Garage conversation footings

travis-powers

 As part of some work on my house I’ll be converting my garage, my bricklayer is saying to satisfy building control I need to dig proper footings where the door was for the 800mm high brickwork.

Is there a way round this?

Garage floor is a 150mm slab.

stuart45

6 inch lintels across the front is usually accepted. Would depend on the size of the opening.

grumbler

The slab is nothing - you cannot build a brick wall on it.

Surely, there is some way around, but it's likely to be more expensive than a short usual foundation.

E.g.

Or build a lightweight wall instead of a brick one.

travis-powers

stuart45 said:

6 inch lintels across the front is usually accepted. Would depend on the size of the opening.

Standard single garage, I haven’t started yet just looking for options, thought about timber frame and cladding but this needs to sit on bricks so back to square one!
 In general would I need to involve a SE if I go the lintel route!

stuart45

You shouldn't need an SE, or it wouldn't be cost effective.
The price really depends on who digs out the trench. If digging it yourself it's not worth using lintels. 6 inch lintels at that length are not exactly light.
Talk to your BCO and look at the prices. 

Section62

stuart45 said:

You shouldn't need an SE, or it wouldn't be cost effective.
The price really depends on who digs out the trench. If digging it yourself it's not worth using lintels. 6 inch lintels at that length are not exactly light.
Talk to your BCO and look at the prices. 

Hopefully it would be obvious to anyone reading the thread that the lintels need to be concrete ones - but just in case it isn't..... 

travis-powers

stuart45 said:

You shouldn't need an SE, or it wouldn't be cost effective.
The price really depends on who digs out the trench. If digging it yourself it's not worth using lintels. 6 inch lintels at that length are not exactly light.
Talk to your BCO and look at the prices. 

It’ll be my bricklayers labourer as I see it now if he has to dig out to put lintels in I might as well go down a metre and pour concrete, 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!
On a house built 20 years ago with an integrated garage is there a chance that I may find footings below the slab?

GDB2222

How much extra are you being quoted for digging the foundations?

stuart45

Travis-powers said

On a house built 20 years ago with an integrated garage is there a chance that I may find footings below the slab?

There is a chance, sometimes they pull out more than the piers.

Section62

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.

stuart45

Another reason is that the cavity infill should be 225mm below DPC, so any moisture getting through the outer skin will go well below. Building straight off the slab means the moisture sitting at DPC level.