Calculate total fenestration area as a percentage of nett floor area for each storey.
By the end of this lesson you should be able to calculate the percentage that drives the applicable performance limits.
The vertical fenestration percentage is checked per storey. Add the fenestration area for the storey and compare it to that storey's nett floor area. Do not average a large ground floor with a smaller upper floor unless the rule you are applying specifically allows it.
Fenestration area includes the whole opening element: glass plus frame, whether fixed or openable. Use width multiplied by height for each element unless the project has a more precise approved measurement method.
As fenestration percentage increases, the thermal and solar performance requirements become more demanding. A project that passes at a lower glazing percentage may fail after larger doors, clerestories or additional windows are added.
Enter areas consistently. If you enter width and height in millimetres elsewhere, confirm the calculator converts to square metres before comparing percentages.
A single storey has 52 m2 nett floor area and three glazed elements: 1.8 m2 at U 2.8 / SHGC 0.32, 5.0 m2 at U 2.2 / SHGC 0.25, and 1.1 m2 at U 3.0 / SHGC 0.35.
Enter each glazed element with its area, orientation, U-value and SHGC. Use the result cards to check glazing percentage and weighted performance.
The important decision is not only whether the numbers pass, but whether every value can be traced to drawings and supplier data.
Was the area calculated for one storey only?
Window A: 1.2 m x 1.5 m. Door B: 2.4 m x 2.1 m. Window C: 0.9 m x 1.2 m.
Flag the missing evidence, use a conservative assumption where appropriate, and avoid claiming compliance until the information is confirmed.
Fencalc XA2021