[Ferro List] Slab On Grade

[Walter Jeffries]

On May 1, 2008, at 1:30 AM, Christopher Glasspool wrote:
> Go look at Rob Roy's Cordwood Home book; he goes into great detail  
> about building a heavy masonry building on a floating slab on grade  
> in the state of New York. The slab rests on sand, and is completely  
> insulated underneath. the slab edges are thickened. Proper drainage  
> is really important for this system as it relies on it being  
> drained dry underneath to stop the usual frost heave.

This is much like we did it - a floating slab. We're over ledge.  
There is no going down without serious blasting or burning of the  
rocks. Instead we made a few anchor points to the ledge - the  
foundation keys into the irregularities - and then laid a bed of  
packed gravel in the middle with insulation and then a vapor barrier.  
Inside the gravel are drainage tubes to keep it dry.

The house was 100% level when we poured the foundation a year and a  
half ago and now two winters later is still perfectly level. The  
house itself weights a bit over 100,000 lbs now.

The slab varies from typically around 12" thick along the outer edge  
to about 4" thick in the middle of the floor. There are thicker areas  
such as under interior walls.

We insulated on the exterior of the concrete walls so the thermal  
mass is inside the insulating envelope. Cost is still under $7,000 -  
it's a tiny cottage at 252 sq-ft which does help with keeping the  
cost down.

There are only a couple of contact points between the structural  
concrete of the house and the outside at the ledge as well as via  
some rebar that was drilled into the ledge. No nosebleed problems.  
Part of this may be because we get such early deep snows in the  
winter. We had zero inches of frost depth this year. Most year's it  
is about three or four inches of frost depth.

I personally would not try this on clay or tundra although I have  
read it is done in Alaska and Canada...

Cheers,

Walter Jeffries
Sugar Mountain Farm LLC
Orange, Vermont
Pastured Pigs & Sheep
http://SugarMtnFarm.com/blog
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