Settling allowance

[Bucksaw]

Using my self isolation time to do some cabin construction planning. 
I winter cut about 40 large eastern white pine and will be cutting to log length soon and removing and sawing when the snow is gone. 
I will be sawing to 8x12 and stacking/sticking on the 8" and covering with old metal roofing/ tarps for construction next spring. 
The questions I have are as follows: 

1) Should I cut over size to allow for shrinkage and if so how much to end up with 8x12 or close to it? 

2) How much settling allowance above doors and windows? 
3/4" per foot of log wall at 8-12" rounds is 6". 
Is this sufficient after a year or so of air drying?
The cabin will be 8x12 dove tail with a 1 1/2" chinking gap. 
Thanks!

[Andries]

So, the big black "covid cloud" has a silver lining; we can do a bit more planning and prepping. ;) 
My experience is with WRC log cabins 

and others with dovetail timber building will chime in for sure . . .
Answers:
1. Mill the logs 1" bigger to allow for drying down to 8x12. Some will warp and twist - over sizing will allow you to re-mill the twisters. If you plan on running a hand planer on the inner face, allow for that too. A smooth finish on the interior is easier to finish and maintain. 
2. When we build our log buildings, squash blocks of six inches for a wall is normal. Your dovetail building will dry out faster than rounds, but the final amount should be about the same. Having the timbers air dry for a winter will get you a headstart on the settling, but you can expect that to continue for a few years after construction. You're allowing the same amount for windows and door frames, right, by using key and slot joinery? 
3. (Bonus answer) When you're milling, choose the inner and outer faces. They'll probably be the faces with fewer defects and pitch pockets, etc. Use a thin kerf blade in a Skil saw to make a kerf in the bottom face. Then, as the timber releases inner tension and dries, most of the checking will happen on that face. The exterior face should be as check-free as possible, so that rain or snow doesn't promote rot. 
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Good luck,  and post as many photos as you can stand to.
 We love to follow along.

[Bucksaw]

"You're allowing the same amount for windows and door frames, right, by using key and slot joinery? "
Yes. 6" should be sufficient?
How deep should the saw kerf be in the bottom of the Timber?
Thanks!

[Bucksaw]

Should the outer face be picked after checks appear to have them facing down and then make the saw cut on the bottom face?

[Andries]

How deep should the saw kerf be in the bottom of the Timber?
Thanks!

I've seen 1 1/2" done, sometimes 1" is OK too.
Make the kerf on the bottom 8" face in the event water somehow enters, it'll drain away.

[Andries]

Should the outer face be picked after checks appear to have them facing down and then make the saw cut on the bottom face?

Things work better if you commit up front, right after milling. 
There won't be many checks visible yet, so pick your outer/inner faces, and then localize any checking that happens on the side that the saw kerf is on. The saw kerf/bottom side should be the side that has the most checking because of the "relief" that the kerf gives.

[Andries]

"You're allowing the same amount for windows and door frames, right, by using key and slot joinery? "
Yes. 6" should be sufficient?

Your estimates sound good to me.
If your logs settle a huge amount, you'll be glad you allowed extra for that.
Let's say some logs shrink and settle less - then your keyways haven't been fully used. Not a bad thing, right?
Logs are like people, biological critters each with a history of it's own. No two will behave the same way. 
Hey, it's a dovetail timber building - some character is expected!