I am planning on building a small hunting cabin using the info I have found here on post and pier foundations. There are 4 of us that will be building and we were able to get a great deal on some CCA PT lumber last year Lowes had put on clearance to make room for the new ACQ PT lumber coming in. We got 62-2X4X16's, 50-4X4X16's and 45 sheets of T111 for $600! I already have all this lumber and prices have risen dramatically since then so I'd like to use it for even the 2 main support beams. My thoughts were to take 2-4X4X16's and sandwich a 2X4X16 in between. I would use 8 1/2 lag bolts with washers and lots of heavy duty construction adhesive to attach them to each other. This would give me a beam 16' long, 3 1/2 wide and 8 1/2 tall. I would use 2 of these beams on concrete piers to support a 16X16 cabin. Will these beams be sufficient. Thanks in advance for the help.
Ed
You can make the beams you have devised work. What you need to calculate is the load coming down from the roof (and loft if you will have one) and main floor. This will accumulate on the beam. Then you can design the pier spacing (the beam span) so as not to overload the beam (or to dig more post holes than needed).
The Victoria cottage plans have a simple layout and post and pier foundation plan for a 16' wide cottage that you could easily modify (http://www.jshow.com/y2k/listings/44.html), or you could have this worked up with a short consult with a local engineer.
PS - Also please review the handling guidelines for using CCA treated wood: http://www.bancca.org/CCA_Handling/CCA_Handling.htm. (From a group who would probably err on the side of caution as you can see by their web url. Still, this is solid good science advice.)