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The SBEM engine can adjust glazing areas in Notional buildings so they may not reflect your inputted data.
For a Notional building, the area of glazing is not acquired from the area defined in the Actual building, but is defined through the NCM Database using the activity class of the glazing type and modified accordingly to match area percentages based on a standard building type.
From the NCM modeling guide:
"In the Notional building the activity assigned to each zone determines whether the zone will have windows, rooflights or no glazing at all, regardless of the type of glazing applied to the equivalent zone in the Actual building. The glazing class assigned to each NCM activity is determined in the "activity" table from the NCM activity database"
TABLE 3 Glazing in the Notional building
g-value(EN ISO 410)
Exposed facades will have windows with area that is the lesser of either 1.5m high x full façade width OR 40% of exposed façade area
For example, an office activity is classified as Side-lit, so the Notional building will only consider Windows for this space. Any rooflights defined in the space in the Actual building will be ignored and the total glazing are will be defined as 40% of exposed façade area or 1.5 x full façade width.
The NCM modeling guide sets out the following conditions for windows, doors and rooflights in the Notional Building:
Areas of windows, doors and rooflights:
36. The areas of windows, doors and rooflights in the Notional building must be determined as set out in the following sub-paragraphs and must also conform to the measurement conventions set out in the guidance beginning at paragraph 183.
a. Copy the areas of high usage entrance, pedestrian, and vehicle access doors that exist in the corresponding element of the Actual building.
b. In the Notional building, high usage entrance, pedestrian, and vehicle access doors must be taken as being opaque (i.e. with zero glazing) and use the U-values from Table 1
c. If the total area of these elements is less than the appropriate allowance for glazing from Table 3, the balance must be made up of windows or roof lights as appropriate.
d. If the total area of the copied elements exceeds the allowance for glazing from Table 3, the copied areas must be retained but no windows or roof lights added.
e. For DSM software the shape of windows in side-lit activities should be modeled as a full façade width window with sill height of 1.1m. Where doors have been copied across from the Actual building, the window will occupy the remaining façade width, and the height adjusted such that the total area of opening areas still satisfies Table 3.
37. Display windows in the Actual building are not copied across to the Notional building
39. No glazed area should be included in basements. In semi-basements (i.e. where the wall of the basement space is mainly below ground level but part is above ground), the opening areas in Table 3 must apply to the above ground part (note that in such situations the 1.1m sill height rule would not need to be followed), with zero glazing for the below ground part.