Full Basement Redo

We are about to embark on pouring a new slab (replacing a rat slab so possibly digging down). We would like to do radiant heating and are looking for any advice from anyone. We renovated our first floor largely ourselves, are very handy and hoping to do as much as we can but are out of our depths.
Thank you,
Caitlin

Guest User | 7 years and 1 month ago

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Lurker | 7 years and 1 month ago

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Digging deeper in the basement is a great idea, but a very big deal. It is absolutely not a DIY job. You can potentially and easily collapse your home, and your neighbor’s, accidentally open your sewer or water or gas line. If you begin without permits a neighbor should and will call, and then you might get kicked out of your house if an inspector decides it’s dangerous.

It’s also just a big deal to break, and dig, and dispose of, and then prep and pour and all that. This doesn’t even touch the radiant (short answer for that–it’s awesome! But you have to get a pro because of the requisite boiler install you’ll need. Also, you might consider having it done on top of your floor so it can more easily be maintained in the future without having to dig up your slab).

As an idea, here’s what we discovered when we had it done on a permitted job.

You presumably know this, but if you dig down, that means your walls are now too short—ie, you have to gut your entire basement to drop the floor. You will need a gigantic 30 cubic yard dumpster, to deal with all the stuff you dig out, and will have to pay someone to deal with all that. Removing a 1 foot deep of dirt/slab x ~1,000 feet floor is a large volume of material.

Structurally, you’re supposed to get soil samples done to make sure you aren’t building on a swamp or sand, and also make sure you aren’t digging too close to the bottom of the foundation, otherwise you may need to underpin your walls. You also will need to put down new foundations for all the lally columns you’ll need to replace under yourmain beam.

Also to dig a 4 inch slab you also need a few inches of gravel, and below that a few inches of insulation, so really a 4 inch slab requires digging 8-12 inches deep. As others said above, you run into issues where you almost certainly will expose buried sewer pipes and water supply. So there may be a limit to how low you can go— your floor can’t be below those, and if you expose them you have a good chance of discovering cracks or holes, which mean you’re on the hook for replacing a lot of plumbing. Which also means lots of permits and cash and time.

And of course if your basement is a furnished living space, for it to be code-compliant you need more than 50% of the height of the room above grade. If you drop the floor you alter the ratio and it may never be code compliant.

In short, of all the jobs to skip the pros, this seems like not a good one.

randolph | 7 years and 1 month ago

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> @chemosphere
> also be done above the slab, correct? with a floor over it?

yes i think so.

chemosphere | 7 years and 1 month ago

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radiant heat can also be done above the slab, correct? with a floor over it?

Guest User | 7 years and 1 month ago

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As an architect I agree this kind of installation should be done by a professional because it would be more costly to fix your amateur job than to pay a professional and have it fixed under warrantly in the long run in the event anything happens.

dougb | 7 years and 1 month ago

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Might need longer support columns along with new footings in the basement for starters. If doing radiant you’d want polyiso insulation below it so that you’re heating the room instead of the earth. I think 2″ is recommended. Also before all this is completed probably should check status of sewer drain pipes, if they’re below the basement floor. Easier to change now, especially if the pipes are 50+ years old.

daveinbedstuy | 7 years and 1 month ago

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As usual, I agree with randi on that.

randolph | 7 years and 1 month ago

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> @caitlinthersey
> radiant heating

i think you will want to hire a pro to do this especially if you are putting the water lines in the new concrete slab. not much room for error.