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Jonny Homefixer 11-01-2006 10:35 AM

Site work question
 
My question is about prepping a new building site for a footer/foundation/slab on a 5% grade.

While I am just in the planning phase of my new house that I will be starting late next summer, I have a question about site prep work.

The house will be on a 5% grade from front to back and I want to build a single story on a slab.

I was thinking of bringing in fill from another part of the property this fall and grade it to sub slab height. My rubber tired machine is 10 ton so it should compact ok in addition to the dirt sitting for close to a year before working with it.

Next year when I am ready for footers I was going to hoe out a footer trench.

Is this the right way to do this?
My finished slab height in the front will be 1 foot above present grade to keep water run off-out of the house while the slab at the back of the house will be about 5 feet above present grade.

My soil composition is as follows:

0-8" Plow layer brown sandy loam loose
8-23" Brown to tan sandy loam granular
23-38" Mottled Hard Fraigpan?
Got this off of my perk test report

Is this ok to use or should I bring some stone in? The quarry is about 20 minutes away.

Thanks!

Jon

concretemasonry 11-01-2006 11:53 AM

A foundation should be placed on natural soil.

If it is placed on fill material, the soil should be compacted to a degree required by the engineer. This will depend on the material.

Your little 10 ton rubber tired machine may do nothing but make you feel good that you are trying to do something. The one year of sitting may also accomplish nothing unless you have a surcharge.

Your perk test has nothing to do with the quality of the fill you will place, but it is an indication of the surface soils, depending on the elevation of the hole.

You should have an engineer specify what kind of material should be used for your fill and what method of compaction you should use. He probably will tell how much moisture you should have to get the best compaction with the least effort.

Different soils require different types and amounts of compaction. Some require heavy loads, some require vibration, some require different layer thicknesses. If you don't have the right moisture content, you can beat on it all day and do little ggod.

Granular materials are easier to compact, while fine soils (clay,etc.) take more effort and thinner lifts. A one size rock can also be tricky to compact well and settlement can show up after the house is on it if not fully compacted.

If you do not use granular materials, you can fool yourself and have settlement over a period of years.

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Jonny Homefixer 11-01-2006 12:47 PM

Thanks for the reply
The entire foundation will be on undisturbed soil.
The fill is only going under the slab.
Will I still need an engineer to tell me what kind of fill is best under the slab?
I want to do this right the first time.
It's going to be a 5000 ft slab with radiant heat.

concretemasonry 11-01-2006 01:02 PM

Glad to hear that the structural portion of the house is on undisturbed soil.

You should not gamble with a 5000 sf slab that has embedded heating. Any unplanned cracks or settlement could be costly and messy.

Regarding the fill - You don't necessarily need an engineer (unless required by municipal standards), but you do need well compacted soil. The guy with the dump truck and cat may not be around if there is a problem.

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Jonny Homefixer 11-01-2006 01:48 PM

Thanks again
Just want to make sure I understand
When you say that I shouldn't gamble on a 5000 ft slab - Could you expand on that? Do you mean that I shouldn't pour a slab that big with radiant heat or that I should just make sure my fill is compacted well and made up of the right material?
Thanks for your time.
Most of what I know about houses is above the concrete so I want to make sure I get it right the first time.
I've done a few pours before but they were small and easy. I will be getting professional help with this one. It's a whole lot easier building when you have a good level base to start with.:wink:

concretemasonry 11-01-2006 02:16 PM

Site work question
 
My comment about the slab was that you have a lot invested in the slab and that a slab with radient heat may be a little fussier regarding any cracks or settlement.

Concrete can have minor shrinkage cracks, but they are not a problem if they are controlled.

Radient heat in a slab is not unusual, so just consult with the installer to see if anything special is required for your home. Sometimes they make any joints agree with zones, etc.

Just have a level, well compacted area for your slab.

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Jonny Homefixer 11-02-2006 08:43 AM

Thanks again


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