# Converting crawl space to poured slab



## TheIcehouse1809 (Oct 28, 2014)

This old house is suffering from more and more stormwater due to continuous development in the area. The crawl space not only shares a great deal of moisture with the stick frame floor above it, it is taking on sedimentation as the natural flow creeps under the structure through the water table to the stream out back. Additionally, the area is now prone to flash flood due to an overload of impervious cover in the watershed.

I believe the best solution is to fill the crawl space with a poured floor. I envision a drain in the floor to quickly evacuate floodwaters, and to support the odd hose down as necessary. I would also like to incorporate PEX tubing to support radiant heat throughout the footprint of the structure(s).

I am thinking: undisturbed dirt / vapor barrier / 4" gravel / rigid foam insulation / sand (?) / concrete

There's plenty of head room to work with. The existing stick frame flooring/joists are rotten with multiple layers of plywood distributing load and a few rocks supporting failing joists. 

Or, I could just rebuild joists and floor - but I would like to build for the stormwater that I know is here and for what is coming.

Thoughts? Concerns?


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## TheIcehouse1809 (Oct 28, 2014)

FYI: previous discussion here = http://www.houserepairtalk.com/f17/creating-pseudo-contiguous-poured-basement-floor-17463/


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## nealtw (Oct 28, 2014)

I was wondering where you got to on this place.
Before you do anything you have to solve the flash flood problem. Like a catch basin on the high side and a covert right under the house big enough to handle what ever. then an independent perimeter drain to look after ground water.


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## TheIcehouse1809 (Oct 29, 2014)

Hi Neal!

Thanks for the reply, and I WISH! There's some effort going into flood prevention in the area, we'll see how effective it is. Unfortunately, all I can do on that front is show up at budget hearings and pre-submission meetings for developers. The last flash flood brought 4' or more with it. 

The water that is rotting the floor joists in the basement is seeping up through the crawl space. No standing water that I am aware of, so the regular moisture flow of the water table is where I'm really trying to make a difference.

I'm pretty lucky compared to my neighbors. Many of their homes take on multiple feet of water in their basements, some buildings are actually built of the stream itself! Last flood, my place was the only one that did not take on water. I attribute that to good placement, and thoughtful and knowing landscaping from the folks who owned this place over the last hundred years. 

I think I can also make heating the home more efficient this way.


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## nealtw (Oct 29, 2014)

We build houses on hill sides and mountains and once in while we get things like underground streams filling the hole before we get the foundation in. Most of the time that is looked after with a perimeter drain and sometimes a sump pump. One time they located where the water wanted to go and dug a trench and filled that with 3" crushed rock and we built the house on top of it.
Most time a perimeter perferated drain on the outside just below the level of the slab or crawlspace floor will keep it dry.


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## slownsteady (Oct 29, 2014)

nealtw said:


> We build houses on hill sides and mountains and once in while we get things like underground streams filling the hole before we get the foundation in. Most of the time that is looked after with a perimeter drain and sometimes a sump pump. One time they located where the water wanted to go and dug a trench and filled that with 3" crushed rock and we built the house on top of it.
> Most time a perimeter perferated drain on the outside just below the level of the slab or crawlspace floor will keep it dry.



Based on this post and others by the OP, we're not talking about ground water, but a rush of water in a storm. Trench and /or wall on the affected side? Jack up the house? The slab may be helpful, but water has proved it can beat the [email protected]!t out of almost any barrier.


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## nealtw (Oct 29, 2014)

slownsteady said:


> Based on this post and others by the OP, we're not talking about ground water, but a rush of water in a storm. Trench and /or wall on the affected side? Jack up the house? The slab may be helpful, but water has proved it can beat the [email protected]!t out of almost any barrier.



I suggested a basin for the flood, but you still have to deal with the day to day high water table.


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## bud16415 (Oct 30, 2014)

Around here storm water retention has taken on a life of its own. They are building more retention ponds than they are new construction. I saw a Dairy Queen built where the curb about 10 foot into the parking lot was paved and a pad paved one car length at the drive thru window the rest gravel. I asked the owner when he was getting the lot paved and he said never. He couldn&#8217;t afford and didn&#8217;t have the room to build a one acre pond. In fact he even downsized the store because the total sq. ft. covered was going to be more than the lot size could support even though his property was surrounded by 500 acres of farm land. If he wanted a bigger store so people could sit inside he then had to build the pond under his property with huge tanks buried in the ground with pumps and such. 

The fact your house has stood all these years is that there was naturally storm water retention until the land uphill from you was allowed to run off freely. A lot of this is nonsense but in your case I feel you have the law on your side and I would be going up the chain of command until I got some results. It sounds like your local planning commission is looking the other way or something and I would get together with your other neighbors in the same place you are in and raise some real Hell. Call in the feds to have a look at this if the locals are not. This is such a hot button issue these days once you find the right people something will get done. 

