Extreme DIY – Double glazed Sliding Sash Windows

By Andy the stuff doer

* Extreme DIY Warning * This is project not for the faint of heart.

I have already built one sliding sash window as a working prototype. It’s been installed now for for over a year and I’m happy with the basic design. For more details of the prototype build please visit my Sliding Sash Blog.

The next step is to have a bit of re-think on some of the details and make five more for the rest of the house. At the same time I’ll be recording, photographing and possibly videoing how to make them.

The intention is to provide the resource I was looking for when I started out on designing and building sliding sash windows a couple of years ago.  I would have been quite happy to buy the plans at the time but could find any.  Details are available of traditional single glazed windows but double glazing means quite a re-think.

The cost of purchasing modern sliding sash windows from a manufacturer or skilled joiner is way out of my budget. I’m also not convinced that all the design details they incorporate are appropriate.  It seems to be a booming market at the moment and I think there are some poor designs being manufactured and sold for a lot of money.  I want  design that will work for many years, that looks right and doesn’t cost the earth.

This leaves me with the only alternative to design and make my own sash windows.  

I have spent hours and hours researching and testing various ideas to come up with a near perfect design.  I’m hoping it’s going to be worth it. For a start instead of paying around £1000+ per window I should be able to build my own for less than £300 each. On Six windows thats saving me more than £4200. Certainly more than enough to pay for the extra woodworking tools I’ve had to buy.

On top of this I intend to sell the plans as a e-book to those who appreciate the effort I’ve put in and fancy benefiting from the time I’ve spent. 

When I’ve finished this batch I will have the plans, construction details and methods completed.  These will be formatted as a step by step guide to building your own Double Glazed Sliding Sash Windows. 

I’ll also but some articles together that covers the subject of sliding sash windows, double glazing in timber and the rational behind the design that I’ve put together.

21 Responses to “Extreme DIY – Double glazed Sliding Sash Windows”

  1. This really is extreme DIY. Sash windows are certainly not the easiest thing in the world to make yourself and it sounds like you have put countless hours into making these to the highest standard possible.

  2. FourEd, Yes it’s extreme DIY but fairly moderate woodworking. It’s not so much the making that takes the time but coming up with a design to solve all the little details to high standard for performace, longevity, aesthetics and ease of making.

  3. Hi, I have read your original window blog with interest. I very much like the idea of making my own sash windows (or similar), but lack the confidence to know where to start. I would really appreciate a step by step (very basic) guide, and would be willing to pay (a modest sum) for. Especially If I could ask you questions as and when I get stuck. Would also be interested in what tools I need (as I don’t have many) and would need to figure out what is worth investing in etc.

    I am by no means great at woodwork, but am generally handy enough, especially if I have good enough instructions. Like most of these things it appears to me that it is having the nerve to get in a try it (and learn from mistakes) that is the key.

  4. Ben,
    I hope I’m going to end up with exactly what you need. In the way of plans and instructions to make the windows.
    I justified buying the tools I need from the saving over buying bespoke windows. On top of the normal woodworking handtools I’ve been using :
    Thicknesser, Table saw and Table mounted router. I’ll not be detailing all the ins and outs of using these, so you might want to start looking into whats available and how to use them.
    I’ve done a review on my planer / thicknesser and put some basic info together on buying timber and preparing timber. These might start you in the right direction.

    There’s lots of advice available on the web and some great forums. I find Get Woodworking very friendly and encouraging particulally to those wanting to start out.

    “Learning from Mistakes” I’ve done plenty of that. It’s part of the process, if you can keep that in context, you can do almost anything!

    All the best

  5. Thanks Andy,

    I have been doing a lot of reading over the past few weeks, to try and decide exactly what tools to invest in etc. There seems to be some decent second hand routers etc on ebay. Do you have any views on plunging routers as opposed to table mounted, as in, some people seem to say that you can just mount a plunging router under any given table, others don’t seem so confident. There seems to be way more plungers on the market than fixed base routers.

    In terms of saws, there are very few table saws around. Would a mitre saw suffice for most jobs, or is there a specific reason why an actual table saw in neccessary?

    Thanks Again

  6. Ben, A plunge router is what you need to mount in a simple table. The plunging mechanisum then works as the depth control. As for recomendations, the best advice is get the best you afford. Try some of the forums for specific advice. (I have a Trend router in a Record Power table)
    You need a Table saw or band saw to cut down (rip) the length of timber, a mitre saw is for cross cutting only.


