Secondary Glazing

I mentioned before how the Conservation Officer (erroneously in most people's view) sweepingly declared that "you can't have double glazing in a listed building".  That was in relation to a brand new sash window (far right below) which replaced a metal Crittal door and two windows on the side of the house (near right below), which seemed an inexplicable decision; I made sure that the design of the window will allow for double glazing if I so choose in the future, and the CO never realized!  I should point out that I agree that, in a building like this, one should not remove old sash windows and fit uPVC ones as they always look wrong - the thickness of the glazing bars is a real give away apart from the lack of wavy glass - but I did think that DG in a new window would be allowed. Anyway, with that history, I was never going to bother to mention the subject again to the CO, and so the house has remained draughty with a corresponding high gas bill last winter. As a result, I turned my thoughts to secondary glazing, and recently this came to the top of my list of "Things to do before winter". 

Secondary glazing is acceptable on period properties without conservation consent as it a reversible change (other than a few screw holes), and also it is not like double glazing, in that the space between the two panes is not sealed so it does not provide the same barrier to heat loss.  Basically it does reduce heat loss to an extent, but it also reduces draughts and noise.  The sash windows in this house are ideal for secondary glazing as the frame of the sash provides a good flat surface for the inner sheet.  You can get complicated systems which, for instance, add sliding glass in a frame, but I chose a simpler system which comprises a sheet of acrylic with a soft plastic edging strip, held against the sash window by little nylon clips and screws. I'm sure there are other suppliers, but I bought all my stuff from Tubeway Easyfix (http://www.tubeway.co.uk/).  They were kind enough to send me, free of charge, a plastic mitre block for cutting the plastic edging, which got omitted from my order.  Since this item retails at £7.05 + VAT, I'm glad I didn't pay for it; you would think they would always throw such a little bit of plastic in for nothing.

There are relatively few issues with this system, although the price of the acrylic sheet surprised me; I used 2mm thick sheet, although you can use 3mm or 4mm (even more expensive!).  One issue seems to be the size of the sheets; most of my windows are 90cm wide, and so need acrylic sheet which is about 95cm wide; of course, one of the standard widths is 92cm so I had to go to the next size up, with consequent additional waste and cost.  One potential difficulty is cutting the acrylic; I was told that could probably score the acrylic and break it like glass, but even with 2mm thick, this just did not work reliably.  Hence it had to be cut and I quickly proved that you cannot use a hand saw as this causes cracks along with a very rough edge. However my jigsaw with a fine blade proved to be the business so long as you don't move it too quickly, but even then you need to support the edge at the point of cutting or you get a jagged edge with cracks.  Straight edges help with positioning the clips, so I always made sure I had an edge cut by the supplier along the bottom when I fitted the first clips.

I've now done five windows, including the large one in the main bedroom.  This one was so large that I was unable to buy a sheet of acrylic big enough, so I have made a wooden horizontal support which runs across in line with the join in the sashes, so that it isn't seen from outside.

This support was made from four bits of stripwood, and there is a groove top and bottom to hold the edges of the acrylic; the strength is primarily from an expensive piece of hardwood (30mm x 10mm) which forms the visible side in the room. Photos of the system are quite difficult to do, as all they show are the windows and you can hardly see the edge of the acrylic, which is the whole point really.  However, here's a detail picture so you can see the edging and the clips:

The draughts have largely gone and the difference in room temperature is quite noticeable; it really does make a difference and there is now less need to keep all internal doors closed.  I've still got to do one in the hall, one in the extension and a pair in the bathroom (left); the bathroom ones fell to the end of the list due to the refurbishment work needed on the window frame and the fact that I will have to re-fit the venetian blind on another bit of stripwood to hold it away from the acrylic. The main renovation of all these windows will get done next summer (if we have one) and the main aim will be to keep the old glass wherever possible.

Having eliminated a lot of draughts, I will have to make sure that the house is still well ventilated - there has been no dampness or condensation anywhere in the last year since it dried out, apart from what we caused with cooking and showers.