Aims of this presentation:
- To convey the importance of taking a holistic approach when assessing damp and timber concerns.
- To examples of successfully diagnosing such issues.
- To assist property professionals in becoming more proficient at reporting meaningful and pertinent information to clients.
When surveying a property, how far do you go in identifying the causes of damp and timber defects and then how much advice are you confident in offering to your clients?
Do you consider it acceptable to identify manifest symptoms and then sign- post to an independent specialist or Damp & Timber Contractor to do the rest?
- Understanding damp and timber is a varied and complex subject. Where serious problems are encountered as with structural failure / ongoing movement, such cases require specialist investigation. By understanding some core principles, the quality and quantity of information reported to the client, can be significantly increased.
- An holistic approach is advocated to provide a thorough understanding of a building from which an accurate diagnosis is obtained. Until this has been achieved, the surveyor is unlikely to be in a position to offer meaningful advice. E.g. Homebuyers or even full Building Survey reports regarding damp issues can be ambiguous, using previously cut and pasted scripts or simply signposting to damp specialist’s.
- Building professionals may see buildings through their personal and professional filters. E.g. an Architect may say, ‘Just look at the lines across that front elevation’, while a Valuation Surveyor may remark, ‘Amazing! A Georgian rectory south of Cambridge with land and no road noise.” Meanwhile a Building Surveyor has been told about a problem with a floor in a Victorian 2 up 2 down and notices immediately, while parking the car, that the air bricks are blocked and partially submerged under successive tarmac coverings on a built up pavement.
- By combining the significant amount of knowledge property professionals already possesses, together with an emphasis on the ‘contextual ‘ or holistic approach, this paper aims to encourage the reader that it is possible to become increasingly confident in reporting clearly and authoritatively on damp and timber issues.
What do you mean, “A holistic approach”?
If concise and accurate reporting to our clients is our goal, appreciating and understanding the property in its wider context is the primary starting point. It is as if large amounts of basic information are put into a hopper and, via a series of processes combined with the skill and knowledge of the Surveyor, a clear understanding emerges.
Context refers to information such as topography, exposed or sheltered position, orientation, aspect, soil type, water- table levels, drainage etc.
The standard assessment procedure regarding the assessment of age, type, style, materials, design, condition, local knowledge as well as key details such as ground levels can then be appreciated more fully against this wider local context.
Finally, when the internal considerations are assessed and damp and timber symptoms are noted, via a process of logical investigation and elimination, a picture begins to emerge with increasing clarity regarding the likely causes.
E.G You suspected that the cast iron down- pipe on the south west facing 9” outer wall of a 30’s semi had a leak when you detected rust at the back section facing the wall. You also noticed that where the metal bracket fixes into the rendered wall, the process of expansion has produced cracks in the render. As the bitumen damp proof course was two bricks above ground level, not surprisingly, no evidence of rising damp on the internal walls was found. However, when the area of internal wall (original lime plaster) which corresponded with the down pipe was checked, while there is no obvious damp in this area, a test with a moisture meter indicated a vertical column of penetrating dampness, from half way up the wall towards the floor. Further investigation revealed signs of localised fungal rot (cellar fungus – Coniohora puteana) in the adjacent section of skirting board.
Formula: local geographical context + external building details + knowledge and surveying skill + reflective thought > prospect for > accuracy of diagnosis = reliable information reported for sound decision making by client.
N.B. The effects of remedial issues noticed are not to be the sole focus. What is important are the causes or background considerations ie how background factors have interacted with various internal considerations, resulting in a manifest problem.
There is always a logical reason why a remedial problem has occurred. The job of the Surveyor is to investigate and eliminate possibilities in order to identify what is actually happening. From this analysis, future problems can also be predicted and the particular reasons for these identified. This approach can also help reduce the risk of negligence claims as the passage of water from the outside to the inside as in following a line of enquiry, is being explored.
Another key task of the Surveyor is to put problems and defects into a context whereby the potential purchaser or property owner can understand them in clear terms. If the Surveyor has a firm grasp of the background causes of the issues, they will be better placed to offer succinct and meaningful advice to their clients. Most calls to damp and timber companies are anxiety based enquiries, largely because the average householder has limited knowledge of such concerns. Significant value is therefore conferred to a home purchaser / owner, where remedial problems have been set into a meaningful context based on a good understanding of what has created the problem in the first place.
So what do we mean by damp?
There are three states of moisture content to be aware of.
- Air dry (hygroscopic )moisture content. This refers to a building material being in equilibrium with the air and is referred to as ‘dry’.
- The capillary (free) content. This is where the pores or capillaries of a material are filled with water from an active source of moisture.
