Dampness in building elements

Although roofs are one of the most important building elements you will survey, in many ways they are the most ignored. Surveyors may get quite close to architraves or skirting boards, but roofs remain very much in the distant view.

Moisture ingress through the roof is inevitable in the UK climate if lapped coverings such as slates, tiles, shingles, or metal coverings are not weather-tight, or if jointless continuous membranes (asphalt, bedded felts, waterproof coatings) are not watertight. Therefore a thorough roof inspection should be a first priority in most dampness investigations.

Have a sketch plan of the roof, complete with notes on condition. This can be useful when compared to the top floor plan. Damp patches to upper ceilings and walls can be easily linked to questionable detailing or obvious flaws to roofing above. But note that damp patches on ceilings can be due to historical leaks, where the fault has long since been rectified.

Binoculars are very useful for an initial view of condition, but must not be the lazy surveyor's ladder. The use of drones equipped with cameras can be a very useful addition to the surveyors equipment, as they can remotely survey a roof from the ground and photograph or video the survey. For a bungalow you can, in fact, see much of the roof from the surrounding garden (although small gardens limit the view); and for a 2-storey terraced house with an 'up and over' roof you can count quite accurately the number of missing or slipped slates from the roadway and rear yard. For any building higher than 2 storeys you will usually need a long ladder and a good head for heights. (The type of ladder that house surveyors normally take to site in their car boot is only really useful for gaining access to a loft from a top floor landing or a garage roof.)

Certain parts of the roof may not actually be visible from ground level. The parts you cannot see may have been neglected over the years (see figures 1 and 3).

Figure 1: Exposed valley timbers rotting

Figure 2: A surveyor using binoculars from the ground would not see accumulated debris blocking the chimney back gutter, but should at least inform the client of this likely problem, explaining that the tiling is too shallow where the roof has been extended over the rear parts of the property

Flat roofs may not be visible, or may only be partially visible from an upper window or a neighbouring vantage point. And bear in mind that your predecessors may have failed to appreciate that surprisingly short front and rear roof slopes often extend down from a flat roof that cannot be seen. This roof could be in poor condition if it has been neglected over the years. You may be convinced that a pitched roof appears in satisfactory condition, but it is harder to make a similar claim for a flat roof, which is subject not only to potential rain penetration from above, but could suffer from internal condensation problems or plumbing leaks.

Figure 3: Flat asphalt roof not sufficiently laid to falls causing rainwater to pond on the roof surface. Cracks and fissures through the asphalt leads to water penetration into the upper flats. No roof insulation leads to a very cold roof slab, which results in the additional problem of internal condensation

Remember that larger holes higher up a roof slope will let in less water than smaller holes further down. The nearer the flaw in a roof covering is to the final outlet or guttering, the greater will be the flow of rainwater finding a way through it.

Closely examine the way rainwater runs off a roof onto eaves guttering. It is usual practice to lap sarking felts just into the eaves gutter to make sure that any rainwater running over the felt does not penetrate into the building near the eaves, but some sarking materials deteriorate in time. For slated or plain tiled coverings there should also be an additional course of slates or tiles at the eaves. The eaves undercourse of older roofs is often in poor condition, and without an underfelt the roof leaks at this point. Check how far the tiles or slates project over the gutter and also check the drop to the guttering. Is all the rainwater running into the guttering? It might be worth pouring water over the roof covering to see how it behaves. Damage or disturbance to tiling or slating at the eaves could have been caused by careless maintenance work, and this part of a roof is also subject to wind damage in exposed locations. Some roofing tile manufacturers can furnish a surveyor with exact fixing instructions for replacement or new roofs if the exact location of the property can be provided. There is separate guidance on risk to wind lift depending on the local topography, region, location and nearness of surrounding buildings and landscape.

The rule is that the greater the risk of exposure the greater the number of mechanical fixings, in sheltered city locations tile fixings maybe every third or fourth course as compared to fixing at every course for rural exposed locations.

If the roof covering or guttering has been changed or modified the relationship between the two could have been compromised.

Figure 4: The original timber guttering in the picture above has been replaced with plastic guttering. This means that the old pantiles are now set too far back from the new guttering and the guttering is further away from the wall face. The changes mean that rainwater misses the guttering and runs down the fascia, causing it to rot, as well as soaking into the wall. This type of serious problem would not have been understood if viewed from the ground below

Underlay is a second line of defence against rain penetration, and it helps to protect the building from extreme weather conditions when wind-blown rain or snow could find its way through the normally effective roof covering. If the roof has the benefit of an underlay, inspect it for holes and tears in the loft, but if the space under a pitched roof is used as habitable space, it will not be possible to inspect underlay or roof coverings from underneath, and leaks may be more difficult to trace.

