Measuring the Window Aperture and 1-inch Gaps Top and Bottom Post questions and find answers on glazing, double glazing, upvc glazing, conservatory glazing, fixtures and fittings etc....

[zerodefect]

I'd like to install some new double glazing. The current double glazing is over 20 years old and is rather ineffective - noticeable during the summer/winter months. For the record, I've been the property owner for the past few years. The property was build in 1969.

I've been measuring the aperture of the windows, and I note that the windows have around a 1-inch gap (yes, 1-inch!) at both the top and bottom (see attached images). This gap appears to be filled with a combination of expanding foam and mortar. I notice a similar sort of gap on the neighbour's windows (the building is the same sort of style/build).

I had a few questions (and a few thoughts):
1. Has this gap been made for some special reason?
2. Is this gap to accommodate the lintel somehow (but why the gap at the bottom)?
3. Is this gap there because hey fitted some sort of standard window size to minimize costs? Aperture height is around 1400mm (aperture height _not_ window height)

I'm slightly hesitant to remove some of the mortar (for further inspection), but I'm wondering if I'm left with no other option?

Any assistance would be much appreciated.