I bought a small cabin on 35 acres.  It came with a 16'x32' out building.  It is single story, block foundation, frame construction, built in 1988.  The floor joists are 2x10 spanning the 16' without any additional support.  The floor has a lot of bounce and the most of the floor joists in the middle of the structure are broken or cracked.  The end walls are vented but the middle must be lacking in ventilation because I saw some dry rot in addition to the cracks.  The joists near the vents are solid and clean.  It's just the ones in the middle.  I figure I'll have to replace 6 - 8 joists.  No power and no lights so it's just been a flash light inspection so far.

The crawlspace is 3 blocks high and seems dry.  I'll trim the trees back and add gutters to move any water away since the place is overgrown by pine trees.

I don't have a clue what I'm getting into.  I know the broken joists need replaced.  I assume I need a center beam and piers running the 32' length to support the floor joists.  How big of a beam do I need?  How many piers? 

Thanks.

Hi DS, welcome to the forum!  Did you notice what the joist spacing was?  Or by chance the grade stamp on the wood?

The International Residential Code (link here) has a joist span table (Table R502.3.1(2) ) that shows a 2x10 #2 grade at 16" spacing can span from 14' to 15'-7" depending on species.  If your 2x10 are something like Southern Pine or aren't #2 grade then you can get the floor you currently have.

Any beam placed under the joists should work provided you support it with enough piers.  Guidance on that is provided in Chapter 6 of the IRC, in Table R602.7(2).  You could use a girder built up from two 2x6 as long as you had support posts and piers every 4'-6".

I helped on a similar job when I was 15 removing termite-damaged joists.  We replaced each joist one at a time, using a sledge hammer to knock out the old joist then replacing it with a new one using a bottle jack to force it into position.  Crawl space was about the same height, maybe 24" if we were lucky.  If I were doing it now I would definitely put visquene down on the entire area.  You get pretty filthy squirming around on your back otherwise.

It was too dark and the wood was in such bad shape that we didn't see any grade stamps.  I'll look this weekend when I'm there again.  The spacing was 16" on center with metal braces between the joists.  I was planning on putting a vapor barrier down anyway so I'll do that before we try replacing joists.  My buddy who frames houses said the construction looked okay.  He was very surprised at the extent of damage to the middle joists.

I'll read up on the information you suggested.  I was thinking three piers and a double 2x8 but I'll check the standard and see what they recommend.  Any point in using LVL for the replacement joists or am I just spending money?

If you were starting from scratch on this floor it would be important to have the beam and piers sized appropriately.  As it is, if you replace the old joists with good quality 2x10 you shouldn't actually need a support beam in the middle.  Adding a beam would be a belt and suspenders type of situation.  With them being 16" on center I'm having a hard time imagining how they could get that damaged.  Were there rave dance parties with loads of people jumping on the floor perhaps?      Or are there any interior walls that may be bearing on the floor?

The load bearing walls are sitting on the good floor joists.  Otherwise the place would probably fallen in.  The walls partition both ends of the building into 8' x 16 rooms, one on each end.  the middle section is completely open.  Each wall has a post that runs up to the main roof beam.  From the amount of mold I saw this time I think it's as much of a ventilation problem as anything else.  I'll replace the bad joists, add a vapor barrier in the crawlspace and add a beam and piers just to be safe.  The posts that support the roof look a little undersize as well.  The rafters don't have any cross ties.  The roof structure could use some reinforcement.

I'll fix the foundation issues first, beef up the support posts for the roof, add cross ties and ceiling joists.  Once the structure is solid, I'll trim the trees back, add new shingles and gutters.  It has a lot of potential but it was underbuilt and suffering from neglect. 

I read the resources you suggested.  I'm waiting for my book on framing to arrive.  It should be a fun project.  Thanks for your help.