extending window sills for exterior wall insulation

[stewartcampbell]

Hi, we will be getting exterior wall insulation done in the next few weeks months and as it is free on a government initiative as far as i am aware there is no choice on the sills apart from a white plastic oversill, i am not keen on these so was thinking about extending the 3 front sills in concrete and just wanted to know thoughts on this from more experienced construction diyers or professionals.My plan is to drill and insert bolt anchors into the existing sills and using wire attach a 1m theaded steel bar between them resting on the bolts,sills are about 2m so will need 2 each sill then build a form and i think extend the sill downwards too so it is thicker as i think this will look better, can anyone see any problem with this? thanks.

[stewartcampbell]

E on are doing it as far as im aware to meet targets on carbon reduction or something to avoid big fines, its in scotland by the way.