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Relocating purlin

Hi there. I'm in the process of remodeling a section of my attic into a bedroom. Or rather I'm in the final stages of the planning. Everything should be all set, however the purlins (I believe that's what they're called; the horizontal members going from one rafter to another on the opposite side of a gable roof) are in the way. They are 6 ft up from the joists. I'd like to relocate them about another foot up for headroom, for a total of 7 ft. I am aware that this may be a problem (roof sagging). However I am also placing knee walls (should be about 4 ft high) at 5 ft from the eave on both sides. Would this be enough to provide sufficient support for the roof? Also, I plan to sheetrock the entire area (knee wall to rafter to purlin, across the purlin, down the rafter to the knee wall). Would hanging the sheetrock from the purlins cause any issues? I'm aware of how what needs to be done (insulation-wise and whatnot) otherwise. Thanks.

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Posted 2011-06-02T23:47:11+0000  by GottaDIY GottaDIY
 

Hello GottaDIY.  Welcome to the Home Depot Community!

That’s an interesting project you are taking on.  Properly insulated, you have room for a nice living addition to your home.



Your attic area looks like it had good quality original construction.  The "purlins" you refer to I think would more properly be called either collar ties or rafter ties.  The rule of thumb is to locate these cross braces one third of the distance below the ridge.  These help prevent separation at the ridge, (as a tension brace), and also help prevent rafter sag from roof loading, (as a compression brace).  Many older buildings are constructed in this fashion.  Below is a simple diagram of common terms for roof construction:

 

GableRoof.gif

 

Here's where what you want to do gets interesting.  In theory, raising the collar ties to the 7 foot height and compensating for potential rafter sag by using knee walls as props should work just fine.  As long as the attic floor joists are properly supported by load bearing walls below, your plan makes sense.  Whether your local building inspector will see things this way is unknown.  Since you will need a permit to do the attic to bedroom conversion, here's what I recommend:

 

Make a simple drawing, with dimensions of both distance and lumber sizes of your current attic.  Make another with the changes you want.  Take both, (and your pictures), to your local building department and talk to an inspector about what he/she thinks you need to do.  My experience has been that this approach is greatly appreciated by local officials, and they will be very helpful in making your project go smoothly.  These people also know the local requirements that may vary from standard building codes.

 

Please don't hesitate to return with any other questions, or to show us pictures of your new bedroom!

I hope this helps,

 

Newf.

Posted 2011-06-03T14:28:04+0000  by Chris_HD_CHI
 
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