Replies

1. 
   DanH | May 24, 2017 01:46pm | #1

   Problem is, a given piece of green wood could dry straight as an arrow, or it could curl up like a corkscrew.

2. 
   florida | May 24, 2017 02:45pm | #2

   It will certainly shrink and possibly will warp. If you have time buy them gree and oversize and cut to the finish size in 6 months to a year. If you can't wait I'd suggest rough cedar as it's usually cut oversize and may work as is. It moves less than the other woods you mentioned.

   Are you replacing rotten rafter tails that need to match?  If so all you need to do is scab them along side the rafters with the rotten tails. It throws off the layout a little but is quick and easy.

3. 
   oldhand | May 24, 2017 10:12pm | #3

   Why do you need green wood? If you need full dimension wood specifically, local mills may have some semi air dried stock around. 

4. 
   user-6825730 | May 25, 2017 07:37am | #4

   I'd like to build a roof over the old one to add some overhangs to the existing. 

   Those are great tips. Thanks.

   I can buy 2x10 Douglas fir, let it dry till next summer and cut to 2x8xrafter length. Probably the best option. 

1. 
   oldhand | May 25, 2017 05:32pm | #6

   2 more reasons..

   Besides being crazy heavy green rafters or joists are plastic more than stiff and will usually sag under their own weight. Once the boards are dried the sag is difficult or impossible to straighten.

5. 
   finefinish | May 25, 2017 01:06pm | #5

   Hey there, I think it is still a little unclear what you are trying to do...  If you are building a new roof over an existing, meaning stacking new rafters right on top of the existing, then I am not sure why the dimension matters..  If you are simply trying to extend the rafter tails to add an overhang then, like Florida suggested, just scab onto the side of the existing and create the overhang that way.  As for green lumber, it will definitely shrink as it dries but this may not matter depending on what the roof trim is.  It shouldn't affect the roof deck or shingle appearance either way.  Also, if the new rafters are actually structural you CAN NOT rip them to a specific size.  In other words you can not buy 2x10s and rip them to 2x8s.  Same goes for floor joists, etc.  When lumber is inspected and stamped at the mill, knots, checks and other defects have to be so far away from edges etc.  If you rip an edge off, effectively moving one of these defects closer to that edge, you will potentially destroy that member's structural integrity.  That is why ripping framing lumber is not allowed.  Sure, rip whatever you need for blocking, fillers, etc, but not for anything that will get loaded.  Good luck and if you haven't gotten the answers you need circle back around with a little more information.  

6. 
   DanH | May 25, 2017 07:16pm | #7

   I'll note that there are several commercially-available treatments/coatings which purport to greatly reduce the amount of shrinkage and warping that occurs in green wood.  If you do undertake this project, using green wood, you might want to employ one of these -- they presumably do some good, even if not the magic they promise.

1. 
   florida | May 26, 2017 01:25pm | #8

   Are there really? Please tell us what they are becuse in my 45 years of construction I've never seen nor heard of one. I know my firiends in the sawmill business who deal with cracks and shrinkage every day would love to know. Did you see the ad on late night TV?

1. 
   DanH | May 26, 2017 02:37pm | #9

   Sorry, but I no longer subscribe to the magazines where I'd see these advertised.  But Google finds several products, such as this one: http://www.woodworkingshop.com/product/sk60000/  And deck coatings are often claimed to have the appropriate properties.

1. 
   florida | May 28, 2017 03:26pm | #10

   Magazine ads? LIke I said, late night TV has all kinds of amazing things advertised too, it's just that they're fake. How about the only thing that matters? Whats your personal experience with products that stop wood checking and splitting?