Building a sun room - should I use double gazed glass?

Question

I'm turning my alfresco into a sun room by putting in two sliding doors by 4.5m X 3m.

I'm in Canberra, Australia and it'll be west facing. I'm trying to decide whether to opt for double gazing for the doors.

Cost is not that much more but my main concern is that it might heat up too much in summer because there is so much glass.

In winter (it can get to be 0c here) we can just put a space heater in that area. But in the summer it'll hard to take the heat out without opening the sliding doors which we probably aren't keen to keep open all the time.

Since it's initially an outdoor area, i'm fairly sure the ceiling won't be insulated either (although we can fix that too at some point) so not sure if it'll be that energy efficient even with double gazing.

We live in a quiet neighbourhood so noise is not an issue.

I'm also not interested in putting in blinds etc. because that alfresco is one of the entrances into our living room and having blinds will make that room too dark.

Since double glazed windows reduce the heat transfer and half this room is going to be glass, I'm scared it'll act as a greenhouse effect and make the room too warm.

Should I bother with double glazing?

Answer 1

Double-glazed windows can reduce heat gain as well as loss - particularly if you purchase types with internal coatings to optimize solar heat gain coefficient (SHGC) (rejection/reflection of heat from the sun, while passing visible light.)

In the USA, I found that I couldn't reasonably get double-glazing with decent heat gain (I'm very heating-skewed, climate-wise) as the heat rejecting coatings were the only thing sold in my area (would have been about 3x the cost to import more suitable ones, so I didn't.) That is separate from the U or R value of the window unit.

Australia appears to use the same terminology. I am neither associated with nor endorsing the linked site, simply pointing to it as a place explaining SHGC and U value from the Australian POV, rather than a USA-centric site. If there is a more-complete or more-neutral (e.g. Australian government) site, feel free to update the link.

For your stated criteria/concerns, you would want glass with a low U-value (high R value - U is 1/R) for keeping heat in when cold out, and out when hot out; and a low SHGC for low solar gain (unfortunately, regardless of it being hot or cold out.)

Answer 2

If have no limit on funds then consider gettig electrochromic double glass doors. Two layers connected to computer can reflect light to outside when is hot and to inside when is cold. And You can chose one way mirror type.

Answer 3

For me it's a no-brainer, assuming your windows are operable. You want to collect heat at times. That's more effectively done with insulated windows. You want to heat the space at times. Ditto.

Your concern about the room heating too much is nullified by the fact that the windows can be opened (or it's too hot to matter).

Answer 4

Having been to Canberra, I would say, yes to double glazing. It will be more cost-effective than heating in Winter.

I suspect, you are liable to use it more in the afternoon, in which case I would get them with a low-emissivity gas or tinting to stop the glare.