This is the second post in a sequence of three where we review key aspects of how our heritage buildings influence our health and wellbeing: this time the focus is on ventilation. If you missed the previous blog on (the related) dampness and mould click here.
Last time we highlighted how heritage buildings need careful treatment and management to minimise the presence of damp to avoid microbial pollution; a ‘friend’ of dampness is insufficient ventilation.
How much ventilation is enough?
Each building is constructed differently, exposed to different amounts of moisture from prevailing weather, building maintenance, and so on. The number of occupants and their use of moisture-emitting sources e.g. showers, kettles, cooking, wet clothing etc. all vary.
‘Enough’ ventilation therefore requires a degree of occupant management and vigilance to the internal conditions to expel humid air. Ventilation can be described as the number of air changes per hour (ach) required to a space. As a rough indicator a rate of 0.4-0.5ach is generally considered appropriate for occupants and activities (Kent, 2015). Kent goes on to highlight CIBSE recommends traditional buildings require twice this level to ‘…remove moisture generated by their breathing fabric’.
How can ventilation be controlled?
Buildings can be naturally or mechanically ventilated to remove moist air.
The appearance of heritage buildings is often heavily controlled by the local authority – for example within a Conservation Area. If the building is also Listed changes to both the exterior and interior require consent. The easiest, quickest, cheapest and most sympathetic means of managing ventilation is to use natural ventilation. This avoids challenges of seeking listed building and conservation area consent for mechanical services.
This immediately removes unwanted air. The easiest way to do this is to open a window!
More effective is to create ‘cross ventilation’: a draught is created between open windows on opposite sides of the building – any intermediate doors should be opened to facilitate (fire doors should not be propped open of course!).
Other non-mechanical means include:
Building fabric – a heritage building whose walls retain its breathable quality will inherently aid the removal of some of the moisture in the air by absorption.
For a solid wall construction to act in this way the walls should have all modern paints and concrete render removed inside and outside, and breathable paints and lime render used instead. For more on the impact of breathable and non-breathable paints click here.
Plants – regulate internal air moisture.
Certain species these can also assist to cleanse the air of toxins. To find out more on which plants can help rather than hinder moisture levels in your building click here.
Trickle ventilation – air enters and leaves the building in an on-going manner.
Modern timber windows can be supplied with trickle vents, if requested.
Location – be mindful about where sources of moisture are placed in a room.
For example, if wet clothes are hanging up – which is sometimes unavoidable – locate these close to source of moving air near an open window etc.
If you find patches of mould in a room the building is sending a message the amount and type of ventilation is insufficient, or there may be a source of excessive moisture occurring from outside the building (see our previous article here).
If you need guidance on how to appropriately ventilate your specific building do seek professional advice from your local conservation architect or building surveyor. If your building is Listed or in a Conservation Area and you are considering the installation of mechanical ventilation review the idea with a conservation architect to ensure works are appropriate or to arrange to gain the necessary consents.
Living with heritage buildings, not despite them, can be a learning curve, but a great place to start is connecting with Heritage Revival via this blog.
During 2019 blog posts are scheduled for release on Fridays every fortnight. Do follow us so you don’t miss an update.
Kent, D.D. (2015). Containing the Questions. In: Prizeman, O. (ed.) (2015). Sustainable Building Conservation: Theory and Practice of Responsive Design in the Heritage Environment. Newcastle upon Tyne: RIBA Publishing.
CIBSE – The Chartered Institution of Building Services Engineers