Rear extension where original wall is staggered/L-shaped

[Londoner]

Hi, just wanted to get some opinions. I'm planning to do a rear, 1 storey extension, permitted devt etc.

My original rear wall is not flat but staggered - part of it is set more forward than the other creating a L-shape (or Z-shape, you could say)

View media item 64199
One side is a galley kitchen, the other side is the dining room. My plan was to extend out the full width and also remove the existing separating wall so it's all open. However, one of the builders who've quoted says that the L-shape of the walls above means I can't do that, and I will have to retain some of the original wall as a solid pillar which would end up in the middle of the extension. I can't simply put up steels like a goalpost, due to the step in the shape.

Weirdly only 1 out of several quoting companies have told me this. I see the logic of it but is there any way round this that isn't hugely expensive, or do I just have to live with the pillar?

 

[freddiemercurystwin]

You can do anything if you throw enough money at it. There's no immediate reason why a beam slung between the existing and new wall to support the corner would not work. That's the trouble with talking to builders without drawings though, you're at their mercy. I know many a good builder who will not even guess a price unless they have a decent set of drawings.

 

[Londoner]

You can do anything if you throw enough money at it. There's no immediate reason why a beam slung between the existing and new wall to support the corner would not work. That's the trouble with talking to builders without drawings though, you're at their mercy. I know many a good builder who will not even guess a price unless they have a decent set of drawings.

Which existing and new walls do you mean? If you mean the existing one in the middle of the house - that's the one I was wanting to remove completely - so it wouldn't be there any more.

 

[freddiemercurystwin]

You could sling a beam sideways across the width of the house and then take a beam from this beam at 90° to the rear of your new extension wall to support the dogleg masonry, then another beam from side to side to support the wall that's further out, lots of beams, probably all quite deep, some columns at each end maybe, all doable no doubt but ££££s. Like this innit with the red as beams and columns blue.

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• freddiemercurystwin
• 25 Jul 2013
• 1

Or maybe just two beams and 4 columns like this:

Picture Title 22

• freddiemercurystwin
• 25 Jul 2013
• 1

Or masonry nibs would be needed to take the beams instead of columns. Columns will need pad foundations.

 

[Londoner]

Thanks freddymercurystwin. Yeah it does seem possible - if i go ahead with that builder I'm going to question this.

 

[tony1851]

He could even use some 152 x 89 UBs!

 

[ey143]

Londoner,

How did this end, I'm very curious because it's exactly what we want to do but across a width of 10m and have been told by others that its either not feasible or very cost prohibitive. We also have a L shaped rear like you and planned to do an 8m rear deep on one side and 4m on the other.

How big was your extension and did you get PD approval because our council rejected our application and from what others including the helpful freddymercurystwin as indicated on my threads, it might not be possible for me to do a wrap around. We also wanted to take out the central wall.

 

[Londoner]

We haven't done it yet but the architect said a pillar isn't essential. We should be able to do it with two steel beams in parallel.

So basically conflicting opinions from builder and his architect. Until we go ahead and do it, I'm none the wiser!

 

[ey143]

Would you be interested in sharing notes on private chat? I'm looking to do a goal post but including the weight of the existing house on the area I want open up. But everyone saying it won't be cost effective.

 

[tony1851]

It's interesting that your architect advises that pillars aren't necessary (assuming that by 'pillars' he means steel columns supporting the beams?).
In practice, that's almost certainly correct and your project would be satisfactory without them.

However, if you have calculations done by an SE and submitted to Building Control, it's possible that the council's checking engineer will bring up the issue of 'lateral stability'. This aspect is raised when you remove a large proportion of a main wall, and usually results in fixing steel columns to form 'goal posts' to enhance the stiffness of the building.

Be interesting to see what your architect and SE come up with here.

 

[ey143]

I had a structural engineer round and he suggested not having horizontal breaks of 10m as it might result in lateral deflection or something like that - basically when the weight of the beams itself starts to deflect inwards in its own wight and then put pressure on the bifolds etc. I've since told my architect to put a round steel column in. Should hopefully save money too.

My extension width is some 15m.