BSJ Oct.Nov 2015

RICS PROPERTY JOURNAL

R

3 8 N O V E M B E R 2 0 1 5

RESIDENTIALBUILDING PATHOLOGY

Images © Michael Parrett

The whole story

Cast-iron gutters and

rainwater pipes,

prevalent through

the Victorian and

Edwardian periods,

need paint protection.

Unfortunately,

painting schemes may miss the inside

faces of these goods, which then

corrode. Similar problems occur with

internal cast-iron service pipes, such

as soil stacks.

Connections are vulnerable where

flat-roof rainwater outlets meet internal

pipes, which often suIer blockages

from airborne detritus. In winter, pooling

water freezes and can crack the outlet.

Either problem may cause water to leak

outside the drainage area down the

outside of the internal pipe.

Surveying cast-iron goods can be

tricky due to restricted access. I use a

mirror on a telescopic pole to check the

rear of pipes and gutters, but this may be

insuLcient if problems are beyond the

reach of a 3m surveyor’s ladder. These

issues are greater in tower blocks, which

require safe working access.

When installing PVCU systems,

allowing for linear expansion is often

missed, causing them to buckle.

Expansion is needed on all elevations,

especially when south-facing, but

following manufacturer’s instructions

should mean guttering, pipes and

connections are cut appropriately.

Guttering alignment is critical, but

falls are often incorrect, causing flows

away from the outlet and spillages over

Michael Parrett concludes his series on damp and reminds

surveyors to take a holistic approach when diagnosing issues

the gutter. Some modern systems can be

laid level, with outlets designed to create

a vortex to draw water out of the gutter.

Drainage design on buildings is vital

to properly discharge rainwater. I have

investigated spectacular failures where

the design has been ‘hydraulically

short’ and size, spacing or number

of rainwater pipes insuLcient. The

calculations for correct designs are

complex, because they consider factors

such as rainfall intensity, roof area, roof

angle and parapet wall height.

I saw an example of this on a sports

centre, which had a shallow-pitched roof

surrounded by a high parapet wall. Unable

to discharge water eIectively, the box

gutters filled, causing water ingress into the

building. This was exacerbated by blocked

outlets from stray sports balls. Roof access

also required a safe working platform but

the cost limited regular maintenance.

1 2

RESIDENTIALBUILDING PATHOLOGY

is essential and problems can usually

be solved by replacing or repairing

rainwater goods. Owners may be

reluctant to change the lowest section

of a cast-iron rainwater pipe because it

is resilient; bicycles may be chained to

them, for example. In reality, if the

upper sections are defective then

so will lower parts, which should be

replaced (possibly using modern

cast-iron versions).

Cast-iron pipes can let directly into

an underground branch drain, often

overlooked in replacement programmes.

But if this is defective, water can seep

into the ground and building at low level.

Branch drains should be part of survey

and renewal programmes as they often

fail through blockages or frost action.

Leaking water pipesIn the 1960s and 1970s, it was common

to run copper heating and other water

pipes through solid floors. Denso tape

or fibrous wrapping were often not used

or poorly applied to protect the bare

copper from acidic cementitious floor

screeds; as a result they corroded and

caused leaks. When mixed metals were

joined, i.e. copper and steel, this caused

an electrolytic reaction that accelerated n

Tree and leaf litter obviously cause

blockages. I know of examples where the

bottom section of pipes (particularly when

entering a branch drain) was completely

blocked and heavy rain caused spraying of

water from each joint.

Warning signs: Leaks onto outside walls

are diLcult to detect, particularly on solid

walls when dampness may only be noticed

when it has penetrated. There may be no

internal signs on a cavity wall. If the cavity

is not blocked, leaks may stay undetected

for a long period. A good way of spotting

leaks is to conduct a survey in heavy rain.

On north-facing elevations there may be

algae under a leaking gutter joint, but on

sunny south-facing elevations, leaks are

more diLcult to see, although there may be

staining. One sign is if water falls straight to

the ground causing rain splash, especially

noticeable if it extends onto flowerbeds.

