Opening wall to install bifold door: how close to corner?

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Hi All,

We decided to start doing some work in the house and put a bifold door facing the garden.
I've made a very rough sketch of what we are aiming to do. The indoor wall is about 3m wide, structure is cavity walls.

The idea is to remove as much of the wall as possible and install support before fixing the bifold doors (made to measure). This part of the house does not have an another floor above it except a "balcony" and ceiling is made up of concrete slabs.

I've spoken to two SE and both seem keen to provide calculation for goal post/picture frame type of structures but they cannot commit on the size of the two support on each side which means I might be left with a return bigger than I expect (and additional cost to design and install these).
Seperately the two builders who came to give quotes both suggested that we should be able to put catnic for cavity wall and still have a very small return in the corner.

In your experience do you think that a goal post/frame will be small enough to be concealed in the walls and allow the bifold to be the full width of the room?
Or would a simple catnic allow for a small return and how much of a return do we need to keep?

Thanks for your advice


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Perhaps there has been some confusion over exactly what you are proposing:

Five site opinions from professional people and no solid confirmation seems odd.
If experienced, any one of the five should instantly have come up with a solution.

Others on here might be more confident but i feel a site view is the only way to proceed with a question like this.
 
On the strength of what is in your post, we feel that your pair of SE are t*ssers, ditto your. two builders
Never heard the likes for goal posts on an opening that size.
Regulations state opening to be 2100 max high.
External brick piers to be a min of 665, (three full bricks)
Compressive strength of the loaded leaf of cavity wall to be a min of 7.3N/mm2 .
As you have concrete roof suggest you use a heavy duty load I.G. or ditto catnic.
Regards oldun
 
It's not possible to answer your question without knowing the loadings. With a balcony and concrete slab roof the chance of a Catnic being suitable is quite small. Press your finger and thumb together hard - I'd estimate about that much chance! Instruct an engineer to calculate the loads and produce a detail Then you'll know the dimensions of the frame and opening.
 
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thanks for your quick answers

There is not doubt that I need the calcs to be done I just want to be sure I ask for the right deisgn to be drawn (lintel, goal post, picture frame). The goal post structure was suggested to avoid having to keep 3 full bricks and make the opening the full width of the inside wall.

The SE suggested that using a goal post or picture frame we should be able to have no return (which I understand mean that the post will fit where the current 100mm concrete block is and maybe in a bit in the cavity?)
 
I don't think the vertical loads are the issue here. The SEs will have suggested a picture frame arrangement to resist lateral forces.
A masonry return pier would do the same thing but will be a lot longer.

You aren't going to get away with a perfectly flush wall, although if you have a cavity wall and can recess your steel column some way into the internal skin and cavity then you might only have a small protrusion which will be barely noticeable once it has been clad, maybe in the same material as the bi-fold doors.

If you can recess the column into the cavity you will have to be careful to avoid cold bridging.
 
Thanks Ronny,

I understand that we are not allowed to let the colmn recess fully into the cavity but it seems that we might be able to recess a bit (will need to ask the BCO about that).

If there is only a small amount of protrusion then it should be fine (few cm). We will only order the bifold once we know the exact opening size.
 
Following further conversation with builder and given the additional cost of the goal post/frame we might go for a simple catnic lintel.

Can the 665mm external brick pier be reduced to something smaller if the SE does some calculation to justify it (some research on this forum suggests that it is possible)?
 
Can the 665mm external brick pier be reduced to something smaller if the SE does some calculation to justify it (some research on this forum suggests that it is possible)?

Yes, it can be done, though you would still need some sort of return if relying wholly on masonry. The problem is that many SEs don't like doing calcs of that type because it takes time - it's much easier to use a spread sheet to design some steelwork.

The issue is not so much the load-bearing capacity of the pier, but one of lateral stability under wind load.

You can have the SE design and detail a 'goal-post frame' with moment-resisting bolted connections. Alternatively, Ancon supply wind-posts which are small enough to fit within the cavity - google 'ancon wind-posts'.

TBH, a lot depends on your existing structure, which is not clear from your sketch, and no-one here can give you a definitive solution.
 
Thanks Tony,

Would it help if I post pictures?

The reason I am asking for help is to avoid having to settle for someone saying "no sir, this is how it has to be" if there is actually a way to do it (as you suggested if SE do not want to do the calc then it might be an easy answer for them to give in which case I'll ask someone else).

If we can reduce the corner to 400m or 450mm then I will have a fairly small return inside the room (100mm to 150mm) which I am happy with.

Would the wind post go inside the side walls or in the corner? If it goes in the side wall I am not sure how they "insert" it? (deconstruct the wall, insert it and rebuild the wall?)
 
If we can reduce the corner to 400m or 450mm then I will have a fairly small return inside the room (100mm to 150mm) which I am happy with.
It's unlikely you would be able to prove that a 400mm pier was able to resist the applied lateral load.
Masonry doesn't work at all well under lateral loads, hence the reason that either long piers or steels are usually specified.

How would a wind post work Tony?

I always thought wind posts were used to restrain masonry panels, not whole buildings?
 
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I always thought wind posts were used to restrain masonry panels, not whole buildings?

True; but I assume this is a single-storey, flat roof extension. If it doesn't project too far out, wind load shouldn't be too great. I've used those posts on a couple of occasions in the past in similar circumstances, and they work (so far!).

But yes, if it was more heavily-loaded vertically (eg the back wall of the house removed completely), then conventional steel frame.
 
Tony, you are right, it is some sort of single storey "extension" with flat roof which was part of the original house (build c. 15 years ago).

The extension is about 3.5m long and 3.07m wide, the roof seems to be concrete slabs.

Anything past the massive RSJ, where ceiling comes down, is single storey (old picture when we were having some other work done)

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