Any ideas on putting an arch in coursed stonework?

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Part of my residential conversion of an industrial building involves cutting some windows in the front wall
The wall construction is engineering brick inner, stone outer, coursed but with random heights, something like this:
coursed-random-dressed-walling2.jpg

There;s no cavity per se, the brick is like English garden wall bond and the header row is mortared to the stone, with extra bits of stone rubble thrown into what would have been a cavity

I need to cut up to about 400mm away from the top of the stone wall, and put a slight arch on, but the planning have insisted I don't use any dressing like a lintel, or stones running in a curve as one might expect an arch to be formed, with a keystone etc. It has to look just like an arch shape was cut into the straight layers of stone, so i'll need some support for it

The stone leaf is about 300mm thick, the brick is about 200mm thick (on average). The windows must be recessed 150mm

I could use a curved lintel, or even just a bit of suitably thick bent steel (the load isn't significant).. Should I try and fit it without removing the stones (I.e. cut a groove in the stone, fit the steel, then cut the arch after it's all set)? or should I remove all the stones, number them as they come out and put them back in the same place (shaped with an angle grinder to fit the curve of the steel) - this might end up leaving part of the lintel on show, even if I recess it into the underside of the arch. Maybe the steel could be set into the stone further up than the underside of the arch, leaving the stone to wrap around the arch edge.
I could maybe tack mesh to the back of the stone and render it up or make a formwork and vibrate some concrete in. Coupled with the window frames being aluminium and arched at the top I think there'd be suitable support.
I could perhaps form a concrete lintel (the span is only 1.2m) and install it, or better, take the stones out and form them into the concrete as it's setting
I could just fit a stone lintel (I have some colour-suitable from elsewhere in the building) and see if anyone notices

All these seem less than ideal in some mix of terms of time, effort, cold bridging, aesthetic, legal repercussions etc

can anyone think of any better options?
Thanks
 
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Where are they getting this design idea from - the arch with no arch bricks I mean. Is it a technique used in other buildings near you? I can't think that I've ever seen anything like it.
 
As above, that is a ridiculous requirement from your planning dept. If the building is faced in stone, it would be usual to expect an opening to be bridged either by a hefty stone lintel, or an arch of one form or another.

An arch is a self-supporting structure which works by keeping all the masonry in compression, and looks wholly natural and logical in a stone building.

Whoever has told you to do it by cutting the shape in the stone clearly knows nothing about basic building structures. It will look totally naff if you do it that way. It may be a listed building(?) but even so, there is a limit: arches are built, they are not carved
 
One can only assume that planning want to differentiate between an original built arch and a later addition cut into the stone.
Is their criteria only applying to the outside skin? So you can build a proper arch on the inner skin?

Just a suggestion:
I would draw the proposed arch onto the outside wall, then select appopriate whole stones to remove in order to position ( 1 or 2 ) needles right the way through the wall. These whole stones can be re-inserted after the cut stones have been re-inserted and the mortar set.

Will the window frame be strong enough to support the arch?
Otherwise, do as you suggest on the outer skin, with some bent steel. If it's positioned 150mm in fom the outside edge, the window frame should hide it, especially if a little of the underneath of the cut stonework is relieved to allow the steel to be recessed. Ensure that the inside edge of the stonework is properly bedded, even packed with slate/tile, etc.
 
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One can only assume that planning want to differentiate between an original built arch and a later addition cut into the stone.

That's quite likely the reason - but that doesn't make it right in design terms.

OP is required to set the windows back 150mm, presumably to do it the traditional way - which is fine - but then has to carve an arch shape out, which is certainly not traditional.

Will the stone decay where it is cut and exposed on the soffit? How will it actually be cut to an arch shape? If it has to be supported by a shaped steel arch, what happens when that rusts and stains the stonework, as it eventually will?

This is an example of a dull planning- or conservation officer not thinking it through.
 
Will the window frame be strong enough to support the arch?

