Block and beam vs raft and slab?

[low_and_there]

Hi folks, looking for thoughts on which approach makes more sense for our relatively small extension:

 

it’s about 26sqm total - a mid terrace kitchen and side infill. SE had specified a slab on the basis that he thought it was a slab there when he jumped up and down on the floor. But actually on lifting up the floor it turned out to be half slab and half suspended timber.
 

The ground conditions underneath are basically soil (elsewhere on the ground floor it’s more clay). And it’s not clear how much would need to be dug to remove the soil layer… possibly a lot.
 

We need to put vents and quite a few pipes underneath the new floor and given the soil situation we’re wondering if block and beam would actually be more appropriate.

 

Thoughts appreciated.

[jayc89]

If you have the option, go with a slab. I have both, with a beam + block floor over an old cellar and would prefer a slab all day long. It’s also cheaper if you’re DIYing it. 

[JohnMo]

Never really understood why anyone goes block and beam for anything. Cold breeze under the house when ever it's cold outside.

 

Maybe a good reason, but I wouldn't.

[nod]

18 minutes ago, JohnMo said:

Never really understood why anyone goes block and beam for anything. Cold breeze under the house when ever it's cold outside.

 

Maybe a good reason, but I wouldn't.

Most don’t have a choice nowadays 

[low_and_there]

On 17/11/2023 at 20:37, JohnMo said:

Never really understood why anyone goes block and beam for anything. Cold breeze under the house when ever it's cold outside.

 

Maybe a good reason, but I wouldn't.

Given the rest of the ground floor has a ventilated void I guess I thought may be good to keep consistent airflow instead of just telescopic vents under a slab 

[JohnMo]

9 minutes ago, low_and_there said:

instead of just telescopic vents under a slab 

You don't need vents under a ground bearing slab. You would need the telescopic vents under block and beam to ventilate the space.

[low_and_there]

10 hours ago, JohnMo said:

You don't need vents under a ground bearing slab. You would need the telescopic vents under block and beam to ventilate the space.

No, you don’t need vents for a ground bearing slab. Unless it’s adjacent to a floor void that does need ventilating. And therefore you need to have a route for ventilation to get through.