Enclosing a Patio: Proper Thickness for Concrete Slab

Learn what should be the proper thickness for a concrete patio slab when enclosing a patio to make an additional room. Find out how a six-inch concrete patio will not support walls for an addition.

LESLIE: Jimmy in Texas has a patio project. What can we do for you?

JIMMY: Hi. Yes, I was wondering – I want to enclose my patio and make it a family room. But I want to know if the concrete slab is thick enough. It’s only about six inches thick.

TOM: It’s not.

JIMMY: I want to know if – no?

TOM: It’s not thick enough, no. And it’s good that you’re calling now, Jimmy, because too many times, in the years I spent as a home inspector and in the many years I spent on the radio, I’ve heard about the results of enclosing a patio or creating an enclosed space – like it’s an addition to your house – on top of what was never intended to be the slab foundation for the room. And so right now it seems pretty easy to just add a door, add a window, add some walls. But what happens is you’re going to see a lot of movement in that soil and you’re going to get a lot of gaps. And so it’s definitely not OK to just wall over a patio and put a door on and call that an extension to your room. If you want to do it you have to tear out the patio that’s there and pour a proper foundation for one, then a new slab …

LESLIE: What would be the recommended thickness?

TOM: Well, you’d have to have a foundation with a footing. You’d have to have a footing that goes down about three feet …

JIMMY: (overlapping voices) Oh, I see.

TOM: … and then you could pour a slab on top of that. You can’t just use that patio slab – like you say, it’s six inches thick –

JIMMY: Right, so …

TOM: – and make that the base of the walls.

JIMMY: OK, I wouldn’t be able to pour another slab over that then?

LESLIE: No.

JIMMY: (overlapping voices) No? OK. OK.

TOM: No, you would have to put a foundation around it. I’m sorry, Jimmy, it’s not that easy and I’m glad you’re calling though because a lot of times we hear about this, you know, many, many years later when, you know, one guy puts up some walls and another owner comes in and puts in some windows and somebody else puts in some doors and then somebody finally adds heat and then the whole thing starts to fall apart and you wonder why.

JIMMY: Right. OK. Well, I wish it was that easy, but I guess not. OK.

TOM: Alright, Jimmy? Thanks so much for calling us at 888-MONEY-PIT. And just enjoy that patio outside. It’s lovely weather (Leslie chuckles) in Dallas, Texas.