kind of huge staples maybe, since it isn't structural.
Bob
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I'm not 100% sure I understand your problem but a few comments, just the same.
If you are insulating an attic and you are not planning to occupy it, the easiest solution is to put the insulation on the "floor". If you are going to make living space, only then do you need to worry too much about having something to nail to.
If you are "stuffing" insulation where the roof meets the walls, it is probably better to cut out some of the insulation. A smaller amount of insulation tha is "fluffy" is better than a lot that is compressed.
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I don't understand why you need to add wood to add insulation. The insulation doesn't have to be between anything. Just put 3.5-inch insulation between the rafters, then run more across (assuming you are using roll fiberglass) over the rafters, holding it in place with lightweight wire or some such. I also wonder if you mean rafters or joists. -- H
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wrote:

You only put insulation in between the ceiling joists, NOT the rafters.
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guys, thanks for the answers. this is a cathedral ceiling, so the insulation will have a very small space between the ceiling and the roof decking when all is said and done. the rafters (they are rafters if they hold up the roof decking right?) are only 2x4's but now i plan on attaching 2x6's using some kind truss plates to provide enough space for R30.
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