  7. I looked lots of blogs to something about to this subject…. Thanks alot

  8. I have built two double glazed sliding sash windows which I have installed in my house. I found it challenging to say the least and I am still not satisfied with the final result. I have used 14mm deep double glazed panels so that the sash stiles and rails would not be thicker than they would have been in the original windows. Spiral balances are used instead of traditional sash weights, because double glazed sashes are so much heavier. I am mainly dissatisfied with how difficult it is to raise and lower the sashes since there appears to be considerable resistance to overcome. Also, I should have considered going the whole hog with double glazing and using 24mm thick argon filled units. I now wish I had installed draught proofing seals between the sashes and the frame.

    I have seen samples of professionally made sliding sash windows with 24mm thick double glazing units and I am impressed by how easy it is to raise and lower them. Rather than spiral balances a chain is attached to the sashes which enters the frame through a pulley. I do not know if the chain is attached to weights or a spring inside the frame. There are draught proofing seals throughout the construction. Finally the glazing units are mounted from the outside and the beads to secure them are on the inside of the sashes.

    If anyone could tell me where I can obtain plans to construct double glazed sliding sash windows to this standard I would be interested.

  9. Hi Maurice, Thanks for commenting and well done for having a go at building your own.
    You can probably tell I’ve done a fair bit of research and thinking about double glazing in sliding sash windows. Hopefully I’ve got some sensible answers for your questions.
    My first general point is (from another answer) “but the edges of double glazed units causes problems. The sealent around the edges of units can breakdown and you end up with condensation inside them. It is possible to fully bed them in NEUTRAL cure silicone, don’t use the stuff that smells of vinegar and don’t use putty as these can accellerate the breakdown of the seals. The most reliable way of fitting double glazed units is with a ventilated air gap all the way round. ”
    The design I’ve developed for fitting DG units with the ventilated air gap is, as far as I can see, totally uinique, and looks as “traditional” as possible. It does present challenges with the sash frame thickness using 24mm units but I’ve overcome these to the satisfaction of the brief I set myself. The full plans will be available, eventually, I’m just at the painiting stage of five complete windows I’m making to prove all the design details.
    You’re right when you say “wish I had installed draught proofing seals between the sashes and the frame”. Draft droofing is more important for heat loss than double glazing, have you seen the various options/kits available for retro fitting draft proofing. My windows have the draft proofing integral to design and hidden from (nearly all) view.
    Many designs with DG units do have spiral balances. They simplify the design, construction and lower costs, compared to weight counter balances. The balances are available for different weights and, I think, are adjustable for exact balancing, so you should be able to tweak them to get a slide. My brief however was for cords and weights, that I know will be easy to maintain 50 years or more in the future.

    Chains can be used, (attached to weights) the idea being they will have greater reliability and longevity than traditional sash cord. I eventually chose sash cord with a nylon core with a rating well above the force that will be applied even on my biggest window. Only time will tell if it was the right decision but that could be 20 or more years down the line, if it is a problem I could replace it chain.

    There has been a lot of interest in my plans and I have to appologies for not having them ready yet. I’ll keep on posting progress and let everyone , who has asked, know when they are ready.


  10. Hi Andy

    I eagerly anticipate your final plans the double glazed sliding sash windows. I have uploaded to a file sharing site some working plans I made for two new windows I intend to construct in my house. These utilize the basic construction I have used in the previous two windows, but I am sure people could refine these plans in certain details. I want to emphasize that this is a basic design that newbies could construct without a workshop full of advanced equipment. You could manage to reproduce these designs with hand tools, a drill and a hand held router as long as you have plenty of time on your hands. I have seen similar low cost replacement sash windows in houses in Hampstead where I did refurbishment work. The sash materials are standard 50mm mouldings you can buy in a timber yard with the rebate routed out to accept 14mm thick double glazed panels. The sash stiles and rails are built up to the required width by gluing a piece of rectangular timber to them. I used softwood throughout, except for the cill which is hardwod. Since most of the moulded timber is standard sash material the finished windows do look like authentic Victorian sliding sash windows and blend in with original windows in the building. You need a joinery handbook for instructions on how to make some of the joints. The joint between the sash stile and meeting rail is particularly challenging. I recommend that you use a free CAD program to make yor plans, because it is easy to get your measurements wrong and the meeting rails do not meet in the middle as they should do.

    Possible improvements to these designs are to make the rebate for the glass on the inside so that the ovolo beads to secure them are not exposed to the weather. The exterior corner of the stiles and rails could be chamfered to imitate the putty on a traditional window. To make the sashes slide more easily you could glue a strip of plastic sheet to the edges of the stiles and have a strip of brush type draft excluder inserted into a groove on the inside of the frame pressing against this plastic.

    To obtain the spiral balances you need to fill out a form giving the weight and dimensions of the sashes. If you live in North London the spiral balances can be obtained from Francis and the timber from T.W.Parker.

    My plans can be downloaded from here: http://www.megaupload.com/?d=4502EPZX

    You need this free AutoCAD viewer to print them: http://www.edrawingsviewer.com/pages/products/eDrawingsViewerpage.html

    This is one of the most enjoyable, challenging and useful woodwork projects you could undertake. I am surprised that that there not hundreds of people on the internet making their own sash windows.

