Window Sill Construction

What started out as a boiler install has now turned into a Bay Window renovation. Quite how, I'm not sure.

Photos to amuse you:

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?pic=27x2autOkay so it seems I have a the original sills made from disintocrete, worst still they are a 'solid' piece from out to in, all that was in front was the lime plaster - long since blown out.

So it looks very much like I'm going to have to recast new sills (especially after an over enthusiastic SDS session!) My aim was to remove the culprit iron reinforcement. Which I've nearly done as you can see, if the frame still stands afterwards a minor miracle (Acro what?) This bay does not have an upper storey you'll be relieved to hear.

Anyhow I obviously don't want a cold bridge of such gargantuan or even any proportions, so what's the proper construction? I'm guessing recast the external sill to less of a depth add insulation and something else load bearing to come to brick level inside. The brick will be faced with 40mm insulated board. So what have I to play with? A double skin of standard brick with zero cavity. What do I put between window frame and the sill? Can I cast all 3 metres of sill in one go? And other similar questions...

-- Mike W