Damp & Condensation in Historical Buildings
When inspecting a listed or period building, it is not uncommon for professionals to locate damp readings somewhere in the property and the presence of high damp readings in a listed building, or any period property, including buildings of special interest, should not be viewed as unusual. The property will usually require sympathetic consideration and treatment, or perhaps no treatment whatsoever, with a view to long term management of any moisture ingress combined with adequate ventilation and heating.
Addressing damp issues
However as soon as even moderate readings are found a standard recommendation can be for the installation of a remedial chemical damp proof course (DPC) to what may be completely inappropriate masonry, or where the insertion of a chemical damp-proof course will have little or no effect. Often this recommendation is neither the correct diagnosis nor solution, as the very nature of a listed building makes it unique in the way it needs to be treated and certainly blanket treatment using modern waterproof products should not be considered as a standard recommendation.
Chimney breasts, and in particular, inglenook fireplaces and/or sandstone surrounds, will virtually always give high readings to modern sensitive moisture conductivity meters. This is usually due to the presence of naturally occurring hygroscopic salts which may have been deposited within the masonry from the burning of fossil fuels over a long period. Again, the installation of a chemical DPC will have little or no effect, but is commonly recommended.
As with any building, all cases of ‘lateral penetrating dampness’ must be addressed at the source of the moisture in the first instance. Once the moisture source has been eliminated, where possible and practical, the internal wall surface should at least be given the opportunity to dry naturally and sympathetic surface treatment is available without the need for ‘drill and injection’. This will not always be acceptable to the client, or there may be too much damage, therefore alternative replacement surfaces may need to be considered.
Considering the appropriate render
With any damp treatment, the quality of the render has as much bearing on the relief of dampness as the presence and effectiveness of a damp proof course. It is imperative that the render applied to the wall is to the approved waterproof specification for the material it is being applied to. In modern renders this will usually be cement based. Where dampness was the original problem, remedial treatment using modern ‘one coat’ lightweight renders should be avoided.
In a listed building the use of cement based render is frowned upon by local Conservation Officers, who prefer the use of traditional lime based render. This is understandable, but not always practical, as lime provides little in the way of a moisture or vapour barrier. Therefore, where dampness is the issue, the use of cement based render is likely to be a more viable and long term option. English Heritage recommend using a lime based render (also known as heritage render). These allow the wall to breathe and dry naturally as moisture evaporates rather than being absorbing into the underlying stone work. However the presence of lime within the render mix will inevitably reduce the waterproof properties of the mixture. This means it will not form a waterproof or vapour barrier, nor prevent the migration of naturally occurring hydroscopic salts from the masonry to the internal wall surface, which in due course could have a significant detrimental effect on internal decoration.
Looking at alternatives
There are acceptable modern alternatives which do not involve the use of cementitious based products or lime based render. One such alternative is the use of breathable “airgap” membranes, or ‘cavity drain membranes’, which are a particular asset in the armoury against dampness in buildings.
This will not suit all eventualities, and if it is considered that the use of modern cementitious waterproof render is the only sensible alternative, then listed building consent or approval from the local Conservation Office may be sought. Should effervescence persist internally and become unsightly, salt neutralising solutions are available and are easily applied. It is known that modern waterproof cement based render has been used in Grade I Listed Historic Buildings.
It is worth noting that on the Wealden District Council web site “damp proofing” is amongst the list of items which require “listed building planning consent”. The assumption is that they refer to “non-reversible” damp proofing, which should not include the use of “airgap” membranes, which are fully reversible.
Builders may have other suggestions to remedy dampness, such as bitumen coatings. Bitumen is a short term solution and should be avoided if at all possible, no matter how many coats are applied. Epoxy resins are a practical solution for solid floors and moisture retaining walls. Epoxy is hard wearing, and very permanent, so where possible, a membrane may be a better option.
Condensation is usually a consequence of modern living and is a balance between heating, ventilation, security and cost. Where there is a lack of balance between heating and ventilation, there may be condensation issues, such as a lack of sub floor ventilation within the void of a suspended timber floor. Experience has shown that condensation within listed buildings is not particularly common due to their ‘drafty’ nature, and often single glazing ensures there are natural ventilation points in a property. However as we start to seal up older properties, condensation can become more of an issue.
Vericure Condensation Control Units can be used to prevent condensation occurring and further information about our condensation solutions can be found by visiting our condensation page.
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