- Total moisture content. This refers to a combination of the previous two, producing saturation of a given material. NB This why moisture resistance meters are not calibrated for masonry and if they were, as masonry differs, comparative results would not be meaningful.
E.g. An engineering brick may be saturated at 10% moisture whereas adjacent mortar may be saturated at 16% based on the difference in density and airspace / pore structure.
In determining whether so called ‘dampness’ in a property is a material concern, this will always be a subjective assessment. The question therefore is who should take responsibility for seeking to provide an accurate diagnosis?
Of those involved in the house selling process - the Estate Agent, the Surveyor, the Vendor and the potential purchaser as well as the damp proof Contractor; who is likely to give the purchaser a clear and authoritative judgement set in a proper context?
Clearly it is important to understand the age, type and the materials that have produced the property as well as understanding the aspirations of the clients. Their view on so-called dampness could range from the purists to liassez faire. However, they will expect to be made aware of any issues, any associated risks that are present or that could manifest in the future. These could include effect on future market value, potential health risks where mould is present, as well as the effects on thermal efficiency.
By understanding the core issues, communicating them clearly in a meaningful context will enable the potential purchaser / home owner to decide with more certainty what is best for themselves and the house.
E.g. A Developer owner of a Victorian mid- terrace house in Norfolk built with clunch and carstone walls (both locally quarried porous materials), requested damp proofing as part of a renovation programme. Instead the recommendation was to lower ground levels and improve above and sub -floor ventilation and to avoid any conventional damp- proofing, using hydrophobic materials and sand and cement renders. The emphasis here is placed upon preventative measures as well as allowing the house to breathe or facilitate evaporation as it was designed to do. No doubt, there will be times when the original (intact) lime plaster will register dampness, this will however be transitory as moisture is quite able to evaporate.
In this instance, moisture is managed rather than damp proofed.
The use of moisture meters
These devices are useful tools to indicate the presence of moisture in a given substrate i.e. to verify the symptoms or presence of moisture. They cannot be relied upon to identify the cause, type or origin of that moisture. Therefore when asked what type I would recommend as being the best type to use, the reply is that you already have the best type , inside your head. The meter can be useful in confirming what you have already determined through the holistic approach as well as the careful and logical process of investigation and elimination.
So called ‘moisture meters’, more correctly termed, radio frequency, capacitance or conductance types are useful when used wisely, but are prone to misuse from a cavalier approach. Remember that they can only provide relative readings, not absolute quantitative measurements. Whilst they are calibrated to assess the moisture content of wood (based upon the wood moisture equivalent scale), if used singularly without a full appreciation for the building you have stuck the prongs into, beware of how you interpret and what you convey to your client!
Using these devices with knowledge of how to interpret wall profiles when used up the wall, can illicit significant amounts of information. As varying types of damp often have consistent signatures, this process can help determine what type of damp you are dealing with e.g. whether it is a classic rising damp profile or simply the effect of condensation or the effects of hygroscopic salts. Again it is the knowledge that you posses that is important not just that the meter indicating the presence of moisture per se.
Case study from a recent instruction – Norfolk cottage
To provide an independent assessment regarding a damp-proofing regime that had been undertaken some eight months prior, to assist the owner in liaising more knowledgably with the Contractor. To make recommendations if further remedial works was required.
A late 19C detached house lying at the bottom of an unmade gravel lane. The front faced west. The soil type was Fenland peat over some clay deposits. The house did not have significant wind break cover from a wide expanse of Fenland from the south- westerly direction.
My concern therefore was the relatively exposed position as well as the probability of poor drainage, lying at the bottom of an unmade track without normal drainage. The weathered mortar joints and the extensive green algae at the base of the brick work indicated that these concerns were justified as I initially began to observe the property.
The external building elements:
There was evidence of poor workmanship with localised re-pointing in sand and cement which had produced spalling on the soft red bricks . In addition to stepped cracking above the front doorway, most notable were the unfilled channels dug on the front and south elevations that did not appear to lead to a suitable soakaway. Presumably, these were to become ‘French drains’ but in this case were in danger of becoming French moats!
Significantly, the north-facing gable wall had not been dug and had a concrete hard-standing area between the two adjacent houses abutting the brickwork. This became more significant when it was realised that the internal solid floor level was approximately 350mm below the external ground level.
Extensive damp-proofing had been undertaken on the entire ground floor footprint of the property. Specifically, there were several causes for concern, namely continuous plastering down to a solid floor with no protection at the vulnerable ‘floor / wall junction’, no tanking provision for the below ground areas as well as clear bridging of the damp proof course that had been injected.
In this instance, the initial damp assessment had presumably not considered the background context. The issues therefore were centred on location, workmanship and condition of the property itself. The aspirations and intentions of the client were important to understand. In this instance he was aware of the difficulties and wanted to address the non- technical concerns himself. However if the property was placed on the market and a client requested a full brief to rectify the remedial issues, it would be important to convey the benefits of any remedial work in relation to the likely increase in value the property may accrue.
