Sunday, September 2, 2007

Do it yourself Secondary Glazing


"I can't believe it's not glass!" Our dining room with secondary glazing installed on painted wooden frames. Sweet basil and a potted avocado tree in evidence.

What is Secondary Glazing ?

Secondary Glazing is retrofitted plastic double glazing. You get significant benefits in heat and sound insulation from the trapped air between the panes. An additional benefit is much reduced condensation on the windows, which is very beneficial to your old wooden joinery if you happen to have it.

Costs
The commercial systems are generally about half the cost of retrofitted glass double glazing. The prices for glass and plastic respectively being in the regions of $400 per square metre and $200 per square metre in New Zealand. Doing it yourself works out under $50 per square metre.



The Plastic
Cast acrylic sheet is relatively cheap at around $35 per square metre dollars for low grade. Don't let the grade worry you too much. One supplier I approached tried to convince me I needed A grade UV resistant plastic at about $100 a square metre! Yeah right. I eventually found Award Plastics and talked to Aaron who assured me that they had done this before and the cheapest grade was more than adequate. It certainly looks fine with little distortion or visible marking. The plastic is installed inside the glass so the worst of the UV is filtered out before it hits the plastic anyway.

The plastic comes in 1.2 x 2.4 metre or 2 x 3 metre sheets. I supplied the company with a cutting plan that I hand optimised to fit the sheet sizes available with the aim of producing as little waste offcuts as possible. To glaze wooden joinery one needs to measure the window to the inside of the frame and then add about 30mm to each dimension. This gives 12mm per side for the magnet and a few mm of tolerance. Award Plastics took the cutting plan and cut the plastic as required for no extra charge.



The Magnet
To attach the plastic to the window frame I used brown vinyl magnetic strip, similar to the magnets used in a refrigerator. This can be bought from magnets.co.nz. I bought the 1.2mm x 12mm strip. There is the option of buying the matching A/B pair but this is more expensive and only comes with self adhesive tape. I found that most of the single side strip that they sell will mate with itself correctly in one orientation but not the other. The A/B pair is designed to correctly mate in either orientation. It pays to check with the staff of your supplier to ensure that the magnet will indeed mate with itself.

Improperly mated magnet - note the offset sideways.


Properly mated magnet


The Glue
Initially I tried using self adhesive magnet on both the window frame and the plastic. This worked for a while but the self adhesive glue stays tacky and slowly creeps with the weight of the plastic. The consequence was that the sheets of plastic started detaching, usually on the frame side. In the end I realised that a curing glue was required and so I switched to using Ados F2 contact adhesive on both the frames and the plastic.

Fitting
You will usually need to cut recesses into the plastic and magnet to clear your window fittings. I did some of my windows with a coping saw and some with band saw. I finished the recesses off with a belt sander. The amount of energy you spend on this step will depend on how tidy a finish you require.

Assembly
It is important to prepare the surfaces to be glued carefully. On varnished frames the varnish should be scraped off to reveal bare wood. On painted frames the paint just needs to be cleaned, provided that it is in good condition. When using contact adhesive one only gets one shot at the positioning of the glued pieces so be very careful.

The steps to assemble one window are as follows:
  1. Cut the magnet, two strips to fit each edge of the plastic for a total of eight strips.
  2. Peel the protective film off one side of the plastic.
  3. Apply glue to the edges of the plastic where the magnet will fit.
  4. Apply glue to the the magnet that will be fitted to the plastic.
  5. Once the glue is tacky, carefully fit the magnet to the plastic.
  6. Hold the plastic in position on the window and mark lightly the location with a pencil.
  7. Apply glue to the window frame in a 12mm strip next to your marks.
  8. Apply glue to the the magnet that will be on the frame.
  9. Once the glue is tacky, mate the frame magnets to the magnets already glued to the plastic. Make sure that they are mated properly (see pictures above).
  10. Carefully hold the plastic in position on the window and press it into place.
  11. Press around the edge of the plastic to make sure it is glued down.
  12. Remove the plastic carefully from the window by separating the mated magnets.
  13. Press firmly on the magnet glued to the frame to ensure a good bond.
  14. Peel the remaining protective film off the plastic.
  15. Replace the plastic back on the window.

Just a little update 28 May 2010 - I've recently become aware of systems that use a mating pair of plastic extrusions or a single plastic extrusion with a living hinge. These systems have the advantage of not requiring magnets. If these had been around when I did my secondary glazing I probably would have used them. The UK is far ahead of NZ in this market. Check these out...

http://www.omegabuild.com/diy-secondary-glazing.htm
http://www.theonestopplasticsshop.co.uk/diy-secondary-glazing-c-204.html

A further update. April 2011. Thanks to Sarah in the comments tipping me off to the fact that Award Plastics now offers a range of systems for DIY secondary glazing from Tubeway Ltd in the UK। The pricing is fairly steep for the EasyGlaze which is the system that looks the best to me.

