Articles published in 2012
The Cost of Fresh Air
The Design Air Permeability
With respect to air, the traditional British house has been too leaky. So there has been much emphasis over the last decade on improving airtightness. From this hectoring, it has been easy to get the impression that the more airtightness the better. This is not necessarily the case. (See Footnote 1: Too much airtightness?)
The theory of ventilation shows how much ventilation is required for the health of the occupants and the health of the building, and it shows the size of the heat/energy losses that result. But the theory is both difficult and fuzzy. What the house designer/builder needs is some guidance about optimal airtightness in order to set a figure for the design air permeability. Unfortunately, such guidance is hard to find, especially for the less common ventilation systems.
Testing airtightness: The Blower Door Test
Apart from the formality of getting a better SAP rating, you may wish to obtain the right degree of airtightness in order to minimise your future heating bills and carbon emissions – without compromising on ventilation. For example, if you intend to install Mechanical Ventilation with Heat Recovery (MVHR, System 4), you need to obtain a high degree of airtightness (eg, q50 <1 m3 / m2.h). For natural ventilation with extract fans (System 1), q50 should not be greater than 6, say.
And, of course, the only way to know the airtightness of your future home is to have the air permeability, q50, measured – by means of a blower-door test.
Ventilation: Wrapping it up
Last month I interrupted my mini series about Ventilation and Airtightness to give a report on the recent Homebuilding Show at the NEC. Anyway, we have now reached the last article in the mini-series, and I’m wrapping it up with a last look at ventilation systems and how ventilation (or the lack of it) affects our health.
‘Wrapping it up’ is also a reminder that, whatever the ventilation system you intend to install, for good energy efficiency you need to wrap up your home with an air barrier of appropriate airtightness.
The NHBC Foundation: Reporting on new technologies for house building
Last month we had a look at the National House-Building Council, which offers selfbuilders the Solo structural warranty and approved inspections (for building regulations). In 2006 the Council expanded its remit, and, in partnership with the BRE Trust, set up the NHBC Foundation. The NHBC supplies most of the money, and BRE most of the expertise.
The purpose of the Foundation is to deliver ‘high-quality research and practical guidance to help the industry meet its considerable challenges’. In my view, the word ‘research’ is becoming devalued. Nowadays, simply making enquiries on Wikipedia is said by some to be doing ‘research’. I prefer a definition in my 1934 Oxford Dictionary, ‘to discover facts by scientific study’.
The Innovation Park at BRE: A collection of housing exemplars
Last month we had a look at BRE, where the letters originally stood for the Building Research Establishment. On their site in Watford they have an Innovation Park, where there are examples of innovative design and technology applied to housing. Members of the public are invited to visit, either for an Open Day (£12), or for a Guided Tour (£30) – booking in advance is necessary.
On the Park at present are seven buildings (detached houses or pairs of semis) plus a healthcare centre which serves as an exemplar of a non-domestic building. Two more houses are to be built shortly.
Quantifying Airtightness
The ventilation of most houses, both old and new, is achieved by natural ventilation, which is powered by the wind and by the stack effect. (The stack effect? – Warm air rises.) Infiltration and matching exfiltration occur through cracks and gaps in the fabric of the house. In addition, controllable ventilation occurs through trickle vents. (Extract fans in wet rooms supplement the natural ventilation.)
In contrast, when a Heat Recovery Ventilation system is to be installed, natural ventilation is unwanted. To maximize efficiency, the house should be as airtight as possible.
Achieving Airtightness
We saw last month that if you set a value for the design air permeability of your new home, the figure usually depends on the ventilation system you intend to install. It might vary from, say, q50 = 5 m3 / h.m2, for natural ventilation (System 1), to q50 = 1 or less, for Heat Recovery Ventilation (System 4).
A typical, modern house built without any attention to airtightness might have q50 = 10, and this is the maximum allowed by Approved Document L1A if you choose to have the air permeability measured. Achieving q50 = 5 is fairly easy, and requires little more than taking common-sense measures during and at the end of the build.
Achieving q50 = 1, or less, is much more difficult, and requires consideration at the design stage and throughout the build.
The National Homebuilding Show
The big show of the year for selfbuilders is the National Homebuilding Show, held during the spring at the National Exhibition Centre near Birmingham. Last year I missed the show so thought I should go along this year to keep in touch with the latest developments. The show was held over four days, March 27-30, in Hall 5, the largest hall at the NEC. Tickets cost £10 per day purchased online, or £15 at the door. Subscribers to Homebuilding and Renovation, the magazine which promotes the show, were amongst the people who received offers of free tickets.
The National House-Building Council
Many readers will be aware of the NHBC, not least because of its Solo selfbuild warranty and its approved inspections for building regulations. Nowadays the Council is not controlled by builders, although that is how it began its life in 1936 – as the National House-Builders Registration Council. The NHBRC enabled its registered housebuilders to offer insurance against defects in the houses they sold.
BRE: Formerly the Building Research Establishment
Last month, we looked at the NHBC Foundation, for which the NHBC supplies most of the money and BRE most of the expertise. So what is BRE?
BRE is a part of an organisation which has a complex structure. To understand the name and the organisation, we need to go back in history.
BRE began life as the Building Research Station (BRS). This was a government funded laboratory set up in 1921 with a dozen staff – the world’s first building research organisation. Originally based in London, it soon moved to its present site in Watford, Hertfordshire.
The Innovation Park II: Recent housing exemplars at BRE
Last month we had a look at the early exemplary housing on the Innovation Park at BRE’s Watford site. (BRE have another Innovation Park at Ebbw Vale in Wales, and a Scottish one is being developed at Ravenscraig, near Glasgow.) To complete the account, here are details of the more recently built houses on the Park at Watford.
