Concrete Slabs - how should they be joined 1

[edz202]

I am having a new larger conservatory built and I would like to know what is the recommendation for the joining of the new concrete base to the exsisting concrete base.

I thought a steel pinning would be required as I live in an area with subsidence, but the company doing the work says that this is not neccesary.

I would appreciate any advice

 

[RUSSRASCAL]

IF THE STRUCTURES ARE TOTALLY INDEPENDENT, IT IS NOT NECESSARY TO JOIN THE FOIUNDATIONS.

IF THE STRUCTURES ARE ATTACHED AND DEPENDENT ON THE FOUNDATIONS PERFORMING AS ONE, YOU WILL HAVE TO LIMIT SETTLEMENT BETWEEN THE STRUCTURES AND DOWEL THE STRUCTURES TOGETHER. THE GOAL OF GAINING TOTAL HARMONY BETWEEN THE FOUNDATIONS IS NOT VERY LIKELY TO BE ACHIEVED, BUT THEY WILL BE CLOSE ENOUGH FOR MOST SITUATIONS. SITE PREP IS IMPORTANT TO ACHIEVE YOUR GOAL. HENCE IT MUST BE WELL COMPACTED AND ANY PIERS MUST REST IN THE SAME BEARING STRATA AS THE EXISITIN PIER.

GOOD LUCK.

 

[RUSSRASCAL]

A GRAVEL BED UNDER THE FOPUNDATION MIGHT BE HELPFUL TOO ALONG WITH A WELL COMPACTED BAQSE UNDER THE GRAVEL BED.

 

[Focht3]

Where is the site located? That's a very important consideration - since the key factors are the subsurface conditions and prevailing weather.



Please see FAQ731-376 by [blue]VPL[/blue] for tips on how to make the best use of Eng-Tips Fora.

 

[edz202]

The house is in the North of England, ex Mining District, weather typical English ****

 

[haynewp]

I have wondered about this before also. I have placed a footing next to an existing one without dowels and the buildings be tied together without any problem, but I would hesistate if the soil is poor, the loads are very high, and if the 2 buildings are being connected rigidly or with a brittle material.

 

[edz202]

This conservatory is Glass (very brittle) with pvc being laid on an existing concrete base/additional concrete base as it is being extended from the original size

 

[pba]

I list of points for consideration in no particular order.

You don't say how old the original base is - This may be relevant. You refer to a base - are we talking about a strip footing under the wall line or is the conservatory to sit on the edge of a ground bearing slab?

In either case the cost of inserting dowels cannot be significant. If you want them - get them.

Most PVCU conservatories come with a warranty. Check to see if this covers the foundations.

Glass is indeed a brittle material but this is probably of little relevance to the issue of foundation movement as the distortion will effect the PVCU frame first. The glazing units usually have a gasket seating which will accommodate all but gross movement. If you are expecting gross movement than the foundation solution is WRONG regardless of dowels.

 

[edz202]

Thanks for the good point about the warranty covering the foundation, I will raise the matter with the company concerned.

We are not expecting any gross movement, just slight subsidence, the original base is twenty years old and is a ground bearing slab.

The cost is not the issue, just the company saying it is not required.