Retrofit double glazing

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mailmarshall

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#290533 17-Nov-2021 19:22

Hi there we live in Wellington and have a 1970s property that is fantastically sunny in the summer but cold in the winter. We are thinking of doing retro double glazing on existing aluminium windows . We looked at full replacement and PVc but our budget couldnt extend.

Keen to hear from others that have done retro fit. Has it made a difference?

Jase2985

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#2814841 17-Nov-2021 20:02

is the rest of the house insulated? roof/underfloor/walls?

timmmay

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#2814868 17-Nov-2021 20:45

What's the difference to you between retrofit aluminum vs PVC?

We replaced all our windows with PVC a few years ago. They took out the old wood windows and retrofit PVC into the existing frames. It helped a bit, but we already had the "magnetic double glazing" which basically put a 3mm thick PVC layer inside the window. If you went from single glazed it would make more difference. It helps with condensation, but you need to ventilate well, ideally a system that forces fresh filtered air in.

Making sure you have really good, consistent, thick ceiling insulation with no gaps was the best thing we did. Originally we did loose fill wool but it compacted down over time, so we did think pink batts even two layers in some places. Each layer of ceiling insulation made a big difference. Vapor barrier and underfloor insulation helped with moisture. Wall insulation helped a little.

PolicyGuy

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#2814888 17-Nov-2021 21:12

I found that retrofit double glazing made a more noticeable difference to noise than temperature, although it definitely made things warmer in winter.
I had a mid-1970s (no roof insulation other than the 75mm planks) Lockwood in Tawa.
After double glazing, the train noise was noticeably reduced.

IMO the priority order is

Close up gaps to eliminate drafts;
Ceiling insulation;
Under-floor insulation; and only then
Double glazing

itxtme

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#2814943 17-Nov-2021 22:59

Ultimately you will have the disadvantage of no thermal break. What PolicyGuy says is 100% true there are much lower hanging fruit that are more effective in terms of R value and more cost efficient. The other consideration around your existing windows is the mechanisms and hardware. Are they toward end of life?

Are you trying to rid of moisture transferring - this will likely still occur on the frames of non thermal broken windows, and technically is still possible on thermal broken ones too.

We just replaced our windows with Double Glazed, Low-E argon filled thermally broken alu windows. Our hardware was knackered, with single latches meaning frames were bent and draughty in places. Not massively but a couple mm which equals wind in a North Wester blowing in. New glass wont fix these problems. Windows are now foam filled around the framing, and draughts from the external parts are non existent, again retrospective wont fix that issue if you have it.

One other thing is new frames give you the opportunity to change looks. For example most of our windows were half height framed awning windows. We changed them all to full height awning windows which improved our view and also brought the cost down, as aluminium is more expensive than glass :D

Have a look here, consider what PolicyGuy has said, and think about what you are trying to achieve, you can see the R value gains on retrofit are not amazing. Your current windows will have an R value of 0.16

https://www.smarterhomes.org.nz/smart-guides/construction-and-materials/glazing/

Wheelbarrow01

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#2814950 17-Nov-2021 23:33

Just my 2 cents...

A typical single glazed window has an R value of around 0.15. A standard double glazed window comes in at around R 0.26. Yes that's almost double, which sounds good until you realize that a properly fitted and installed thermal curtain can have an R value upwards of 2 (and costs a fraction of double glazing).

I have double glazed aluminium windows and they are ok, but I also have good, thick thermal lined curtains. If I pull the curtain open on a cold night, I can instantly feel the cold air trapped between the curtain and the window glass. This indicates to me that my curtains do a better job at keeping the heat in and the cold out than the actual windows do.

I think people (including MBIE) also underestimate the power of wall insulation. When I bought my house, it already had the double glazing, under floor and ceiling insulation - but no wall insulation - and I froze my a$$ off that first winter. I'd have the heatpump working hard on 30 degrees for many hours on end but the house just didn't retain heat. 5 minutes after switching the heat pump off the house would be an ice box again. I'd wake up in the mornings in winter and the house would be 4-5 degrees (in Christchurch). I even installed a log burner which did make the house more comfortable and easier/cheaper to heat, but when I let it burn out, the temp still plummeted frighteningly fast.

After a lot of research, I had Insulmax dry blown insulation retrofitted into my walls for around $5000. The difference was dramatic and immediate. Not only is the house significantly quieter, but it warms up heaps quicker and stays that way for many hours. The heatpump or the log burner can just idle away in the evenings and I can retire them hours before bed without the house losing all that heat. On a winter morning now, the house will still be somewhere between 15 and 18 degrees on the coldest of mornings.

The double glazing in my house was retrofitted by a previous owner but I'm not sure I'd have spent the money if it were me to be honest. I feel you're likely to get better bang for buck by going for as much insulation as you can afford (including walls) and good quality fitted thermal drapes that are floor length and have no air gaps between the curtain and wall.

You haven't stated whether your 1970's home has been properly insulated underfloor, in the walls and ceiling. If not, I'd go down that road first if I were you. Then review your curtain situation (I also hear good things about well fitted honeycomb blinds). If your house is still leaking heat after that, then that's the time you could reconsider the glazing issue.

JayADee

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#2814972 18-Nov-2021 07:01

If you already have ceiling and underfloor insulation, get good, lined, floor length curtains, makes a huge difference.