Check out this, A thesis on secondary glazing!

26 comments:

PhilScadden said...

Fantastic. The house has commercial ones that are falling off. Really interested you choice of glue. I will put them back up your way.

Felix said...

Yes, the choice of glue and careful preparation of the surfaces are important. There may be a better glue out there...

Steve OShaughnessy said...

Did you notice any distortion over the summer due to expansion of the acrylic?

Felix said...

No distortion. The acrylic sheet is very stable and the small amount of expansion and contraction is handled by the magnet fixing system.

arthur said...

Thanks for the idea,saved me a lot of trouble,Arthur from south of France

Kerry said...

seeing how old the original post is, I dunno if I'll get a reply... but what thickness acrylic did you use?

Felix said...

I used 3mm. 3mm acrylic is fine. You could go thicker for large windows but then the weight begins to be a problem.

Jenelopy said...

Thanks for the excellent idea, and detail descriptions. Can you remember roughly how much of the Ados F2 contact adhesive you got through? The tin doesn't give any idea of the coverage. I don't want to end up buying loads of little tins, but equally well don't want to buy a huge tin and barely use any of it!

Felix said...

@Jenelopy I found a tube of F2 did about three or four average sized windows. Sorry to be vague...

Tess said...

Hey thanks Felix, we want to DIY some secondary glazing and your blog has been a huge help to us. thanks again

ian shaw said...

Felix,Very interesting:mymain concern is noise control;3mm v 4.5mm?{traffic noise}are the new fittings you mention available in N.Z>Thank you.Ian

Felix said...

@Ian Shaw. Not sure whether it will make much difference moving to 4.5mm plastic. Probably not worth the extra cost. I know there are companies selling the (non-magnet) clip system installed in NZ. Whether a private individual can get hold of some for DIY is another matter. If you manage to please let me know!

Sarah said...

Great to find your post Felix ! I went to Placemakers for pricing sheets when I had the idea to do and they told me around $6-800 a sheet !! I found your site after a search as I was determined to find a better option. The link to Award Plastics got me back on track and I see they also do kits for fixing now! Thanks for your terrific work.
SARAH

Felix said...

@Sarah Thanks. Great to see people are finding this info useful.

Felix said...
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Matt said...

Hi Felix. Great post. I have a conservatory with a nearly flat glass roof sitting on top of exposed beams. I'm considering attaching acrylic sheets to the underside to double glaze it as it gets very cold in winter. I have my approach well sorted in my head, but I'm trying to decide between 3mm and 4.5mm. I'm worried that 3mm will sag when laid horizontal. Each sheet will be about 600 x 1600mm. I'm not sure if you can answer this, but do you think 4.5mm is much more rigid? Thanks.

Felix said...

@Matt. If your sheets are supported all the way around then 3mm should be okay I don't think you will get a significant benefit from going to 4.5mm as it is also heavier. I suggest you have a contingency plan of adding a support beam across the sheet if it does bow out too much. good luck.

Unknown said...

Glad you like your double glazing, it is proving very popular, we have a whole new range of double glazing products, please dont hesitate to contact me if you have any enquiries.
Graeme
Award Plastics & Displays
www.awardplastics.co.nz

permanentlypuzzled said...

Great article Felix. Do you forsee any issues using four screws, one for each corner being used to secure panel to wooden frame rather than clip/mag strip system. Trying to keep the costs down. I was thinking countersunk holes with rubber washers for the small screws.

permanentlypuzzled said...
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Felix said...

Using screws is fine as long as you don't mind getting out the screw driver every time you want to clean or remove moisture from behind the pane. Also, you will need to think about what sort of screws to use if you have soft cedar window frames. The larger the better in this case. I also wonder how many screws will be required to hold the plastic flat to the frame and give a good air seal. The better the seal the less moisture and spider web issues you will have. Let us know how how it goes... Felix

Stu Ashby said...

I used this type of secondary glazing nearly 30 years ago in UK but instead of 2 magnetic tapes I used white adhesive backed steel tape fitted to the window.

downunderxj said...

Thanks for this, I found your blog last year and have now used your ides to put in secondary glazing in a large bay window, already feeling the difference. The dining room is next - I used Awards Plastics for the plexiglass and Magnets.co.nz for the magnetic strip. Relying on the sticky tape at the moment but will keep an eye and change to the Ados if required - Big thanks for all the ideas, notes etc.

Anamika Singh said...
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Stuart Twplastics said...
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Felix said...

With regards to the glue to use... I'm now favouring a co-polymer clear silicone adhesive.