Double glazed windows
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3 lessons about double glazed windows

Libby looked up from the pile of drawings on the desk and said, “You should write a post explaining the three things we just learnt about double glazed windows.”  We’d spent a couple of hours one afternoon poring over the house plans, window specifications and a supplier’s quote.  This tiring exercise highlighted how important it is to sweat the details.

1 – Review the window specifications, then do it again.

The first time we saw the drawings, we were just glad to see that windows existed and there was a list of sizes.  The locations looked right and the sizes seemed OK.  Having these details meant we could get started on quotes for window and door suppliers.

Comparing window quotes and our design specifications brought the issue back on our radar.  Sitting down with the drawings, specifications and an itemised quote tends to focus the mind.  There were discrepancies.  A couple of window dimensions differed between the drawing and the specification list.  Small windows in the drawings didn’t appear on the specification list.

Should have checked all the details on our double glazed windows

With hindsight, we should have spent more time reviewing the drawings and specification list before sending them out to window manufacturers.  The extra time would probably eliminate the issues we spotted and avoid a bit of confusion with quotes.  This is a rookie mistake but that’s learning on the job for you.

Note to self – thoroughly check the details at the start and then keep checking.  At this stage of the design, we realised that once we approve a drawing or specification, that’s what will be built or delivered on site.  The windows not the right size?  Awkward!  Costly! Time consuming!

2 – Visit double glazed window supplier showrooms.

We have two objectives for our double glazed windows.  Be effective at reducing heating and cooling requirements.  Look attractive and fit with the overall look of the homes.

Manufacturer websites are a good place to start the search.  The Window Energy Rating Scheme (WERS) explains all the terminology and enables a quick performance comparison.

All double glazed windows manufactured by Australian Window Association accredited businesses must comply with Australian Standards.  These standards cover factors like air infiltration and glass deflection.  Then, AWA and WERS apply some computer wizardry to work how good a window is compared to the standard single pane and frame.  As expected, the tables show variations in window performance.

However, websites only take you so far.

We planned a road trip to the local manufacturers to see doors and windows in the flesh.  The main attraction would be seeing and hearing the tightness of the seals when closing a window.

Two seals together

No, not that type of seal!

Why bother?  Any time air leaks around a double glazed window it kind of defeats the purpose.  The data on air leakage between frame and pane looked good on paper.  However, nothing beats opening and closing a window (or door) to feel the seals working.  Would we hear that satisfying squishing sound as the seals were pushed together?

If the seals passed the test, we then considered the frame material.  There’s plenty of choice – wood, aluminium, uPVC or various combinations of these three.

Based on our field research, Miglas is the leading contender.  We like a combination frame that has an aluminium exterior (low maintenance) and wood interior (fits with the natural product theme).

3 – Don’t assume double glazed windows come in every size.

Making assumptions

Only after having enough design details to ask for quotes did we discover that suppliers can’t always make what we wanted.  For example, we asked for 900mm wide casement windows.  Miglas said they can’t make them wider than 700mm.

That’s when a good relationship with the supplier kicks in.  Miglas  provided alternatives for us to consider.

More investigation is required to weigh the pros and cons for modifications.  Is it important to use a wider casement window that allows more sunlight in during winter?  Is a narrower casement window better to help ventilate the home on summer evenings?

One more thing to learn about double glazed windows.

Are we there yet?

Low e coatings can boost the performance of double glazed windows

Still some work to do so we can understand the optional extras.  Should we specify argon gas ?  Would a special glass coating be helpful?  Which side of the glass should be coated?

Back to the websites to get some answers.  Luckily Miglas is also happy to work through the options with us.

Let you know when we know.

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