One of the oddities of our home in the Netherlands is that while the ground floor was almost entirely double-glazed, the first floor was not. This was apparently the building standard of the time it was built - 1972.
The windows are large in our house, so they're more important than they might be in a house with smaller windows. However, the rooms without double glazing are those upstairs which we don't really need to keep particularly warm.
For some time we've been weighing up the pros and cons of spending money on glazing for rooms which don't necessarily need to be kept at a particularly high temperature, and eventually made the decision to go ahead with the work.
We were influenced more than a little by a study about the effectiveness of HR++ glazing which gives some figures suggesting that the HR++ glass is particularly effective. Also, the cost was more reasonable than expected (the second company we asked have a quote which was less than half that of the first), and as it was possible to replace the glass within the same hardwood window frames and not have to replace the frames as well (we're not huge fans of PVC windows), we decided it was a good idea.
We don't expect it to make the same big difference to our heating bill as cavity wall insulation did, as the thermostat in the house is downstairs and relatively unaffected by the temperature upstairs. However, it will presumably mean the entire house is better insulated so have some effect on the ground floor as well, and of course it also means the end of condensation on the bedroom windows, which froze on the insides in the winter and made it difficult to open the windows.
Yesterday it happened. New glass in the first floor windows.
We're hoping this makes conditions a little more pleasant for our teenage daughter in the front bedroom, which due to receiving least sunlight was the coldest room in the house in the winter.
So far, our heating bills have been lower each successive winter since we've lived here, as each time the house is a little better insulated than the previous winter. It's a pattern I'd like to continue.