Draft stopping everywhere also makes a huge difference. Fill all gaps around doors and windows. Get a draft stopper on the bathroom extraction fan vent if the fan vent is an older one that didn't come with one. Fill holes around pipe and cable entries. I'm still in the process of eliminating all drafts. My 1950 house with wooden joinery has gaps everywhere, some of them large. Walk around on a windy day to find them.

Our house has a million huge windows and five external doors, three of them French! The non French doors are glass with glass side panels. I put curtains on all the French doors. I'm thinking of what to do with the entrance doors, seems kind of weird to put curtains on them so we've always had them without.

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mailmarshall

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#2815373 18-Nov-2021 17:06

Wow lots of useful info. The house is a Lockwood type (Modulock). We replaced the roof recently and added ceiling insulation (R3.6) was max we could get in.

The rubbish single sheet metal garage doors have been replaced also with thermal broken ones - and the rooms above the garage have insulation. New custom floor length thermal curtains have been ordered also for delivery in Mar.

The existing aluminium is in good condition - checked by a retro vendor. They are proposing Xcel glass, low E, argon.

The cost of ripping out the windows and replacing them with thermal broken was close to $72k and for normal double glaze (with argon, low e etc) was $56k. The retro is $35k.

mailmarshall

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#2815374 18-Nov-2021 17:07

Sorry forgot to mention no inwall insulation as its the Lockwood type house…

JayADee

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#2815384 18-Nov-2021 17:36

You'll be amazed at the difference with good curtains and draft proofing. Sound proofs more too. Can you get poly plastic on the dirt under the house and insulation underfloor? It made a really big difference to our tongue and groove wooden floorboards. I have a big dog so no rugs. These days they blanket under the floor rather than place between joists. I have the between joists white spun acrylic stuff.

neb

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#2815436 18-Nov-2021 20:35

JayADee:
Our house has a million huge windows and five external doors, three of them French!

Damnation to the French! (raises glass).

Jase2985

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#2815443 18-Nov-2021 20:46

wait and see how it feels after the curtains

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Technofreak

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#2815460 18-Nov-2021 22:14

mailmarshall: Sorry forgot to mention no inwall insulation as its the Lockwood type house…

We also have a Modulock. It's almost impossible to add insulation except for under floor. Cathedral ceilings with almost no gap for any decent insulation, the only way to add anything means taking the roof off. No air gaps in the wall to add any insulation either. To top it off we have windows to the ceiling in some rooms where the curtains don't go to the top of the windows due to the slope of the ceiling.

Hot in summer, cold in winter.

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Eva888

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#2815468 18-Nov-2021 22:54

We also have a Lockwood, great summer homes not great in winter if they have high cathedral ceilings. We had a polythene ground barrier laid and it made a huge difference to a musty basement smell after rain that sometimes wafted upstairs. Our windows are single glazed and we often need to replace the rubbers that shrink in the corners where wind and cold blow in.

I agree that lined curtains do make a difference. I bought thin cheap plain fleece throws or blankets in a neutral colour from the warehouse and attach them with curtain hooks to the back of the drape's tape over the already ruffled curtain. Very warm, light and not noticeable at all. The trick is to attach them flat not ruffled. You don’t need tape, you just stick the hook through the material as it doesn’t fray and cut the hem to size. Cheap, effective and doesn’t add much weight. Remove in summer.

Our bedroom windows face the street so have always had privacy nets and drapes. The huge windows were always full of condensation and the nets would brush against the window creating mould on the nets. Last winter had an idea for a quick fix. Went to Bunnings and bought the stiff medium to heavy weight clear plastic by the meter often used for table covers. Also bought stick-on Velcro dots

The windows are wide and tall with a mullion across the middle and they open above the central mullion. I pulled the plastic right across only the bottom half of the window and attached it with the stick-on Velcro to the wood frames around the aluminium window and at various spaces in between. From outside you could not see the plastic and from inside you can see clearly out of the window as if it’s glass. The nets covered it.

Result no more wet nets that could grow mould wiping up against the dripping window each time the drapes were drawn as the plastic keeps them at least 10cm away. The windows don’t get near as much condensation either. I can open the windows above the plastic without a problem. The plan was to remove the plastic in summer and replace in winter, but it is so invisible that I won’t even bother. I don’t have nets on any other windows so this method wouldn’t be attractive, but I was thinking of putting it behind slatted blinds on non opening windows in spare rooms we don’t use much.

Friends got the magnetic retrofit and I don’t think it made a huge warmth difference except for less condensation. Two bedrooms and a lounge with windows and French doors cost 13k

Eva888

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#2815471 18-Nov-2021 23:04

Technofreak:
mailmarshall: Sorry forgot to mention no inwall insulation as its the Lockwood type house…

We also have a Modulock. It's almost impossible to add insulation except for under floor. Cathedral ceilings with almost no gap for any decent insulation, the only way to add anything means taking the roof off. No air gaps in the wall to add any insulation either. To top it off we have windows to the ceiling in some rooms where the curtains don't go to the top of the windows due to the slope of the ceiling.

Hot in summer, cold in winter.

We also have high gable windows in the bedroom. Impossible to curtain efficiently. Years back we had a simple cedar frame made that sits inside the window frame and it was glazed with Perspex. I was worried about glass falling on our heads in a strong wind or quake. After many years it still lives but the Perspex has razed and sparkles like stars. It doesn’t get much condensation at all and possibly adds a little insulation.