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Last edited 11 Mar 2020
Draughts in buildings
See also: Draught proofing.
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.
Draughts can be caused by:
- Poorly fitting doors and windows.
- Poor quality or defective windows or doors.
- Open chimneys.
- Defects in dot and dab.
- Ventilated crawl spaces under floors and gaps between floorboards.
- Penetrations through walls such as pipes and wires.
- Letterboxes and key holes.
- Vents in walls.
- Open doors or windows in another part of the building.
- Trickle vents in windows.
- Defective or poorly set up building services.
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.|
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'.
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.
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:
- Refurbishing doors and windows.
- Installing secondary or double glazing.
- Installing or repairing weather seals around windows and doors.
- Filling gaps around penetrations through walls.
- Sealing gaps between floor boards.
- Closing gaps in wall constructions.
- Closing off open chimneys (although it is important in this case that the chimney remains vented, both at the top and the bottom, and is filled for example with vermiculite, to prevent the accumulation of moisture).
- Installing or sealing internal doors or other openings to reduce the movement of air within the building.
- Changing operations so that doors remain closed (such as loading bays or receptions).
- Changing building services installations.
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.
 Related articles on Designing Buildings Wiki
- Accredited construction details ACDs.
- Air change rates.
- Air permeability testing.
- Air tightness in buildings
- Airtightness of energy efficient buildings.
- Cold bridge.
- Computational fluid dynamics.
- Draught proofing.
- Energy audit.
- Floor plenum airtightness.
- Indoor air quality.
- Indoor air velocity.
- Leaks in buildings.
- Primary air barrier.
- Thermographic survey.
- The history of non-domestic air tightness testing.
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