beam overhang

[leinom]

Hi, what is a safe amount of over hang for a doubled up two by ten over each side of the post and pier foundation? I am buying the lumber tonight  and my 9 posts are spaced out 15 feet one way and 12 the other, so I was figuring two feet maybe the length of the cabin to get 18 feet? Also if I framed up the floor in pieces at home, what would be a safe about for my floor joists to overhang on each side (using two by sixes). Thanks

Mark

[John_C]

You haven't given a whole lot of information.  I went back and looked at your previous posts and I think you are building a 16x16 structure.   I can't tell if it's 1,  1-1/2 or 2 floors.  The spacing you indicated doesn't make sense to me for a 16x16 building.  Do you have plans?  What is indicated on the plans?

In very general terms a doubled 2x10 would be quite light for a beam and would need piers close together.....  perhaps every 4 feet.  I doubt you would want more than ~ a foot of overhang or it might slowly sag over time.

If the piers are 12' apart you would need a stout beam.

With 9 piers I am guessing there is a centerline beam?   That would be necessary to make 2x6 stiff enough.

If I was building a 16' cabin I'd use 4 piers down each load bearing wall a paced a little less than 5' apart.  I'd space them so the beams would overhang about a foot. Depending on the size of the bearing surface the clear span would be around 4'  and the beam could be of moderate size.  It would need to be determined by the actual loads, including snow, storm and earthquake depending on where you are located.

Joists overhang each side by ~9"  ...  2x10  joists 16" oc.  If you put in a centerline beam 2x6 would be stiff enough but even then 2x8 would give more room for insulation.

YMMV  post some more details about the cabin.  maybe some others will jump in here with differing opinions.  Good Luck.

[leinom]

Ah sorry for the lack of information I typed it up really quick before work. I'm thinking of 14 x 18, changed from the 16x 16 to get a nicer roof line. I have nine posts, in three rows. In the long direction they have 7.5 feet spacing, the shorter side 6 feet. If 1.5 foot over hang off of each side of the beams is too much, I can go 14 x 16 or whatever would suit. I just had a chance last night to use a skid steer hole digger and I couldnt turn it down so measured and drill the best I could. This is going to be a 1 story, with just a small sleeping loft, 10-12 pitch roof, 8 foot walls. 4 foot deep post pier foundation. Thanks for the comments!

Mark

[glenn kangiser]

Probably one of the better things you could do would be to get the Little House Plans.

Since you haven't done a lot of building, they would answer a lot of your questions and give you a positive direction to go without problems.  You would probably save the $54.95 they cost in time and not wasting materials.  Loading changes with each size of beam and footing arrangement.   From what I see on the plan it looks like you need more footings .  It uses 2 beams with footings on 4' centers giving 12 footings.  Your 3 beams - with 9 footings I assume may be more prone to settling.

While footings may be lacking, it looks like 2' overhangs on the 2x6's should be ok.

Depending on soil conditions the footings may work.  4x8 beams use 4' pier spacing so it seems 4x10 @ 7'6" would be marginal.  I think there is a beam calculator you could use in the referals section of this forum.  

[MountainDon]

Well, when  asked John about increasing the post spacing and what size beams to use for my 14 x 26 cabin based on the Little House plans he suggested 8 foot spacing for the posts using a built up 6 x 12 girder/beam. That's [highlight]tripled 2 x 12's with two 1/2" plywood spacers[/highlight]. The two girders overhang a foot over each end post, but the plans may continue to morph and end up with maybe 2 feet overhang at each end. The girders are spaced 9'6" apart on center with 14 foot 2 x 10 floor joists on top. I chose 2 x 10 so the floor would be ridgid enough to allow ceramic floor tile and for more insulation.

The 6 x 12 girders will cost a bit more than smaller, but in the grand scheme of things it's a small percentage of the entire investment and forms the basis for a stout cabin. Ditto going 2 x 10 for joists.

[glenn kangiser]

That sounds more like it on the beams, Don.  I'm just going off comparisons in my head -- the scary place. :-/

[MountainDon]

I'm also used to walking on terra firma or slab-on-grade. A bouncy wood floor would be disconcerting for me.  

(self induced drift here...) I put a new motor in the RV furnace. Forgot what it should run like... the old one deteriorated so slowly over time. I guess 23 yrs use is not too bad for one motor.    Tomorrow we'll drag it back up to the mtns. and re-install it and get along with the land clearing.

[John_C]

You mihght want to poke through this thread
http://www.countryplans.com/cgi-bin/yabb2/YaBB.pl?num=1166598189/40

Mtn. Don is building a 14' wide cabin and has some nice drawings there.  His beams are buit up 6x12  (Three 2x12) ...  a lot heavier than what you proposed.

I was going to say the Little House plans would be a good idea but Glenn beat me to it.

With a centerline beam you would have a few other options if you wanted to carry some of the roof load down to one or more of those piers.  That would involve at the least a load bearing ridge beam, and probably a post to trasmit some of the load to the pier that is in the center of the cabin.  This involves what John calls a load trace.  A load trace on such a simple structure is not rocket science but does involve some math and some reasonable assumptions regarding dynamic loads.

Don's 14x26  is supported by 8 piers and your somewhat smaller building will be on 9.  The trick is to calculate the load and spread it around.

[John Raabe]

As a general rule you can safely cantilever 1/4 the span of a beam or joist - especially when it is supported at more than one point. So, assuming you are supporting just the floor and the end wall loads on the beam and not a heavy point load, you should be fine with a 2' extension.

Yes, it would be different if you had a ridge beam load coming down the middle of the end wall. Then you should have a direct bearing pier under the load.

[MountainDon]

Thanks John. If my wife reads that our cabin will grow the extra foot each way.