Foundation query


9 Aug 2020
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United Kingdom
Morning all.

Recently had a quote from a builder to replace our porch slab as it is cracked. The porch was added after the house was built and is an infill between the house and garage which projects out from the front of the property. The back wall of the porch is I believe a stud wall, cladded on the outside and rotten. We would like to replace with a single skin brick wall as we are unable to maintain it save for going on neighbours property. Builder mentioned putting a new footing 12" wide, would this be sufficient to carry the wall please? Who decides what size footings are appropriate? SE just said dig new footings in secure ground. I intend to contact building control to see if we need to involve them but the porch doesn't form part of living space so I'm not sure we will be able to make an application.
Had a bad experience with builder on internal renovations so feel extremely nervous about further works.
Any advice would be much appreciated. Thanks.
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A porch does not come under building control.

The width of a foundation is determined on the witdth of the wall and the ground, but normally at least 3x the wall width. Depth is more important, and should be at least 600mm.

Does this slab actually need to be replaced, a cracked slab does not automatically mean it needs to be replaced? Why has it cracked?
Hi Woody.
Thanks for your comments. SE said porch will affect house. Crack is through centre ( weakest point) but in places is higher on one side of crack to other. Pretty much concrete on earth I believe. Cracking/separation around internal walls doors which appeared suddenly, presumably when slab cracked.
As to why, Woody I have no idea!
A crack is just a symptom not a cause, and you need to know what actually caused the crack and to deal with that.

Floors and walls crack for several potential reasons, and that does not mean things need to be replaced, to need to know why, else whatever you repair or replace with may well just crack again.
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If only Woody! I pressed and pressed to know why porch had cracked around perimeter after no problems for 27 years, or why slab had cracked, told I was trying to find fault with my home! I could write a book and no-one would believe it! Not something I would discuss on here.
Thanks for you help Woody.
May I ask another question Woody please. If we brick up the rear wall in single skin would it need pillars? The wall would be 1.5 m long and supports garage roof. We wouldn't have room for a pillar on the left as it would obstruct the door. Please see crued drawing attached.


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