Home Slab Pointers 4

[chuckhydro]

Can anyone suggest a good reference to review which will cover the high points to consider for a residential slab? My future slab will be on sandy soil - hard clay under approximately 3 feet of sandy soil.

 

[RDK]

You local structural engineer.

Rick Kitson MBA P.Eng

Construction Project Management
From conception to completion

http://www.kitsonengineering.com

 

[jheidt2543]

The Portland Cement Association (PCA) has a publication that covers floor constrution details. You can find them on the web.

 

[chuckhydro]

Thanks for the feedback.
The PCA site appears to be a goldmine of information.

I agree that it is prudent to have the finished concept reviewed by someone with the appropriate experience; that is probably a governmental requirement to obtain permits also.

 

[boo1]

check out

http://www.concretenetwork.com/concrete/preventing_concrete_cracks.htm

 

[chuckhydro]

boo1, that is a great web site for slab information as well as other idea starters. Thanks!

 

[boo1]

Consider talking to a few foundation contactors or the building inspector for ideas too. Typically residential foundation slabs are so over designed unless u have unusuall conditions or high load cases.

 

[Grouser]

Also check the American Concrete Institute's publication:
302.1R-96: Guide for Concrete Floor and Slab Construction if you can stand the $91.50 price (before shipping).
The web address is

http://www.concrete.org/BOOKSTORE/bkstr.htm

If you live near a university, they may have it in their engineering or architecture library. Boo1's 1/20/04 post has good advice.

Good luck.

 

[chuckhydro]

Thanks for the good advise. I will discuss with a few contractors and will try to locate the reference in a library. The price is a bit steep for a one use purchase. The construction has been delayed for a while; this leaves some time to develop plans and check details a bit more thoroughly.
Thanks again to all.

 

[dirtsqueezer]

Just a word to the home constructor about your reinforcing steel when it comes time to place your slab. This may seem like a fine point, but I see it enough to find it worth making. If you're placing on sandy soil, the dobies may have a tendancy to sink, leaving your steel flat on the ground come time for the concrete trucks to arrive. If it were my house, I would want to see that steel with 3" clearance from the sand, not just because it's recommended, but for the soundness of the slab for my children and my children's children, ect. Steel on the ground will wick the moisture up, rust the steel. As the steel rusts, it expands, and it will either crack or spall your slab, plain and simple. If the dobies have sunk, you just put another on top of the first. In the end, the steel should be strong enough to walk on, just like the laborers will do during the job. If it's not, put more dobies in. Like I said, it might seem simple, but I think there's some curse on dobies that prevents them from being put in. So, best of luck w/ your project, big points and small.

 

[sc]

A job I did yesterday seems quite relevant to this question.

I looked at a slab that was setout and ready to be poured for a home for a client. The client is the type that reads everything and then applies the new found knowledge (which is great when they get it right). He changed the entire house layout from single storey to double storey to reduce the size of the slab to save money (a bit of tail chasing because the cost of the additional level was similar to the cost of the extra slab). He then talked the designer into providing a reduced interior beam depth and to state the sandy silt as being suitable for founding on (BP 100kPa but will be easily effected by moisture related movement).

During our discussion he mentioned that he was pleased he saved $5000 on the slab cost, now he could place imported tiles and have the more expensive taps in the bathroom. He then got rather upset when I told him that he was a fool. I explained to him that yes he has saved a dollar on the critically important footing of his home but had then blown it on the trivial internal fitout items.

The designer (drafting firm) was promptly contacted by myself and was advised that the slab was marginal in design. The designer advised that the building surveyor had passed the drawings so it wasn't his problem any more. The building surveyor said that the design complied with the relevant standards (despite a lot of marginal assumptions being made by the designer and the building surveyor).

I have advised the building surveyor, designer and owner in writing that my site classification report should now be considered void because the recommended founding depth has been ignored. I can't wait for the law suits in 2 years time when the damn thing moves.

So the moral of the storey is yes do your own research so you can better understand what people are telling you, but take their advice and don't use your new found knowledge to try and cut costs.


regards
sc