All buildings will require maintenance. Decay is an inevitability. Humidity is the single largest problem and the cause of 99% of all forms of decay has moisture at it’s root. It is therefore imperative to make attempts to reduce the relative humidity and try to maintain low levels within the structure. Management and Maintenance should be regarded in the same light, each has impact on the other.
Traditional buildings are of a different age, that had very different standards, habits and requirements of the inhabitants to that of our 21st century society. Expectations differ now from when the houses we need to retrofit, were built. That retrofit requirement is generally seen as one purely of energy usage and trying to ensure that future energy requirements are reduced. The buildings, in order to work must first be understood and that is where correct management becomes vital, if we are to continue using those buildings in a future sustainable existence, which will require reducing the decay processes.
The first thing to understand is that historic buildings are, in the main, made from natural and sustainable materials with corresponding skills and understanding and it is important on many occasions to maintain and use sympathetic materials and that, to a certain extent, will require a slight change in our expectations. Long term construction - multi- generational use is more sustainable than our modern short-termism. The continued re-use, via ‘retrofit’, requires understanding and a sympathy with the construction and its materials. We cannot seal up walls, for instance, in order to maintain an isolated controlled humidity free and heated interior air quality, without knowing, that this method will guarantee moisture within the structure and will end in decaying timbers and floor structures when, as they are, necessarily in contact with that damp structure.
Houses and all buildings prefer to be used fully. If left for extended periods they will fester and relative humidity will increase. A lack of door opening and heating - therefore minimal air movement and virtually zero air change, in individual rooms, will have a negative impact on decoration and general condition. If a space is not used or warmth is not introduced for long periods, then the air will not be replaced and air-borne humidity will increase, diffusion will decrease. Structures become colder and dew points will rise.
Historically, open fires were the preferred and in 99% of all houses, the only form of heating.
This has many advantages- principally- Dry Heat, Air Movement [drafts…]. Obviously this will result in air changes and some warmth [inefficiently kept in] which will remove air-borne humidity.
The walls of historic houses were also designed to act with diffusion and help reduce humidity levels by absorbing any humidity and through diffusion throughout the structure, remove it to the outside. By living and occupying a space, the relative pressure is increased over the external pressure which becomes negative. Diffusion acts under the influence of pressure.
Historic houses worked because of air movement, dry heat and diffusive walls. They were built to work because we have always needed to be warm and dry .
Due to the manner of construction, the types of materials used and lifestyle, historically houses sat in an equilibrium with the occupation. Equally, society was different and our expectations also differed. Nowadays, we seem to want to wear ’T’ shirts all year round. We no longer seem able to withstand a few degrees colder in our houses and solve the problem by putting on more clothes.
This comfort requirement now requires efficiency from our buildings that without significant intervention, they cannot provide. If however we simply ignore the requirements of the building and concentrate on human comfort, then we will cause very significant problems with the historic structures being used, shortening their ‘in-service’ life, rendering the whole process less sustainable.
In the meantime, the initial decay of those structures also promotes pathogen attack and human health issues as a direct consequence. Asthma and other respiratory diseases are a commonly known effect of ‘black-mould’. An un-healthy house does create unhealthy people.
It is therefore extremely important to maintain air movement. Simply keeping some circulation within the building will regulate humidity levels throughout the building. Do not allow doors and rooms to be closed for months on end and very especially without any form of heat to those rooms. Equally, heat alone will not necessarily maintain a humidity free environment.
Allow some warmth to circulate throughout the building along with the air. The two obviously go together.
Treat the building as one whole and not a series of rooms, used in isolation with permanently closed doors. Use the whole building. There will always be a low down cold corner somewhere, that will reveal itself eventually and air movement or circulated heat in that area will resolve that localised issue.
As with all things - A stitch in time, saves nine!
Externally - Gutters and downpipes are the simplest things that keep water out of a building. These need to be checked and cleared annually. The best time for this is just at the end of Autumn and before the winter rain really sets in. A leaking gutter or downpipe can cause extreme damp issues which, if left unchecked can take years to remove the consequential issues. often these issues are not felt internally but humidity within the structure can cause rot in associated localised timbers such as lintels over windows below the leak or floor joists bedded into the structure.
Holes in roofs should be mended, the moment they are seen. Cracks in window cills can let in very significant levels of water. Large windows with inadequate drip details below can lead to significant levels of water ingress from the simple run off from the glass. Bad lead details to roof/ wall abutments and around chimneys can cause longterm unseen issues. Cementitious or hydraulic materials and other impervious or capillary materials added to the external faces, whether pointing or renders always lead to increased humidity levels.
Always use the best possible ‘air lime’ and suitable aggregate to ensure the material allows any ingressed moisture to escape. Do not simply chose or allow a ‘sand’ that visually and superficially matches an earlier used mix. Choose an aggregate not only for it’s visual match but also for it’s porosity. Porous aggregates work better with lime to ensure humidity is removed to the outside.
If possible use lime wash to coat the exterior. This material is very traditional, has been used for many thousands of years because it not only allows a wall to evaporate it’s humidity but also closes and fills water traps in the surface. The modern term for this process is ‘breathability’ although this term is too simplistic for the process that is actually happening in a traditionally built structure.
Do not ever use modern plastic or other proprietary paint products to coat the external face of walls. These materials are catastrophic for the structure and retain any moisture that may find it’s way into that structure including any attempts the walls may be making to remove internal humidity.
Internally - Walls that have either fully traditional coatings or that have been ‘retrofitted’ with air-lime as traditionally specified must always be maintained in a like-for-like manner.
This is not difficult or expensive. It just requires some understanding and a willingness to not simply go to ‘B&Q et al’ to buy proprietary plaster repair mixes and paint [at least until those outlets stock suitable enlightened materials].
For plaster repairs, Vivus Solutions has a range of plaster skim and skim repair materials specifically designed to match not only the visible material but the nature and type of material and it’s performance characteristics in relation to humidity control.
For repainting lime walls, limewash, distempers, and modern breathable paints of good reputable quality can be used.
If walls have been papered, the same surface paints [if painted] as above should be employed. Everything is about allowing the walls to work at removing internal air-borne humidity.
If paper is pealing it says that the humidity levels have reached a ‘tipping point’ and that the management/occupation regimes need to be altered as described previously.
To re-adhere the paper simply use paper glue and re-paste back onto the wall.
Never use heavy paper, especially ‘shiny’ printed or strong glues as these will remove any ability the wall has to act as a humidity buffer. This will then negate the use of the lime materials and render the wall impervious.
Make sure any air vents are clear as these have often been installed to cure a localised humidity issue as previously described. Trickle vents in windows are important and need to be opened frequently. The issue with these is that generally they let in cold air and are difficult to reach and fiddly and so never get re-opened once closed.