The following basics should be considered:
- Channel the French drains off into a soak-away a good 5 meters away if possible.
- Apply a studded tanking membrane to the outside wall where the drains are dug and back-fill with aggregate and pea gravel.
- Cut a gap in the concrete approx 150mm away from the base brickwork on the north flank wall and again apply a studded membrane against the brickwork, below ground level.
- Re-point the brickwork using a suitable lime-based mortar and incorporate crack stitching where necessary above the main door. Where possible, gently remove the sand and cement and remove badly spalled bricks and replace.
- Periodically check the roof tiles and guttering / rainwater goods for effectiveness with heavy rain.
- Cut the ‘damp bridge’ where the render / plaster is continuous to the solid floor.
- Incorporate a liquid vapour membrane or epoxy floor membrane to the wall / floor junction to effect a seamless join between the current epoxy covering and the new damp course i.e. return up the walls to meet the DPC.
- The north elevation which is clearly saturated from the effects of hydrostatic water pressure from the high ground externally will continue to be a problem unless addressed with an effective tanking slurry system.
- Ensure that the kitchen and bathrooms are fitted with extractor fans complete with humidistat sensors to provide adequate air extraction in these areas of most internal moisture production.
Condensation: What exactly is it?
Moisture changing form from an air born state to a liquid, settling upon cold surfaces e.g. windows, cold water pipes, north facing walls. As a so called ‘damp problem’ it is very prevalent in a wide array of housing types, particularly in dwellings and especially bungalows built between the 1950’s to the end of the 80’s. The new mantra is build (air) tight and ventilate right. This does not mean that the risks to modern properties are over. Having a firm grasp of the principals this subject will always be important for people who assess property.
Why does it occur?
Water vapour is easily held within the air at normal room temperatures but converts to water droplets when the temperature falls below what is called the saturation or ‘dew point’.
The key to understanding this subject is based on ‘relative humidity’(RH). This relates to the principle that the higher the internal house temperature the lower the relative humidity, because warm air holds or ‘carries’ more moisture. Conversely, the lower the temperature, the higher the relative humidity, because the air can no longer hold the moisture thus it becomes nearer to saturation point or 100% relative humidity.
In colder months, October to March, as central heating goes off at night, building fabrics become cool, which presents a surface for condensation to form on. Many 20C properties built with cavity walls have poor insulation and which can create thermal bridging around windows etc. Also, since many building materials e.g. gypsum plasterboard and timber are hygroscopic (water absorbent) this is when problems can occur.
Is it capillary damp or condensation?
It is important to distinguish between damp in the substrate i.e. rising or penetrating damp and moisture from the inside i.e. condensation. To do this, results from resistance type moisture meters should be interpreted with care, as they read only the surface of a wall for moisture with a scale that has not been calibrated for masonry. Therefore what often can pass as rising or penetrating damp in a wall, is often condensation and will require a very different solution.
Essentially, rising and or penetrating damp is an issue of external moisture rising or moving through the capillaries within masonry from outside the building envelope; whereas condensation originates primarily from within the dwelling, mostly as a consequence of everyday lifestyle activities. E.g. One person 10litres moisture/day.
It is possible but not always easy to determine one form from the other, and should therefore be assessed along with other key indicators, particularly what is going on outside the corresponding section of wall. Likewise, condensation problems often come with other tell-tale signs, such as mould on cold wall corners or behind pieces of furniture.
Ultimately a correct diagnosis is necessary to provide the correct advice. Any advice regarding remedial works should obviously be effective at addressing the cause of the issue at hand and not become an unnecessary expense to the property owner.
So what causes it?
Condensation is predominately a complex interrelationship between the following four factors:
- Insufficient levels and types of ventilation
- Fluctuating heating regimes (temperatures)
- Lack of or insufficient levels of insulation
- Normal lifestyle e.g. washing, cooking etc
For example, consider a property which has been externally rendered with a cementitious covering over 9” solid walls and where double glazing and central heating are installed. The original fire places have been blocked; limiting air movement. Additionally there is a large family with pets, clothes are being dried on radiators, and there are inadequate extraction devices in the kitchen and bathroom. Condensation and mould growth is likely to be a problem in this environment. Humidity levels will fluctuate significantly over a 24hour period. It is the early hours of the morning when temperatures have cooled the fabric which causes humidity levels to spike. N.B. Once an RH% of 70%+ has been reached, this is sufficient moisture for mould spores to begin to germinate and colonise. An ideal RH level is 50% any lower and the air can be too dry.
