Draught-proofing
It's estimated that the average house loses 25% of its heat through uncontrolled ventilation. Draught-proofing is the process of sealing gaps in the external fabric of the building to prevent heat loss by air flow. See our section on Ventilation and Airtightness for some background.
Modern homes are constructed with airtightness requirements defined by Building Regs, but older homes are often extremely leaky. Fortunately, it's usually quite cheap and simple to draught-proof your home. Effective whole-house draughtproofing can usually be installed for around £100-200, far cheaper than achieving the same benefit by adding insulation.
It’s worth reiterating that some level of ventilation is essential to maintain good air quality. Breathing, cooking and washing all create humidity which needs to be able to escape otherwise you could develop moisture issues. The aim isn’t to completely seal your home, but to achieve a balance between necessary ventilation without excessive loss of heat. Signs that you might not have enough ventilation include -
Excessive condensation on windows and/or walls
Lingering smells, especially smell of ‘damp’
Mould growth
Identifying Leaks
The first stage of draughtproofing is to identify any areas where air is entering or leaving your home. The best way to do this is with an infrared thermal imaging camera which will clearly show cold areas where you have cold air entering the house.
You can also survey the outside of the house to see where warm air is leaking out. This is typically more pronounced on the upper floors due to the 'stack effect' (heat rising). This thermal camera view shows yellow and orange around the windows where heat is leaking out. The bright yellow spot in the centre of the image is the bathroom extractor fan – an example of controlled ventilation that you'd be ill-advised to seal.
For those without the luxury of a thermal camera, you can rely on the sense of touch to identify cold areas (or contact us about a thermal survey). A smouldering incense stick producing a steady stream of smoke can also be useful for detecting gentle air currents. Failing that, you can simply use the headings below as a checklist of common areas where draughtiness can be a problem.
Windows and Doors
Windows and doors are typically less well insulated than the walls of your house, but they can cause further problems if their frames are poorly sealed, allowing air leakage around the edges. Wooden windows and doors are particularly bad for this as they shrink, swell and warp during the seasons, potentially leading to large gaps.
Most DIY stores sell self-adhesive foam draughtproofing strips. We've found the performance of these to be poor. They become detached easily and, in many cases, prevent the door or window from closing properly. We had more success with mechanically-fixed seals such as the Q-Lon "Retro" series. These are cut to length and pinned around the frame on the closing side. They have a flexible gasket that sits snugly against the moving part of the window or door. They only cost a few pounds each and take minutes to install. A far better solution than the self-adhesive strips, in our opinion.
This image shows a set of wooden French windows draugh-proofed with "Retro 21B" strips. These compress to form an airtight seal which is tolerant to movement in the door relative to the frame without stopping it from closing.
The bottom edges of doors are more difficult to seal. The Retro strips aren't appropriate because they would be damaged by people treading on them. Two alternatives are –
Filling the gap with silicone sealant (like the stuff you'd use to seal around your shower). You can prevent it gluing the door shut by applying a liberal coating of Vaseline to the moving surface. be sure to leave the door at least 48 hours after applying the sealant before opening to allow it to set properly.
A brush seal. In our experience this is less effective than the method above and is only recommended where you don't have a suitable door jamb to seal against.
This brush seal screwed to the lower edge of a front door looks like it’s keeping draughts out but the thermal images below show that it's not necessarily very effective.
Before and after draught-proofing a front door. The cold (blue) areas around the sides and top of the door in the first image are caused by air leakage. These have disappeared in the second image after installation of Q-Lon Retro draught-proofing seals. The bottom edge has had a brush seal installed but the second image shows that this is less effective. The letterbox is the next area that could be improved.
Sash windows are a particular challenge. Because they slide rather than swing open it's more difficult to attach a seal without affecting the operation of the window. The best method is to add soft "brush pile" seals around the contact surfaces, however this is a specialist job that involves dismantling the window and can be expensive.
Image credit - www.renovategreen.co.uk
Chimneys
Although you'll rarely feel cold draughts coming down chimneys (because warm air rises up the chimney, rather than cold air being drawn down) you can lose considerable amounts of heat through the 'stack effect'. You can check for air flow up a chimney using a smoking incense stick or similar – you will likely see the smoke being drawn up the chimney (let's not forget this was the original purpose of the chimney!) indicating warm air being lost.
