Home Addition Slab-On-Grade

[AgMechEngr]

I am working on a home addition that will add 200 sq ft off the gable end wall side of the house. The existing home is a 4" slab on grade with masonry stem walls. At this time, I do not know if the slab is floating or poured into the stem walls. The addition will be a bathroom and an extension of an existing laundry room. The laundry room portion is what I am concerned about. Since this will create a room that spans the old slab with the new, I do not know how seamless of a transition I can reasonable create. I certainly would not recommend tile to be installed, but engineered hardwood has a chance.

My current solution is a masonry stem wall on the three exterior sides. Dig down to the existing footing and drill and epoxy #5 dowels to tie into the new slab, which will be a thickened slab on the interior. It is common in this area for the top course of masonry walls to be a L header to serve as the form for the slab.

More info, this is in south Georgia and the soils are not expansive.

What do you all think? I think it all depends on how the original slab was poured at the stem wall where the addition will begin. The easiest solution is to suggest a partition wall with a pocket door at the transition from the new slab to the old, so the flooring could have a more natural transition.

 

[MotorCity]

I like the idea of doweling the old slab to the new slab. That can minimize the chance of any noticeable differential movement. A wood floor would obviously be less susceptible to cracking than a tile floor, but for a laundry room I'd do everything in my power to make it a tile floor. If the joint between the old and new slab is a straight line, I would lay tile such that the tile grout joint mirrors the slab joint. You could then grout that joint or perhaps fake the joint with a caulk or semi rigid epoxy to match the grout color.

 

[AgMechEngr]

MotorCity, that is a good suggestion. I like that.

 

[EdStainless]

My brothers house has laundry in an addon extension. His is only 3' added.
And they purposely made the new floor 2" lower than the original.
They also added a floor drain so it serves as a catch pan under the washer.
The 'short' washer and dryer would drive me nuts but his wife thinks that it is fine.
And no worries about flooding the house.
I think that MC's idea of aligning tile joints and caulking that one is great.

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P.E. Metallurgy, consulting work welcomed