| Comment | With tenaments it's a bit of a "how longs a piece of string" type question, a lot of whats specified depends a lot on exactly where the works are being specified, we always assume the buildings to be some degree of badly made (by modern standards) so all works need to be seen as at worse, not worsening any underlying problems the building has, and at best, offering betterment to the property (big thing with kitchen conversions nowadays, building control use them as an excuse to shoehorn in the upgrading to latest fire safety standards).
With an opening such as yours, widening existing lintels is not something that is possible, generally speaking getting a 'flush' finish really isn't possible, expect a wee \~10cm framing each side & a new steel beam over, in some instances a precast concrete lintel can be used but from your brief descriptions they don't seem appropriate (I'm assuming it's up next to a party wall.
It'd be pretty pricey, particularly with the cost of tradeys & materials at the mo', probably not £5k pricey, bout £600 in steel & fabrication, £1000 in building/struct work altering the wall, temporary propping site fitting beams, £500 in plastering/decorating & whatnot, as a very very rough guide |
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