Garage conversation footings

travis-powers

I’m updating this as it may be of use in the future.Section62 said:

travis-powers said:

...don’t make sense that a slab deemed strong enough for a car isn’t strong enough for a dwarf wall but rules are rules!

It isn't so much the strength as the problem of differential movement.

The base of the slab is very close to ground level and can be affected by things like seasonal drying out of the ground.  If the slab moves about a bit through the seasons, or under the weight of your car, it doesn't really matter too much and you probably won't even notice.

On the other hand, you will notice if the new wall founded on the slab starts moving around relative to the original walls.  Cracking is one possibility, the other is loss of weathertightness.  The wall could be designed to accommodate the movement, but typically that's going to cost more than a bit of extra digging and some concrete.

I'd also not want to use the slab as a foundation as it could bridge the measures to keep damp and cold out.  Again that's something that can be designed out, but I'd rather keep the floor slab wholly within the inner envelope and not run the risk of having problems later.

This makes a lot of sense, having spent a lot of time finding matching bricks I would have a meltdown should they crack.
Building control came out to inspect the footings for my new garage and has asked for a minimum of 225mm of concrete for the garage conversion.
 The earliest I’m ever on a new build is when it’s up to wall plate, I’m finding getting to the over site stage is a lot of expensive hard work!

stuart45

When you say the earliest is at plate high, who does the joists?

travis-powers

stuart45 said:

When you say the earliest is at plate high, who does the joists?

True I have on occasion fitted posi-joists and flooring but to be honest with the exception of the occasional cut roof I not really interested in 1st fix.
 I’ve spent most of my working life in historical buildings 5 years ago I left it and worked on a new build site which was a big shock but even then I was on 2nd fix and finals.
Now I only work on extensions and improvements.

stuart45

Older properties are generally a lot more interesting. New builds are often about slashing it up.