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Have the window installers coming tomorrow to fit some of the 3G UPVC windows and I'd just like to ensure that they are doing it the 'correct way'. We've agreed that they only install the windows with me doing the finishing off later with cills, taping etc. So I just need to be sure that they fit the 88mm frame at the mid point of the 175mm SIP wall. Externally, I will have wall fitted with cladding. Questions So my only questions today are around tomorrow's fitting of the window, all the other weather tightness aspects will come later. But the placement of the window will be important to get right of course as that will impact the follow-on work. So currently in my head, I have: Breather membrane (that's currently sealing up the window opening) to be cut and folded inwards over window reveal. DPC on top of breather membrane extending outwards under cill and over cladding (NB note the 30mm air gap between cladding and SIP). How do I stick it down - or just use the weight of the window frame? Fit frame directly on top of the SIP (on DPC layer) or on compressible layer? I have concerns about compression/shrinkage of the panels - From what have read there won't be much compression of the SIP panels but I'd like to cater for any movement and any pressure on the window frames by not filling the gap around the window and SIPs with anything solid. I think I have a 20mm gap around the window so there is hopefully sufficient allowance for any 'movement'. During installation I'm looking to leave that 20mm gap (i.e. not get the installers to just sit the window frame directly on top of the panel) by putting some temporary packers/shims in there to ensure non of the frame is touching the panel. Once the frame is all screwed in, I was going to fill the gap between the frame and SIPs with foam (Soudal non-expanding type/equivalent). Or should I go for a compressible filler? But what should I be using? I've looked at Compriband stuff, but that is just too pricey for my liking, so was hoping to just use Soudal type stuff which I could do if the window is sitting on removable shims I've attached a window detail that I found on the www (from Nordan) that I have amended. Ignore the window frame detail itself - mine is UPVC. If anyone could comment on the above 3 items that would be great. The guys arrive tomorow and I just need to ensure that the correct materials are in place before they start doing it all 'their way'. TIA! OB