A standard raft foundation can be considered for a simple house plan of one storey, subject to engineers design.
This kind of foundation doesn't seem to be covered in Part A of the building regulations - in Part A all loadbearing walls are required to be suported by a strip foundation.
Loadbearing walls in a two storey house can include internal walls or loadbearing studs to support first floor joists or slabs, giving a line load to be transmitted to the ground.
Houses may also incorporate point loads where there are columns or concentrated loads for example at the ends of beams, at and around stairs opes, and at masonry chimney breasts which can occur on internal or external walls.
As long as the point loads, concentrated loads and line loads have been assessed and the design amended to cater for them, a slab foundation designed by a competent structural engineer may be appropriate in the case of simple, symmetrically planned houses.
The main benefit appears to be cost, but the applicability of this kind of construction is limited to very simple or very large and complex structures, because in the mid rage, where most houses exist, the preference is for well designed strip or pad foundations, or piles in extreme cases with ground beams.
In addition, unless your engineer has properly investigated and prepared the ground beforehand and designed the foundation type appropriate to the conditions, merely installing a standard spec raft foundation with some extra rebar can be a disaster waiting to happen.
Rafts can crack due to uneven settlement due to ground conditions and can even "tip" in extreme cases, where for example the ground on one site of the house is more supportive than on the other side.
Where the raft, installed by someone on a "job" basis is a generic raft, but the house isn't evenly "balanced and centred", the raft can be eccentrically loaded which can lead to cracking or differential settlement.
This problem can be exacerbated where a raft is used as a cost-effective foundation to an extension and instead of biting the bullet and tying in the new work at foundation level with a strip similar to the existing dwelling, the raft is chosen for cost and may well end up being costly, sould the raft settle and the extension rotate around the interface with the existing house.
In addition specifying a raft now for a bungalow, without internal loadbearing walls will make it difficult to allow for the later conversion of the attic.
The floor loads will require to be supporte mid-span and that means line or point loads being transmitted through studs that are not design as loadbearing elements.
If you strengthen them or replace them with loadbearing studs or loadbearing blockwork the loads they transmit must be suported by the slab, which has not been designed for this.
So the lesson to be learnt is - build cost effectively now and fail to allow for later vertical extension and you may come to regret it.
In no case proceed to site without proper site investigation, preparation and foundation design by an engineer.
FWIW
ONQ.
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All advice on AAM is remote from the situation and cannot be relied upon as a defence or support - in and of itself - should legal action be taken.
Competent legal and building professionals should be asked to advise in Real Life with rights to inspect and issue reports on the matters at hand.