Rainwater Disposal

The rapid and efficient disposal of rainwater is essential for the well-being of any building, but is particularly important for those of traditional construction. However, not all buildings were designed to have gutters and downpipes. Thatched roofs, for example, are steeply pitched with deep overhanging eaves to help throw water away from the walls.

During the seventeenth and eighteenth centuries, lead-lined gutters and lead downpipes became commonplace on larger houses. The use of lead, a malleable material, allowed scope for ornamentation. Hopper heads — box- or funnel-shaped receptacles at the top of downpipes — were sometimes adorned with the initials of the person who had the house built and the date of its construction. Lead hopper heads and downpipes are of considerable historic interest; wherever possible they should be repaired, rather than being replaced. Georgian buildings occasionally have internal gutters, constructed of lead-lined timber chutes, running through the roof space to discharge water through an external wall. At that time, the roofs of higher status houses were often complex in their design and internal gutters were necessary to remove rainwater from inner valleys and flat roofs.

Cast iron superseded lead from the end of the eighteenth century and its use became common on smaller houses. Early cast-iron guttering had a half-round section and was fixed on long spiked brackets driven into the wall or attached to the ends of the rafters. In the mid-nineteenth century ogee profile guttering became fashionable, although half-round gutters remained the norm on more humble buildings. Ogee guttering has a flat back and is supported on a projecting eaves course of brick or stone, or screwed directly to the wall or a timber fascia board. Downpipes are fixed to the wall by means of ears, which are cast into the sections of pipe, or separate clips, known as ‘holder bats’.

The casting process allowed the Victorians, in particular, to develop many highly ornate patterns. Gutters on glass canopies often had decorative cresting, whilst the design of downpipes can vary from barley twist to embossed motifs. Cast-iron hopper heads also tended to be highly ornate. The level of detail varied with the size and type of house, and simpler rainwater goods prevailed for smaller buildings.

What to look for: 

Overflowing gutters and hopper heads.

Suggested action: 

Clear gutters of plants, leaves and debris, particularly during autumn and winter. Check that gutters discharge water into the downpipe without ponding.

Overflowing gutters and hopper heads can lead to damp walls and decay, and the problem should be identified and addressed without delay. Fortunately, the most common cause is a blockage formed by vegetation, leaves or debris that can easily be removed by hand. Before undertaking any work at height, however, consider the risks and make sure you will be working safely. 

If your gutters are very high or difficult to reach, you may wish to hire a scaffolding tower or mobile lift (cherry picker) or employ a contractor.

Check that gutters are not sagging and are correctly aligned to discharge water into the downpipe without ponding. This is a common problem with UPVC, which tends to be the shortest lived of all gutter materials.

If you have internal gutters running through the roof space, regularly check them for blockages and any deterioration in the lead lining or timber chutes. Arrange for necessary repairs to be carried out without delay. Internal gutters are effective, but they must be very carefully maintained as failure can rapidly cause a considerable amount of damage to the ceilings and furnishings of rooms below.

If gutters and hopper heads are overflowing, but the cause cannot be found, the system may be too small to cope with the volume of water being discharged at times of heavy rainfall. However, where the existing system is of historic value — for instance, one with ornate lead hopper heads and downpipes — replacement with larger units may not be acceptable. The installation of an additional downpipe and the adjustment of the gutter alignment may be a suitable alternative.

Some buildings have lead box gutters behind parapet walls. If the outlet is not of sufficient size, the water level can rise within the gutter, with the risk that it will find its way into underlying timbers and the wallhead. It may, however, be possible to adapt the system to include a secondary overflow outlet and chute. This has the advantage of not only throwing excess water away from the wall, but also providing a clear indication when greater vigilance is required. Seek advice from an architect or surveyor before undertaking any adaptations to ensure that they are correctly detailed. If your building is listed, this work may also require consent.

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What to look for: 

Cast-iron gutters and downpipes - leaking joints and split pipes; loose or detached downpipes.

Suggested action: 

Search for signs of leakage and where possible clean and reseal leaking joints. Replace split or severely rusted pipes on a like-for-like basis.

Provided that it is well maintained, cast iron is an extremely durable material, although it is brittle and will shatter if it is struck hard. Trapped water can freeze and split pipes so install leaf guards at the top of rainwater outlets to help prevent downpipes from becoming blocked.

Holes at the back of downpipes can be difficult to spot, particularly with rectangular section pipes, so look for tell-tales signs of saturation on the adjacent wall, including rust and water stains, washed-out masonry joints, and moss and algae growth. If the leak is allowed to continue, water damage can appear on the inner face of the wall and this can create the ideal conditions for wet and dry rots to take hold.

