Damp investigations
Stage 2: investigation using moisture meters
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Additional equipment for stage 2
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Taken together, the stage 1 and stage 2 investigations can be carried out within the time frame and resources of an RICS/ISVA Homebuyer Survey and Valuation.
Usually the stage 1 inspection will be undertaken as part of stage 2.
On your walk-over make sketches, particularly of the floor plans, marking location of drains, water mains, kitchens, bathrooms, any symptoms of damp problems. Note on the sketches any building details or features relevant to the investigation, and indicate where you have noted defects.
Sketching floor plans makes surveyors start to think about the building as a whole, how it is put together, and how different parts relate to each other. Photographs are almost essential for elevations, with sketches too if necessary. Defects may also be photographed for inclusion in reports and for your own files. No matter how closely you may view a small area or fragment of the building through a magnifying glass, you need to keep things in perspective and think holistically. Professor Malcolm Hollis has described surveyors as, by nature, good 'lookers'; you also need to be good thinkers.
You might usefully remove a small length of wall pointing or even a small section of plinth to expose the dpc, and then make good, if you possess the necessary skills. (It is not possible to make statements regarding the condition of a dpc in its entirety, except at a time shortly before the first course of masonry is laid on it, after which it almost disappears from view.)
Key facts to note include the weather conditions at the time of survey, and the status of the property (vacant or occupied). Both will have important implications for your findings.
Figure 1: Peeling wallpaper on external solid walls caused by the effects of condensation; staining on the wallpaper is in evidence and the early stages of mould are beginning to form on the surface of the paper
Your visit could be just after rain, during rain, or in dry weather. In more extreme conditions there could be snow or(potentially damaging for roofs) melting ice and driven snow.
If it is a dry day, you can 'create the rain', perhaps employing a gardener's watering can or a hose, if available. This will give you valuable insight into the efficiency and condition of rainwater goods, and it could enable you to check gullies for blockages, or to see how surface water drains off paths and yard surfaces near the walls. Cills and other projections can also be tested to see how effective drips are. It is also useful to see how porous some surfaces might be.
Basic drains tests could help you to track down a drain blockage or leakage, site conditions allowing. If it has rained before the survey, you might see standing water in gutters, on flat roofs, or in yard areas, that alerts you to potential penetrating damp problems.
Figure 2: Having noted the damp stain by (a) the stairwell window opening, a quick look outside links this to (b) the suspect rainwater downpipe connection outside. Such a sharp bend in a rainwater pipe is always going to leak: a connection like this is usually only a dry interlocking connection
Your visual inspection will give you some idea of which walls are load bearing and with foundations, and which are partitions built off a floor. Carefully note the condition of plasters and decorations, and any visible symptoms of dampness (stained or peeling wallpapers, debonded and crumbling plasters, rot affected timber). If these symptoms are evident, you will need to trace the water main – one of the likely moisture sources.
The time of year of the inspection can also be significant: there may be signs of condensation-led mould that had developed many months prior to the survey, in the condensation season (October–March). Remember that condensation is far less of a problem and far less likely from April to September. But in cases of overcrowding, condensation can feature as a serious moisture problem during the colder summer days or nights.
You might even find walls to be significantly damp in the middle of the summer if a moisture problem has built up many months earlier in the winter period. Traditional masonry walls may soak in water quite readily, but are usually very reluctant to let go of it. Surveyors usually expect brick walls to dry out at 25mm thickness per month, assuming that there has not been any attempt to hurry the natural drying-out process using air blowers or dehumidifiers. A snapshot survey would not usually allow you to confirm whether moisture content is increasing (progressive), decreasing (regressive) or in a state of steady equilibrium.
It is also possible that symptoms of dampness problems have been removed or concealed by occupiers, or simply decorated over. Be aware in the 'real world' of the possibility of sabotage, where an occupier has the aim of concealing evidence of condensation-led mould, which they feel might reflect badly on their lifestyle. Over-zealous cleaning of floors or walls using water too carelessly and liberally can add to moisture problems in the home.
In a stage 2 investigation the moisture meter is the core item of equipment, but it must not be used on its own or blindly. Proceed with caution, and ensure that you are fully acquainted with the theory and practice of using the instrument (see Surveying equipment and tests). Case studies 1 and 3 also offer some useful guidance.
After you have conducted a close visual examination of the property inside and out, record any moisture readings on your sketches. The readings must be viewed and analysed in the context of site observations made before and after use of the instrument. There will be times when you home in on a suspected damp zone after noting relevant symptoms of potential defects inside or outside the building, and high moisture meter readings will back up your original suspicion that a damp problem is likely. In other cases the recording of high moisture meter readings may initiate closer inspection inside and outside the building but subsequent closer visual inspection leads you to realise that the readings do not indicate significant dampness. (Remember, for example, that metal foils behind wall coverings can lead to false readings.)
Use 'triangulation' when dealing with moisture meters. That is, collect various pieces of evidence in order to reach a more reliable judgment on the cause of dampness. Triangulation could include observations on building condition, visible symptoms of a dampness problem, moisture meter readings and your professional interpretation of collected evidence.
Establish an efficient work pattern. This speeds up surveying and reduces the risk of missing potential problems. You cannot ignore any wall or surface, but it is sensible to spend more time in the likely damp zones that your visual inspection has highlighted. And remember to take low benchmark or control readings in 'dry' walls and skirtings. Take readings around external openings, or where you have noted potential penetrating damp positions. Also take readings where materials appear irregular in surface finish, or marked or stained or damaged in any way.
When using a moisture meter:
- remember that it is you that has the brain, not the instrument;
- do not be unduly influenced when lights flash or bleepers sound; do not take the words 'AT RISK' at face value;
- remember that the % symbol on the screen only means % moisture content in timber from 8–28%; and
- the electrical resistance meter with pin probes gives information on potential dampness only at the point of contact; the capacitance meter measures a little beneath the surface.
Advice to client
So far you have made no direct measurement of moisture content in walls. As with the stage 1 inspection, if you feel that further investigation is needed to verify whether significant dampness exists to part of the building, or to advise on causation or the need for remedy, you may offer the service of a further investigation yourself, depending on your expertise.
In the context of a pre-purchase survey, there is often pressure to reach practical decisions on building condition in order for the client to make a quick decision on whether to proceed with a purchase. You need to explain to the client the implications (and risks) to yourself, to the building and to the client of ending your own investigation at stage 2.
You need to use careful professional judgment here. In some cases you may be able to give a professional opinion on the likely cost of repair in a worst-case scenario. For example if, in a modest house, you discover a localised damp patch along a section of a wall or to a front bay, repairs or improvement to make good defects would not realistically amount to more than £1,500. You explain this to the client, who is then able to make an informed decision on whether to proceed with purchase. On the other hand, in another property you might record high relative readings throughout the property, and would be unable to assess the full risk to the property without further investigation. You should strongly advise that further investigation is organised by yourself or others.
Each case needs to be judged on its own merits. You must always explain to the client when you cannot confirm diagnosis or develop a strong professional opinion until further investigations are carried out.