Please see the following post for background info on my project:
http://forums.taunton.com/n/mb/message.asp?webtag=tp-breaktime&msg=72332.1&search=y
After digging out a big old stump from a 3′ diameter tree that was left right next to the slab on the short side of the sunroom addition, (6″ from the slab), it seems there is no foundation under the outside edges, at least not were the tree was. So I dug down near the outside middle of the long side and also found no evidence of a foundation. From what I can see the slab is about 12″ to 14″ thick around the outside, not sure about in the middle, with 6″ to 8″ showing above ground.
I talked to our inspector last week, there seams to be little record on file of the addition, not much was required back then (better now), he wants to take a look and can’t believe they did what I explained to him. Will see him this week.
My questions are, if there is no foundation under the outside of the slab, why after twenty some years is there no evidence of movement were it was attached to the house addition? Could it be possible there are piers somewhere under the slab? What else should I investigate before I see the inspector? If required to add a foundation, what work should I expect? I can’t seem to find anything in the archives or on the net about building/pouring a foundation under an existing slab to help me visualize what to expect.
Thanks,
Andy
Replies
A good example of slabs without footings are concrete driveways. If the ground beneath it is fully compacted, not clay soil or hard undisturbed ground, it (4" slab)will support a loaded cement truck. A foundation is no guarantee that a slab will not sink.
There are breezeways that have a structural roof between the garage and house. Later, walls are added that are not bearing walls. In some areas the room is called an Enclosed Breezeway, Sunroom or Enclosed Patio. To call it a family room, it would require a footing.
Are you in an area that requires frost footings? If not, you probably have a slab that is not set on soil with much organic matter. Organic matter continues to decay in the soil and compress, causing the settling.
If it must be supported, one method is to have someone come in and screw in some helical piers.
Yes we are, 42" for footers. I called the concrete guy today we'll see what he says.
How far does the slab span? Is it possible that the thickened slab has enough re-bar in it to create a grade beam along the outside edge? They may have done this to save the tree, assuming that it was cut down after the addition.