He can't do that because the frame would then become a structural element, which has to have suitable fire resistance, so Building Control won't allow that.

Perhaps OP should go back to the idiot at the council who wants this nonsense and ask him or her exactly how he should do it?[/u]
 
Where are they getting this design idea from - the arch with no arch bricks I mean. Is it a technique used in other buildings near you? I can't think that I've ever seen anything like it.

It's the latest "craze" in planning in terms of converting old buildings - new features added as part of the conversion should be obvious to even the most stupid of passers by that they weren't an original feature; think a quaint cottage/croft style house with a thatched roof and whitewashed walls, and its extension is an all-steel-and-glass-and-angles affair.. I know it's hypocrisy - things that aren't "in keeping" are rejected. Things that are too in-keeping are rejected. It largely depends on who makes the decision, I suspect. Planning officers will go the "should be able to tell which features are from which period in history" approach, council committee (busload of old ladies) will go for he "I want something in keeping/indistinguishable" approach. Academic/theory vs real-world/practice probably.

The only other windows on this façade have lintels and sills, and castellated stonework around them typical of the period.. These new windows, first went to planning with lintels, sills and castellations; flat out "no". How about just lintels and sills? again, no.. They literally want the windows to just puncture the stonework so they're obviously not 1926, structurally inferior and prone to letting in damp. Ludicrous, but that's the system :/
 
Where are they getting this design idea from - the arch with no arch bricks I mean. Is it a technique used in other buildings near you? I can't think that I've ever seen anything like it.

It's the latest "craze" in planning in terms of converting old buildings - new features added as part of the conversion should be obvious to even the most stupid of passers by that they weren't an original feature; think a quaint cottage/croft style house with a thatched roof and whitewashed walls, and its extension is an all-steel-and-glass-and-angles affair.. I know it's hypocrisy - things that aren't "in keeping" are rejected. Things that are too in-keeping are rejected. It largely depends on who makes the decision, I suspect. Planning officers will go the "should be able to tell which features are from which period in history" approach, council committee (busload of old ladies) will go for he "I want something in keeping/indistinguishable" approach. Academic/theory vs real-world/practice probably.

The only other windows on this façade have lintels and sills, and castellated stonework around them typical of the period.. These new windows, first went to planning with lintels, sills and castellations; flat out "no". How about just lintels and sills? again, no.. They literally want the windows to just puncture the stonework so they're obviously not 1926, structurally inferior and prone to letting in damp. Ludicrous, but that's the system :/
The idea of using materials and techniques that could easily be identified as not being part of the original fabric is nothing new, (William Morris at least!) but such alterations still need to be structurally and practically appropriate. Sounds to me like you've got an idiot straight off a SPAB course who didn't quite understand it. Cutting a stone façade to the shape of an arch with no form of support is just about the most ridiculous idea I've seen in a while. And I think you should tell them that. An inspector will never support such an idiot. Tell them to refuse it and go to appeal.
 
Was there a designer overseeing all this foolhardiness?

In terms of aesthetic design, you mean? It's been a drawn out discourse with planning, taken well over two years, with a mix of architects, ATs and myself.. What we have right now is, I feel, enough of an achievement in terms of size, aesthetic and justice to the building that it wouldn't be productive to discuss things with planning further (not to mention the fact that the rejection reasons over time have been somewhat contradictory and confusing)
 
These new windows, first went to planning with lintels, sills and castellations; flat out "no". How about just lintels and sills? again, no.. They literally want the windows to just puncture the stonework so they're obviously not 1926,

So why should they demand an arch-shape if they want it to look 'modern'? They should then go the whole way and ask you to cut a straight window-head, which could probably be done with a single-leaf Catnic lintel - that would then look completely 'modern', not 'half-modern' (if there is such a thing!).

As jeds, you would be foolish to even try and jump through this pointless- and structurally dubious hoop, and should really consider an appeal.
 

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