Builder substituting flat block wall for cavity wall

H.E. Pennypacker

Hi,

I have a relative who is getting a single storey kitchen extension built on a standard '90's three bed semi detached house. An architect drew up plans which specified cavity walls on two sides of the extension. The third side, facing the garden has two flat block corners supporting a steel beam which runs over a large sliding window/door.

The builder has built a cavity wall on one side and a flat block wall on the other side. There is no clear reason for this. The architect claims that the engineer specified it after the plans were drawn up. The engineer doesn't seem to think so. The builder claims that its a stronger wall and is necessary to support the steel beam, even though that runs from the flat block corner at the end of the cavity wall on one side to the flat block corner at the end of the flat block wall on the other side. The cavity wall runs in line with the party wall whereas the flat block wall is on the side entrance side.

Does this make any sense? Is there a reason why a flat block wall would be favoured over a cavity wall in this scenario?

BryanF

It one of 3 possibilities imho

1. there is no arch and/or Eng involved.
2. If there is, they have not managed to explain to their clients what the purpose of the walls are,
3. or the client hasn’t understood what they were told.

Without willing or wishing to offer any structural advice: typically the Block on flat is more suitable than cavity block.

H.E. Pennypacker

Thanks for your reply.

Number 2 on your list is definitely the case. The client is anxious to understand what's going on but neither the builder or architect want to explain. The architect recommended the builder and they seem to be working as a team - there isn't a sense that the architect is representing the client's interests.

One of the main concerns is that the builder has deviated from the plan. Should the architect amend the plans to reflect the build? As things stand, if their client wants to sell the house in ten years time, there won't be accurate documentation of the build.

tradesman

The builder sjould not deviate from the construction plans. That is what he has signed a contract to build. He is technically in breach of contract. Block on flat is definetly stronger

Gileadi

Block on flat would be stronger but will have different insulating properties than a cavity wall (which likely is to be filled with insulation)

BryanF

Gileadi wrote: »

Block on flat would be stronger but will have different insulating properties than a cavity wall (which likely is to be filled with insulation)

Hold on a second

Op
Can you clarify we’re talking about cavity block (breeze block) and not ‘cavity wall’ (block/cavity/block)?

H.E. Pennypacker

BryanF wrote: »

Hold on a second

Op
Can you clarify we’re talking about cavity block (breeze block) and not ‘cavity wall’ (block/cavity/block)?

Sorry, I should have been a bit clearer.

There's block/cavity with insulation/block on one side and flat block on the other. The builder plans to insulate the inside face of the flat block wall.

BryanF

H.E. Pennypacker wrote: »

Sorry, I should have been a bit clearer.

There's block/cavity with insulation/block on one side and flat block on the other. The builder plans to insulate the inside face of the flat block wall.

This should not changed unless written direction was provided from architect. And engineers structural confirmation of foundation suitability