Beam and Post Foundation

[dhatley]

I am in the planning stage of building a new cabin in the U.P. of Michigan. My intention is to stick build a 32' wide by 36' long single story cabin, utilizing a post/beam foundation. The post will be of 6X6 pressure treated lumber and the post holes will be backfilled with concrete. I plan on the bottom of the floor joist to be 3' above grade. Using wood beams between the post with the floor joist placed aboved the beams.

What would be your recommendation for spacing between each post, or post positioning? Also what size beams would you recommend?

[Don_P]

If it were mine I think the first run through I'd try 4 rows of piers with posts spaced 9' apart under those 4 girders. The joist span would be something under 10'8", the girder spans something under 9'.

From my read, the 4 rows of girders could be built of triple 2x12's, the joists could be 2x8's.

I would pour a footing under the post, set the post, and fill around it with either gravel or clean dirt. Pouring around the post is not a real good idea usually. Try to find "foundation grade" treated posts. These will be free of heartwood (that doesn't accept the treatment chemical) and treated to a high retention level (.60 pounds per cubic foot usually). Don't cut the end of a post you stick in the ground.

[dhatley]

Thank you Don for the input. Thinking this issue thru further, would you advice placing the floor joist above the beams, or would you hang them between the beams with joist hangers?

[Don_P]

My feeling is, whenever you can, put wood on top of wood instead of relying on connectors. You then know the joist is definitely bearing on all the members of the girder, not a connector that is nailed to one member, that is nailed to another member, that is nailed to yet another member. Sitting on top of it all, the nails really don't do much. Hanging, the nailing becomes a key structural element.

[dhatley]

Don, sounds like good advise and I believe thats the way to go. Thanks again for your input.

[rfwoodvt]

Hi!

I've read this particular post and now that my head is swimming I think I need clarification! :confused:

Actually its not that bad...

I'm re-habbing a 24 by 30 foot cabin that has a typical joist floor with box headers (rim joists?). they are made of 2x10's with the the joists running across the 24 foot dimension.

My best estimate on live and dead loads is that it would be similar to a 2 bedroom home with a 12/12 pitch AS roof in an area that typically has 8 to 10 inches of snow on the ground from late december to early April. The building will be unheated most of the winter and much of the snow typically slides off the roof within a short period of time after it falls

As far as I can tell the foundation is simply railroad ties around the perimeter along with a central lay of ties under where the joists meet in the middle. I guess you would call it a center carrying beam.

The building is single story with a 12:12 pitch roof with a loft area and central load bearing wall.

Walls are 2x4 and ceiling joists 2x10 rafters 2x10.

What I am planning on doing is jacking up the building about 4 feet and placing a pier and girder foundation under it.

I have yet to find much helpful info on what size lumber I need for the girders and what span I should consider.

I am just as happy to go with a 7'6" between the piers to support the girders but 10' oc makes my work easier.

I thinking I need a minimum of 3 girders, one under the center where the joists meet and one each on the outboard sides of the building about 2 feet in from the drip edge of the wall.

Othewise, I was thinking 4 beams with the two outer ones in about 2 feet and the other two evenly spaced towards the inside. Though this seems like over kill.

The outer ones we want under the building because we are going with an FPSF for the posts. Each corner post will be braced for forward and sidwards stability

I will be using PT 2x lumber for the beams and either 6x6 PT or filled concrete block for the posts

What size lumber and how many boards thick should I use for building up my beams under the following scenarios:


3 beams each supported at 7'6" oc
3 beams each supported at 10' oc

4 beams each supported at 7'6" oc
4 beams each supported at 10' oc

I've seen this done on a number of cabins but never stopped to measure them. I hope someone here can help!

Warmest Regards,

Rick

[JOEL S]

hello,

I am getting ready to build a small 20' x 16' cabin in a secluded area of the southern tier (Western NY) I am planning on using two 20' beams ( two 2x8x20's per beam) and five 4x4x8 treated post spaced 4.5 (center to center) and buried 42" leaving me roughly 3' above grade to build. the floor joist will be 2x8's 16" on center, Beams will be located approximately 2' from outer joist and 12' between the beams, does anyone see any fault with this plan!

Thank you,

Joel