Energy Matters Forums

[Nige]

Hello as this is my first post I may a well hit a subject close to heart.

I have purchased a house, late 1960's construction which has absolutely huge windows in the bedrooms.
As these are on the southern end of the house you can imagine the heat loss via the glass is probably quite high.
When I say large the master bedroom the glass is almost three meters long by 1.6 mtrs high. Thats without the three windows at the end two of which open for ventilation.

With a hunk of glass this big changing the frame & window out for a whole new custom made double glazed unit woud be exceedingly expensive. As people in the industry are only interested in selling me some you beaut nano tech coated super glass blah blah vomit inducing sales pitch...

Have any of you just done your own DG? Fortunately for me I have a place not a million miles away that recycles buildings so if I left them the measurements I suspect a piece of glass of the appropriate size would show up in next to no time. Thoughts anyone? I just want to modify my window to accept a second piece of glass to help insulate, even better if it is recycled. I just do not understand the myopic self serving attitude I come acros when asking such a simple question. Surely two pieces of glass suitably spaced will have some thermal properties. Regardless of wether it is the correct type of glass???

ta

Nige

[Gordon-Loomberah]

Hi Nige, and welcome to the forums

I reckon you are on the right track with doing your own double glazing. I doubt whether the $uper expensive stuff they try to sell you is really all that much better than regular window glass, and certainly isn't justified due to the expense of it. I would think any potential energy savings due to performance differences are unlikely to ever cover the up front cost of buying the expensive stuff. If you can re-use some 2nd hand window glass, then I suspect you are taking the more environmentally sound course of action

Years ago when I had a flat panel solar hot water system, the front sheet of glass was broken during a storm and I was told I needed some special expensive glass for it. I ignored them and went out and bought some regular glass of the same thickness and I never noticed any performance difference at all

[Nige]

Hello Gordon,

You hit the nailon the head there. I am fed up with people trying to sell me some you beaute product when what I really want to do is get back to basic by building my own solution using recycled materials.
Tomorow I will measure to see what or how much of a gap I can build in here but my main concern is making a proper seal around the second piece of glass so there are no condensation isues getween the two panes.

Now surely there are others out there who have built their own? This list can't surely be totally populated by people who buy everything new off the shelf.

[Gordon-Loomberah]

... my main concern is making a proper seal around the second piece of glass so there are no condensation isues getween the two panes.

Try to pick a day with a very low dewpoint for sealing the glass in, best would be a cold dry day when the DP can be well below zero- keep an eye on your nearest weather station. It might not hurt to drop in some silica gell in an unobtrusive container of some sort too.

Another thought- if you cant get a suitably large single piece of glass, you could build a frame to hold 2 smaller pieces... at the expense of having a slight vertical obstruction down the middle of the large window.

[lad]

My understanding is that there is a vacuum between the sheets of glass. As there are no particles running around in a vacuum there is nothing there to transfer the heat from outside to inside the double glazed unit (or vice versa). You won't get this additional benefit as you will have air in between, transmitting heat.

You will certainly get some benefit from DIY double glaze but not quite as good as it could be.

[PeterM]

My research on this says that the glass treatment does make quite a lot of difference; much more than whether the gap is filled with Argon or a (partial) vacuum. But, as you say these treatments are expensive.

The gap between the sheets of glass needs to be rather larger than many seem to think. 16 mm is optimal in some sense. And I think adding a sprinkling of silica gel along the bottom spacer to mop up any initial excess moisture is a good idea.

[Gordon-Loomberah]

My understanding is that there is a vacuum between the sheets of glass.

It would only be a very low vacuum if there really is one, large sheets of glass would seriously bend together with much of a vacuum.

As there are no particles running around in a vacuum there is nothing there to transfer the heat from outside to inside the double glazed unit (or vice versa). You won't get this additional benefit as you will have air in between, transmitting heat.

A vacuum certainly cuts the heat transfer via conductance down, but not radiation... sunlight makes it all the way here through 150million km of vacuum! In any case, air is quite a poor conductor anyway.

You will certainly get some benefit from DIY double glaze but not quite as good as it could be.

Conversely, your hip pocket will get a major benefit from DIY

[Nige]

Success!

A friend has purchased an old fibro house which has two suitably large pieces of glass within it's structure.
Now all I need to do is gleam as much information as I can before the old house is a demo job which should be in about 12 months time.
So at least one step in the right direction for the recycling of the glass. The frame is big enough to accomidate a 16mm gap so now time to learn more about the glazing business.

Any tips no matter how trivial they may seem to you may help me in leaps and bounds.

Cheers

Nige

[Gordon-Loomberah]

Great that you located some glass to use so quickly

I reckon it might be worthwhile to subcontract a glazier to help you out- they will be able to safely carry the large pieces of glass and cut them to size too.

Oh, one more tip, get the glass out of there before the fibro demolition, you dont want to be breathing in any asbestos!


The straw bale chook house we are building at home will have one ~ 1m^2 window facing E, we are going to make that a double glazed window, since we have 2 windows about the same size ($10 from the tip recyclers).

They will have an air gap of about 400mm! and a removable or hinged shutter to keep the sun out on summer mornings.

[pboyle]

Hi Nige
I have installed some DIY double glazing. I have extensive single pane windows (timber) fixed and opening awning windows. I did a fair bit of research on the best options, as the cost to install double glazed units was too much for me. Luckly the timber beads holding in the glass are 12mm, which is ideal for the gap between the panes of glass (without having to go to argon or other gas to reduce heat loss). It appears that anything greater than 12 mm with normal atmosphere results in a thermal convection occuring in the gap (hot air rises in the gap, the air movement in the gap resulting in greater temperature transfer, hence using a heavier inert gas to reduce the movement in larger gap double glazing). And with talking to people, most gas filled windows lose the gas over time. A vacuum in the gap can also result in bowing of the glass.

So what I did was got a bit of glass cut to size, ran a good quality silicone bead on the existing wooden beads. I then attached the new glass and added additional wooden beads to hold the glass. I have done this for one window only to see how it performed over the year. I have had no fogging or moisture inbetween in this time. Also, when there was a particuarly cold night, the neighbouring windows some condensation but the double glazed one had none. So all up, a success - now my next step is to do the rest of the house. Yes a custom built double glaze with low e glass and argon fill would probably perform better, but the home made job seems to be good and cost less than 10% of the custom job.

An option is to use a plastic spacer between the windows (12mm) that you could get from a glazier. The benefit of this potentially is you can use some silicia gel in the spacer to absorb any moisture, but as mentioned, do it on a dry cold day to reduce moisture in the gap.