Damp investigations

First impressions

A lot can be gleaned before you set foot on the premises, and a thorough look at the external area of the property and its neighbours will be invaluable as the survey proceeds.

• Roof: the roof of the building acts as a huge catchment area, collecting rain and channelling it and concentrating its flow through various downpipes, as well as enabling some rain to either soak into its porous surfaces or run down the faces of the building. Dampness penetration can occur where the flow of rainwater concentrates in rainwater goods or at key building details and then leaks into the building. External yard areas can act as funnels for large volumes of rainwater. If they are not thought out and designed correctly they can collect rainwater like huge upturned umbrellas and direct it against the base of the building.
• Patio: Patios can be of considerable surface area and act as a distribution system for rainwater from sky to walls. Pathways and patios ought to be laid to suitable falls to help drainage of surface water. Water should be channelled efficiently to the main drainage, a soak-away or some other means. During the survey it may be worthwhile to pour a bucket of water over external surfaces to assess if they drain effectively.
• Typical problems: includes surface water gullies bedded too high in relation to the finished adjacent surface, creating a lip so that water cannot drain into them. If there is quite a drop from a pathway down to a gully grating it may mean that the external yard level is much higher than originally. Make a mental note that you will need to check to find out if the dpc is still sufficiently above the finished external yard. External areas raised up over the years may not only be too high in relation to the dpc, but could also be causing water to run through vents into the subfloor void and the vents could have become partly covered.
• A hard surface: enables driving rain to bounce up higher against the base of the wall to soak into porous finishes, meaning that the minimum 150mm height of dpc above ground surface may not be sufficient to prevent wall soaking above the dpc by rainsplash. A characteristic green staining at the base of the wall will be the typical evidence of such soaking.
• Drives that slope steeply down: from the pavement may well be causing a 'river' of water to impinge on the base of the house walls. Some form of cut-off drain would prevent such a water flow causing dampness problems to walls.
• Blocked rainwater gullies: causing water to soak into a wall can be checked by pouring water into them.
• Inspection cover: if you cannot see an inspection cover within the property curtilage, look next door for clues as to the location of drains. A fresh air inlet may be the clue, as will the position of soil and waste stacks, gullies etc.

Figure 1: During severe cold weather water storage tanks and associated pipework in loft voids become vulnerable to freezing and eventual bursting. This can lead to widespread internal flooding. Snow on the roof for sustained periods can be indicative of either a well-insulated loft void or a property that is unoccupied/under-occupied (little heat loss from habitable areas escaping into the loft to melt the snow on the roof slopes). Roofs that are not under-sarked can be prone to snow drifting into the loft void between gaps in the interlocking tiles/slates or gaps resulting from dislodged or broken tiles. This can lead to water penetration into the upper rooms when the snow melts

Figure 2: An ornate stone patio and pathway abutting the rear addition solid wall to a late Victorian property is bridging the horizontal dpc. The repointing carried out to the wall at low level did not help resolve the internal damp problems, which were clearly being caused by the bridging of the dpc. A chemical dpc had also been recommended, but this would not have helped remove the dampness

Be wary of the 'instant makeover'. Recently, probably millions of square metres of patio slabs and bedding sand have been sold. Few DIY installers will have thought to grub up the original yard finishes. This 'patio fever' has been fuelled by televised DIY programmes that instil in the public the perception that buildings and their landscaping can be radically changed virtually overnight, at modest expense and with very little skill, effort or preparation work. In fact, laying patio slabs or blocks evenly is probably more difficult than laying bricks plumb vertically in a wall. Look out too for those crazily angled DIY brick barbecues – a warning sign that the same DIY enthusiast may have made a poor job of some vital pipe joints.

At the front door

Even if you have not had the luxury of time for the desktop research, you will probably be able to make a fair approximation of the age of the property in the time it takes to walk from the car to the main front door. You will probably also have seen evidence of the dpc and evidence of potential soaking just above it, all before you ring the front door bell.

Over the threshold

If you step down as you cross the threshold there could be a badly ventilated floor to note in your report. Once you have gained access you must always take time to walk around the building inside and out, familiarise yourself with the layout, the basic construction of the building, and perhaps identify problem areas to focus your available time on later. The walk-over is extremely important because it helps you to understand the building and its setting and grounds in 3 dimensions, before you move on to focus on key elements or individual parts. In the survey of a typical 3-bedroomed semi you could usefully spend 15 minutes on the walk-over.

A walk around outside the property will also draw attention to the shaded elevations, the exposed elevations, and zones for potential dampness problems. Once you know the compass orientation of the property, it is then possible to ascertain which elevations are most likely to receive the brunt of the weather, and therefore which walls are least likely to dry out effectively after a period of persistent rain. Southwest elevations often face the prevailing winds, but northerly aspects benefit least from the warming sun.

Elevations should all be photographed. Dark alleys may require a powerful camera flash and often a wide-angle lens. Modern scanning of images and digital photography give you the opportunity to process and annotate the photographs by computer in your reports.