The habitable space will be closer to protective roof coverings and potentially more vulnerable to damage caused by damp penetration. In the same way as a well-ventilated ground floor void helps walls to breathe at their base, so a well-ventilated roof space helps upper masonry breathe (for example, if chimney or parapet masonry without the protection of an effective dpc becomes significantly damp during periods of persistent rain).

Guttering, downpipes and gullies 

Although there may be signs of leakage to plumbing even on a dry survey day, if at all possible visit the property when it is actually raining to check the adequacy of guttering, downpipes and gullies.

A common problem with modern plastic rainwater downpipes lies in their slippery and smooth finish; they tend to slip downwards within their brackets, leaving upper sections pulled out of gutter outlets. There is also a general tendency for downpipe and gutter brackets to be fitted at centres further apart than recommended by manufacturers, causing gutters to sag, discharging collected rainwater over elevations or causing downpipes to become generally detached from masonry. If left unattended for too long serious moisture penetration may result. Some sections of plastic guttering may become distorted and therefore rendered ineffective if a boiler flue heats a section of gutter above it.

Conversely, many plastic gutters and rainwater pipes are not fitted with linear expansion in mind. Manufacturers offer guidance on the allowances to be incorporated for expansion. There is often a fixing marker found in gutter joints, outlets and end stops where the gutter should terminate to allow for expansion.

Expansion of rainwater pipes can often result in forcing the gutter higher, reversing falls away from the outlet. The replacement of cast iron rainwater downpipes for plastic can often result in an increased risk of vandalism to the lowest section of the pipe, particularly on blocks of flats. Bicycles often get chained to the down pipe for security and continual use can result in damage to the less durable plastic pipe.

Cast iron rainwater pipes from flat roofs that are routed integrally down through the building can be prone to blockage at roof level from general detritus collecting on the roof area. Also from frost action and icing where the cast iron pipes and flat roof outlets crack, resulting in water escape down through the building.

Cast iron rainwater gutters can present problems due to the lack of painting to the side of the gutter closest to the facia board, this section often does not get painted resulting in corrosion and disintegration of that part of the gutter. In terraced houses of different ownership some sections of gutter get replaced by adjoining owners in modern plastic profiles, creating jointing problems to the older cast iron - though some manufacturers of modern plastic gutter systems will either stock or specially make a cast iron to plastic connection.

While falls on many gutter systems has always been important, some modern deep flow plastic gutters can actually be laid level and instead rely on the dynamic shape of the outlet connections to rain water down pipes to draw the water from the gutters by creating a vortex effect.

Note carefully the position of any internally ducted rainwater outlets. They are notorious for causing damp problems internally if they are not perfectly linked to downpipes. If square section rainwater downpipes have been used, look carefully to see if the rainwater shoe or the short leg at the bottom of the pipe feeds properly over or into the gully. A square section fitting/connection at the bottom of a pipe cannot be revolved precisely for a good alignment or direction of pipe in the same way as a circular section.

Roof space

An inspection of a roof cannot be considered complete until you have inspected the void, if there is one. In loft conversions there may well not be – but you must, of course, check that the roof modification has complied with the Building Regulations that were in force at the time of conversion.

If you cannot examine the roof space (for example if there is no access trap), you must state the consequences of this in any report or conversation with the client. In most cases recommend cutting a roof access. This involves little more than trimming ceiling joists, and using metal straps or joist hangers to support timbers. Linings, stops, architrave and hatch are then needed – and any future surveyor will be grateful for a loft light. Surveying Buildings provides a very useful checklist for the examination of the roof void.

Remember that the condition of ceiling and wall plasters will often offer important clues about the condition of the roof above. Ceiling plasters should always be tested for integrity using a wooden batten or even a broom handle (with care). Loose ceiling plasters, particularly the older lath-and-plaster types, present a major risk to building occupants if they become loose and finally drop to the floor in sometimes quite heavy sections. Such a devastating event can be caused by long-term vibration damage often in combination with an increase in weight due to water absorption from a leakage.

Tracking down the source of moisture can be difficult in flat roofs. For example, water may drip through joints in ceiling boards or light fittings that are positioned below flat roofs at some distance from the fault in the roof covering. There can be considerable difficulty in differentiating between penetration, condensation, or a plumbing leak because of the quite complex 'sandwich' construction. In some cases specialists may need to be involved to confirm diagnosis, or you may need to make some calculations to help establish exactly where condensation is likely to be occurring within the sandwich. Quite sophisticated electronic detection methods are used to detect leaks in the larger commercial and industrial buildings. Infrared thermography from inside or outside the building can highlight temperature differences that indicate where damp penetration is likely.