Last edited 05 Oct 2020

Draughts in buildings


See also: Draught proofing and air draught.


[edit] Introduction

A draught is a noticeable current of air inside a building and can make its occupants uncomfortable. Draught is the UK English spelling, the US English spelling, is ‘draft’, although in the UK this means to prepare text or drawings. The word ‘draught’ is thought to derive from the Old Norse ‘dráttr’ meaning to draw or pull.

Whilst all buildings require ventilation, that is, the replacement of ‘stale’ internal air with ‘fresh’ external air to dilute contaminants, remove moisture and so on, draughts are the uncontrolled supply of air that can be both uncomfortable and costly.

[edit] Causes of draughts

Draughts can be caused by:

Draughts can also be experienced where there is a significant change of surface temperature within a building, such as a downdraught felt next to a cold, single-glazed or poor-quality window.

[edit] Indoor air velocities

Generally air velocities inside buildings are relatively low compared to the outside, however it is possible for the range of air velocities to be quite large. There may be entirely stagnant areas where air velocities are close to 0 m/s, whilst in tall spaces or in large mechanically ventilated spaces, internal air velocities can reach several m/s in some places.

Some more typical ranges are set out below:

0 m/s Stationary air.
0.1 m/s The assumed internal air velocity in some simple heat transfer calculations.
0.1 to 0.15 m/s and above May be felt as a draught in a cold climate in the winter.
0.3 m/s and above May be felt as a draught in a cold climate in the summer.
0.8 to 1 m/s and above May be felt as a draught in a hot climate.

For more information see: Indoor air velocity.

[edit] Air tightness testing

The Air Tightness Testing and Measurement Association (ATTMA) defines ‘air leakage’ as the '...uncontrolled flow of air through gaps and cracks in the fabric of a building. It is sometimes known as infiltration or draughts. Air leakage is not to be confused with ventilation, which is controlled airflow in and out of a building'.

An article on YouGen, suggests that In the typical UK house draughts will account for at least 10% of the total heat loss. If there is an unused open fireplace that figure can rise to more than 50%.

According to the Building Services Research and Information Association (BSRIA), 'Project teams should design and construct the building fabric to be reasonably airtight, and also provide natural or mechanical ventilation systems that maintain good indoor air quality while minimising energy use. In other words: Build tight, ventilate right.' Ref BSRIA Topic Guide - Airtightness.

In England and Wales, airtightness testing has been mandatory for virtually all new buildings since 2006.

See Airtightness testing for more information.

[edit] Remedies

Generally it is possible to feel draughts, however, they can also be detected with thermal detectors or located with candles.

Once located, remedies might include:

However, it is important that intended ventilation paths are not blocked. Air bricks, trickle vents, ventilation to under floor cavities and roof spaces, are provided for a reason, removing or blocking them can cause damp, mould and rot, as well as allowing the build-up of contaminants. Some appliances, such as wood-brining stoves must have ventilation provided if they have an output of more than 4.5kw.

During construction, the overall aim is to ensure the highest quality of workmanship on site. Materials and products in isolation very rarely fail; similarly drawings and specifications rarely fail. Generally, problems arise due to poor workmanship.

See Management and quality control measures for more information.

[edit] Related articles on Designing Buildings Wiki

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