Cost implications
It has to be recognised that there is a difference in climate between Land’s End and John O’groats, and a difference in solar gain between northfacing and south-facing elevations. However, dealt with properly it can be considered that, on this issue, there are no significant cost differences between sustainable and non-sustainable builds. Windows and doors are a necessity for any build, so they don’t represent an additional cost for the sustainable builder other than the £200-£300 needed to pay for airtight installation. The cost of the units will be the same. Triple glazing is where the costs can start to rise. want sunlight to get into the room, and a retractable awning or the louvred effect of a brise soleil will do that. Part of the cunning of a brise soleil’s design is that it naturally blocks out more light from the high summer sun, while in winter, when the sun is lower, more of its rays will find their way past.
Internal blinds do not work very well for keeping radiated heat out, as they are on the wrong side of the glass. Double-glazed units with blinds between the panes of glass work better, as some of the heat is trapped between the panes, but ultimately nothing works as well as external shade.
Another option that a committed sustainable builder may wish to explore is planting deciduous trees — plane (deciduous) trees are a good option. Provided they are the right distance from the house, these will provide shade in summer when they are in leaf, but let sunlight through in winter.
Ventilation
Any high-performing house (with an airtightness better than 5m³/hr/m²) will need a mechanical ventilation system with heat recovery (MVHR), meaning its windows will be used for purge ventilation only — that is, when you need to get rid of fumes after painting or burning your toast. If you take one thing from this article, make it this: trickle vents are the devil’s work and must never be fitted! All they do is ruin the airtightness that you have worked so hard to achieve.
Bear in mind that good fenestration will give you sun-warmed rooms, and an MVHR system will be able to distribute that heat to other rooms.