I am about to fit 4 Seitz S4 windows to my self build. I have a wall thickness of 52mm made up of 18mm GRP box, 25mm insulation and 9mm plywood. I understand I need to use a timber filler strip between the inner and outer frame but I can find no information on how to do this, what size or the best material to use. I read on this forum that someone used pvcU not timber. Any guidance would be most appreciated
Hi and welcome to MHF.
It's a dependant on the length of screws you use, but there is a limit on how big a gap you can have, 50mm is about as big as I'd ever want to go, you have to consider the opening between the roll of blind material, and the outer frame, too big and youy lose small children and pets down the gap, I built on a panel van so only had a 1mm wall and about 20mm filler.
You'll need to remove the insulation where the two frame halves clamp together, the normal way is to fit the Seitz windows first, 10mm bead of black Sikaflex on the outer, to form a seal, a filler strip of treated timber (or UPVC) slaters lathe cut thickness, about 20mm x 30mm, 20mm being the filler dimension, 30mm giving you enough to clamp to and screw them together, leaving 10mm to fasten the ply to, you could go wider of course, screws should be 3.9mm thick for the Seitz frame, don't overtighten them, nearest I could find were plaster board screws, so I oiled them to help prevent rusting, I since found 3.9 in stainless, but I can't find the link right now, you could go 4mm http://www.ebay.co.uk/itm/4mm-8g-PAN...-/190732326744
and probably be okay
Have a look at these
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