Wednesday, 18 August 2010

Airtight Homes -Good or Bad

Airtight dwellings good or bad for health

It is clear that to deliver on our UK objectives we must look at the building fabric to ensure it is more airtight so then we must also adopt mechanical ventilation technology.

It is now part of our future that we must embrace mechanical ventilation with heat recovery (MVHR) in order to meet Code for Sustainable Homes (CSH) energy requirements at code levels 5 and 6.

It is generally considered that ventilation levels for a UK dwelling is generally 0.5 to 1 air changes per hour. This is level is adequate to maintain humidity levels below 70 per cent and keep the condensation and mould growth at bay.

While our standards and regulations look after the building of new dwellings, Conversion & refurbishment of existing properties may not be covered by these same standards are therefore carried out without the same inspection process.

It is a well documented fact that ventilation up to now is a low priority in design and that existing housing stock occupants paying little attention to the use of ventilation systems provided.

Some of the health problems caused by poor measures and lack of best practices are documented below.

Internal air Quality

The air inside our homes can have a varying range of pollutants. The most common being chemicals used in the makeup of household items ie paints. furnishings, insulants, carbon monoxide and nitrogen dioxide from gas appliances and smoking.

The kind of health problems associated with these pollutants in the home are respiratory complaints ,dry coughs and dryness of the skin.

A well maintained mechanical ventilation system through filtration of the incoming air can have a significant reduction in the harmful particles.

Research by other goverments has shown that occupants notice an improvement in health after relocating to new airtight dwellings with MVHR systems installed. The research also demonstrated however that occupants may not be using the MVHR systems correctly.

Infestation and Mould Growth

If a dwelling has high levels of humidity within this will encourage condensation and mould growth this in turns leads to the collection of dust mites with has an effect on our health.Moulds and dust mites are linked with chest respiratory problems also asthma

A general indication to a well ventilated dwelling is the absence of condensation and mould. It is considered that the use of MVHR as with indoor air pollutants can help.

Dwelling Overheating

There are no standards in the UK for levels of internal temperature in within our buildings

A report published on design for the future has definitions for warm and hot temperatures with 25oC as warm and 28oC as hot with 35oC being the temperature at which heat stress has an affect upon our health. In 2003 the Uk experienced a heatwave that resulted in over 2000 more deaths and with increase in temperatures the levels of ozone gas are higher which can be irritant.

As Insulation in our dwellings increases so then will the internal temperature and a greater need then for evening ventilation and there is some concern that the MVHR systems will not be able to deliver the 8 air changes per hour required for recommended cooling. This is where shading plays a major part in the design of new houses and refurbs to reduce the requirement for air conditioning systems.


Radon gas found is found in ground with limestone and granite mainly but can still be found in other types of soil and rock. The gas which is radioactive is a produced through the decay of radium and is drawn through the ground from the different atmospheric pressure levels that exist in a dwelling.

By fitting an gas membrane to the solumn / ground we prevent gas coming thro into the dwelling

In the UK today radon gas accounts for an estimated 1000 – 1100 cases of lung disease and cancers each year

Some would say that window double glazing increases radon levels by over 50% and decreasing the levels in turn would be the blocking up of chimneys and the installation of insulation to floors.

In Summary

Evidence would suggest that an energy efficient dwelling has a huge effect on the health of its occupants both mentally and physically.

Even with basic upgrading and improving internal temperature within dwellings reduces the risk factors to the occupants although we still need guidance on the safe minimum level of ventilation as the standard at present is 0.5 air changes per hour.

In the UK there no case studies that are conclusive on ventilation playing part in ensuring good health or the actual ventilation rates that are being achieved.

Several European countries can show us the way with air quality standards and can have the technology that could be adopted in the UK.

To Close

As Sap Service UK have close ties with Passivehaus and Passive House Design there are definate and clear case studies over a twenty year period that sets out a different way of living for occupants and we look forward to sharing some of this information in our airtight chronicles.

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