I've finally moved in my 1960's house which over the years I intend to turn into an Eco House - mainly by insulating as well as possible. One job that's unexpectedly turned up is the window cill in our bedroom has light visible underneath it. So I've decided to get the cills off as we're already redecorating the room and replastering a few spots where the top cloat of plaster has come away. As I'm going to have the cill off I now started investigating the idea of retrofitting cavity closers. The previous owner has had Low-E UPVC units installed 3 years ago, and thankfully the frames are sitting in the outer skin of brickwork - leaving the cavity free. (I'm appaled at the workmanship on the draft sealing though. I though the units had noisy seals but it's actually sound / drafts getting round the edges of the units :-(. All they've done is glue a 1" strip of upvc beading round the frame to tidy up the join onto the old wooden sill I think that's why there's also an light gap - the old wooden frames would have been joined onto the sill via a mortice like V grrove. Been checking various window websites and the outside AND inside of the frame should be masticked to the inside face of the brickwork.

So onto the point of my thread...

The main problem I'm going to have is getting the built in DPC at cill level of most of the cavity closer systems to work with what's there already. They’re supposed to be put in on a new build with the DPC running 2-3 courses of bricks lower at the outside. (Think of a stretched Z) Or has anyone come across a product designed to work specifically in this application.

Likewise there's nowhere to overlap the front part of the T that most systems use in the reveals. So I need to find something that's more like an L with a means of fixing only to the internal blockwork. Possibly will have to get a T and cut one side off with a hacksaw? I assume it will be best to do this before getting cavity fill insulation - definetely a reason to avoid beads! Someone I know has an extension built and when they cut throught the wall you can guess what happened. :-(

I'm also wondering how to treat the lintel. EST guidance seems to use a strip of internal insulation as per page 19 of this guide…

http://www.energysavingtrust.org.uk/uploads/documents/housingbuildings/CE83%20-%20Energy%20efficiency%20refurbishment%20of%20existing%20housing.pdf

Any other ideas would be welcome. Such as a supplier of insulated cills which double up as a cavity closer?

I think that you would be OK to let the cavity fill to run right up under the window board. No cavity closer needed, BUT air seals to window, bricks and board are.