Foundation for workshop

[Kenfyoozed]

I got my permits to start construction of my shop. While looking over the plans and mulling things over in my head i have a question. My shop will be a post frame construction 30'x40', with a monolithic slab, 4" thick in the center with 8" thick edges. My question is this.... Can I place other "footers" in the center of the shop and still pass inspection? My plans call for "footers" along the edge and none in the field of the slab. The reason I ask is beacuse i may change the interior of my shop over time to different configurations. For instance I may build an office and loft for storage. Wouldnt the walls for such an arrangement need to sit over something thicker than the 4" field of the concrete slab? Or am i over thinking things? And again would more "footers" fail the inspection since the plans do not call for them?

Thanks in advance, and sorry if this is elementary questioning, but my first building project with inspections. And yes i will have friends and family, who work in the industry guiding me along the way.

 

[Carl_NH]

I have done the floating slab here in NH for two buildings and the only time they wanted a footer was for post and a support beam (two story garage) that was 18" deep and 24" around to support the weight of the second floor.

For your case interior walls spread the load across the floor area and arent load bearing - your roof truss system is bearing the load.

But if you plan to put a second story within the truss area and you want an clean span on the main floor you will need to have the trusses made for this at the start.

So technically no you do not need interior footers if they are non supporting interior walls but check your codes for the second story and loads etc..

When I built my barn I said "storage" for the second floor and its a clear span no poles on the base, and the town said "storage" you need 60LBS/PSF joists - $$$. For a normal house second floor they spec 40Lbs/PSF.

 

[vtsnowedin]

I'm an "inspector", Not quite the kind you are dealing with but pretty close. When I check a piece of work against the plans I am not looking for places where they added extra, just places where they failed to do all the plans showed. But in this world where the permit gods are king throwing in an extra footer or two might show you have plans and intent that you haven't yet asked permission for. This will be a clear attempt to evade their permitting process and will be dealt with most severely unless your family or a golf buddy. Good luck.

 

[pat32rf]

Around here the concrete slab thickness on the print is a MINIMUM.(just as code is a minimum) If you want to build better than code, its up to you.

 

[Carl_NH]

Around here the concrete slab thickness on the print is a MINIMUM.(just as code is a minimum) If you want to build better than code, its up to you.

I agree - specs for our area 16" deep, 24" wide and I went 18x24 perimeter berm and looped rebar into the middle of the pad and 6" thick in the pad in most areas. Along with 3 courses of rebar tying the looped rebar together.

 

[Kenfyoozed]

Thanks for the info. I do have some points to consider.

 

[CBW1999]

A couple of "uneducated" thoughts. How much of a difference in cost to increase from 4 to 5 inches (or 6). This might be more "universal" in changing floor plans later. As long as you aren't adding a second level.

I see the point (adding footers) that it might be construed as planning something not on the permit but, you might also consider it slab strengthening to support heavier equipment that might end up in the shop.

 

[sdkubota]

Excallent suggestion...a 4" concrete floor is designed for foot traffic not equipment of vehicles. Also, it takes the same amout of labor to place a 6" slab as a 4" slab so the increase in costs should be only the concrete. The other thing to make your project floor stay nice looking is cut joints at 12' max. spacing for the 6" and 8' for 4" concrete. The cut spacing needs to be in both directions. If you don't cut them they will form on there own and won't be straight or look nice.

 

[Gary Fowler]

You can eliminate the need for saw cutting the joints at 12' by adding nylon or polyethylene fiber to your concrete. This not only strengthens the concrete but allows the concrete to shrink when drying without cracking and if later you have settlement cracks which occur sometimes, the fiber helps hold the joints together.
Ask your cement supplier about this and the cost to add. It isnt cheap but you get much better concrete and should be cheaper than adding 1/3 more concrete.
4" slabs are routinely loaded with heavy equipment like mobile cranes in refineries and chemical plants daily with no adverse effects. Unless you plan to put equipment in your shop that weighs more than 20,000 # a 4" slab will suffice. A 6" slab will help hold a load better on a poorly prepared soil foundation but is not needed and could still break if the soil base is not properly compacted, after all the concrete isnt supposed to hold the load, the soil is. The concrete just distributes it over a wider area. Some areas require the slab to be placed on compacted rock while others only need compacted dirt. Follow your local code requirements for proper base prep and a 4" slab will work for your shop.

 

[sdkubota]

Sorry...but you are incorrect. Poly fiber helps prevent some micro hairline cracks but will not stop or prevent shrinkage cracking. What poly fiber does is make concrete more capable of taking mutiple loading cycles. I have never seen the amount of fibers in concrete come even close to the manufacturers recommendation and without meeting that lbs/CY...you are wasting your money. As an engineer...this is what I would recommend: make sure the sub-base is well compacted or consist of original, non expansive soils, provide 8" og well compacted road gravel below the concrete, provide concrete thickness as I initially stated given the proposed usage, cut contraction joints within 24 hours at the spacing I previously stated, have conctractor spray curing compound immediately after finishing surface.

If the concrete will be exposed to freezing and thawing...have the concrete mix air entrained at 6%. It is an additive the concrete supplier can add...price around $5/CY for the additive.

 

[RDrancher]

Sorry...but you are incorrect. Poly fiber helps prevent some micro hairline cracks but will not stop or prevent shrinkage cracking. What poly fiber does is make concrete more capable of taking mutiple loading cycles. I have never seen the amount of fibers in concrete come even close to the manufacturers recommendation and without meeting that lbs/CY...you are wasting your money. As an engineer...this is what I would recommend: make sure the sub-base is well compacted or consist of original, non expansive soils, provide 8" og well compacted road gravel below the concrete, provide concrete thickness as I initially stated given the proposed usage, cut contraction joints within 24 hours at the spacing I previously stated, have conctractor spray curing compound immediately after finishing surface.

If the concrete will be exposed to freezing and thawing...have the concrete mix air entrained at 6%. It is an additive the concrete supplier can add...price around $5/CY for the additive.

Yep, SD's right-on on this one. You have to sawcut or tool control joints, even with fiber. Even on tooled joints I've always returned after the pour and sawcut to a depth of 1" in the joint. Over the last 35-years of pouring concrete its worked pretty well.

 

[sdkubota]

Sawed joint depth needs to be a minimum of 1/4 the slab thickness and 1/3 in much better. Also make sure you saw within 24 hrs or you may be too late. It is best to saw as soon as possible without the saw tearing aggregate out of the slab.

 

[CAT97]

I agree with the last 2 posts. I have also been doing this for 35 plus years and I highly recommend a saw cut either every 10ft
or max of 12ft each direction. Fiberglass mesh additive is a waste of money IMO. 6x6 wire mesh #9 is very good in the field and
minimum of 3/8 re-bar ( 1/2 inch preferred) 3" up from bottom of footing and 2" down from top of footing. As far a an extra footing
down the middle, wait until after you get your inspection and before you pour concrete go ahead and dig your footing and no one
will know the difference.

 

[sdkubota]

Poly fibers allow concrete to take cyclic loading without failing. I wouldn't necessarily discourage their use most most times they are not applied at the lbs/CY rate required. Not a fan of metal mesh as most times it gets trampled to the bottom of the slab where it does no good. Rebar requires a significate depth of concrete and carefull placement to do any good. Any metal reinforcment in the cent of the slab does almost zero good. Bottom line...if you do everything right, it will still crack where you didn't want it to.

 

[crazyal]

I'm not sure that talking about saw joints is really needed since the OP is in Mobile AL. Unless money is real tight I would also suggest going with 6" in the middle (if not a full 8").