Expert: Stephen Major (Owner--Major Design Group) - 7/11/2007

Question
Hi Stephen;

I'm planning to build a small cabin in a remote region of eastern Alaska, and have two questions that I'd like to ask your help with.

The Cabin is to be 12'x16', single-story with sleeping loft.
I plan to build the supporting "deck" structure this summer, which will become the floor platform for construction of the cabin in years to follow. I am planning to frame with double-2x12 rim joists, a double-2x10 center beam running the long (16') direction below 2x10 floor joists spaced at 16" O.C. Supports will be wood posts at 4' O.C. supported by some kind of pre-cast footing. I plan to use Simpson-type connector hardware in all possible locations. Excavation is extremely difficult, will be limited, and is to be done by hand.

My questions are:
1)Will this number (15) and type of post w/ pre-cast footer be sufficient to bear the weight of the cabin?  Is this a reasonable approach?  If so, should I use 4" or 6" posts?  I don't know the area of the bottom of the footer, but I can anticipate that it may be something like 8"x8" for a 4" post.  Also, it appears that many others who have built cabins in this region have not positively connected piers to footers to earth; is it useful or meaningful to tie posts to the footer if the footer is not located below grade?
2) How shall I "mate" the two 2x12 rim joists together to get the maximum composite strength from both?  I understand that the tops of the joists are in compression and bottoms are in tension; is anchoring numerous nails / screws in different locations enough?

Thanks for your time, I appreciate any input you may have.

Answer
Pete,

I've been re-reading your letter but I still can't fully envision what you are trying to do.  Are the footings underground or above ground?  Are you in an area of permafrost?  Are your planned footings made of masonry blocks?  

From, your description the floor frame seems overbuilt.  2x10s at 16" o.c., of the right lumber grade/species, can span 12' easily, without the center beam.  But, you might plan to impose other loads at or near the centerline, that I am not aware of.  

Use PL400 or similar construction adhesive between the doubled members, and spike them together with galvanized 16d nails set at a slight angle.  It is best to drive them by hand, with the beam set solidly in a flat straight position during nailing.  Use groups of 3 nails at 18 to 24" apart.  Nail from both sides.

Post size (4 vs 6) depends mainly on their length.  15 posts for a 12x16 camp is too many, but it is OK to overbuild if you believe it is necessary.  What are you doing to keep the posts from tipping, if they are not buried well into the ground?

Sorry I have so many questions, but I'd like to give you pertinent information.

--Steve Major