The problem with downlights

Downlights decorate the ceilings of thousands of houses, apartments, bungalows and homes across our country. However, this modern appeal with ‘clean lines’ may be a design trend with unseen consequences.

Downlights remain ‘weak points’ in our efforts to control humidity, heat and the movement of warm air in our homes.

Usually about 20 percent of the incoming air escapes the property via the roof area, increasing the danger of condensation and reducing the energy efficiency of the roof.

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Ceilings have small gaps, for example surrounding the roof hatches which provide a route for air to flow between the living space and up into the roof space.

There are also more complex airflow services: for example, through the cavity walls and behind the layer system. The heat and moisture generated by the normal activity of households in occupied spaces in the house under the ceiling, raising the temperature from on the outside ambient conditions. Some of this heat and humidity exits the living areas of the building, and passes through the ceiling into the roof through a mixture of diffusion, conduction and air circulation.

In cold climates this movement adds to the movement of air and significant loss of warmth from the house, fs to the further increasing the prospect of condensation in the roof. Lessening the flow of air through the ceiling as far as practical will both save energy and reduce the risk of condensation. Even in the warm climates, various sources in the house can add to the overall water vapour content in the internal air: bathing, cooking, washing machine, clothes drying, and non-flued gas heaters all produce water vapour.

About 20 percent of the air entering the roof space comes through the ceiling from below. Water flows from the space occupied from the house to the roof space through a variety of routes.

Some of these can be easily identified and sealed, including:

AC vents;

where pipes or other services pass through the ceiling; and

around downlights

For Downlight Covers to help prevent air escaping or entering, visit a site like

In the UK, air leakage around a number of types of downlight has been measured as a function of the pressure difference. The results showed that there is a very large variation of the rate of air leakage.

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By reducing the percentage of air leaks through the ceiling using downlight covers moisture movement by air flow can be reduced significantly, greatly reducing the risk of condensation in the roof space.

Other routes of airflow are more complicated:

through cracks in the ceiling and behind covings

behind the coating system

through cavity walls and penetrating into the inner leaf

Common problem areas are behind the bath panel through gaps or penetration in the vapour control layer.