Unless a fireplace is actively used – which is much less likely nowadays – you can seal the chimney to save energy. There are a few ways to do this -
Block the chimney with wool insulation. If the chimney flue isn't too wide, you should be able to seal it by simply stuffing some wool-type insulation into the opening. This will allow some air to pass through (good ventilation) while preventing uncontrolled loss of warm air.
Fit a "chimney balloon". As the name suggests, these are inflatable bags which can be fitted up the chimney before being pumped full of air. If positioned correctly they will seal the chimney flue. Bear in mind that they may need topping-up with air occasionally.
If you have access to the roof, the chimney can be capped to create a complete and permanent seal.
Floorboards
If you have an unheated space below your ground floor (either a full basement or the void beneath a suspended floor) then you need to consider the ground floor as an external surface where you can lose heat. Victorian houses were commonly built with suspended timber floors which are good for avoiding damp issues, but they allow significant leakage of cold air. The recent trend for removing carpets to expose the floorboards has exacerbated this effect because cold air can flow unrestricted through the gaps between the boards.
If you suffer from this issue, you can purchase sealants specifically designed to seal the gaps between the floorboards. This is only a partial solution however since it might reduce the draughtiness but the floorboards are still a poor insulator and will remain cold underfoot.
The best retrofit measure is to add under-floor insulation. This generally requires the floorboards to be removed, and some form of insulation to be installed between the joists, before re-attaching the floorboards or replacing them with modern plywood sheets. This solution will fix the draughts and provide a well-insulated ground floor which feels warmer underfoot. See our section Floor Insulation for more information.
Service Openings
They may not all be visible, but every pipe and cable that enters your home passes through a wall, floor or ceiling at some point. This includes gas, water supply, telecoms, etc. You may also have holes in your ceilings for spotlights, and holes in the walls for the light switches. Each of these openings in the building fabric is a potential source of draughts if not properly sealed.
The ideal way to seal these service penetrations is with an airtight "grommet" built into the wall construction.
For retrofit situations, adding grommets often isn’t practical. Instead, we can use gun-applied silicone sealant for small gaps or expanding foam for larger gaps. For very large gaps you may wish to fill them with insulation before sealing.
This image shows three service penetrations in the external wall behind a boiler. These 150mm diameter holes were cut for the adjoining bathroom extractor fan (bottom), a tumble dryer vent (centre), and the utility room extractor fan (top). No tumble dryer was connected so the middle hole was completely open! It was sealed with some wool insulation in the hole and self-adhesive tape over the inside face. The gaps around the bottom pipe were sealed with Soudal 'Genius Gun' expanding foam which costs a few pounds from any DIY store.
Keyholes and Letterboxes
These are obvious ones! Keyholes are small but easily sealed. For unused keyholes (or those used from one side only) you can seal with a little strip of self-adhesive tape. Sellotape will be almost invisible and we've found it to be surprisingly durable, even when stuck on the outside.
For keyholes that are regularly used the best option is a little swing flap which can be screwed or glued onto the door with epoxy adhesive.
Letterboxes with flaps and brush seals are available and are worth considering if your current letterbox is a source of draughts.
Loft Hatches
If your loft is unheated, a poorly sealed loft hatch may let warm air escape. Around the edges of loft hatches is a location where the DIY store self-adhesive foam draughtproofing strips may be suitable.
If you're insulating your loft don't forget you can also insulate the hatch itself. A small rectangle of PIR (polyisocyanurate) board cut to size can usually be glued to the top to avoid a cold spot. If you don't have space for the thicker PIR boards then an insulated foil blanket is an alternative, although these often have limited insulation effect in our experience due to their thin construction.
Skirting Boards
Unsealed skirting boards are another common path for cold air to enter your home. A thermal camera survey is the best way to determine whether you have draughts coming underneath the skirting boards. If so, it is usually quite easy to seal the gaps using a bead of decorator's caulk. Note that you may need to seal both top and bottom edges of the skirting boards.
