Draughts in your extension? Blame wind washing

Building Advice on preventing drafts across your home

it sounds like air is flowing into the internal space, and you are feeling the discomfort of a fluctuating internal atmosphere

Dear Brigid, 

We added an extension to our 1960s home nearly 20 years ago, and while loads of rigid insulation went in and membranes etc, it’s not nearly as warm or ‘airtight’ as we’d have thought.

It’s a timber and steel frame, clad externally in cedar with a monopitch membrane roof, has aluclad double glazing and is set open plan off the kitchen/family area.

However, we notice draughts around sockets, switches and the many ceiling-mounted downlighters, all of which had to have an uninsulated area over each light fitting at the time.

We’ve since fitted LED lights. Is there some way to reduce those areas around the lights or otherwise insulate them or isolate them, and if so it would have to be done internally not from the roof above.

Any other ‘retro’ tweaks to cut down air flow, or is it necessary for the timbers?

Thank you, 

Tim and Donna, 

Hi Tim and Donna

Air movement in timber frame and steel frame is not an uncommon complaint. We put two diametrically opposed construction products together and expect them to get along. The truth is, timber expands and contracts (moves) while steel doesn’t.

Where you get movement, you might also get gaps between fabric. But this movement is designed in, and what we do to offset the material incompatibility is tape, strap and seal, as well as use membranes that prevent timber from sweating. Nevertheless, you will get undesigned gapping over time.

Where there are openings in the fabric, for whatever reason, excess air may find its way through. Depending on your house’s exposure level, wind can wrap around it and play havoc, pushing at one side and pulling at the other.

This can often lead to air movement under pressure between the external and internal walls of the building and a breeze, some with impressive speeds, may occur. Where there are openings, holes or fissures that link to this wind path to the warm side of your insulation, you get what’s called wind washing, where your internal heat is sucked out of your building and the heating system keeps engaging to bring up the temperature, potentially costing a pretty penny.

In your case, it sounds like air is flowing into the internal space, and you are feeling the discomfort of a fluctuating internal atmosphere. This is similar to a stack or chimney effect, where air is being drawn through your internal space.

Before we look at sockets, switches and downlighters, consider having a walk around your extension and the spaces your extension feeds into. What you are looking for is a ‘draw’, for want of a better word. This is what pulls the air through the building fabric. Is there an open fireplace in the room or the adjoining room(s)?

Are the draft seals to all your windows and external doors poor or leaking? Are you opening windows somewhere in the rest of the house and forgetting to close them? Is there an attic hatch in the building and if so, is it properly sealed? Do you have passive ventilation (wall vents) in the extension or the main house?

As you have an open plan, I’d start in these rooms and then fan out to the rest of the house.

Then consider, putting a balloon in your open fireplace, when not in use. Get your window provider to audit your windows and doors and remediate (draft seal) or change out. Close the doors in every room to cut down on air movement. Go old school and put one of those stuffed snakes at the external doors.

Please don’t stuff your wall vents to prevent air flow. They are part of air quality control and are designed to be open. Where you have permanently open trickle vents in windows instead of a wall vent, likewise, do not block these. Instead, shut all internal doors, again to reduce the draw.

Now for a few tips on the downlighters, sockets and switches. For your downlighters, one of the most effective solutions is to use airtight covers (also called downlight hoods) that enclose each downlight, sealing around it so that warm air can’t leak out, and cold air can’t be pulled through.

For sockets and switches, there are foam or rubber gaskets designed specifically for behind socket and switch plates to reduce draughts. These are relatively cheap and very effective.

When purchasing products, please consider fire safety. Fire safety is very important in any type of renovation, light or heavy. 

Another thing you might look at is the external envelope. Are there places where openings may have occurred either at construction stage or after? These might crop up around windows and doors. Look around window reveals and under sills. Where you see holes/gaps fill them. Look at service penetrations. Sometimes these might be for new services, and the installers may have been a little iffy on sealing them. Perhaps seals have failed and need to be reapplied. Investigate any external junction boxes, they are notorious for poor construction detailing.

If these tips and hints do not alleviate the issues, it is best to get in someone to survey your home. They will advise you as to possible sequence of works to your building. Don’t panic, just get a suitably qualified professional e.g. a chartered building surveyor, and they will give you best advice or will refer you to the appropriate person. Thanks again for your query and I wish you both a Merry Christmas.

Brigid Browne is a chartered building surveyor and chair of the Southern Region of the Society of Chartered Surveyors Ireland. She is the owner/ managing director of Cashel-based Fortress Planning which offers a range of services including assigned certifier, design certifier, building surveyor, and conservation consultancy to clients all over the country — www.fortressplanning.ie

If you have a property related query or issue you would like to raise with Brigid, please email
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