You should make a sketch of the floor plan and of the external areas of the property and use this to note features and defects.

The inspection: interrelated elements

Figure 3: A need for disabled access means outside patios or access pathways need to be level with the door thresholds

Many modern design buildings, in meeting the disabled access standards required as a result of the Disability Discrimination Act 2005, often have the outside patios or access pathways level with the door thresholds. This presents a very tricky piece of detailing for architects and designers in meeting the access requirements and mitigating rainwater run-off from entering the habitual space or entrance lobby.

Traditional load-bearing construction is made up of walls, floors and roofs. You cannot survey any element in isolation from other related elements: walls must be viewed in relation to the floors and roofs they may support.

One of the first things you need to establish is the basic function of the walls – whether they are load bearing or non-load bearing, and whether they are built off floors or off their own foundations (which could be lying on wet subsoil). You also need to establish the height of floors in relation to external ground levels, because some walls may be below ground and in structural terms acting as retaining walls, and differences in relative levels may compromise an otherwise effective dpc. Such retaining walls may be subjected to considerable penetrating dampness below ground. You may need to establish the presence of dpcs to internal walls (perhaps by looking under the floor) so that you will be able to confirm whether or not dpcs have been installed under floor wall-plates.

Bear in mind that dpcs became compulsory for the first time under the Model Building bye-laws of 1877 (see A History of Building Control) but original buildings built before dpcs may have been extended at a later date and so some walls could now incorporate them.

Tests

During the course of the survey you will need to carry out tests. Always proceed with caution.

It is easy to be fooled when a moisture meter reading is influenced by the presence of a metal foil underneath wallpaper or linings (see the 'Dampus metallicus' - foiled again case study)

There have also been notable cases where certain building bricks or blocks that contain carbon have caused a moisture meter to register very high 'damp' readings, when actually being influenced by the conductive material present in the construction materials.

A damp-proofing company recommended wholesale removal of damp wall plasters to a property in Wales in connection with a chemical injection damp course insertion they recommended. A lab test of the wall plasters – which the builders considered very dry when they were hacking them off – revealed that the wall plasters contained coal dust, which influenced the moisture meter readings.

Cases such as this highlight the need to undertake more than just a 'moisture meter survey' prior to major works to alleviate actual or supposed dampness problems. The Building Research Establishment (BRE) and manufacturers of moisture meters have been urging surveyors to use the full range of moisture meter accessories for some years, and manufacturers have always made it clear that their instruments may be influenced by salts, metals or carbonaceous materials.

Carpets and floorboards

The HSV Practice Notes advise surveyors that 'loose corners of carpets which can be lifted without use of tools may of course be lifted'; and the RICS guidance note Building Surveys of Residential Property advises that:

'sufficient boards should be lifted, if practicable and permitted, to enable the construction to be identified and its condition checked for any damage due to infestation or dampness'.

If permission is granted, you may have to lift 1 or 2 floorboards to establish the type and condition of the structural floor. It is usually easy to lift a fitted carpet from a corner sufficiently to reveal at least 1 floorboard that can be readily lifted, typically where electrical or plumbing work has occurred. Note that levering up a board is liable to leave a dent in a board even if quite carefully executed. This may be disappointing for a client or occupier if the plan is to leave boards as the decorative finish, so always explain your intentions. Once a board has been raised you can rediscover the lost art of 'torch and mirror' to view as much as you can of the floor void.

In upper floors you will probably find some central heating pipework running across the top of a line of joists, set in a notch (probably centrally on a floorboard line). Electrical wiring ought to be located through holes in joists. If you encounter any cables running in notches on joists, regard them with extreme suspicion: they may well be evidence of an electrical installation not carried out in accordance with regulations.

Do not cut a floorboard unless you are convinced that there are no pipes or cables in the way. In any case, cutting a floorboard would be best carried out with a builder in attendance.

A carpet stretcher might be a worthwhile investment for a house surveyor, and certainly for a specialist damp investigator. Problems with flooring include foam-backed carpets that are glued or taped at their perimeter, floor coverings in kitchens or bathrooms, or where tongue and groove boarding has been installed. With the latter, there is the option of drilling a small hole in a board or between boards through which a borescope or humidity sensor could be pushed, but you must make sure there is not a pipe or cable in the vicinity. The All above board? case study describes an underfloor inspection where carpets and boards were lifted, and a simplified viewing technique (torch and mirror) was used to assess the problem.

Many building survey reports contain a limitation clause to the effect that fitted carpets will not be lifted during the survey. The possible reasons for such a clause are various. First, lifting carpets and floorboards could cause damage. It also has to be said that surveyors under commercial time pressures in a competitive fee market would not consider it profitable to allocate too much time to floor access work. However, a surveyor has a duty to follow trails of evidence in house surveys, and ought to make the client fully aware of the implications of not lifting carpets and boards to inspect potentially defective floor areas, as well as the advantages of so doing.