A draught sealing buyers guide

The range of gap sealants, and manufacturers, is huge. There is a sealant to do any gap sealing job in any material. Many sealants are low- or zero-VOC, most are paintable and flexible, and many are suitable for outdoor extremes.
As we head towards winter, draughts can make your home far less comfortable than it should be. Lance Turner looks at options for sealing up your home for a cosier cold season.

It is generally recognised that unwanted draughts in a home make the home perform poorly thermally, compared to a home that is well sealed. With airflows into and out of a home, energy also flows due to the temperature differences between the interior air and the air outdoors. In summer, air flowing into a home can heat it up, while in winter, warm air flowing out of a home is replaced with cold air, cooling the home and making heating work harder (and cost more to run).

There are desirable draughts, which are usually controllable, such as when you open windows at the end of a hot day to vent out accumulated heat, and there are undesirable draughts, which you have no immediate control over. Generally speaking, unwanted draughts can be caused by gaps between building components or around built-in appliances and equipment such as lighting (particularly recessed downlights).

A home’s level of airtightness is rated in the number of air changes per hour that occur when there is a 50 Pa (pascals, a mere 0.007 psi in the old measurements) difference in air pressure between the indoor pressure and that outside. The ultimate sealing standard for homes is the Passive House standard, which allows for no more than 0.6 ACH50 (air changes per hour at a pressure differential of 50 Pa). This is an extremely tight standard, and very few homes meet (or indeed should meet) this standard. In Australia, the average home is more likely to be 20 ACH50 or worse.

So how airtight should your home be? For most homes, to maintain an acceptable level of comfort without requiring excessive heating or cooling (assuming the house is also correctly insulated, orientated and shaded), an airtightness of 5 ACH50 is enough, with few Australian homes reaching this level. See box for more on testing airtightness.

Why seal gaps?

There are many reasons to seal gaps in a building envelope. The first, as mentioned, is to keep conditioned air where it belongs: inside the home. This reduces air conditioning (heating and cooling) energy use and bills, but also reduces other negative effects of excessive air leakage that may not be immediately obvious.

For example, in winter, draughts can reduce the comfort of a home by making you feel cold, even in a heated home. You may not feel the draughts, but cold air pools at floor level (cold air is denser and hence heavier than warm air) and so can result in cold feet and a general feeling of being cold. This is known as stratification, where differing air temperatures form into layers. This can be particularly noticeable in winter if you have warm air coming from ceiling ducts or high-mounted reverse-cycle air conditioners.

Severe air leakage can even result in noticeable air movement inside the home, such as feeling a cold breeze inside the home when it is cold and windy outside. Wind pressure can force considerable amounts of air through even small gaps and can result in a very uncomfortable home in severe winter conditions.

The incoming air may also bring in more or less humidity than desired, making the home uncomfortably humid, or excessively dry.

Air leaks also let in more than just air, bringing dust, pollen and other pollutants into the home. Large enough gaps can even let in insects, spiders and small critters such as mice.

Gaps also let in something else that can affect health and wellbeing: noise. More noise creates more stress, especially noise that is particularly undesirable, such as traffic or construction site noise. Sealing gaps can help reduce indoor noise levels.

Draughts can also affect the operation of thermostats. For example, a cold draught near a thermostat can make the thermostat run the heating more than needed, overheating other parts of the home.

Where are the gaps?

So, you are tired of living in a cold home in winter (or a hot home in summer) and want to start sealing gaps. But where are they, and how do you find them?

Air can leak into and out of a home from many places, some visible, some far less so. Sealing as many gaps as possible can dramatically improve the thermal performance of a home. Diagram: Sustainability Victoria

Well, gaps have a number of causes. They can come about from poor building practices, such as misaligned cladding and lining, poor fitting of window frames into openings or poor fitting of built-in appliances. Gaps can also appear through wear and tear, especially of door and window seals or even cracks in walls through soil movement. The most common causes of air leakage in the average home include:

  • gaps around window and door frames where they meet the wall linings, that were not sealed when the windows and doors were installed (poor building practices)
  • gaps between the window frames and the window jambs (old sash windows are notorious for this)
  • gaps around doors where they fit the frame, especially older doors that have warped over time
  • window and door seals that have failed over time; this can be a problem even for the best designed windows and doors, especially in dusty areas where dust abrades the seals as the windows and doors are operated
    along skirtings, cornices and trims, where these mouldings are often just nailed on or held in place with a few blobs of glue. This is particularly a problem for older homes with uneven walls, ceilings and floors.
  • pipe and cable penetrations to bring services into the home. This includes wherever holes are drilled from outside to inside. Pipework in particular can be a problem, with gaps (sometimes very large gaps) often being found around pipe entry through walls and floors
  • duct penetrations, including air conditioning ducts, rangehood and clothes dryer ducts where they pass through walls and ceilings
  • electrical outlets; these are less obvious, but a poorly fitted electrical outlet can also let in draughts
  • around built-in appliances such as air conditioners and dishwashers, especially where the appliance penetrates the inner lining of the house. Often, lining is poorly fitted or omitted altogether behind built-in appliances (poor building practices) resulting in huge holes in the building envelope
  • between floorboards, especially in older homes that don’t have tongue-and-groove boards. The sheer area of a wooden floor can make for a vast area for air infiltration.
  • chimneys and flues where they pass through walls and ceilings. Also, solid fuel heaters such as wood heaters can leak air via the air inlet/firebox/flue flow path, even if the heater is not in use
  • skylights and lightshafts, especially if interior diffusers are ill-fitting and the external light dome isn’t well sealed, or the duct itself leaks air, which can allow air to flow between the roof cavity and the house interior
    manhole hatches. These often have no form of seals, especially on older homes. They often consist of a simple board sitting inside a frame, with any misalignment in the frame construction or warping of the board resulting in gaps
  • lighting, particularly light fittings that penetrate into the roof cavity, such as recessed downlights. These can allow large quantities of air to flow between the roof cavity and the house interior, especially if the light fittings are of the older ventilated type
  • exhaust fans without draught seals. These are effectively large holes in the ceiling and can allow a great deal of air to flow, producing considerable draughts
  • wall air vents. These are usually found in older homes and are now generally considered unnecessary due to the elimination of most open-flued gas heaters and open fireplaces. They can leak a considerable amount of air, as indeed they were designed to do!
  • dog and cat doors. These usually have minimal or no seals, and so allow considerable air ingress.

Testing for airtightness

Airtightness testing on homes is done using a blower door test (en.wikipedia.org/wiki/Blower_door). This involves closing all windows and doors, and running a special blower fan that has been sealed into one doorway or window for the test (see photo).

The blower is run to produce a pressure differential between indoor and outdoor pressure of 50 pascal (Pa). The rate of air flow out of or into the house at this differential gives the airtightness rating of the house, as an air changes per hour figure. For example, if air exits the house envelope at a rate that would turn over all the air in the home 5 times every hour, then the rating would be 5 ACH50.

From the rate of airflow measured by the blower door test, the effective leakage area can be calculated, allowing leakage at other pressure differentials to also be determined. A ‘normalised’ pressure (typical of air leakage for low-rise buildings) is around the ACH50 rating divided by 20 (bit.ly/2SMRtQm). Different normalised standards are used in different countries, and apply in different situations, so there is no simple conversion between ACH50 ratings and typical ACH figures. As an example of the complexity of airtightness testing, read AIRAH’s document ‘Air Tightness Metrics to Improve Australian Building Envelope Integrity’ (bit.ly/2tP4ajJ).

Detecting draughts and leaks

While some gaps are obvious because you can see them, others are less so. There are a few ways you can detect leaks, but one simple one is to close all windows and doors, turn off any air conditioning but turn on any exhaust fans that vent to the outside (the fan will have a vent grille on the wall or cap on the roof if it vents outside) to create negative pressure inside the home which will draw in outside air through any gaps. Then wander around the house with a lit incense stick (or some thin strips of tissue paper on a stick or coat hanger) running it along skirtings, windows and door frames and anywhere else there are joins in the building envelope. Draughts will be visible in the smoke as incoming air pushes the smoke back into the room. This method is a good start, but also check out the Your Home website at yourhome.gov.au/passive-design/sealing-your-home for more tips.

There’s much more in the full buyers guide! Find it in Renew 147.

The full guide includes 6 pages of how-tos on how to seal doors, windows, ‘fixed’ gaps, floorboards, appliances and chimneys. Plus what can renters do, what you should think about before building or renovating, sourcing help to draught seal your home and a list of suppliers of sealants and draught sealing products.

Warning: draughtproofing safety

Don’t undertake draughtproofing if you have an unflued gas heater or any open flued heater (see bit.ly/2CuI36Q) as, in a tightly sealed home, the gases from such appliances can present a carbon monoxide poisoning risk. With other gas appliances, special care needs to be taken including regular servicing and cooktop extraction to outside. See bit.ly/2MCUjEv

About the author
Lance Turner is Technical Editor of Renew magazine.
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