Advice & Guidance
Damp
Before the 19th century buildings were usually built of stone, brick, timber and earth (cob or wattle and daub) held together with earth or lime-based mortars.
These materials
are absorbent and allow
moisture to penetrate the fabric and then evaporate away harmlessly when
conditions are favourable. For this
reason, traditional buildings are said to ‘breathe'. In such buildings,
dampness is controlled by
the building's ability to allow moisture to evaporate.
The wind and sun aid the evaporation of water from the external surfaces whilst internal air movement through the roof covering, walls, windows and other openings helps moisture evaporate from internal surfaces.
As long as the moisture can evaporate freely, the traditional performance of the structure will function as intended and the walls of the building will remain acceptably dry. To aid this natural process, traditional buildings were carefully detailed to encourage the shedding of water from their surfaces.
Features such as deep
overhanging eaves, protective lime renders, lead flashings, wide gutters
and
sturdy plinths at ground level were used to protect the wall surfaces as
much
as possible.
If such details are altered or unable to function the building might be put at risk. The Victorian fondness for removing old lime renders to expose the masonry underneath inevitably made some porous stone walls much more vulnerable to decay.
Managing damp
In a sense, good maintenance is simply a question of managing the level of dampness to ensure that the building remains comfortable and usable.
However, alterations to the fabric of the
building through the years can affect its equilibrium, leading to
excessive
levels of dampness.
If this is the case, the important point is to aim to treat the cause rather than symptoms.
The telltale indications of excessive moisture include tide marks on walls or floors, patches of white powdery salt crystals on wall surfaces, green algae or mould growth and blistering paint or plaster.
It is also important to be alert to changes in ground levels around the building. A common example is the gradual rise of external ground levels relative to internal floor levels due to burials in the churchyard over many centuries but ground levels can also change as a result of creating flower beds or relaying paving.
If any excessive dampness can be attributed to raised ground levels the question of remedial action will require careful thought. Whilst it is sometimes appropriate to lower ground levels locally around problem areas this can destroy archaeological evidence in the soil and needs to be tackled sensitively.
Professional advice from your architect or surveyor and from an archaeologist will almost certainly be necessary.
Action point: The best advice is to be alert to changes in the condition of the fabric that may indicate that there is a problem. Look out for any signs of excessive damp as you walk around your building.
If you suspect that there
might be a problem with damp consult your architect or surveyor for
independent
advice rather than a remedial company with a vested interest in their
own
recommendations. Once the cause has been
identified, appropriate remedial action can be taken.
Be aware that injected damp-proof courses, water-repellent solutions and proprietary wall coatings do more harm than good when inappropriately applied to old buildings.
Further Reading
- SPAB (1992) SPAB Technical Pamphlet 8: The Control of Damp in Old Buildings, SPAB
- Trotman P, Sanders, C and Harrison, H (2004) Understanding Dampness: Effects, Causes, Diagnosis and Remedies, BRE
- Burkinshaw, R and Parrett, M (2003) Diagnosing Damp, RICS
- SPAB Technical Q&A Number 20 - Rising Damp
© SPAB 2010
