Adding a storey to anexsisting single-storey extension
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Adding a storey to anexsisting single-storey extension

by lardy2001 » Sun Nov 28, 2010 11:07 am


Firstly great forum - keep up the great work & advice - very helpful.

We are looking to extend out on top of a single-storey extension, to create a bedroom, but I have been given conflicting advice regarding foundations for such.

I heard that after a certain year, any single-storey extension HAD to have foundations deep enough to allow for 2 storey's regardless of how high the original extension will be. Is this the case? If so, which year did this regulation come in as I can't find any information regarding this on-line.

Many thanks in advance for your help with this.



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by andy01 » Tue Feb 01, 2011 11:11 pm

thats not true, foundations have evolved over time from bits of slate and belled out bricks to digging to a certain depth and width (due to bearing capacity of the soil) and pouring in concrete.

you dont have to make them wide enough for two stories, it just makes sense as your doing the initial work anyway, and to build a 300mm cavity wall on a 450mm wide found is not as easy as a 600mm wide found, due to tolerance and messing up setting out/ digging trench

assuming you dont have piles or had ground improvemnt carried out, dig down the side and see if your founds are as deep as the rest of the house. (assuming the house has founds complying with current design stanards would expect about a meter on clay) also how wide are they? depending on bearing capacity would expect min 600mm wide, possibly will require 750mm wide depending on floor span directions and roof span direction

obviously if you deside to continue you will need a structural survey carried out to comply with building regs

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by SPUD1701 » Wed Feb 02, 2011 8:28 pm


Andy is correct - foundations tend to be fitted depending on structure being built and ground conditions, nothing more.

You can either check by digging down existing house foundations or sometimes better contact Local Authority speak to duty Building Control officer or Area officers - local knowledge to see if there is any non standard foundations in area - i.e not strip.

If standards check on line for small buildings guide usually in pdf form gives good advise.

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