House extension - quote from structural engineer

Clive_Woody

We are having a conservatory replaced with a brick built, tiled roof extension. Our architect is working on the building regs drawings and advised that we need a structural engineer to complete various calculations.

The extension is a simple 4m x 5m rectangular design going out from the back of the house (detached house) and comes under permitted development rights. The current opening between the house and the conservatory will be made wider when the extension is completed so a new RSJ needs to be installed.

Our architect (a family friend so I don't think would take the mickey) has recommended a structural engineer who has quoted £400 + vat for his work. I will be honest and admit that I have no idea how complex these calculations are but this seems quite expensive for what is in my mind a fairly straightforward design of extension (rectangular box stuck on the back of a house).

Can anybody advise if this seems reasonable; I appreciate that without seeing plans this may not be easy to do? We live in the South East (Sussex) so appreciate that prices are generally higher down here.

Thanks in advance

Moby_Tide

As your friend and architect has recommended them it's safe to assume you are being ripped off and should proceed without them

gavinh1175

We had structural calculations for extending 2 openings for bi-folds.
2 x RSJs. £300 + VAT. I live in Kent.

System

is the engineer purely calculating the new opening requirements or is the quote for foundation design/roof design etc of the whole extension including the new opening to existing house?
£400 plus VAT is less than a days work for most chartered engineers that I've seen
if you are not happy with it you could send the drawings to another couple of engineers to get quotes

Clive_Woody

the_r_sole wrote: »

is the engineer purely calculating the new opening requirements or is the quote for foundation design/roof design etc of the whole extension including the new opening to existing house?
£400 plus VAT is less than a days work for most chartered engineers that I've seen
if you are not happy with it you could send the drawings to another couple of engineers to get quotes

Thanks

To be honest I have no idea what calculations the engineer will be doing, presumably whatever the architect can't do. There is no break down of work in the quote from the engineer.

This is the first time I have had work like this done so I am completely naive of what is required in terms of who does what. I had assumed that roof design etc would come under the remit of an architect but thinking about it I guess there are lots of fun load bearing calculations to be done (no idea if that is covered at architect school...).

Foundations again is something I don't know much about, I appreciate that the building inspector can demand particular depths based on soil type, proximity of trees, etc, but again I guess this needs to be specified in the building regs drawings before being sent to the council.

Potentially this is sounding like the engineer will be doing a bit more than just a couple of hours work so the fee may not be unreasonable.

teneighty

If the architect is a family friend why dont you ask them what the engineer's brief was?

I would suggest that is is very unusual to have special engineer designed foundations and a complex roof design requiring calculations for a small residential extension. Surely the architect would have mentioned that as it will have major implications for the build cost. So I suspect it is just the beam calculation for the new opening.

If that is true they are taking the mickey. They should be able to work from the plans and charge about £200. Once you know the scope of works get other quotes but of course that runs the risk of upsetting your architect and his chum.

System

teneighty wrote: »

I would suggest that is is very unusual to have special engineer designed foundations and a complex roof design requiring calculations for a small residential extension. Surely the architect would have mentioned that as it will have major implications for the build cost. So I suspect it is just the beam calculation for the new opening.

maybe it's different here in scotland then, we normally have an engineers design certificate to cover the structural design - which always includes building specific foundation/roof and frame calcs

teneighty

maybe it's different here in scotland then, we normally have an engineers design certificate to cover the structural design - which always includes building specific foundation/roof and frame calcs

Blimey, I hope they never introduce that system down here. Engineers are enough trouble as it is. If they start sticking their noses in every aspect of the design the costs will be astronomical.

Interesting point though, I always forget how different things up there.

Clive_Woody

Due to large trees in close proximity to the planned site of our extension and clay soil it now looks like the foundations may need to go down to 2.5m

I am guessing the amount of digging and concrete needed for these foundations compared to a more standard 1m depth is going to add significantly to costs.

I know it's a long shot but could anybody guesstimate how much extra an extra 1.5m depth of foundation might cost on a 4m x 5m extension? There is good access to our garden so the builders could bring in a mini digger.

Thanks

grannyjo

we are having a 2 storey extension approx 7m by 3m. If the foundations have to go deeper than the quoted 1m, the builder says it will cost an extra approx £3000. He says he has to get a specialist company in.

Clive_Woody

grannyjo wrote: »

we are having a 2 storey extension approx 7m by 3m. If the foundations have to go deeper than the quoted 1m, the builder says it will cost an extra approx £3000. He says he has to get a specialist company in.

Thanks grannyjo I suspect it was going to be £1000s extra.