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Secondary glazing might slightly reduce the thermal bridging of the window reveal as well as improve the window bit, since it will be closer to the insulation. Assuming you aren't wrapping insulation around the reveal?
hoefla-
i think we might be able to have the thinnest (27mm?) insulated board in the reveal, depends on the width of the windows which I can’t measure as still not completed on the flat.
also not sure on having breathable board or foil backed as this non-cavity wall is tiled on the outside so i guess it’s not breathing and it’s ok for it to be sealed on both sides.
Mr_Smyth
Yes the same crittall ones, really wanted aluminium but it looks like that’s never going to happen, found a decent profile/system (Aluk or sheerline) which would be 12k but having had a site visit they need 5 stories of scaffolding and to cut back into the reveal for the added depth as there is zero sill projection outside and Dulwich estates say it has to be flush.
I haven’t had the full quote back yet but i’m guessing it’s going to be stratospheric and then plus a bit more as they probably don’t want to do it anyway.
I also have to pay Dulwich £400 just to apply.
As much as we want premier fenestration and insulation we are not blowing half the refurb budget on it. so plan B the cheaper option is a deep terrazzo sill (28-30cm) and the secondary glazing at about half way giving a usable windowsill.
As much as the existing windows look great the U value of single glazing is rubbish so a new deep sill will give us a trinket/plant shelf and help offset the not so pretty secondary panels.
Have seen a few where the secondary glazing is flush and it looks shit.
That wall is recessed and single skin not cavity like the others hence adding insulation out to the new sill depth.
The Mrs likes 23º so it’s insulation and Tado time as fuel is never going to get cheaper.