Should I build over this???...

B7500 · Jun 25, 2003

I want to build a storage/wood shed. The trouble is the perfect spot to build it is right over where I had buried tree stumps. I plan on "floating" a slab for its base.
Some people say not to risk the stumps rotting and then cracking my slab. Others say it should not be a problem.
What do you think?
Thanks in advance.
-Terry

MarkV · Jun 25, 2003

Terry,

The standard in the building industry is you never build over buried organic matter. Eventually it is going to decompose and create a void leaving your slab unsupported. Of course unsupported means the slab will flex and cause it to crack. When you mention a floating slab I assume you are talking about building a pole building where the poles will act as the load bearing members for the structure. Those poles need to be set below frost line and on undisturbed ground to keep the building from moving. I don't see how that would be possible with the area having already been dug up to bury the stumps. I believe I would be looking at a different site if it were me.

MarkV

Egon · Jun 25, 2003

It would usually be advisable not to pour a slab over a base that will settle as the stumps rot. The type of soil should also be taken into account.

Thicker slab, more wire and rebar may do the trick depending on what kind of loads will be put on the slab and the type of soil conditions underneath it.

Note: your question is very hard to reply to in the affermative without detailed knowledge of the soil conditions. Othewise were all quessing.

Egon

BB_TX · Jun 25, 2003

Terry - You don't say how large a slab you are considering. If you are considering a flat slab with no beams poured in it, I would say NO (caps intentional). The usual way (at least around here) to pour a slab is to dig trenches around the perimeter about 1' wide by about 2'-3' deep to provide beams around the outside, something like bridge beams. Put extra heavy rebar in the beams. Then as the slab size gets larger, additional beams are poured in a crisscross pattern, front to back and side to side. The number of crisscross beams would depend on the overall size and the likelyhood for settling problems. Of course, the more beams, the more concrete required. If you have enough beams spaced close enough together with enough rebar, you may get voids form under the slab, but it ain't likely to break

B7500 · Jun 25, 2003

Mark, Egon and BB thanks for your reply. I had a feeling it was a bad idea but the area is so perfect....
Anyway, I'll look into another area to build. I don't want to go through all that work and then have it crack.
Thanks guys,
-Terry

heehaw · Jun 25, 2003

how hard would it be to dig the stumps up and move them?
heehaw

B7500 · Jun 25, 2003

Very hard! I had an excavator dig up and bury them when I had my 300 ft road put in last year. These baby's were huge! My Kubota can do wonders but this would be a pretty big job to put her through. Plus, like an idiot, I started work already by having two tandom loads of gravel delivered. I then spread it out and tamped it down. NOW I start thinking about the potential problems from the stumps. At least I didn't build anything yet.
-Terry

tc35dforme · Jun 25, 2003

How big a shed ( footprint ) are you looking at ?

How vast ( area ) is the stump-pit ?

If the shed is larger than the pit, you could always span the 'hole' with some strcutural members and go from there. This is only practical if you can get good footings.

What type of loading are you looking for for the floor. Wood is an option. Just look at old barns. You could probably order up some full dimension ( non-planed ) PT material ( 2" x 6" ). Set these on 12" O.C. joists and you'll have a very strong system.

Now you know why its not legal to bury stumps in some areas...insects, structural issues ( sinkholes ) and the possibility of building over them and not knowing ( a bigger structural issue )!!

Don't give up just yet ... just look at the options...the associated costs, then give up /forums/images/graemlins/wink.gif !!

B7500 · Jun 25, 2003

Thanks tc35dforme ,
No I won't give up just yet but I'm close. The "footprint" is a 15 x 30. The stump pit is all of that or more. Plus, to add to my troubles the water table is about 3ft below ground level.
Now can I give up??
-Terry