Why is it a problem? – Condensation leads to mould growth, especially Black Mould (Aspergillus niger) which often grows on corners of cold walls. In addition to being unsightly, there are potential health risks associated with mould especially for asthmatics. Mould can be easily removed with a mild bleach solution. However unless the high humidity problem is dealt with, the mould will return. This is because the root of the fungus is left intact, buried into the wall substrate and which will re-establish, if a sufficient level of humidity reoccurs. Condensation can also develop in sub floor voids and loft spaces causing joists and other timbers to rot, especially if floor/ roof vents are inadequate and timber becomes subject to moisture levels of 20% and above.
Where properties have single glazed wooden windows, over the long term the wood is liable to rot if not kept dry and well maintained. Gypsum plaster may show up as damp patches e.g. salt damp patches on a chimney breast in winter months.
Control strategies – Limiting the levels of relative humidity by window ventilation e.g. when cooking and washing. Open windows and trickle vents, encourage air movement throughout the property. Ensure clothes dryers are vented to the outside. Undertake simple assessments by using ‘stick on’ humidity indicators. Fit ideally, appropriately sized humidistat sensor type extractor units in kitchens and bathrooms. E.g. 250m3/hour in a kitchen and a 90m3/ hour in the toilet/bathroom.
Where serious levels persist, fitting a positive air unit to help minimise relative humidity and still air, can be effective to help ventilate the whole house. They work by producing a slight increase in air pressure as well as by continually circulating air. The effect is to push out moisture laden air and this lower the level of humidity.
Ensure that insulation is adequate not only in the loft space but also in cavity walls where present and seek to maintain a more even or consistent heating regime in the winter months as opposed to an on off programme. Use specific masonry biocides for effective mould control and not bleach.
BRE studies have shown 1 in 6 properties to of suffered with condensation. It is symptomatic of a problem with primarily insufficient ventilation together with irregular heating patterns, inadequate insulation and the particularly the occupant’s lifestyle. As each property is unique with many variables affecting this condition, whilst there are some key principal causes, each situation should be considered carefully to understand the predominant factors before a simple solution is offered. Changes in lifestyle can however sometimes yield dramatic results.
Where Landlords and tenants are at loggerheads regarding this issue it can be explained that both parties need to take responsibility. Tenants’ can help by facilitating additional air flow and avoiding the drying of clothes internally, while Landlords may need to consider, suitable air extraction and or greater levels of insulation. Ultimately, there are solutions for the problem of high humidity and it’s effects including successful mould eradication.
Woodworm is the commonly used name for ‘Common Furniture Beetle’ CFB (Anobium punctatum). It is found throughout the UK attacking dead sections of trees as well as furniture, joinery and structural timbers within buildings. CFB has been the subject of heated debate among the Property industry in recent years.
One of the many interrelationships between dampness or more precisely humidity is that it can create the conditions where CFB can develop and thrive or simply remain in a state referred to as incipient level (their but not active state) of infestation.
Whilst CFB can significantly degrade structural timbers like floorboards and old spindly joists presenting a potential health and safety hazard, it is not that common. For wood to become this vulnerable, is it is likely to be limited to what is known as the ‘sap wood’ from the outer part of the tree. There is a view that suggests that Victorian dwellings were produced from timber that was older, bigger and slower growing and therefore had more heart wood which is resistant to wood boring beetle infestation.
Identifying active woodworm involves recognising freshly produced ‘frass’, namely the material the larvae produce having eaten their way through the timber and which has been pushed out as the pupa emerges as an adult beetle in the spring / summer months.
Assessing this condition is one thing but putting it into a sensible balanced context is the real skill. Again, although a subjective judgement, it should be made honestly being aware that home owners invariably consider it a real issue, when the truth is that woodworm very seldom presents an actual risk to the property fabric.
Wet rot known as cellar fungus (Coniophora puteana) – is one of the most common types of fungal rot often encountered where moisture in excess of 20% is consistently present on untreated timber e.g. backs of skirting boards, where there is an issue at the wall/ floor junction. N.B. The decay process is often going on beneath the painted exterior of the skirting board and so visual observation alone may miss the presence of this fungus.
The strands have a characteristic long black, spindly spiders web type of appearance. Whilst the effects can resemble Dry rot (Serpula lacrymans) it is invariably not as extensive or destructive apart from the immediately affected area.
Mark Duckworth – Building Surveyor
Tel: 01353 667191.
© Martin & Mortimer Chartered Surveyors
1. BRE Publications – Understanding Dampness: Trotman,Sanders & Harrison
2. Recognising woodrot and insect damage in buildings:Bravery,berry,Carey & Cooper
3. Property Care Association (CSRT) Course notes- Coleman
4. Rising damp- The Building Conservation Directory : Hutton