Timber Framers Guild Forums General General Forum Questions Timbers cut 6x8 or 7x7, what difference in joints/strength

I am having some spruce timbers milled in the next few days. Some of the sawlogs don't have the small end diameter necessary for the 8x8 timbers I had planned for( 16 x 24 ft tall post frame). If I reduce the timber size, should I go with 7 x 7 or 6 x 8. These will be used as common rafters and or top plates. All other timbers will be 8 x8, and 8 x10 (main girts). Any suggestions appreciated. This is my first project and I anticpate modifiying the frame plans accordingly. Thanks

6x8 would be plenty for a common rafter... probably 4x8 would be enough...

If tip diameter won't yield you 8X8's and you already have enough rafter stock, you might consider going to 7X7's in your gable bents. They are carrying less load than the posts in the inboard bents and in that you are not joining pieces from both sides the smaller section does not compromise joinery.

If you havn't already planned on it, milling your brace stock FOHC is a worthy end use for these butts.

A little wane never hurts either !

Be your best

Hi Chance.

Form a strictly engineering standpoint, a 6x8 is stronger than a 7x7, at least in bending and deflection. Although intuitively I agree with Mark that either is strong enough, one should do tha math that takes into account the rafter spacing and span. Personally, I prefer the look of a rafter with a rectangualr cross section over a square one. Good luck with your project. CB.

Thanks again for the responses. The timbers are milled, and all but 4 of the logs produced the 8 x 8's that are reqired. Unless I have to reject more than a few, there should be enough. The 4 smaller ones produced 6 x 8's. The majority of the timbers have the heart well centered. Should I be concerned about the few where the heart is noticably off center?