Paul Farren is an architect at ASSIST Design. He completed a three-year 'Healthy Housing' study in partnership with Irvine Housing Association and the University of Strathclyde, and his Doctorate research includes the design and construction of two low-energy dwellings. Farren's collaborative research paper, 'Build Tight, Ventilating right?', was awarded the Chartered Institute of Building Services Engineers' Napier Shaw Bronze Medal.

Julian Turner: Please talk about the impetus behind the 'Build Tight, Ventilating Right' project?

Paul Farren: ASSIST Design worked with a client to develop a low-energy house, and a key focus of that project was finding a solution to the problem of poor air quality and high carbon dioxide (CO2) levels in modern homes. CO2 is now regarded as a pollutant and is likely to keep bad company in the form of volatile organic compounds (VOCs) such as formaldehydes, which can be very harmful.

In partnership with Strathclyde University, we started looking at how to successfully balance energy efficiency and indoor air quality. The 'Build Tight, Ventilating Right?' research paper came about in direct response to a Scottish Government-sponsored report published by the Building Research Establishment (BRE), which suggested ventilation rates and air tightness levels were satisfactory.

ASSIST disagreed with the findings of the BRE report because it only measured whole house volumes and largely ignored the small, sub-divided spaces that we were used to working with as architects.

Increasingly, people are living in smaller spaces and rely on trickle vents to provide ventilation, so we focused on living rooms and bedrooms, where the effects of poor air quality are more drastic.

Project partner MEARU at Mackintosh School of Architecture were able to provide data on further houses they were monitoring which confirmed the problem was occurring regularly in new builds.

JT: What is air tightness and why does it result in poor indoor air quality in modern UK homes?

PF: Air tightness refers to air permeability or, more simply, how air is prevented from flowing in and out of a property through the building fabric. Modern energy-saving policy dictates that these drafts be reduced as much as possible so as not to lose heat. However, air flow also provided valuable ventilation, which has not been replaced. As a result, you end up with stuffy buildings full of stale air.

JT: What methods did you use in order to measure levels of air tightness and CO2?

PF: For our experiment we took a passive house, a very low energy property, and reverse engineered it by installing an air blower door fan in the bedroom. We also placed a tarpaulin with holes in it across the open windows to let a draft in until the air tightness levels met 2010 building standards, which stipulated that homes without a planned ventilation strategy - in other words, trickle vents in the windows and natural ventilation - must have an air tightness value of between five and ten.

"CO2 is a good measure because humans produce it, therefore we know when the room is occupied."

We then had the family live there for a couple of days, and measured the subsequent changes in temperature, humidity and CO2 levels in living rooms and bedrooms - and discovered it was high. CO2 is a good measure because humans produce it, therefore we know when the room is occupied.

JT: How is CO2 generated and why are excessive amounts of it harmful in a small space?

PF: Outside, CO2 is present at roughly 400 parts per million (PPM) and environmentalists are worried that that backdrop level is rising, one of the key issues that is being discussed in Paris [at the 2015 Climate Change Confernece].

Internally, as soon as a person enters a room, the level of CO2 increases sharply and until recently it was considered that 1,000 PPM was a decent safety level. The UK Health and Safety Executive (HSE) states that safe levels of CO2 in the workplace should be around 5,000 PPM for an average of eight hours a day, while in a school, that figure currently stands at roughly 1,500 PPM.

However, in October a study at Harvard University exposed 22 people in an office to CO2 and the results suggest that cognitive ability was drastically reduced. At 550 PPM, similar to outside, people performed extremely well, but at around 945 PPM, cognitive ability dropped by around 15%.

If the CO2 is increased to 1,400 PPM, that figure drops to 50%, which in a workplace has a profoundimpact. If your staff are only working at 50% capacity - or much less at 5,000, since the figure goes up around 21% for every 400 PPM - are you really getting the best results out of your staff?

As an architect, I'm interested in whether or not these large variances occur at home. People spend two thirds of their lives in their houses - a third of that in the living room and a third in the bedroom - and prolonged exposure throughout a lifetime may potentially have serious health repercussions.

JT: What specific symptoms can result from prolonged exposure to poor indoor air quality?

PF: A Norwegian study in 1996 measured the impacts of exposure to CO2 in schools. Up to 1,500 PPM, there were reports of headaches, dizziness, fatigue and difficulty concentrating. From 1,500 to 4,000, you are starting to look at nose and throat irritations, coughing and respiratory problems.

If you are an asthmatic, then the air quality in your house will impact your breathing, predominantly because of house dust mites. Modern houses are warm and damp, and when the relative humidity is above 60%, house dust mites become active and feed on human skin, reproducing exponentially. An asthmatic breathing in dust mite faeces is more likely to eventually suffer a related asthma attack.

Excessive moisture is another symptom of poor ventilation. People produce moisture as do showers, baths, kettles and stoves. Modern dwellings don't tend to let moisture pass through them; in short, we are building warm, damp houses, and risk exposure to health problems from moulds and fungi.

JT: How did your research for the Scottish Government lead to a change in the building standards?

PF: ASSIST and its partners began a second study in collaboration with the Scottish Government's building directorate in which it placed CO2 monitors in over 70 new-build houses constructed after 2010. The usable data from 40 or more homes confirmed our initial findings but on a larger scale.

"We would have liked to see the Scottish Government do more than simply fitting alarms."

As a result, the Building Directorate, which is responsible for setting the formal building standards in Scotland, decided to change the regulations to incorporate CO2 alarms in the bedrooms of new homes from October 2015. We are still waiting for feedback to see how this impacts the behaviour of residents.

We would have liked to see the Scottish Government do more than simply fitting alarms, because as architects it's difficult to convince residents that they should spend more on better ventilation when they are not forced to. The government hopes the monitors will act as a deterrent and that builders will be motivated to construct properties that have better air quality in order to remain competitive.

JT: What is your healthy house methodology and how has it informed the design of two 'healthy sustainable homes' that demonstrate natural and mechanical methods of improving air quality?

PF: ASSIST hopes to build two prototype houses in 2016 that demonstrate how we can balance energy efficiency with adequate ventilation.

One will incorporate natural ventilation and the other mechanical, and we plan to monitor their energy and air quality performance for at least a year as a demonstration for industry.

The ultimate aim is to highlight how ventilation technology can be made affordable through supply chain solutions or government subsidies. Housing Associations have limited budgets for affordable housing and in theory they would have to build low-energy, healthy homes for less than £100K.

Unless efficient and affordable ventilation strategies can be found, striking a balance between energy efficiency and indoor air quality may potentially mean giving up the idea that every building can be zero carbon in order to deliver healthy homes for everybody.