Double Glazing unit thickness

Standard is now 28mm 4x20x4 (glass thickness x normally argon filled space x glass thickness)

In message , Arthur51 writes

Or even upto 28mm nowadays.

Thicker gives better heat and sound insulation.

Thinner needs a shallower rebate and maybe a little cheaper?

Presumably an old single glazed frame? Even 14mm would be pushing it

-you need to allow a bit for bedding it against the frame, and enough space for the bading which normally holds the units in place.

chris French wibbled on Monday 22 March 2010 18:58

There is a sweet spot though, where a bigger air gap gives a diminishing return on the thermal properties. The acoustic properties continue improve though IIRC.

I know this because when I was evaluating my old ali DG windows (quite small air gap as was common in the 70's or early 80's) I discovered a table somewhere that indicated it wasn't much worse (within 90%) of modern DG units with their massive air gaps (like for like comparisons obviously - mine don't have K glass).

Where mine fail more is the thermal break in the frame is only 4mm, which is better than nothing, but nothing like as good as modern ali units. My overall conclusion was that it was not remotely worth replacing them, even though I will have to replace a lot of the glass due to it having misted.

If anyone wants proof, I will try to find the table, but it was a couple of years back...

Up to a 20mm air gap, the larger the spacing between the panes of glass, the better the insulation. Above that, air can circulate within the window, which makes larger gaps less effective. Smaller thicknesses are usually easier to retrofit.

Colin Bignell

"Stepped" units can be useful for shallow rebates. IIRC they don't look too clever from the inside though.

ISTR some years back a Matthew Marks describing how he routed out some French Windows to fit DG sealed units in them.

Ok if you've got room for the router body, but you rarely have round windows. I did a similar thing round a door frame with an edge trimmer and a 3mm bit. Tedious, but you can get in a lot closer because the shaft is offset from the motor. They're designed for laminate trimming but mine gets used for anything but.