Triple glazing and mechanical ventilation with heat recovery (MVHR) systems come as standard in a Passivhaus home, sealing the interior against the elements and radically reducing your reliance on conventional heating. For the second in our series of Passivhaus hacks, Kate Jacobs asks our panel of experts how to draught-proof and effectively heat our own less-than-perfectly-constructed homes.

Heat control can mean various complex things in a Passivhaus, many of them integral to the way the house is built, but it’s a simpler matter in most conventional homes. William Gottelier of cross-disciplinary architecture and research practice Becoming X points out that there are many ways to level up the heating system in a typical house or flat. “You can use good modern thermostats that can work alongside an existing boiler to split the house into different heating zones so that, for example, only the live-work area needs be heated in the daytime. Meanwhile, the Hive system can include thermostats on individual radiators for greater control.”

To achieve Passivhaus standards, high performance double- or triple-glazed windows are an essential to eradicate what can be a major source of heat loss. In existing homes, these options aren’t always available; whether it’s a rental, a historic house, in a conservation area, or because of budget constraints. If you are in need of new windows, all the architects we spoke to advise avoiding UPVC, as Fergus Knox of RIBA-chartered architecture practice Knox Bhavan explains: “In our view, UPVC is never the best choice. Well-detailed timber windows are more durable and far more elegant.”

Edward Farleigh-Dastmalchi of fardaa architecture and urban design agrees: “Timber is a natural insulator and uses less carbon to produce”. He advises shopping around window companies in surrounding counties to compare prices, balancing this with transportation costs. To lessen the financial and environmental load when creating a new opening for a window, he recommends searching auction sites such as eBay for new but unused windows. Farleigh-Dastmalchi often specifies Rationel windows; for roof windows and skylights, daab design’s Bléhaut recommends Velux. “They’re an amazing, forward-thinking company, empowering owners to replace existing Velux windows with a triple glazed model and to fit external awnings, thermal internal blinds and/or black out blinds to their Velux windows, which is easy to do and very effective.”

There are other options that will make a difference to heat loss and outdoor sound transmission, without replacing the whole window, including upgrading the glass, with many homeowners now opting for vacuum glazing – two panes of glass separated by a vacuum cavity – as Ogi Ristic of TYPE architects explains: “Vacuum glass is around 6-9mm thick, a similar thickness to a single pane of glass. It performs as well as double/triple glazed units, since it has a vacuum within it, but it’s light and thin enough to fit into existing window frames. This means it works well on sensitive refurbishments such as listed buildings or conservation areas. And it helps reduce waste, since perfectly good frames aren’t being disposed of.” TYPE are working with FINEO glass on a current project; LandVac Glass are another vacuum glass company to check out.

Another more affordable solution suggested by Ristic is to use polycarbonate sheets as a form of secondary glazing. These are cut to size and can be installed with silicon and rubber seals. “This set-up can last two to three years if done properly and is easily reversible, so could work on heritage properties, subject to agreement with the local authority.” Similarly magnetic secondary glazing uses acrylic panels held in place with magnetic strips that can be removed each summer. “It’s important in all cases that the secondary glazing fully seals the air in the gap. You can easily tell this has happened as you shouldn’t get condensation on the original windows,” says Ristic.

Dropping down a notch in terms of budget, there’s the window film option. Generally used as a1-2 year winter fix, it involves attaching sheets of clingfilm-like material to your window frames and using a hairdryer to shrink it into place. Ristic recommends seeking out the more robust variety, such as Stormguard Secondary Glazing Film, although his tip is not to bother with the tape that comes with it. Instead, use Everbuild Mammoth Double Sided Grip Tape. Be sure to check the fire regulations and advice around any secondary-glazing products chosen.

Existing windows can also be draught-proofed, either by a professional company that can strip, clean, add insulating brush strips and rehang for a snug fit, or by the homeowner, who can use brush pile and other tapes to close any gaps between the window’s working parts. Look out for sustainable options including sheep wool tape. Whatever the level of intervention planned, if tackling the whole house seems daunting, Farleigh-Dastmalchi has good advice: “To have biggest impact, identify the most important windows to target first; any that are completely shot, north facing, or larger, overshadowed windows.”

Good windows will also reduce the amount of solar gain in summer but again, there are ways to tackle that without a huge investment. Bléhaut advises starting with solar control on the outside of the building where possible. “Solar shading is more efficient externally because once the sun is inside it has already converted into heat. You can reduce solar gain with external awnings, heat control films or deciduous plants and trees creating shade, even on balconies.”

For our full series of Passivhaus hacks see:

The Green Series #1: an insiders’ guide to insulation

The Green Series #3: how to make your home airtight

The Green Series #4: how to make your home breathable and thermal-bridge free