Secondary Glazing for Mullioned Windows

This page does the calculations for building secondary glazing for mullioned casement windows using @Windows' design largely based on off-the-shelf PSE components.

THIS PAGE IS UNTESTED SOFTWARE. USE AT YOUR OWN RISK.

Measurements

Please provide, in mm, the following measurements from the existing external windows

Height (reveal):
The height of the entire space in which the secondary glazing can be placed
Width (reveal):
The width of the entire space in which the secondary glazing can be placed
Opening width (left casement):
The width of the opening for a single casement
Frame thickness (left):
The distance from the left of the window reveal to the left of the first opening
Visible sash thickness (left):
The distance from the left of the first opening to the left side of the first glass

We assume that your existing windows are symmetrical across the run of casements and within each casement.

Existing Windows

Your existing windows have casements with openings at the following locations:

We recommend that you check the locations of the openings and if more than a mm or two out, check the original measurements you provided and correct as necessary.

If you find that the locations are significantly out, you may not have a symmetrical set of existing windows and you might consider whether a symmetrical set of internal glazing will work for your particular situation. This tool can only produce measurements for symmetrical internal glazing.

Secondary Glazing

There will be one casement in the secondary glazing for each casement in the primary glazing.

All secondary casements will be the same size as each other and arranged symmetrically.

The openings in the secondary windows will never be smaller than the openings in the primary windows, but may be larger.

We align the edge of the secondary glazing's glass to either the edge of the primary window's opening or to the edge of the primary window's glass if our choice of materials means that we can't align to the opening. Failing that, the edge of the secondary opening will be aligned to the edge of the primary opening.

Diagram

Here's how your secondary glazing will look.

The vertical lines show the positions of the openings and glass in the primary windows. You should never see vertical lines passing through the jambs or mullions of the secondary glazing.

Parts List

Here are the parts you will need for your secondary glazing:

Data

Here's a dump of the data for your secondary glazing including a parts list: