The subject of rising damp and how to solve it is surrounded by considerable controversy. This is partially due to its complexity, partially due to ongoing misinformation.
Here are the most common misconceptions vs. scientific facts.
Click on any of the sections below to reveal more information.
The full answer to this myth is given in detail here.
The short answer: the amount of independent, third-party information about the existence of rising damp is really staggering, the phenomenon being well-documented since the 1840s.
There are hundreds if not thousands of university research papers from highly-trusted sources describing many aspects of rising damp in detail.
The world's largest peer-reviewed research platform, Elsevier ScienceDirect, at the time of this writing lists 579 peer-reviewed research papers about rising damp.
Several architectural and professional books starting from the mid 1800s have described the problems of rising damp, also advising about the use of damp proof courses.
Here are some titles:
Old books from the Victorian period have also consistently documented that problems caused by rising damp were well-known in Victorian England for nearly 200 years, describing significant damages to period 16th - 17th century cottages and country houses.
All these books and references are freely available from the Internet Archives as part of Google's old books digitization project, to be viewed or downloaded by anyone. Here are just a few relevant titles:
The full answer to this myth is given in detail here.
The short answer: rising damp and condensation are different phenomena.
Measurements performed on old buildings in wintertime have revealed an interesting detail: an old wall in depth is WARMER than on the surface, For e.g. in December, the depth of an old wall (red) was on average about 3°C warmer than the evaporative surface (blue).
This actually makes sense as walls store and retain heat due to their large mass. Similarly, the temperature of the soil below the surface is warmer than the surface - ground-source heat pumps utilize this principle to extract heat from underground. The surface of a damp wall is usually coldest due to ongoing evaporation.
We have also approached the problem from the opposite direction, taking it all back to a well-heated lab where no condensation can take place. Yet, we were able to reproduce rising damp in a condensation-free environment, which indicates that rising damp and condensation are different phenomena.
This is not true.
In fact, rising damp is being recreated in the lab routinely during various research projects. Many research papers publish photos of their experimental setups. Here are some examples of such papers:
In fact, anyone can make water rise by placing some old-style porous bricks in a tray of water. The height of rise will depend on the type of bricks used - it tends to be higher in traditional bricks and lower in less porous, modern bricks fired at higher temperatures.
Here is a time-lapse video showing the speed of rise in old-style porous bricks.
The rise height of water in porous brickwork depends on several parameters, such as: the porosity and properties of the masonry, the thickness of the walls, the moisture saturation and salinity of the soil, the type and breathability of plaster used etc.
The maximum rise height can be calculated with formulas which are given in various research papers.
One of the important variables here is wall thickness. Thicker walls with large volume can absorb and retain a lot more water than thinner walls, thus the rising damp height also increases proportionally:
- 0.2 m wall thickness: 0.71 m rise height
- 0.5 m: 1.12 m rise
- 1.0 m: 1.58 m rise
- 2.0 m: 2.24 m rise
- 3.0 m: 2.74 m rise
Most residential buildings in the UK have walls up to 0.5 - 0.7 m, hence the 1 metre rise height, based on observation, is correct. Non-breathable materials such as cement can modify the rise hight, making it higher.
The scientific literature, however, documents a number of well-known old buildings where the rising damp height is significantly higher than 1 metre. Here are some examples.
This peer-reviewed research paper1Hoff, W.D (2007).: Rising damp: Capillary rise dynamics in walls. Proceedings of the Royal Society. A Math. Phy. 463, 1871-1884, https://royalsocietypublishing.org/doi/10.1098/rspa.2007.1855 documents a rising damp height of 5.3 metres in the Church of San Bernardo in Rome where the wall thickness in certain areas reaches 4 metre.
Here is a photo of this church with the tidemark (drawn by us) being just under the red line.
As highlighted by this peer-reviewed research paper2 Franzoni, Elisa. (2014). Rising damp removal from historical masonries: A still open challenge. Construction and Building Materials. 54. 123-136, https://doi.org/10.1016/j.conbuildmat.2013.12.054, in the Basilica of San Marco in Venice, where the wall thickness is between 0.7 - 2.0 metres and marble slabs are present of the surface, the rising damp height is well above 6 metres. The base of the walls affected by rising damp is near saturation.
Here is a photo of the basilica.
