DIY Home Improvement Forum banner

Slab on Grade in NY - slab removed...

8K views 6 replies 6 participants last post by  JoJo-Arch 
#1 ·
Hello All,

I am considering buying a small house (approx 1500sf) in Upstate NY (Zone 5/6 border) that was built using slab on grade foundation construction back in the Mid 1940's.

The slab has been removed by the previous owner (apparently it was heaving?) then got foreclosed upon.

I am an engineer by trade with some experience in concrete design, but in my experience it is best to talk to the guys that build the stuff engineers design to get the best understanding and education about practical application of all that book theory!

I have never built or renovated a slab on grade. Can anybody direct me to some good info?

I know I have to tie back into the "stem" with rods and reinforce in (fiber or steel), but I am a bit foggy on joints and subgrade plumbing?

Thanks for any info.
 
#3 · (Edited)
You do not HAVE to tie the floor to the foundation wall. Floating slabs are quite acceptable up here. Were I in your position, I'd take full advantage of it and dig deeper, replacing at least 6" below the new slab w/ EPS over a good vapor barrier (10 mil black poly, StegoWrap, etc). Isolate the edge of the slab from the foundation wall with foam as well, to kill a thermal bridge' 2 to 4" if aesthetically acceptable.
 
#7 ·
Slab on ground.

In Melbourne, the common method is slab on ground, and I would estimate 80% of new houses use it. If designed properly, it's indestructible, and ideal for filled or problem sites. Only on very steep grades would one consider using timber floor framing and flooring. Timber is more expensive, subject to rot and in termite prone areas, can be attacked by them.

The problems associated with concrete slabs are minor, and with careful design can overcome the biggest problem: shrinkage. Concrete shrinks in it's length by about 1/3-1/2 the distance brickwork grows, so if no expansion/contraction joints are provided to the brick wall, it's not uncommon to see a long brick wall with no joints overhang the concrete slab by up to 1'' to 2''. Structural engineers prefer to pour a house slab in one continuous slab to avoid joints that can heave out of alignment if shear rods are not installed properly. Another problem to watch is to use a flexible adhesive between stone or ceramic tiles, as tiles expand and concrete shrinks.

The older method used where perimeter walls were built first (usually of brick) and the slab poured afterwards insde is no longer used, because of shrinkage and heave problems. The inner ground beneath the slab cannot be comapcted as well as the natural stiff clay under the perimeter wall foundations. Result is differential movement between outer walls and inner walls, showing up as corner cracks in plaster, diagonal cracks over corners of openings and in severe cases, cracked glass due to stressed window frames.

Structural engeneers design slabs to stop differential movement and make allowances for shrinkage and expansion of different materials. It is illegal to construct a residential slab without a structural engineers certificate of compliance and computations in Australia. :whistling2:
Cheers! from Oz.
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top