Structural engineering advice; open plan kitchen / diner

[Adaminyei]

Evening all,

I am new to DIYnot but have had a read of some of the informative posts on the forums. I hope I can get some useful advice to help me navigate my current position in the best possible way. From the very start of our discussions with the architect and then subsequently the engineer, I have stressed that I do not want an internal column within the open plan space if at all possible.This was also part of the brief. Here is the background:

- 60's detached house, we have planning permission for a ground floor rear extension as well as other work as detailed in the drawings below.
- Ground floor rear single storey extension (flat roof) to measure 2.4mx6.7m (plus a store adjoined accessed from outside)
- The engineer has come back with his drawings which detail a column within the kitchen. He said that this is unavoidable due to the large span of 6.7m.
- I did loose a little bit of trust in the engineer for a few reasons whilst he was in the process of working for us and this is further making me question his comment.

I have attached the engineers drawings and would really appreciate any insight from those in the know.

Should I accept things as they are? Find another engineer? Push for an alternative solution with the current engineer?

Thanks in advance

 

[^woody^]

What's above. Do you have a floor plan including joist layout and loft, and elevations?

 

[Adaminyei]

Thank you for your response woody,

I have edited the post to provide the existing floor plans and proposed which both include sections. I believe the joists run from the front of the house to the back.

It is a single storey ground floor rear extension with a flat roof. There is an existing bedroom above the garage which we are adding a front dormer and small rear extension to. The floor height will also be raised 5 inches in the room above the garage to match the rest of the first floor.

I look forward to your response

Adam

 

[freddiemercurystwin]

Was it discussed how big the beams would need to be (the two intersecting ones at first floor level) to avoid a column? Are you hoping to achieve a flush ceiling?

@George_engineer

 

[Adaminyei]

Was it discussed how big the beams would need to be (the two intersecting ones at first floor level) to avoid a column? Are you hoping to achieve a flush ceiling?

@George_engineer

Thank you. The steel beam sizes required to avoid the column we not discussed. The engineer responded saying that it was not possible to design the structure without a column. We don't require a flush ceiling, a 20-30cm drop for the steel would be acceptable. Anything more than this and we would have to balance it up with the impact of a column.

We had discussed the possibility of a cantilevered system during our meeting.

 

[Diver Fred]

Speaking from experience - we did a conversion on a cottage, part of that was to remove an external wall that became an internal wall. SE said remove it, the builder we employed, who knew the buildings and footings said if you remove the wall then you will have to replace the wall with steels on the footings and up the remains walls as well as across the top of the new opening - i.e. putting a steel 'ring' around the new opening.

 

[^woody^]

From a quick look, in principle it is normally possible to span distances like that with either a deeper beam or a thicker section beam (or beams).

With deeper beams, there is also the option for the beam to sit higher - at ceiling level, with the beam cut in to the wall above - but that brings with it a cost for the beam, the installation, the disruption and the making good. But even if you don't mind the beam sitting below ceiling level it may well be that the section size required means a deep beam and the associated work above anyway.

You have a flat roof design, so any deep beam may project above the roof, but that's a secondary issue and easily resolved, so not a show-stopper.

The alternative for a thicker beam, or beams to remain within the floor void or a little below the ceiling is one for calculation, it may or may not be possible.

The fundamental concern from a design perspective is that the long beam is sitting on that smaller beam and also taking the corner of the house. Thats a massive point load and that requires chunky beams. But again, it's really just something to run some calculations by and see what section sizes are needed - and then check the feasibility of those section sizes.

You need to go back to the engineer with explicit instruction for an open plan with no column, and see what beam designs are required. Then you need to weigh that up with the cost - most things can be resolved with a technical solution, but it all comes down to "at what cost?"

A possible alternative, would be to move the column to align with the wall where the worksurface and hob will be and then incorporate it into the kitchen design, rather than it being a random column in a random place the main room - that a proper engineer's solution that is.

Another alternative may be reducing the opening widths to reduce the spans to allow no columns.

Set your criteria and what you will and won't accept, and design around that. Also bear in mind what price you are prepared to pay for the solution you want.

 

[Adaminyei]

Excellent advice, thank you Woody

 

[Adaminyei]

Speaking from experience - we did a conversion on a cottage, part of that was to remove an external wall that became an internal wall. SE said remove it, the builder we employed, who knew the buildings and footings said if you remove the wall then you will have to replace the wall with steels on the footings and up the remains walls as well as across the top of the new opening - i.e. putting a steel 'ring' around the new opening.

Thank you Fred