Arch said:
Glazing, as opposed to having empty openings, prevents air transfer that would make internal temperature conditions uncomfortable to live in. Both single and double glazing would be my houses weakness but both would work much better than holes. (Johnmath)
I was being facetious of course! The point I was trying to make, obviously not successfully, was that if all the other heat ingress and egress paths are well insulated, then treating the remaining weakness will have a greater effect than if the former wasn’t true.
I am not suggesting the computer model is incorrect, but it only tells part of the story. The real benefit comes when you live in a house that is just more comfortable to be in regardless of the season or weather. Mechanical heating and cooling is just not as nice, in my opinion. The payback period will also be much shorter if you factor in energy price rises, which are likely to continue to double ever five or six years, and if you factor in climate change too 
I have retro fitted various types of secondary glazing to two houses I have owned. For example I have fitted aluminium framed double hung sash windows inside existing wooden and aluminium double hung sash windows. In one case this was a window above my bed-head and was done for acoustics (I lived on a city street corner), but an unexpected benefit was stopping the flow of cold air off the glass making sleeping in winter much more pleasant.
I have also used Clear Comfort and other similar air spaced films which work very well and seem to be durable, and I have used bubble glazing (plastic bubble wrap) on bathroom windows and skylights, which also provide surprisingly obvious benefits, presumable because the other heat paths were already well dealt with.
My main living room has about ten square meters of glass on both the northern and southern sides. I have double glazed the southern side by simply adding glass to the inside of the timber frames on the existing sill. It cost not much more than the cost of the glass. I have yet to do the northern side because it is a double glass sliding door and I need to come up with a different solution. I had an astronomical quote from Magnatite that would also have been an ugly installation. I plan fit acrylic sheets myself for perhaps 1/5 of the price, or less.
Posted Wednesday 5 Dec 2012 @ 4:40:50 am from IP
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But what type of frames did you get and did you design the shape/size together with sun control eaves/sail/shutters? Some simple design work can be more effective than just buying DG.