Triple or Double Glazing Windows on South Face?

selfbuildache

Hi,
We're building a house with good U values, airtightness etc. We're putting in triple glazing on north facing windows and one large east facing window. The supplier is now suggesting we put triple glazing on the (large) south facing windows but from what I know at this stage, I thought triple glazing inhibits solar gain and kind of defeats the purpose of having a lot of glazing on a south face. I'd really like some opinions before we go ahead with ordering. Which should I go with, the double or triple?
Thanks in advance as always.

CJhaughey

We have triple glazing all over, the S facing windows are 2m2 and we have 12m2 of them to the S, you would certainly notice heat loss if they were 2-glazed instead of 3-glazed, in the cold spell we were very comfortable and were able to maintain 28-30deg in the living room and 22 in the bedrooms with just a small woodburner 5Kw running
We don't notice any problems with lack of solar gain with them, in fact we have to shade the S elevation sometimes because they gain so much and the rooms overheat.
I would use 3-glaze all over, I don't regret it one bit.

gizmo555

I replaced my windows with double glazed alu-clad units last year. The extra cost of triple glazing would have been about 12% and I couldn't see how I'd recover the cost in reduced energy use. That said, triple glazing will yield improved comfort levels which you may feel are worth the extra cost. With hindsight, as I expect to stay in my present house for a good many years to come, I probably ought to have spent the money. See here for an interesting piece on this:

http://markbrinkley.blogspot.com/2009/06/on-triple-glazing.html

So far as solar gain is concerned, I would have thought that the times of year when you want it most are exactly the times when you're likely to get it least. I wouldn't take reduced solar gain on its own as a reason not to install triple glazing.

Bear in mind the extra weight of the triple glazing - it may constrain the size and type of openings you can use, especially on the likes of patio doors.

seclachi

As gizmo says, the solar gain will count for little when you need it the most in the winter, with the short days and lower amounts of energy. While there is actually a suprising amount of warmth from it during the winter, by the evening it will be gone.

If you house has alot of glass it will be worth getting triple glazing, consdering that glass uses a huge amount of heat in comparison to an insulated wall, and the triple glazing brings down the U value by a big chunk.

gizmo555

seclachi wrote: »

If you house has alot of glass it will be worth getting triple glazing, consdering that glass uses a huge amount of heat in comparison to an insulated wall, and the triple glazing brings down the U value by a big chunk.

Well . . . since you have to have windows unless you're going to live in the dark, the right comparison is between double and triple glazing and the difference is not that dramatic in the Irish climate.

The double glazed windows I put in have a quoted U-value of 1.6 and their triple-glazed equivalent is 1.2. This means for every degree Celsius of temperature difference between the outside and inside of the window, the double glazed windows lose heat at a rate of 0.4 watts/square metre more than the triple glazed ones.

Take CJ's example above of 12 sq mtrs of south-facing windows. The temperature outside today where I am is 6C. (The average over the heating season is more like 10C.) I want an internal temperature of 21C (each to his own CJ, but 30C would have me stripped to my boxers! ). This means the 12 sq mtrs of window would be losing heat at a rate of:

12 sq mtrs x (21C - 6C) x 0.4 watts = 72 watts.

In an entire day, the excess heat loss from having only double glazing compared to triple would be about 1.7 kWh - not a lot really. It would cost about 12 cents to supply this heat from a reasonably efficient oil boiler.

In countries with more extreme climates, triple glazing is really more of a necessity. In Ireland, it's a very marginal call, notwithstanding the recent cold snap. Of course, if you live in a noisy area, triple glazing can help with this too.

CJhaughey

I am only providing my own experience with 3-glazed windows, I didn't spec them as the company who I got my house from fits them as standard.
Scandinavian spec houses generally have them as standard and to change to 2-glazed units would actually cost more!
That caveat aside it is nice to be able to sit next to a window and feel no drafts, even in a 30 deg room, I don't usually wear boxers, just a T-shirt and a pair of shorts:D

selfbuildache

Thanks a million for those answers. I think we'll be going with the triple glazing so. (And are now considering it for the whole house!) While I haven't worked it out mathematically and the U values aren't THAT much different (1.4 to 1.2) I think the comfort element mentioned is a big factor for us, especially as these particular windows are so large. (Ah sure, it's JUST another 1k extra.:rolleyes: Again:rolleyes:)
Cheers!