  11. Ben, If your running the timber yourself then you will need a table saw. Take a look at flip saws. Fantastic things – I would never have a single purpose table saw on my van again. You could always the the section run from most timber yards. Not that expensive and saves a great deal of time, plus if your asking about routers in the context above you do not have the same skills as the guy who has already made a sash window! Hope thats helps.

    Great job on your windows by the way Andy!

  12. The window market has developed a few imitations in recent years by either placing horns on the bottom of an outward opening sash, or a vertical slider in upvc. Although these may suffice at a glance or from distance, a closer inspection will quickly reveal the truth. No imitation or substitute window will ever be able to replace a real timber sash window.

  13. DoubleGlazingChelntelham, I’m even more critical towards the plastic mock sashes. But then do look look at windows a lot and can spot them a mile off. It’s supprising to see your comments as the website you link to promotes these monstrosities.

  14. Andy – Any progress on the plans? I restored a couple of sash windows about 20 years ago, replacing some damaged timber in the frames and rebuilding and reglazing the sashes, but I stuck with single glazing. They have been working fine ever since, but I now have a couple of other large windows in need of repair, and I’d like to have a go at double-glazing and draght-proofing them properly.

    Thanks for all the useful info so far.

  15. Hi Keith, I’m getting there with the plans. put it slow going now I’m busy with work. I must get them finished. I’ll get in touch when they’re done.

  16. I’m currently researching making our existing single glazed sash windows into double glazed ones, by taking the frames out, removing the glass & swapping it for double glazed units. I’ve found An interesting site called Sash Glass.co.uk – they say they supply very thin double glazed units specifically for old dash windows. Even though the units are thinner than normal double glazed units, the u values are very good.

    I was also thinking (and you might call me a Philistine for this) of sealing the bottom window in permanently, and modifying the top window to be a hinged (at the top or sides) opening window, rather than going to the complication of redoing the sash sliding mechanisms. I’m wIndering about rebatting in some side hinges – the sort you find in UPVC windows (I’ve managed to get some cheap from a reclamation yard). Anybody got any pointers/suggestions/ideas on this? If it works I’ll let you all know. If it doesn’t you won’t be hearing from me again :-)

  17. Hi John, I’ve come across the slim glazing units as well. As you wouldn’t be changing the windows completely they wouldn’t come under building regulations for the “U” value. As I understand when they are argon filled they can meet the previous regulations they can’t however meet the new figures.

    OK you are a Philistine… I think when you look in to it, recording and doublingish the weights using lead would be an easier job than making one sash hinged. IF you kept the top on only sliding, then you could use the old weights from the bottom sash tied to the top weight , saving you the cost of the lead. You will need to take the sashes out to fitt itne DG units, at that point re-cording etc is easy.
    To open out the outer lining of the frame would have to be cut back and if they are a reasonable size the hinges could be overloaded.

    Let us know how you get on.


  18. Martyn Cripps on May 27th, 2012 at 7:41 pm

    Hi Andy
    Any sign of the plans yet mate.

    Kind Regards

  19. Hi Martyn
    + everyone else who is waiting.

    The plans are half complete but I’ve had to put them on hold as there are issues around protection of the parts of the design. I know this is pain when all you want are some decent plans to make your own windows and I should have been able to publish them by now.
    It seems that part of design is unique and solves many problems encountered in commercial manufacture. With this in mind I’ve got to be careful about what I make public. It’s something I hope to be able sort out so window companies can manufacture under licence and those who want to make their own (for their own house) will still be able to after purchasing the plans.

    I apologise for getting your hopes ups about the plans being available soon. I am working on it and hope to be able deliver eventually although I realise it might be too late for many who are interested.

    As soon as there is any progress I’ll let yourself and anyone else who has as expressed an interest know what’s happening.

    All the best

  20. Hi Andy,
    Your project is exactly what I’m looking for! We’ve bought an old house which’ll need 17 replacement sash windows within the next 5 years or so and I’m not willing/able to pay the ludicrous sums asked by the majority of joiners. I’m an engineer with woodworking skills so, like you, am convinced there is a much more modern, streamlined approach to making them – have you got any further because I’d be very keen to buy some plans off you.


  21. Hi Tom,
    Sorting the window plans is something that has gone on to the back burner for now. With working on the whitby cottage at the weekends and then my day job getting busy, I’m short on time. It is something I want to get done as soon as can but I can’t promise when.

    On the positive side it has given the windows a couple more winters of testing. All is holding up perfectly so I’m confident the design is fitting the brief I set myself.

    I me in touch as so as I’ve made any progress.

    All the best

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