Question on building concrete paito (house, living, price)

[ExAirForce]

Our home is about completed being built. As an after thought we decided to have a concrete patio poured. Our builder is recommending having styrofoam put below the slab and I am not sure if we need this or not. We did have 4" of styrofoam installed below the heated concrete slab of the living are but this slab will be seperate and not connected to the main house so I am wondering if the added cost is really needed or not. Any input or ideas?

[kellysmith]

Foam under the heated slab makes sense. It does 2 things. First it helps to keep your heat from traveling down into the ground below the slab, and secondly it keeps frost from forming under the slab that could lift it. Do a google search for Frost Protected Shallow Foundation. The only benefit for putting foam under an unheated slab, which is what your patio would be is it would possibly keep frost from getting under it, but only if the foam extended several feet outside the slab, and even at that, I don't think it would keep frost out if it's an outdoor slab. Just make sure there is at least 6 inches of good gravel under the slab and that it has good drainage and you should be fine. With the way foam has gone up in price lately, I wouldn't put it under an unheated slab...no way!

[forest beekeeper]

One inch of foam acts like one foot of soil. To get underneath the frost you need 4 foot of soil, or 4 inches of foam.

For example when running our new well line from the well to our house, the trench was only 3 foot deep. So by adding 1 inch of foam on top of the pipe [then 3 foot of soil], I was told it would act like it was a full 4 feet deep. [to be safe I added 2 inches of foam].

It sounds to me like they are trying to avoid frost heaves from cracking your slab.

As a side note. It is easier to plan ahead for long term usage than it is to rip out a concrete slab. Do you ever think, ever, that you might, ever, want to extend the house out over that slab?

Once poured, you do not want to ever have to rip out a slab. So to include foam under it, gives you the option 20 years from now of extending an addition out onto that slab.

I suggest going for the foam.

Now have you considered PEX in the slab?

A PEX loop, would give you the future option of adding that as one zone of your heat system. You could flip a switch and in two hours all the ice and snow would be gone from that slab. I have seen homes here where they did this to the drive way. They leave it off most of the time. But for the evening of a big storm, turn it on. If we have 6 big storms in a winter, then it was only turned on 6 times. So it is not really that big of an expense to operate. Or so I have been told.

[dmyankee]

Originally Posted by kellysmith

Foam under the heated slab makes sense. It does 2 things. First it helps to keep your heat from traveling down into the ground below the slab, and secondly it keeps frost from forming under the slab that could lift it. Do a google search for Frost Protected Shallow Foundation. The only benefit for putting foam under an unheated slab, which is what your patio would be is it would possibly keep frost from getting under it, but only if the foam extended several feet outside the slab, and even at that, I don't think it would keep frost out if it's an outdoor slab. Just make sure there is at least 6 inches of good gravel under the slab and that it has good drainage and you should be fine. With the way foam has gone up in price lately, I wouldn't put it under an unheated slab...no way!

Up here you are only safe with 6 feet.

[Northern Maine Land Man]

Don't pour a slab. Put down a coarse sand base and use patio blocks. It will last forever and you don't need to worry about cracks. Nearly all outdoor slabs in Maine crack.

[forest beekeeper]

Originally Posted by Northern Maine Land Man

Don't pour a slab. Put down a coarse sand base and use patio blocks. It will last forever and you don't need to worry about cracks. Nearly all outdoor slabs in Maine crack.

NMLM you are the 'man'

That is a great idea.

[ExAirForce]

NMLM... that thought crossed our minds as well. Our builder said the cost was extremely high doing this versus a concrete slab. This coupled with the fact that our patio here in Germany is blocks and I constantly have to fight the weeds coming up through the cracks each year, had us leaning towards the slab. We were hoping to have it done so when we move back in July, it was "all done" but maybe we will just wait and I will do the blocks myself when we are back. Not afraid of manual labor but a little hard to do yourself from this far away LOL. Thanks for everyone's input. We are counting down the days.

[msina]

If you use Landscape fabric under the sand you shouldn't have much problem with weeds.

[JC3]

ExAirForce, I had 18" patio blocks laid to cover a 12' wide 34' long area in back of my house. They put sandstone under it. After using it and having it for a number of years, I am so glad I went this route. It looks good, no cracks and wears very well.

As for weeds, I use vinegar or a weed killer right down the seams. Works for me and after seeing mine...BIL who did concrete and has cracks..etc..wishes he went with the blocks. Overall, it wasn't that expensive and if you are doing it yourself..all the better.

[JC3]

Oops!...meant to say stonedust...not sandstone. Thank you whoever corrected me.