The Problem with old buildings…
Many who live in Bisley, or one of the surrounding villages or hamlets, may or may not consider themselves fortunate to live in a property built before 1919, particularly when you consider the maintenance burden attached to such buildings. Indeed, several of the buildings in the vicinity pre-date this by as many as 600 or 700 years. There are around 153 listed structures within a 2-mile radius of Bisley, including all manner of houses, barns, churches, monuments, tombs, steps, bridges and even a telephone box! Listing is split into three designations: Grade I, Grade II* and Grade II in ascending order of significance. Contrary to popular belief, the inside and outside of any listed building is protected, along with anything within its curtilage and requires Listed Building Consent to demolish, alter or extend. In addition, there are also hundreds of ‘non-listed’ stone houses, cottages and barns in the area.
The significance of 1919 is that it is generally promulgated as the very tail end of ‘traditional’ construction. The common feature of ‘traditionally’ constructed buildings is that the walls are solid and built with porous materials (e.g. stone built with lime or earth mortar, solid brick walls built with lime mortar, traditional timber frame with infill panels etc.), which both absorb moisture and readily allow evaporation of moisture. For the purpose of this article a ‘traditional’ building is a ‘breathing’ building; this can be a house, a church, a pub, even the Bisley lock-up. In contrast, most modern buildings (i.e. post 1919) are constructed using impervious materials which are designed to exclude moisture and rely on physical barriers such as cavities, damp-proof courses and membranes. It was the late Victorian and subsequent Edwardian architects and builders that instigated the evolution of early brick cavity walls; these soon proved very popular (and continue to do so). This form of construction does not rely on being ‘breathable’.
There is nothing mysterious or complex about the way solid walls are constructed, allowing a building to breathe. Our particular vernacular style comprises locally quarried Cotswold limestone (calcium carbonate), bonded together with permeable lime mortar (calcium hydroxide – which carbonates over time back to calcium carbonate); internally the walls will have been lime-plastered (calcium hydroxide, which again carbonates over time back to calcium carbonate). Externally, most humble cottages will have been lime-washed or rendered (or both), and again this is calcium hydroxide which carbonates over time to calcium carbonate. Effectively, the whole wall becomes chemically one of the same and since calcium carbonate (limestone) is a very ‘vapour open’ (or ‘breathable’) material, it should, in theory, be the perfect building material. In practice this may not be the case: However, in reality most people living in an old house will experience some sort of ‘damp problem’, varying from something simple that is easily remedied to a longstanding issue that is impossible to resolve and may have to be ‘managed’ and accepted. The most important rule is to diagnose the true cause and, if possible, tackle the problem at source, rather than simply treating the symptoms. (Hunt and Suhr, 2008, p. 37).
There are two materials that (from a conservation point of view) have probably done more damage to old buildings than any other.
First cement. The type we use today was invented in 1824 and was seen as a quick and strong binding material, easy to use in all weathers and relatively cheap. However, hindsight has shown us that it is quite inappropriate to use on old buildings, not least because it is impervious and does not allow free evaporation of moisture (resulting in moisture retention/trapping behind the cement). Its plasticity is far less than that of a lime mortar or render – essentially it is too strong, often resulting in cracking, which in itself allows water ingress and subsequent deterioration. Even aesthetically it is inferior to lime, which reflects light beautifully and has a warm, soft, mellow appearance.
Secondly, reinforced bituminous roofing felt. This material was commonly used from the 1950s up to the mid-1990s and is laid as an impervious sheet material under the roof tile battens and over the rafters. Unfortunately, it has been shown that unless ventilation levels within the roof void/attic space are exceptionally high, the potential for condensation is also great. Subsequently, this has resulted in a large number of properties experiencing un-sustainably high moisture contents in their roof timbers. Problems can also be exacerbated by the addition of modern non-vapour open insulation materials, such as fibreglass, within the roof space in the quest for thermally upgrading the building. However, careful consideration needs to be given not only to the insulation material selected but also the necessity (where physically possible or where historic significance is not adversely affected) of vapour barriers and/or additional roof-space ventilation.
The recent development of breathable roofing membranes has now addressed the situation on new-build and re-roofing works but the offending felt is still in place in many buildings. Added to the plethora of problems caused by damp there is the ever present threat of wood-boring insect infestation (including death watch beetle, woodworm and weevil), and also of timber fungal attack (white/wet rot and dry rot). It has been shown that both of these are totally dependent on moisture, not only to initiate but also to survive and thrive (Ridout, 2000), and that any amount of chemical treatment will not necessarily lead to eradication (in fact pumping gallons of liquid into a building will probably do more harm than good). Removing the source of dampness is by far the most successful way towards making any outbreak unsustainable.
Damp can be classified in five basic categories: condensation, penetrating/lateral damp, rising damp, hygroscopic salts and plumbing leaks. It can often be tricky to differentiate between which of these is causing a particular problem.
There is much debate as to whether ‘rising damp’ even actually exists. Some academics claim the process of capillary attraction or osmosis cannot be replicated in the laboratory let alone occur through the pore structure of either brick or stone in-situ. Others, often it has to be said with vested interest (e.g. those selling injected damp-proof courses), offer guarantees to back up their claims. In reality, the symptoms associated with so-called ‘rising damp’ are more often than not being mis-diagnosed. Causation of damp is far more likely to be due to high outside ground levels or defective rainwater goods (penetrating damp), migration of hygroscopic salts, or perhaps condensation (attributed to high relative humidity levels, high moisture contents and inappropriate temperature levels). By tackling the problem at source, the defect can usually always be remedied without the need for modern chemical intervention.
Since damp is the single biggest threat to old buildings, the importance of obtaining appropriate and informed advice cannot be overstated. Whether it be from a conservation accredited architect or surveyor, a well-informed contractor with conservation credentials or indeed a conservator, it is imperative that a holistic approach is adopted which takes into account the buildings requirement to remain ‘breathable’. This will always entail thorough investigation, possibly environmental monitoring, laboratory testing if necessary, accurate diagnosis and finally the selection of appropriate advice and recommendations, including the specification of appropriate and sympathetic materials.
So, in summary, damp is often a major problem in old buildings. However, with expert and informed advice, the correct diagnosis and appropriate specification, including avoiding the use of cement, there is every chance that buildings can be ‘dried out’ to a level that is sustainable and also go on to give many years of comfort and enjoyment, without the need to pump them full of nasty chemicals.
Further excellent advice is available on line from the following:
Society for the Protection of Ancient Buildings (SPAB) at: http://www.spab.org.uk
English Heritage HELM Service at: http://www.helm.org.uk
buildingconservation.com at: http://www.buildingconservation.com/articles.htm
Burkinshaw, R. and Parrett, M. (2004). Diagnosing Damp. Coventry: RICS Business Services Ltd.
Hunt, R., Suhr, M. (2008). Old House Handbook – A Practical Guide to Care and Repair. London: Frances Lincoln Limited.
Oxley, R. (2003). Survey and Repair of Traditional Buildings – A Sustainable Approach. Shaftesbury: Donhead Publishing.
Ridout, B. (2000). Timber Decay in Buildings – The Conservation Approach to Treatment. London: Spon Press.
Young, R. (2008). Lime-based plasters, renders and washes. In Materials & Skills for Historic Building Conservation, Edited by Forsyth, M. Oxford: Blackwell Publishing Ltd.