Old buildings need to breathe. “Breathing” is a colloquial term indicating that moisture can move freely in-and-out of the wall fabric. Breathing allows an old fabric to self-regulate its moisture content.
Non-breathable materials are not the cause of dampness problems. In order for them to create a dampness problem, an underlying moisture source MUST always be present to make moisture accumulate. Without a moisture source nothing accumulates. This can be as light as ongoing vapour evaporation from the soil.
So, when investigating a dampness problem in conjunction with non-breathable materials, one must always ask the questions: “What moisture source is present that a non-breathable material can trap?” – then find it. There is always at least one.
The full answer to this myth is given on the pages dealing with technical aspects of breathability and of moisture barriers.
The short answer is that removing non-breathable materials from the wall fabric and restoring the breathability of the wall fabric - although is a big step in the right direction - it is only a partial fix to the problem.
Research has shown, that moisture accumulates even in a fully breathable wall fabric with no physical moisture barriers present. This occurs due to adhesion forces caused by surface charges or surface energies - tiny electrical charges on the wall surface that attract and trap vapour molecules to capillary surfaces.
These adhesion can be significantly increases in the presence of salts which commonly accompany rising damp. Thus, the lower part of the walls becomes less breathable (even if left open) due to the high surface energies, which act as a chemical moisture barrier rather than a physical one. The hygroscopic effect of salts and moisture retention caused by it occurs due to these electro-chemical surface charges.
Drainage in many cases improves rising damp problems because it decreases the moisture content of the soil, thus reducing the amount of moisture that can get into the walls.
Not all moisture is drainable. Drainage only removes the free moisture from the ground. The bound moisture content of the soil can't be drained - which is more than enough to keep rising damp going, as rising damp is not caused by capillary action but moisture evaporation from under the walls into the wall fabric.. Lab experiments have have proven this fact conclusively.
Moisture retention is further boosted by the presence of ground salts in the wall fabric, salts being an important catalyst of rising damp.
So drainage is a good idea, however it should not be regarded as a solution to rising damp, but only a means of ameliorating it.
The truth is tanking and membranes DO NOT solve rising damp - they only mask it from being visible, making the problem worse in the long-run. What tanking or membranes achieve is they seal the surface, preventing the evaporation of moisture. As a result, moisture starts accumulating behind the moisture barrier, being channelled upwards or sideways.
Tanking and membranes are masking the dampness problem rather than solving it, being only an apparent solution - causing further dampness problems down the line.
They actually do - nothing lasts forever.
Damp proof courses (DPCs), just like anything in nature, are subject to aging and degradation. They are subject to immense pressure from the weight of the building, vibration, the corrosive effect of ground salts - just to name a few important factors influencing their long-term integrity,
Here are some examples of broken down DPCs observed in real buildings:
DPCs have been invented and continuously developed starting the early 1800s as a solution to prevent the rise and accumulation of moisture into the building fabric.
The latest technical research on rising damp has clarified that main role of a damp proof course is not to stop capillary action but to act as a horizontal vapour barrier, blocking the evaporation of moisture from under the wall into the wall - keeping the wall fabric dry long-term.
As a result DPCs provide a very essential role in a building and as such, they are needed.
Drainage, heating and ventilation - although they all help - they won't replace a DPC and are not a substitute for it.
According to existing literature, rising damp is a worldwide problem affecting much more than just Britain. Here are some examples.
Here is an article from the Old-House Journal, a USA magazine devoted to restoring and preserving old houses.
In an article about rising damp, some Southern US states - Texas, South-Carolina and New Orleans - are called "the proverbial land of rising damp".
Here is a research article, jointly published by Belgian, Italian and Dutch universities and heritage agencies, calling rising damp "a recurrent hazard to ancient buildings in Europe".
DPCs are also used in Venice. Here is a quick video compilation about some of the different types of DPCs we observed during our conservation workshops in Venice.
Here are some other related pages that you might want to read to broaden your knowledge in this field.
Here are some of our projects where we have dealt with some of the issues discussed on this page:
Here are some photos demonstrating these concepts. Click on any image to open the photo gallery.
Here are some photos of disintegrated, broken down original slate DPC which have been frequently installed in old buildings in the Victorian period – a means to prevent and combat rising damp.
Here is a 400 year-old old stone building from the 1600s, replastered with lime. The plaster got completely damaged by salts in less than 4 years.
Here are some videos related to this solution. Please unmute the videos when playing them.
