Residential Slab-on-Grade Crack Control 1

[phamENG]

Looking for some opinions. Who bears the responsibility of crack control design, particularly in a residential setting?

In many residential projects, the architectural "permit set" and the structural drawings are completed and submitted while the architect works with the owner to finalize finishes (and other non-code impacting items) to save time. Or...they never do it and it's left for the contractor and the owner to work out directly during construction. Sometimes after the slab is already poured. This makes crack control design nearly impossible. A crack control design for a floating vinyl floor is going to be very different from thin set tile, since the latter will telegraph any cracks and the joints have to be coordinated carefully with the tile. Add in the random geometric changes, influence of finishing (or not...it is residential), etc., etc. it feels like a fool's errand to even make an attempt.

I'm thinking of switching to a general crack control specification that gives maximum joint spacing and details, but doesn't provide a detailed plan of joint locations but also leaves other options open (like fiber reinforcement) to allow the contractor to select the best method for whatever gets decided after I'm left out of the loop (because I don't usually know a house has been built until I a) drive by and see it or b) there's an issue on site). But I'm hesitant to drop below the standard of care if, indeed, the standard is that I should meticulously work out crack control for every house.

 

[Enable]

Contractor should bear the responsibility for a simple SOG with no reinforcing. Once you get into reinforcing it's probably on you. You do a lot more residential than I do but here's how I have seen it handled around these parts:

Option 1: Do and say nothing or say something to effect of "finish / cutting by contractor. Co-ordinate with Architect for desired final product" (~25% of the time)

Option 2: Spec max spacing / min depths / state no irregular shapes (must be reviewed). State acceptable finishes and beyond that must be coordinated with the structural designer (e.g. vinyl flooring okay, large format tile requires a site specific crack control plan, etc.). Provide reference to appropriate ACI standards. Specify 14-day wet cure in general notes. (~70% of the time)

Option 3: Option 2 + provide site specific layout (~5% of the time)

I've only ever seen option 3 on mega custom homes where architectural features are fully spec'd and the architect is anal about getting the desired look all the way around.

I happily sleep soundly with Option 2, which is what it sounds like you want to start implementing. Also note that that the finish installer accepts the substrate once they put their product on it (or at least they implicitly do). So you can put in the general notes that acceptance letter of the substrate by finish trades to be provided prior to application as a CYA. You won't receive this, but if it goes wrong, you basically told them finish contractor was to look at the thing prior to application / make sure it's acceptable (which they are supposed to do anyways); they didn't, so sad.

 

[phamENG]

Thanks, Enable. Option 1 is certainly preferable...but I think Option 2 with your acceptance letter idea is an appropriate standard for most jobs I do. I'll give option 1 to the penny pinchers and option 3 to the open check books...

 

[JLNJ]

You might consider Option #1 with a note directly stating that cracks are inevitable and that you are not responsible for specifying control joint locations or crack control methods. The more direct the approach the better for everyone involved. Then you have the option of asking for more money for this type of non-structural work.

 

[EngineeringEric]

We lean on Enable's Option 3 for all Slab on grades showing a nice grid/aspect-ratio/corner details, but we add in the notes of Option 2 always. When we can, we state that the sawn joint plan is a recommended plan and shall be reviewed with the finishes and concrete placement. it sounds like a punt, and maybe it is, but my intent to reduce uncontrolled cracking, not accommodate all potential finishes at the expense of my structure, sanity, and budget.

For tile, I feel if you are spanning my joint, move the tile to accommodate the structure or detail it so it has a slip-side, i'm sure the manufacture has a detail for a few inches of spanning over a joint. I'm tired of accommodating the whims of Interior Designers!

 

[XR250]

" 4 inch slab per code" is my typical note. I have no confidence in residential contractor's constructing slabs properly. This keeps me out of finger pointing exercises.

 

[JLSE]

I have a set of spec's that covers a lot of it... max spacing, max aspect ratio. Typical details to address some unique areas... like corners, columns. But the best note I have is a sheet note that requires the contractor to submit a joint layout plan for approval. This, in addition to a general note requiring the contractor coordinates with the non-structural, does the job... I think... even if they dont ever submit the layout.

 

[phamENG]

JLNJ - that's an option I'll use some, but probably not the majority of projects. As for it being 'non-structural work'...I'm on the fence. Does ACI classify a SOG as structural? No, unless it's doing double duty as a strut, diaphragm, or other 'structural' member. But it, in conjunction with the base, is supporting code defined loads. I'm also the only RDP on the project with anything resembling expertise in concrete material properties and behavior. So if there's a problem, I can't imagine that I would get off cleanly.

Thanks, Eric. I agree completely.

I know from personal experience that tile installers tend to ignore the substrate...got into a spat with an installer on a house I own when they rotated the direction of the faux wood tile to "minimize waste" (I bought the tile...) but, in doing so, bridged a decent sized shrinkage crack even though I gave them a detail to use over top of it (aligning a long edge, using color matched sealant in the joint). Had hairline cracks within a few months.

 

[phamENG]

I have no confidence in residential contractor's constructing slabs properly.

Ha. That's one reason I want to use Enable's Option 1....because in the end it probably doesn't matter anyway.

 

[MotorCity]

I can't speak to residential work, but for the projects I work on, its the SEOR's responsibility....the design, serviceability, performance, the details, etc. If we didn't show anything, the contractor would not put them in, put them in too far apart, or put them in with some crazy haphazard pattern. We do option 2 and 3 on every project, however we also give the contractor some latitude in the pattern of saw cutting them by providing some overall parameters. Again, its probably different for residential projects because of the scale, but if you have the freedom to specify them, wouldn't you rather choose the control joint pattern and details rather than rolling the dice and letting the contractor do what he's "done for 50 years" only to find out he's been doing it wrong?

 

[XR250]

Most of the tract builders around here have resorted to non-adhered flooring to better bridge over the cracking. I have been to countless tract homes with glue-down flooring to witness it separating over the cracks.

 

[phamENG]

MotorCity - I used to do mostly commercial work and that was how I did things. Started my own business and found that my region was lacking in good structural engineering for houses while residential construction was booming, so here I am.

The issues I've been running into are, among other things, contractors who didn't pay attention to the lines on the plans (or just the plans in general), frequent requests for changes, and floor finishes that change (or get decided for the first time) after construction has already started leaving us with an incompatible joint pattern. So I can either do a bunch of work and have it wasted 75% of the time, or I can do little to no work and have comparable results. I don't like it, but its one of those market pressures that I feel I'm going to need to give into if I'm going to retain my sanity, as Eric said.