Posted By: ArtiglioApologies for being off topic, but i’m currently putting some life back into an old barn/oast, only listed in ‘74 and has all sortsmof add ons and changes to what alledgedly may be bits of a building thats been on site since around 1750 ( personally i’d challenge anyone to find a bit of it). Only one window is properly old, then its 1960’s sashes and 70’s casements , with a few old crittals and a likely 1930’s casement bay.
My local council despite declaring a climate emergency last year , has an outright ban on any form of double glazing, in listed buildings. Though apparently a couple of buildings have managed it on appeal.

I have done it a few times, they don't like you getting rid of the old float glass even in singled glazed windows. The ones I have done have been at the rear of town centre properties.
They focus on the front elevation and the rears they tend to be pretty relaxed about.

I suspect with a normal domestic dwelling they could be more demanding.

Always worth asking as there is enormous variation in what they let you do.

Timber ordered...

90mm x 65mm softwood for the frames rebated to accept 8.8mm laminated glass
18mm x 15mm chamfered wedge bead
Hardwood sills

Just reading up online, the best joint for a relative novice I believe is a basic half lap joint, glued and then screwed? Not quite a mortice and tenon but seems okay?

Going to be an interesting project for myself

Timber has arrrived, just a quick one. As the timber is rebated, would a 45deg mitre joint be best so the rebates line up continuously?

8.8mm Optilam has been in for 4 weeks and one of the panes has cracked....

Supplier taking no responsibility, simply saying they supplied only, not even interested in coming out to look

The glass is Pilkington Optilam so should have some kind of warranty on the product. These are £500 panes!

We ensured there was 10mm tolerance (5mm around the whole glass)

What could have gone wrong?

Posted By: jms452Glass is surprisingly strong and bendy so I'd guess it pressed on some thing hard somewhere weakening an edge or possibly vandalism...

+1

Posted By: jms452had a [much smaller] sheet fail and found an edge pressing on a nail

+1
If the edge was chipped during installation this could create a fracture point that could later run due to some other stress e.g. temperature.

Posted By: jms452You may have some luck with insurance...

Read the policy carefully. Could it have been vandalism or could a stone have been flipped up from a passing car?