Spans for beams under cottage ?

[John van Gurp]

Hello,

Can someone give me a simple way to determine the spacing for concrete posts under a cottage?

I am planning a 28' x 22' gable end cottage with loft, on 10" concrete posts set below frost line.

How about the beams? Someone said to space the posts roughly every 8' and use tripled up 2x8 for beams, glued and nailed to the full 28' length.

Any guidance in this will be appreciated. Thanks,

John

[Goedjn]

If you're supported built-up beams of trippled 2x8s spaced 8' oc, then each beam mid-floor is supporting 480 PLF. If you web-search on "built-up beam span table" you eventually find that a 3-ply 2x8 beam spanning 8 feet is good for 548 PLF, and one spanning 10 feet is only good for 351 PLF. (3 ply 2x10 spanning 10' is 491#)

So every 8' in both directions, internally.

The beams under the walls are only supporting 4' of floor, but you'll also have to figure out the total of the expected live and dead-weights of the walls and roof, (Probably around 20PSF + snow loads) And if there's a ceiling, around 10 PSF for that, and figure out where that weight is applied. For a simple gable, that's usually the side walls, unless you have posts within the house holding up the ceiling and/or roof. (This is a 1 story building right?)

[nicksanspam]

How do you figure that?

Nick

[Goedjn]

20 PSF dead load, 40 PSF live load. 60 PSF total, for 4 feet on either side of the beam.

[John van Gurp]

Thanks for the helpful response. Yes it's one storey and I am going to stick with 8' spacing for the posts. There's only get one chance to do it, so we might as well do it right. Most of the cottages on the lake are up on rocks and stumps and spindly concrete posts, etc. We had one like that previously and ended up bulldozing and burning it.

Cheers, John