Solutions: Clearing gutters regularly

1 Broken collar and corroded section of cast iron rainwater pipe. The defects occurred due to a lack of paint protection and subsequent wetting and frost action. Often when painting cast-iron pipes, the rust is not properly removed, which will cause paint rejection and failure

2 In this flat-roof to pitch conversion, the original rainwater downpipe is still routed integrally through the building. However, the new section of rainwater pipe from the gutter external to the building was defective allowing rainwater to leak down the outer face of the building and cause water staining, which was not visible during dry periods 3 Birds drop seeds onto roofs that collect in gutters and eventually grow, blocking them and leading to an overspill of water soaking into the walls of the building below the eaves. Rainwater penetration into the habital space will occur where the external walls are solid 4 Leaking water main supply pipe under a timber suspended floor causing extensive wet rot decay. The defective section of water main was underneath kitchen cupboards. Detection was possible using a hygrometer probe and endoscope

N O V E M B E R 2 0 1 5 3 9

3

4

RICS PROPERTY JOURNAL

RESIDENTIALBUILDING PATHOLOGY

R

4 0 N O V E M B E R 2 0 1 5Images © Michael Parrett

corrosion. Gun metal was once used for

joints because it is neutral and breaks

these corrosive forces.

In the 1920s, some water mains

were made of lead, but galvanised

barrel pipes were later often laid,

many without wrapping protection.

The galvanised zinc coating acted

as a ‘sacrificial anode’ in aggressive

soils to leave bare steel. The National

Physical Laboratory has mapped UK

soil types to show those containing

metal-eating microbes, which is useful

when assessing the likelihood of

corrosion. Tree roots and desiccation

can also disturb water mains.

Warning signs: A common cause of

dampness is leaking water mains.

These may undermine foundations or

cause overhydration to create heave,

especially in areas of London clay.

When investigating a property, it is

useful to know how mains are routed in

diIerent building genres.

In Victorian and Edwardian properties,

lead water mains and drains often went

under the house (mostly from the front,

but sometimes the rear) from the isolation

valve outside the curtilage. Leaks could

soak into the fender wall of fire hearths

(that do not have damp-proof courses)

and wick up the chimney breast creating

rising damp (but not requiring a retrofit

damp-proof course to resolve it).

During the inter-war years, large

‘cottage estates’ were developed after

slum clearances. Because these houses

were publicly owned, one water main and

isolation valve typically served a terrace of

four, six or eight properties. Mains would

normally be routed alongside the buildings

(through a mid-terrace walkway or at the

end of the row), through back gardens and

then teed-oI into the properties.

Solutions: Responsibility for leaks was

complicated by the Housing Act 1980,

which allowed tenants to buy their council

home. The result is mixed terraces of

public and privately owned properties

with shared water mains. Resolving repair

responsibilities can be diLcult, because

costs are shared between the owners,

who blame each other. Knowing the

location and problems of these mains is

important, because millions of ex-local

authority properties are now held privately.

Surveyors may recommend that owners

apply to their water provider to install their

own separate water main and isolation

valve to avoid this shared scenario.

Once armed with knowledge of the

building genre, water main routes and

any shared supplies, a surveyor can

Defective water mains are often just

locally repaired. However, old pipes

leaking in one section may well begin to

leak in another. Best practice suggests

renewing the whole length of pipe.

ChimneysChimney breasts are generally wholly

internal (on a party wall, usually

back-to-back with a neighbour’s);

three-sided (wholly internal with the

fourth side on an external wall) and

projected (three sides standing out

from the building).

A chimney stack projecting through

a roof, where the roof slope terminates

at the stack, is one of the most

vulnerable parts of a construction.

Chimney stacks are usually the highest

point of a building, so are very exposed

to the elements but often overlooked

because they are diLcult to survey. A

future article will focus on identifying

problems associated with chimneys and

possible solutions.

DrainageSudden dampness can usually be related

to a defective drainage system, caused

by tree root penetration, blockages and

physical defects. Any leaks can raise the

humidity in a building and cause dampness,

especially under suspended floors.

n

5 In this Victorian property, there was dampness to the timber suspended flooring in contact with the fender wall of the hearth, wicking dampness from the oversite into the timber flooring. The discovery warranted further investigation to check for water escape from the lead mains water supply pipe, underground drainage failure, high water table, blocked sub-floor air vents and/or rubble and arisings piled up under the floor

6 Leaking integral rainwater water pipe to a block of flats. A cracked swan neck section of the pipe connecting to the flat roof drainage outlet caused rainwater to penetrate down the outside of the cast-iron pipe soaking into the surrounding ducting and part of the floor slab by way of the inter-floor fireproofing material. Integral cast-iron pipes are prone to corrosion from a condensate forming on the outer surface of the pipe 7 Copper water pipes in a solid floor screed corroded and leaked due to poorly applied plastic wrapping. This exposed sections of the pipe to the cementitious floor material leading to its perforation within eight years of being laid 8 Plastic rainwater pipe with ‘rodding eye’ access removed. The pipe was completely blocked with a mixture of silt and rust from the connected cast-iron drainage outlets to a podium roof directly above

check whether a leak exists. After the

usual internal reconnaissance of timbers,

a key question is whether an immediate

neighbour has also complained of

dampness or any sudden drop in water

pressure. If so, a leaking water main

must be suspected, but where?

