Replacing Railroad Tie box foundation

[rfwoodvt]

Hi!

I actually posted this as a continuation of another thread but thought it best to give it it's own thread.

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

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

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 geographical 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 a simple matter of railroad ties stacked two high around the perimeter of the building and a center "beam" of ties running lengthwise under where the joists meet in the middle.

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 as that makes my math simpler but 10' oc makes my work easier still.

I'm thinking that I only need to support the floor joists near the ends and in the middle where they overlap, that would man only 3 girders.

Do I even need to consider using 4 girders?

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

What width 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

[Don_P]

I would use 3 girders, UNDER the outer walls, no cantilever if possible, don't go looking for trouble if you don't have to. Then directly under the lap/center bearing wall. The girder depth,width and pier to pier span depends on your loads. You need to know in pounds per square foot, usually the building department can give you this. You then convert this to pounds per lineal foot on the beams. There are girder tables and beam formulas from there if the inspector is receptive (actually that information is on his bookshelf) otherwise you'll need an engineer.

[rfwoodvt]

ThanX for the reply,

I did some rough calculations using what I could cobb from web sources but I am not sure how accurate the calcs were.

Can you direct me to a decent calculator I can plug materials and dimensions into to figure the total weight?

I calculated total SQF of the walls floors and roofing and multiplied them by the PSF factors I could find, added the live load from some other tables and the deadloads for snow and came up with several different figures depending on if I discounted items I felt were duplicates. Total weight of building ranged from 69000 pounds to over 100 thousand. Since I have no idea what a building really weights I don't know how real these are.

If the numbers are real then there is no way I can use 3 beams unless I space the piers less than 8' apart and use 4ply 2x12. Doable perhaps, but not very economical.

I thought about 4 beams but that would mean cantelevering something that brings out 5 beams two outside, one on the joist overlap and two inbetween.

too much digging. Woudl be better off going with straight concrete beams.

Any other suggestions to online cabin building resources that sell/provide such foundation plans?

Any further help would be welcome!

[Don_P]

An engineer will be cheaper than online and repairing a mistake.

Table R502.5(1) and (2) of the IRC codebook looks like you're probably in the ballpark with 4-2x12's and a little under 8' post to post on 3 girders. I'm not too concerned about a couple of hundred bucks over a safety issue.

http://www2.iccsafe.org/states/newjersey/NJ_Residential/Residential_Frameset.htm
(table is in chapter 5 of the link above)