Cd be used in EWI situation, rendered EPS, no masonry outer skin?

To carry the window 'outboard' without it needing to touch or get support from the outer skin?

Posted By: tonyDid that by fixing mine to the outer skin only, inside the outer skin.

As you've proven, this can work if you're building it yourself, take time to build templates/formers for the offset openings and take responsibility for filling the gaps around the frames.

Without a template/former the bricklayer is unlikely to get the offset openings right. Fixing the windows to the inner face of the outer leaf also requires a substantial gap to be left around the frame which subsequently needs to be filled with insulation. The average bricklayer will leave a gap here which is either too big or too small and the average window installer isn't going to take the time to cut pieces of insulation to precisely fill these gaps. I also have concerns about the long term airtightness of solutions based on PIR/PUR insulation & polyurethane foam.

A cavity closer which is able to take the weight of the frame allows the frame to be placed more centrally in the cavity without using fixing straps or plywood boxes minimising cold bridging. A cavity closer which is made from something which can withstand the UK climate provides a durable template for bricklayers to implement a check reveal without the risk, for example, of plywood delamination. And a cavity closer which is rigid provides a solid substrate for proven airtightness solutions based on tapes &/or membranes.

All-in-all I think its a better solution than the plywood box & well suited to how things are done on a typical building site. The downside is likely to be cost, but I don't have the numbers yet.

David