Structural calculations and Structural Engineers

[JK47]

Hello,

I need an advice of greater community as I am rather stuck and out of ideas.

I want to renovate my late 70s prefabricated concrete town house. The 220mm hollowcore concrete floor slabs are supported on 200mm concrete party walls. Span is 5m. Currently external walls are 100mm thick timber frames with some long gone insulation between ply sheets. It would not be exaggeration to claim that thermal and sound insulation properties are non existent.
So I want to knock existing external walls down and replace them with 150mm turbo blocks with WallReform type external insulation.
Contacted the council and they said I needed planning permission and Building regulations approval. And to satisfy building regs I would need to show that existing structure can take additional load.
Thinking that planning permission would be much trickier to get then submitting Building notice I first applied for planning permission and while waiting for a decision started to call local and not so local Structural Engineering companies.
I was asking if they can provide the calculations that would satisfy the council’s question of “existing structure being capable of taking proposed load”.
All of them were claiming that would be no problem and none of them called me after looking at the house.
Then one company actually agreed to do the calculations. And, being naive and stupid and quite happy to get someone who can actually do it, I paid them upfront. After sending my drawings I was promised that it would take 2 weeks to do the calculations.
Three months later after me harassing them on almost daily basis they finally sent me the calculations. For a timber frame wall. As they could not assess the structure. Curtains.

(/rant ON)
I am absolutely appalled. 5 out of 5 structural engineers could not do what 2nd year Civil Eng. student should do to pass his exams.
As soon as they see no brick walls / no timber joists / no need for beloved RSJ but necessity to actually so some structural calculations (I know, horror!) they retreat with pleasant smiles and tails between their legs.
(/rant OFF)

I would like to ask if it is realistically possible to get these calculations done (i live in SE London) and if someone can point to / recommend a company that would do the structural calculations on existing concrete structure. (I have all the information on proposed wall, like materials, total weight etc.)

Picture quality is somewhat bad, looks like it has been resized or recompressed when uploaded. But hope still will give an idea of what I want.
[UPDATED] The wall in question is first floor with the door.

Untitled

• JK47
• 11 Oct 2010
• 1

Untitled

• JK47
• 11 Oct 2010
• 1

Untitled

• JK47
• 11 Oct 2010
• 1

 

[jeds]

Tricky one unless you can be absolutely certain of the construction of the hollowcore slabs. I presume these are prefabricated slabs?

 

[JK47]

Tricky one unless you can be absolutely certain of the construction of the hollowcore slabs. I presume these are prefabricated slabs?

Yes they are prefabricated. Some slabs are exposed, so can be inspected. One even has a service hole for electrics so i guess it is possible to look inside if it matters.
Other then that I do not know how or where to get structural drawings / specs for the house. (which would be ideal of course)

Other thing, on second floor there is internal partition wall of solid reinforced concrete resting across 2 slabs dead in the middle of the span.
It is 80mm thick, 2400mm heigh and 3.4 metre long and (assuming density of 2400 kg/m^3) weighting almost twice as much as my proposed wall with door, windows inside/outside render etc. included. (Slabs are of the same depth )

My proposed wall has a blocks/mortar weight of under 500kg and total weight including everithyng is under 900kg. Over 5m span.

 

[Static]

I may have missed something but from what you describe your replacing existing timber framed first floor external walls with blockwork.. now do these walls line up with the block walls below?

If so then the only real issue is addequate foundations.. as you will be adding extra load.. as well as a little stability checking.. maybe some roof straps.

Your better off choosing your SE by the size of the job.. small job.. small local company.. you should go back to the company that did not produce what you asked for, quoting their original brief/quote.. maybe ask for a refund / completion of said works as stated..

 

[JK47]

To Static

I realised that initial post was possibly a bit vague, so I updated it with more pictures.
The wall in question runs alond the whole span of single slab. It is not on ground floor but on the first and below are 2 garages.

 

[RonnyRaygun]

I realised that initial post was possibly a bit vague, so I updated it with more pictures.
The wall in question runs alond the whole span of single slab. It is not on ground floor but on the first and below are 2 garages.

I might be missing something too, but you basically want to replace a timber stud wall sat on a hollow core plank, with a new lightweight block wall, sat on the same plank? The wall itself is obviously not loadbearing?

Can't imagine the increase in load would be that great, but as Jeds said, without knowing exactly what slabs have been used, it's difficult to determine their capacity.

Have you thought about beefing up the heat and acoustic insulation values of the existing wall? Or replacing with a new, improved stud wall?

Alternatively, if you are set on using blockwork, you could give additional support to the existing hollowcore plank by inserting steelwork underneath.
Probably wouldn't be able to bear the beam into a reinforced concrete wall so would need columns or piers too...then footings as well...might get expensive...

Although...I suppose the garages don't belong to you so probably not an option