A surveyor may suggest that a leak

is investigated by the water company.

An inspector will visit the site at night

(when water use is low) and use a

listening stick on isolation valves. They

might ‘hear’ a leak and then use a leak

correlator, an electronic sounding

device, to pinpoint the location.

Another check is the syphon test.

After closing the water main, put the

spout of the kitchen sink tap in a full

glass of water. If the tap starts to suck

the water out of the glass, there is a

leaking water main because the water is

being pulled back through the tap by an

escape of water underground.

6

5

RESIDENTIALBUILDING PATHOLOGY

Michael Parrett is a Building Pathologist, Chartered Building Surveyor and Founder of Michael Parrett Associates. He is an Eminent Fellow of [email protected]

Related competencies include Health and safety, Inspection, Building pathology

Tree root penetration is a massive

threat to underground pipes, particularly

vitrified, salt-glazed clay pipes but also

modern systems (some claim their

interconnecting joints are impenetrable

to tree roots, but I have yet to see this).

Roots may disturb drainage pipes and

alter their alignment.

Desiccation may unsettle drainage

during long dry periods and cause the

ground to move. A water main leaking

near a drainage pipe might cause

overhydration and heave. In either

scenario, where each section of pipe

once neatly and smoothly abutted

the next, pipes will either split or be

misaligned, causing material to collect

on these ledges and create blockages.

Underground drainage systems

constructed before October 1939

combined foul and surface water all

into a single drain, but these sources

have or should have been separated.

In older properties, everything

therefore goes through one drain.

Increasing rainfall intensity, bad habits

of occupants (such as disposing of

plastic nappy liners down toilets)

and larger buildings converted into

separate flats all mean higher demands

on these antiquated systems.

Warning signs: Common indications

include a ground collapse or dampness.

In Victorian properties where the

drainage system runs under the

building, there will be foul smells

(usually every time a toilet is used)

and often high ammonia. These

problems often arise suddenly and

tend to suggest something has

changed in a short space of time.

There may also be localised

flooding from blocked drains,

particularly in back inlet gullies next

to the external walls, where rainwater

pipes terminate. Blockages can mean

back surges with sewage appearing

in the bath, hand basins and toilets.

There may even be a contaminated

flood to the ground floor. Often,

blockages occur in interceptor

chambers and foul water will bubble

out of the top of the chamber,

regardless of its depth, together

with foul smells.

Solutions: Occupiers should be

educated about the impact of putting

waste into the drainage system.

Other preventative actions include

improving the refuse system to

allow people to dispose of rubbish

more easily.

CCTV camera surveys are

becoming increasingly important to

understand the state of drainage and

identify problems. If tree roots are

present inside drainage pipes, all

but the severest can be bored out,

using a special attachment to

allow relining.

With severe blockages, a

pneumatic steel arrowhead can

be pushed through to shatter the

pipe; a new channel can be bored

and a drainage pipe pulled through.

Excavation and complete renewal

may be the only other option.

A surveyor’s approachSurveying buildings for dampness

should be a holistic process and

surveyors should move from

recognising a symptom to diagnosing

its cause and source. This series

on common causes of dampness

illustrates that a failed damp-proof

course should be the last thing

suspected. It will usually be any

one or a combination of these

other causes.

Achieving a professional opinion

on the source of dampness

means improving knowledge and

understanding of building failures

through the various building genres,

and the techniques and equipment

used as part of an overall process

that is called building pathology. R

More information >

BS EN 12056:3-2000 Rainwater drainage design

http://bit.ly/1KgLgFo

Diagnosing Damp; Ralph Burkinshaw & Mike Parrett

http://bit.ly/1G2tEsb

Mike Parrett’s guide to building pathology

http://bit.ly/1zeIO7X

N O V E M B E R 2 0 1 5 4 1

87