RSJ- Building another storey above a single storey flat roof

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Jitno123

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Hi there,

As per the title I have granted PP to build above my flat roof single storey kitchen. I understand that a steel beam will need to be inserted into the load bearing walls.

How does this work in terms of building control, structural plans etc. Will the inspector's need to see calculations for the beams ect when they come to inspect. The builder that's undertaking this job has submitted a buildings notice, and has arranged for this in the building regs along with the new roof.

Also my building knowledge is limited...could someone explain how exactly do they build above the steel, as there is no load bearing wall underneath, just a kitchen ceiling

Many thanks in advanced and apologise for my lack of knowledge!
 
First one (sorry to be cynical) but make sure your builder really has submitted a building notice- phone call to building control should confirm that, tell them what you're planning on doing and make sure that matches with what is on the notice.

Second one- yes you'll be needing a structural engineer to verify the existing walls have the capacity to carry the weight of the build above, their report will usually specify beam size and weight. Your builder may have included this in his quote.

Building above the steel- once the beam is in place and restrained (so it can't twist) it becomes the foundation for your upstairs wall. The beam transfers the weight of the new wall to the existing walls that the beam is fixed into

Hopefully neither of your kitchen walls join to your neighbours houses- if they do you need to look at Party Wall stuff as well

Have fun
 
Hi,

Thanks for your reply,

I can confirm the builder has submitted a buildings notice, as London building control (LBC) have posted me an invoice quoting the works which includes a part 2 storey extension and a new roof. Builders architect did the initial planning application for the new roof and side extension, but i haven't seen any structural reports yet for the building regs, so ill chase him for this.

As the part 2 storey extension is on the building regs letter, does this mean the inspector will do their own checks to ensure the steel is suitable, or at least check the structural plans?

Luckily no part walls are involved!
 
Hi Woody,

RSJ is needed as there is no load bearing wall below, in fact theres no walls at all below where the new 1st floor wall will be built, its just a kitchen ceiling

Thanks
 
So, the wall is set back from the ground floor and there will be some sort of small roof canopy to cover the gap afterwards?

Anyway, yes a steel beam is common, but a standard lintel can be used if the span is not too great. If a lintel is used, then no engineering calculations will normally be needed and no padstones. If beams, the council may want calculations to prove that the beam is suitable and the padstones are too. Ask at the council first, as many accept certain steel beam upto certain spans without calculations.

The council should not want trial pits to check the loading of the existing walls unless its a dodgy extension that is there already.

As this is on a notice, you are reliant on the builder knowing what to do. But be careful, as if he does things wrong, then the inspector will want things put right. And you should not have to pay for any such work, as the builder should build correctly in the first place. Be clear on responsibilities and payments, and ask to be told and agree to any deviations from what you agreed when you instructed the builder. And make sure that you will get what you expected to get, not what the builder wants you the have.

Regarding the beam or lintel, I would advise to make sure that it is put up above ceiling height so that when its all done, you have a flat ceiling with no beam visible below it.
 
Oh, and remember that the building inspector will only come out two or three times to check certain things. He does not look at everything, and wont check quality. So dont rely on the inspector checking the work for you.
 
Hi Woody, thanks for the reply,

I will attach the existing side elevation to show you what i mean.

I do understand buildings notice means relying a lot on the builder, but we have a fixed price agreement on paper for the entire job, stating hes liable for any screw ups basically.
 
Woody,

Heres the existing side elevation link:http://pasteboard.co/wI4CsveAq.jpg

The window you see there will be moving, and that should give you an idea of why the steel is needed. Hope that helps

I dont think a concrete one would be suitable as its about a 4meter span

So the plan is just to brick up that corner to come into line with the house and make a room even though there's no walls underneath, hence the steel
 
Steel lintels are available at that span. It might be cheaper to buy a long steel lintel and not pay for steel beams and engineers calculations.

Sort this out with the builders. Bear in mind that if the builder has a mate who is an engineer, then he could want to give him the work, or it could be a way to get something necessary done cheaper. Just remember that there are options.
 
Thanks for the reply

Just a quick question with the lintel....will it be able to support a cavity wall?
 
Patened steel lintels are designed to carry cavity walls.
4M is a relatively long span, but there are lintels which will span this, at a cost
I suspect it would be cheaper in material to use two standard steel beams, but if Building Control wanted figures from an SE
(= more £££s) to prove suitability, maybe not?
 
Just a follow up to the thread

I've just received the architect's calculation's. He's seems to have specified a timber beam to support the facing bricks, and then a steel beam to support the blocks (cavity wall). I assume the floor joists will be placed into the blocked wall...but my questions are:

Is it usual for the a wooden beam to be specified for facing bricks? I thought only steel was used

Will this be sufficient to carry the load? Also in the future I may do a loft conversion so will this affect it?

I will be asking the architect about this but I thought It would be best to get some advice from you guys first!

Thanks
 
Hi Woody,

Thanks for the reply...

Just out of curiosity, can a timber beam actually support a wall?
 
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