Costs: Natural ventilation for offices | Features

Specification options
Manual operated windows	Capital cost £/m2	Net present value for 60 years £/m2	Life expectancy years

Top-hung casement: aluminium window frame to BS 4873. Finish: anodised to BS 3987 minimum thickness 25 microns. Insulating glass units to EN 1279. Austenitic stainless steel hinges to BS EN 10088–2 grade 1.4301; UK type 304	300	440	40
Aluminium window as above with upper fanlight and outward opening casement	450	610	40
Top-hung casement, aluminium window frame as above with basic coated mild steel trickle vent providing 400 mm2 opening per m2 of floor area	375	530	40
Powered window actuators Top-hung casement, aluminium window frame as above operator remote control window control	475	2,380	15
Top-hung casement, aluminium window frame as above automatic window control based on temperature and rain sensors	625	3,250	15
Table notes
The natural ventilation options are listed in order of increasing control and sophistication. The aluminium side-hung casement window is the reference window to which the other options are added. Life expectancy for powered window actuators and controls is 12 years.
Only aluminium windows are considered, as this analysis is about the whole-life cost implication of alternative natural ventilation approaches rather than a comparison of window frame options.
Cost data relates to capital costs, replacement and maintenance costs only. Energy costs are not included, as these will vary by building, location and use. The difference between the options in net present value gives an indication of the energy savings required to justify a solution on costs grounds alone.
A whole-life cost analysis, including energy use, fabric components and related functional requirements such as smoke control, should be carried out for specific buildings to assess the viability of natural ventilation options.