Not my usual bailiwick, but, I got a referral to some folks who want me to add a 10×12 screen room onto their circa 1961 Levitt ranch. The house is built on a radiant heated slab. The clients insist that the addition will always be just a screen room. The project will be permitted/inspected.
I believe the new concrete has to pinned to the old. Since the new slab will be unheated, would it be advisable to insulate the new slab? Even with the insulation, will the new slab act like a heat sink and draw heat from the house slab? Is advisable to pin the old/new footings then use 2″ rigid foam(?) as a thermal break where the slabs meet?
I trying to get a spec together so I can get some bids for the footing/slab work.
The clients are on a tight budget, the frost free depth is 30″ (Central NJ).
Many thanks,
Jim
The awful thing is that beauty is mysterious as well as terrible. God and the devil are fighting there, and the battlefield is the heart of man.
– Fyodor Dostoyevski
Replies
The clients are on a tight budget, the frost free depth is 30" (Central NJ).
To be on the safe side I would suggest using 36" unless this is in South Jersey
Jeff
Edited 7/21/2009 7:37 am ET by Jeff_Clarke
I'll double check, but, I believe Monmouth County is 30". Please allow me to reiterate with emphasis, the tight budget aspect of this project. If I didn't know the folks are on a tight budget I'd be prophylactically tubing the slab for future conversion to conditioned space, framing with an eye to future insulation spaces, yada, yada, yada.No matter how much I dislike the phrase "it is what is" this is simply a screened in addition to a modest home. I will make it stronger than the code requires, and as handsome and forward looking as the client's budget allows. In the end however.... It is, what it is, and if it's too expensive, it won't get built.
The awful thing is that beauty is mysterious as well as terrible. God and the devil are fighting there, and the battlefield is the heart of man.
- Fyodor Dostoyevski
Edited 7/21/2009 8:26 am ET by FNbenthayer
I'm in Union county. The frost depth here is 36", but Monmouth county is a little further south so it might be 30". In actuality, either depth is much deeper than the ground ever freezes.
We use 36" in Mercer Co. directly to the west of Monmouth.
Why push it?
Jeff
Why worry about either depth? Just use a frost-protected shallow foundation. Run 2" foam under the whole slab and out beyond the perimeter, and you can do just one pour and underslab insulation is built in (sort of).
A thermal break at the existing slab is a good idea but you might want to use heavier bar than normal. Something like #5's at 12" o.c. to account for having to span the foam. Just a guess.