Alternative Double Glazing

Alternative Double Glazing

Here’s a great money saving tip I’ve used countless times. Double-glazingsalesmen will hate it, but you can easily upgrade your windows without installing new ones.

It’s a little known fact that secondary glazing using low emissivity glass is actually more energy-efficient than normal double glazing, as long as it’s well sealed against drafts. The much larger air gap is why. Secondary DG + low E glass exceeds the requirements of building regs Part L (conservation of heat and power) for new windows. These must have U values below 2.0 W/M2k. Secondary D/G has a theoretical range of 1.8 – 1.95 W/M2k, so get more brownie points on the EPCthan normal D/G. Also the comparatively low cost means it could pay for itself very quickly in lower heating bills. For comparison, a single glazed wooden window has theoretical U value of 4.7, and a metal window 5.7! (The calculations are based on the British Fenestration Rating Council’s standard window size – 1230mm wide x 1480mm high.) The disadvantage is that secondary glazing is a bit harder to open and close.

Another alternative is to turn old wooden windows into D/G windows by remodelling them. The old glass is taken out and the rebates (the slot that holds the glass) cut deeper with a router. D/G units can then be fitted. You will usually need a thinner unit than the standard 28mm as the wood probably won’t be thick enough for more. It’s also vital to thoroughly seal all drafts with draft excluders. The brush ones work best with sliding sash windows, those with a flexible rubber skirt are best with casement windows. Sponge draft excluders work well but fall off or apart in time.

If you are doing a conversion or major renovation, Building Control will insist you upgrade the windows to the required standard (U values below 2.0 W/M2k ), or do other works bringing the building as a whole to the required insulation standard. There is a get-out clause though. If the cost of doing the work is more than you’d recover in 15 years of lower fuel bills, you don’t have to do the work. Likewise, if the cost-differential between altering existing windows with thinner D/G units, and complete replacement, is less than you’d save, you can alter the windows instead of replacing. This saves a lot of unnecessary waste. From an environmental perspective, the embodied energy spent on making and transporting new windows may outweigh their benefits to insulation. I’ve successfully used this argument many times with Building Control, but it would be prudent to check first, just in case. Also the alterations are only worthwhile if the window is in good condition. If you then combine this method with secondary DG it should be very warm indeed!

A final method for the real cheapskate landlord is to stretch clingfilm over the casement to form a gap between the glass. This makes instant, cheap but very temporary double glazing. Only effective if you also install draft excluders, see above.

Next week I’ll recommend some cheap jobs you should do at the outset with any new property, then annually, to prevent expensive repairs later.



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