DIY Doctor

U-Values Compared and is What I am Told Accurate?

Postby iane15 » Thu Sep 19, 2019 9:02 am

Our home has both double and triple glazing. A large rectangular 3 pane bay window (glazed area 4.9sq m) is double glazed whereas the smaller adjacent single pane window is triple glazed (glazed area 1sq m). Our builder, a large national company, has told me that:

"triple glazing has been used on smaller module windows to enhance u-value performance, as the frames are less efficient than glazing. Glass performs better than window frames and therefore larger windows in the main will achieve a greater u-value than small section windows."

This doesn't make sense to me. What do you guys think?
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Simply Build It

Postby ericmark » Sat Sep 21, 2019 8:48 am

I lived next door but one to father-in-law, we both had kitchen extensions both old boilers, he had triple glazing we had double glazing and comparing the two houses he had a warmer house and lower gas bills.

However he also had a much damper house, our house was around 60% humidity his more like 80% which to be honest I blame on gas cooking.

The houses were poorly designed, as built no central heating just one central gas fire. Open plan so heat would reach all rooms. However there was no ducting to bring in the combustion air to that central gas fire. So it relied on poor fitting doors to get air into the house, so the doors on my father-in-laws house sealed well so no changes of air, and chance of combustion products getting into the room.

So before fitting doors which seal well, first thing is to fit a heat recovery unit so you do get changes of air without losing too much heat.

In the main triple glazing one pane can be removed in summer and replaced with a fly screen, which I think is a great idea. But as to U valve it's more down to government survey and getting the rating than actually being warmer, the survey of both houses had just 2 points different, that was because he had solar panels which actually did not work. But if those extra points put house into next band it makes it more saleable.

But in real terms the energy report tells you very little, when we came to change houses, yes we looked at the report, but were more interested in what we could see.

We know that under floor heating needs the floor removing and insulating material fitted first to stop heat going down, but once laid you have no way to see if that insulation was actually fitted, so we kept clear of houses with only underfloor heating to some rooms, it may have been good, but no one can really test it without long term energy usage records, and people cheat, you know your selling a house, you know people want to see energy bills, so you wear extra coats so the heating is low so looks good.
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