45 x 20 paito slab addition 1

[ChevyBuilder]

I'm looking to add an 45 x 20 paito slab to the rear of my house and garage. The ground is frozen for months at a time around here, the grade is flat and water has never been a problem. There will be a 10 x 15 shed in one corner and the occasional car could be parked out there for months at a time. I've heard about monolithic slabs, two contractors recommended 12" the other 18". Local code calls for 48" footers for load bearing structures but a slab with a shed has no requirements.

What thickness slab should I require?
Do I want a monolithic slab? If so what footer depth and width should I specify?
Fiber mesh or rebar and wire? Any advantage to both??
How do I specify the control joints?
Is 3" of compact stone enough?
Excluding drainage, What are the potential problems that could occur by putting the slab next to the existing structure?
What are the potential gains of moving the slab a few feet away from the structure?

Building Automation Professional

 

[RDK]

That looks a lot like a driveway slab.

In this part of Manitoba, where the ground is frozen for months at time a driveway is typically 150 mm with a mesh of #10m rebar at 24 o/c. That’s 6” with #3 bars at 24” o/c for those not metric. Control joints are usually 3M (10’) spacing. It’s on 150 mm of gravel. Our soil conditions are sand, which means that drainage is not a problem

You should not have any additional problems if you slope the slab away from the house assuming that there are not pre-existing house foundation issues or unstable soil conditions.

People park vehicles on these all the time. There may be some cracking but it’s usually within acceptable limits, especially for applications other that newly build homes where the excavation is still settling. If your house has been built for several years some additional re-bar would control all cracking. Depending what is in the shed the vehicle would most likely be the governing loading.

Your soil conditions and loading conditions may vary.

I’d talk to a local engineer to get an understanding of local practice before I would pay a builder for 18” of concrete. Just the material alone would be 50 cu yds or 38 cu m @ $150 CDN/cu m= almost $6k. ($US 4k) If you could cut this in half it would more than pay the local engineering costs and you would have someone to blame if there is a problem. Typically it could cost you 4 hours (often a minimum billing amount) at around $Cdn100/hr or less.

Remember to specify air entraining and possibly Type 50 cement as well. If you don’t know what this is, ask the local engineer.



Rick Kitson MBA P.Eng

Construction Project Management
From conception to completion

http://www.kitsonengineering.com

 

[boo1]

Consider a vapor barrier under the shed area.

and see:

http://www.cs.arizona.edu/people/jcropper/desguide.html

and

http://www.concretenetwork.com/concrete/frost_protected_shallow_footings/index.html