Creating 4m span opening in stone built house

[drpepe]

Hi

I'm getting designs for a single storey rear extension done to replace the conservatory on the same footprint - see existing layout plan and pics below. The house is stone-built with approx 45cm thick walls.

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Our architect tech has suggested opening up the rear wall between the existing door and existing window for access to the new extension.

Sounds great for lots reasons, including light and spaciousness etc. However last year in a casual conversation with a builder, he wasn't keen on knocking this all out due to the construction of the house - he thought it might be a bit risky!

Couple of Qs

1. Would it be a simple matter of putting in a steel beam 4m+ long, or are there other considerations due to span and construction type of the house?

2. How much? (ballpark)

3. Is it risky? Would you prefer leaving a central pillar? What options are there to minimise the size of a pillar?

Obviously I will be going back to the architect with queries and be speaking to builders in due course, but any comments greatly appreciated!

 

[^woody^]

Anything is possible if designed correctly. You'll just end up paying more if its designed incorrectly or poorly.

 

[drpepe]

Anything is possible if designed correctly. You'll just end up paying more if its designed incorrectly or poorly.

That sounds like one of my dad's pearls of wisdom!!

Any thoughts on whether it will be complicated enough to be prohibitively expensive for a home-owner on quite a tight budget, or will it just be a bit more than 'normal expensive', if you see what i mean?

 

[RonnyRaygun]

It's not quite as simple to prop a stone property as it is a brick or block one, due to the variability of the masonry units, but I can't see that it is overly difficult if a bit of thought is put into it.
The structural design would be little different from designing for any other masonry structure. The temporary works just need to be carefully thought about. A structural engineer with experience in temporary works would easily be able to design something that worked, and then it's the responsibility of the contractor to ensure that the temporary works are as designed.

You might however need more than just a beam, as it is sometimes difficult to justify the strength of old stonework. If that is the case you may require columns or a box frame to take the load safely to the foundations. On top of this, you may require new pad footings or underpinning.

You need to get an engineer involved with experience in this type of work, as it could be reasonably cheap, or very expensive - there are too many unknowns to be able to say at this stage.

 

[Jackrae]

Those two upper windows will be a factor in the engineering design as they act to break the lateral integrity of the wall (they create weak spots during the demolition phase). You'll also need indemnity insurance to mitigate any problems with your adjoining neighbours' houses.

But, as already suggested - anything's possible.

 

[freddiemercurystwin]

However last year in a casual conversation with a builder, he wasn't keen on knocking this all out due to the construction of the house - he thought it might be a bit risky!

I would hazard that says more about the builders comfort zone/experience ......

 

[tony1851]

Approx 2 years ago I did a 5+m opening in a stone-walled house; it needed two 203 x 203 column sections side by side. The walls are usually filled with quarry waste and cr*p, which tends to come down. You may need to build piers out of 7N block each end as the bearing capacity is unknown.
As others have said, this can be one of those jobs where you only find out what is needed after you start.

 

[^woody^]

It's not quite as simple to prop a stone property as it is a brick or block one, due to the variability of the masonry units

Does it matter if the kN/m run is in stone or brick/block?

 

[RonnyRaygun]

It's not quite as simple to prop a stone property as it is a brick or block one, due to the variability of the masonry units

Does it matter if the kN/m run is in stone or brick/block?

Didn't you know that a tonne of stone weighs more than a tonne of brickwork?

I meant...more difficult to needle...

 

[^woody^]

Any thoughts on whether it will be complicated enough to be prohibitively expensive for a home-owner on quite a tight budget, or will it just be a bit more than 'normal expensive', if you see what i mean?

Lol. OK son .... it was just really a comment on the skill and experience of your 'architect tech'.

Is he just someone who can draw plans for building control or a proper designer who considers design, feasibility, buildabilty and cost? And is he going to involve Mr Cautious or Mr Pragmatic as the structural engineer?

It should not be much more than any other opening of that size. It's worth doing anyway - as long as you want the open plan look with that kitchen.

 

[^woody^]

I meant...more difficult to needle...

You got me good there.
I didn't know engineers thought about the poor builders

 

[cjard]

I reckon 3 to 4 grand, including the lintel, demo and remedial works..

 

[drpepe]

You might also post pics of the proposition's interior and exterior?

see pics of rear exterior above

Looking at the pictures of your house the coursed stonework on those Edwardian houses in Bristol is usually tied into brickwork on the inside which makes the walls a lot more stable than a Random rubble wall.
Ideally you want a builder that you have confidence in. If someone has a builder whose work they have to question on an internet forum it may be worth changing your builder.

Looking at that rear wall internally under floor level, there is no brickwork on the inside - the same kind of stone is visible. Does this mean it is a random rubble wall?

I appreciate what you're saying about trust in the builder, but I just like to get as many opinions as possible when it comes to something as major as this!

 

[stuart45]

I can't see the back walls too clearly, but the stonework on the front looked like it's in courses which does make it a bit easier to prop.
However where I live many of the old houses were built by farmers etc so the stonework is well and truly random. However the walls can still be propped, it just means you might have to use a few more and take a bit more care.
You may find the inside is brickwork above floor level as it was easier to get the walls right for plastering with brickwork.

 

[cAtLeYx]

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