These kind of problems are bigger than what one person can do normally and if you could divert the water you are adding to someone else problems. Sounds like you need a big solution. 

Best of luck and don&#8217;t give up on the fight.


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## TheIcehouse1809 (Sep 20, 2016)

UPDATE to include devastating flash flood 30Jul2016.

This time The Icehouse (my home) took a massive hit. The road washed away exposing my foundations to the base and 4' of sewage pounded and swashed through the freshly exposed coal chutes into my workshop and utility spaces. That crawl space is in the same shape as before, oddly enough. I was expecting the flood plain out back to expand and was prepared for that...not prepared for it to come through the front though. 

Now I'm not the only one thinking slab where the crawl spaces used to be. Not to prevent water from below - specifically to handle water from above. 

So - back to the original discussion, if anyone is interested in chiming in...

6" Gravel, then 30mm plastic, then CR6. Where do I place insulation to prevent radiant floor heat from being sucked down?


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## nealtw (Sep 20, 2016)

You can put the foam under or above the poly sheeting.
As you will always have a chance of flooding I would make the slab 4 1/2 inch thick with a grid work of rebar 5/8" 20 inch grid.
Then after each flood you can check the floor buy tapping it to find hollow spots, and that is fixable with out loosing a floor.

There is a school of thought about no insulation under the slab and sand below is a heat sink that only take start up heat and maintains heat longer when the power goes out.
Water below the floor would kill that idea and I have not seen a study that compares the two ideas.


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## beachguy005 (Sep 20, 2016)

When I did mine, a 960 sqft with radiant, I added sand then 4" of compacted crushed stone, vapor barrier, rigid foam insulation, 6x6 steel mesh that I attached pex to with cable ties. You also have to insulate the perimeter of the slab to act as a break and prevent heat loss out of the slab. Poured a 5" slab on top.
The amazing thing is that even though I was in North coastal MA, in the winter you could turn off the heat to the slab and just lose a couple degrees a day.  Always fired it up for the noreasters.  Slow to heat though, but nice to walk on barefoot.


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## nealtw (Sep 20, 2016)

beachguy005 said:


> When I did mine, a 960 sqft with radiant, I added sand then 4" of compacted crushed stone, vapor barrier, rigid foam insulation, 6x6 steel mesh that I attached pex to with cable ties. You also have to insulate the perimeter of the slab to act as a break and prevent heat loss out of the slab. Poured a 5" slab on top.
> The amazing thing is that even though I was in North coastal MA, in the winter you could turn off the heat to the slab and just lose a couple degrees a day.  Always fired it up for the noreasters.  Slow to heat though, but nice to walk on barefoot.



Up here we have to do the wall or the floor not both.
If you are doing the wall it needs to match the ground level and go the depth of the frost.
Not that both would hurt anything.


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## beachguy005 (Sep 20, 2016)

Not doing the wall with rigid foam but just under the slab and around the perimeter of the slab.  An in slab radiant heat system insulated like that gives you an isolated and insulated monolithic heated slab and you don't lose any heat to the outside.


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## nealtw (Sep 21, 2016)

If you are putting heat in the floor, make a detailed drawing of that, so if you ever have to mud jack the floor you will be able to locate a safe spot to drill a hole or a bunch of holes.


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## TheIcehouse1809 (Sep 21, 2016)

beachguy005 said:


> When I did mine, a 960 sqft with radiant, I added sand then 4" of compacted crushed stone, vapor barrier, rigid foam insulation, 6x6 steel mesh that I attached pex to with cable ties. You also have to insulate the perimeter of the slab to act as a break and prevent heat loss out of the slab. Poured a 5" slab on top.



Regarding <4" compacted crushed stone>
You don't mean crush and run (CR6) do you?
I was thinking CR6 for it's coverage and impervious quality. But then I still need at least 4-6" washed gravel below that for drainage, right?

How does this look:
~~~~~~~~~~
5" slab
remesh - tie in for pex
4-5" EPS foam board
30 mil liner
4" CR6
4-6" gravel

(perimeter insulated by EPS foam board)
~~~~~~~~~~

Looking at EPS for longevity and eco-sensitivity. Seems like I can either go way high end with bells and whistles, or I cap shop for plain old sheets for everyday projects. How do I shop for the right stuff without breaking the bank?


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## beachguy005 (Sep 21, 2016)

I used 2" rigid foam as I recall.  As for the crushed stone, it was recommended for under slabs.  I don't know why you need washed gravel for drainage, it's under the slab.  You don't have to get too crazy with the thickness of the under slab insulation...heat rises.
You also need to be careful in laying out the zones and the spacing of runs of pex.  They need to be runs of nearly the same length and not too long.


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