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The simple answer should be ‘No’. Improvements in the airtightness of a building are designed to prevent uncontrolled ventilation, accounting for as much as 15-20% of the total heat loss in some buildings. However, the strategy of sealing around windows, doors, floors and roofs has to be combined with a strategy to ensure the supply of adequate levels of ventilation and checks that ensure that condensation will not accumulate within the fabric of the building. Without these considerations the answer will inevitably be ‘Yes’.
However, there is a perception amongst some people that, irrespective of ventilation levels, making a building airtight makes it stuffy and that old houses should be left draughty to ‘breathe’. This idea may come from the rush to install double glazing in the 80’s and 90′ along with the use of open gas fires without any consideration for how to ventilate a building, with the subsequent mould and health problems that arose. It may also come from some of the well meaning but disastrous renovation projects that have been carried out recently, using the minimum ventilation requirements as set out by Building Control which are rarely enough and have created stuffy environments. Wherever it has come from it is something that needs to be addressed if we are ever going to seriously improve the thermal efficiency of our housing stock.
Poor ventilation whether with or without good levels of insulation can cause high levels of humidity, allow the growth of certain mould species and even damage the fabric of the building through condensation. Off-gassing from synthetic insulation materials, carpets, furniture and paints can create high levels of VOC’s (volatile Organic Compounds) in the air and these can combine with mould spores to seriously damage the health of those living in the building. Having breathable walls/roof (vapour permeable) goes a very very small way to helping but can only deal with 1-2% of the moisture we typically produce in a day.
Newly built buildings are beginning to incorporate mechanical ventilation heat recovery (MVHR) systems which provide a continuous flow of warm, fresh air to all parts of a house via ducts built into the building. To anyone that has one of these they can be revolutionary as there is no longer the necessity to open the windows to ventilate properly (great for city locations or those with security issues). All areas of the house receive adequate ventilation preventing mould growth, condensation and the associated health issues that go with them. They can even help dry clothes when its cold and damp outside. They are also very much more efficient than heat pumps at recovering heat with some units recovering 10 watts of heat for every watt of electricity used. I personally love mine and would never want to live in a house without one!!
However we ventilate our houses we should be working towards the minimum requirement of 0.3 air changes per hour, something that is impossible with trickle vents in windows unless it is windy. Our last house had no specific ventilation (other than leaving the windows open) and the difference in the health of my children since being in a well ventilated house is enormous. Unsurprisingly my daughter’s asthma has barely troubled her and the usual barrage of colds has been massively reduced.
So, when building or refurbishing the phrase ‘build [air] tight, ventilate right’ is absolutely essential to ensure we move away from fuel poverty towards better health, not worse.