Our Systems
and Products:
Building Durability
Buildings need to last. They need to last both because people have a lot of their capital tied up in them, and also because we cannot as a country afford to replace our building stock more than once every hundred years. In addition the kind of materials we use now in many types of building come from finite resources which are in short supply , so it will soon not be possible to continue to build short term buildings from non-renewable materials. We need to use materials carefully and to build buildings that will last.
For a building to last it has to be
- Physically robust
- Useful/Adaptable
- Hackable
- Desirable
Unfortunately most buildings do not have these qualities. On the whole we are constructing buildings and undertaking renovation in a way that is going to cause huge problems to future generations. This is not only a huge waste of resources and money, but it may lead to vast knock on economic and social effects.
Physical Robustness
Building physical durability is mainly about water. It is estimated that about 75% of building decay is due to water. Water occurs in 4 situations in building fabric:
Rain penetration/ flooding/ liquid water leaks
Interstitial moisture (including low level damp)
Internal condensation
Indoor atmosphere
By far the most significant of these as a cause of decay is rain penetration. Internal condensation and indoor atmosphere are mainly a risk to human health. However interstitial moisture, particularly in the form of condensation, will be an increasing cause of concern as we attempt to increase the thermal performance of buildings by increasing insulation levels and airtightness, if this is not done correctly. Indeed these can also affect the drying of building fabric where there is actual rain or other liquid water penetration (for example from leaking pipes). The reasons for concern have already been explained in the section on Health as regards humidity and microbiological pollutants. Basically the decay mechanisms are mainly biological and these mechanisms can only operate where there are high levels of relative humidity or actual free liquid water. These mechanisms have a much more immediate and serious effect on organic materials than on inorganic materials – ie timber is much more at risk than stone, brick or concrete. For this reason timber frame buildings and the renovation of older buildings where timbers are built into walls become the situations where there is greatest risk, unless there is a coherent and robust strategy for dealing with moisture of all sorts. This moisture control needs to be dealt with both by proper ventilation strategies and by control of moisture in the shell.
Unfortunately most common building systems and renovation processes do not deal with moisture in a way which is robust. Relying on ventilation systems and membranes is not sufficient in itself for buildings which have to last up to 100 years, with all the changes and vicissitudes that will inevitably affect the building. This is what hackability is all about (see below). However even in the process of construction some systems are better than others. As I show in my article on breathability , the common ways of renovating buildings and of building new timber frame structures today are inherently faulty and are not robust, because the vapour resistances are all in the wrong places and the systems rely on delicate vapour barriers for success. As a result of this inherent weakness we therefore have to treat all timber in timber frame constructions and in most renovation projects. This delays the problem for maybe 30 years only, while turning an ecological material (timber) into a toxic problem both for occupants and for disposal. The UK uses a huge proportion of all the timber treatment chemicals in Europe not because we are a wetter climate, but because we have buildings systems which have not integrated a biological understanding of building performance and which are therefore not robust.
Furthermore we continue to design buildings without proper orientation to and protection from the prevailing wind and rain. Building form must follow function in the case of rain penetration because it is such a major cause of building decay. This means pitched roofs with good overhangs, proper falls on flat roofs, protection of exposed gables, avoidance of building penetrations such as balconies in exposed situations etc - the simpler and more robust the design, the better.
Furthermore it is essential to have durable materials in places of vulnerability. For example using cheap concrete tiles which last only 30 years on a roof rather than decent clay tiles, which will last over 100 years, is asking for trouble.
Other issues of durability obviously include structural stability and durability of structural materials. On the whole these are better understood, although the long term structural durability of many modern and particularly composite materials which are reliant on glues is still untested.
Usefulness/Adaptability
To survive, a building either has to be useful or it has to be adaptable for use. It is actually unusual for building forms to maintain its original purpose in an un-adapted form for more than a couple of generations, as even aspects like housing continually require changing as expectations and social structures change. At present there are a great number of people living singly, and consequently many 3 bed houses have been converted into one bed flats, and many new developments have large numbers of one bed flats also. But will there be such a demand in 30 years time, and will the new flats be adaptable for other uses?
On the other hand it is often remarked how the Georgian houses of London have retained their use and value in remarkably diverse uses, from accommodation, to shops, restaurants and offices of all kinds.
Whether a building can be adapted or not is largely a consequence of the basic shell form of the building. Structures and services need to be built with adaptability in mind. Once again the message is: get the shell right now, do as much of the function in the element that is going to always provide the shell, and future proof it as far as possible. Buildings which cannot adapt become extinct.
Hackability
Hackability is related to the two concepts above. It means that a building can be adapted and knocked around, even abused in a minor way, without the performance and the health of the building fabric and occupants being threatened. Fundamentally many building forms today are not hackable, either because of the fragile and illogical nature of moisture control or because of the inflexibility of the basic form. In structures which rely on membranes directly behind plasterboards, this layer can be breached often within days of occupation, as new occupants fit new technologies and services. Eventually this will lead to decay and building failure. Another example is of ventilation systems which rely on particular room layouts. If someone puts a partition up in the middle of a room, or fits a cupboard where there was formerly a vent, can the ventilation system be easily adapted? Or in some more extreme cases, what happens when the occupant sticks a plastic tape over the vent, or pulls the fuse out of the fan?
These issues are all surmountable with good planning and careful hacking. However the more complex the building services or the more fragile the critical elements of moisture control or airtightness the less easy this process is, and the more prone to failure.. On the whole the simpler, the more homogenous and the more self-sufficient (as regards moisture, and thermal performance) is the shell of the building, the more hackable the building will be.
Desirability
A thing that is desired for its performance or its beauty will be treasured and cared for. This applies to buildings on their own and to buildings as part of a community. We are only dealing with building performance in this paper, but it is as well to remember that building better is not only about energy or health or durability. It has to be about social and aesthetic values as well.
