Several years ago we added a sunroom porch and I contracted a person who has done construction of this type for forty years locally, to lay/pour the concrete slab. I specified that it was going to be an enclosed woodframe sunroom, with a roof joined to the main house, windows and its own entrance door. At the time, I did not know anything about building specifications for slab foundation construction and told him I was depending on his expertise and experience. He said fine - with the hard clay soil and level grade we have (no soil movement anticipated), he would dig an area roughly 6 inches deep, lay 3 inches of #2 gravel, rebar wire suspended 3 inches high off the gravel -- the thickness of the slab being 6 inches. I don't believe the slab was anchored to the main house at grade - just poured till it met the brick facade and to meet the 'old' exterior patio door.

Lately, as I've read more about concrete slab construction, I believe he really should have poured a footing for the slab on the perimeter - at least 24 inches deep (trench) with a 6 inch gravel base. The slab dimensions are 14 foot by 18 foot.
We've since finished the sunroom and that's been 6 years now and there's been no sign of movement in the slab but it still concerns me that it should have some type of footing for stability.

Can someone recommend the advisability of retrofitting a footer to the slab on the 3-sides of the slab that are accessible to equipment? We're considering another project where a slab will need to be poured and it would just be convenient to do this now if it's needed.
Thanks for you time - sorry for the long post.
Gary

 

Why are you worrying without any sign of a problem?

You should not take what you read so seriously since every construction site has different soil and weather conditions. - Remember that most articles are written by writers who have no real experience.

If you are on natural, firm, soild clay with no problems, all you would do with a retofit would be waste a lot of money, create a mess and probably create problems.

Dick

 

Dick,
Thanks for replying to my post. What you said is exactly why I post to the forum -- to check/verify information that I find and want to run by the folks like you who work with concrete every day.

However, my concern did originate from what has happened to a smaller slab (about 6 foot wide by 18 foot long) on the front entrance of our home. This slab is elevated about 7 feet above our lower garage/basement and is the walkway to our front door - we use a stairway to access this from the garage level. It appears to have been laid with only 1/2 a concrete block foundation -- half of it is simply on grade and in the last 4 years that grade-half started to sink - so far it has sunk about 4 inches below where it was when level. This caused a crack in the far length of the slab (which is supported by the partial foundation) near the entrance way door. So I know we're going to have to replace and that's why I began to think about the sunroom slab. Maybe it was going to be a problem later. I just figured if we were going to have a replacement slab poured on the front -- what better time to put in a support footer for the sunroom.
The one difference between the 2 slabs is that the smaller front slab was laid on backfill and I'm pretty sure the sunroom slab is on original undisturbed soil.

You don't say explicitly but I assume in your reply the way the sunroom slab was done is a perfectly satisfactory way given the situation I describe?
Anyway, your advice is to just watch for any problems and address them when they occur; otherwise you might be causing more problems ? The sunroom slab was done very well and is level. I did neglect to mention I'm in the SW PA area where winter temps are occasionally -20 degrees F and normally 20 degrees F to 30 degrees F.
Thanks again,
Gary