Silicone sealants may be used as a temporary repair, but leaking joints in cast-iron gutters and downpipes should be taken apart, cleaned, de-rusted, reassembled and sealed using traditional linseed oil putty. Severely rusted or split sections should be replaced on a like-for-like basis. Do not mix materials as it will be difficult to achieve a durable joint between them. Extruded aluminium and UPVC rainwater goods are not suitable substitutes for cast iron on historic buildings, although cast aluminium may be acceptable in exceptional situations where regular maintenance would be difficult.

When renewing or re-fixing downpipes install wooden spacers behind the brackets or ‘ears’ to improve ventilation and access for redecoration.

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What to look for: 

Drainage problems around canopies and balconies with hollow cast-iron columns.

Suggested action: 

Re-decorate using an oil-based paint system.

Remove any rust and redecorate on a 3 to 4 yearly cycle, but more frequently if corrosion is found. If the weather is not suitable, apply a coating of linseed oil to protect any bare metal. The use of non-traditional products that bond chemically with the iron should be avoided as they are susceptible to chipping and cannot be removed or over-painted using more traditional paint systems. Paint the inside of gutters with bitumastic paint.

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What to look for: 

Blistering paint and rust on cast-iron rainwater systems, particularly in crevices and joints.

Suggested action: 

Re-decorate using an oil-based paint system.

Remove any rust and redecorate on a 3 to 4 yearly cycle, but more frequently if corrosion is found. If the weather is not suitable, apply a coating of linseed oil to protect any bare metal. The use of non-traditional products that bond chemically with the iron should be avoided as they are susceptible to chipping and cannot be removed or over-painted using more traditional paint systems. Paint the inside of gutters with bitumastic paint.

What to look for: 

Blocked drains and gullies.

Suggested action:

Clear all leaves and debris regularly, particularly during autumn and winter. Make sure that grilles and mesh covers are in place and not broken.

Always wear stout gloves when clearing leaves and debris from drains and gullies to protect your hands from sharp objects. Rod drains if they become blocked.

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What to look for: 

Open joints, cracks or damage to water channels and paths around perimeter walls

Suggested action:

Repair cracks or damage to concrete water channels and paths.

Make sure that concrete channels and paths around perimeter walls are intact and that water is directed away from the base of the walls. Any water penetrating through cracks will be trapped and concentrated in one place, which can eventually undermine the foundations of the building or cause rising damp. Seal cracks with a concrete sealant in accordance with the manufacturer’s instructions.

If possible, replace concrete paths with gravel or another free-draining material.

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What to look for: 

Damp on the internal face of external walls.

Suggested action: 

Check the level of beds and borders around the building. If necessary improve drainage around the perimeter of the building.

If damp appears on the internal face of external walls, check the level of any beds and borders around the building. Make sure that soil has not risen above the internal floor level or any damp-proof course or airbricks. Moisture penetration from this cause is often misdiagnosed and expensive damp-proof courses or tanking systems recommended, which are often ineffective and unnecessary.

It is important that water is carried away from the base of walls as quickly as possible. This is particularly so for buildings with no rainwater goods, which instead rely on deep overhanging eaves to throw water clear of the building. Drainage around the perimeter of a building can be improved greatly by lowering ground levels, taking care not to undermine the building’s foundations.

Where additional drainage is required because of the high clay content of the soil surrounding the building, for example, a French drain can provide a very effective and inexpensive solution. This involves digging a trench adjacent to the wall and lining it with a geotextile membrane. A land drain of half-perforated clay pipes is laid, with perforations uppermost, on top of the membrane with a good fall to ensure that the water collected is carried away from the building to a separate soakaway. The trench is then backfilled almost to the top with well-compacted shingle and another layer of geotextile membrane laid over it. This membrane prevents fine soil particles from getting into and blocking the drain. The trench is then topped up to the finished level with gravel or topsoil. Make sure that the trench does not undermine the foundations of the building or disturb any archaeological remains. As the foundations of medieval buildings, for example, can be extremely shallow, it may be necessary to dig the trench a little distance from the building. The French drain is, however, likely to be less effective as a result. If in any doubt, seek advice from an architect or surveyor. It can take many months for a saturated wall to dry out, so the benefits of the drain may not be immediately apparent.

Basements are often damp and this can be difficult to eliminate without installing a tanking and internal drainage system. However, this is usually only necessary where the basement contains habitable rooms. In other cases, increasing the amount of ventilation will usually be sufficient to avoid more serious problems, such as fungal outbreaks, from occurring.