SAS Urban Survival Handbook (6 page)

Marshy ground

Whether the building is built on known marshy ground, possibly on a valley floor or foot of a hillside, or in close proximity to a river or lake, it must be expected that problems will occur. New buildings should be built with the possibility of gradual sinking taken into account. Underground rivers or bodies of water may be harder to detect.

Mining

Mining or tunnelling. Dramatic settlement may be expected when mining has been close to the surface. This may not be a gradual process—numerous instances of sudden subsidence have been reported. You should know if your area was once or is still being mined.

Sloping ground

Building on hill and mountain sides may be no problem at all. All over the world there are buildings which have stood in precarious positions for centuries. However, there are also numerous instances of sudden collapse, usually associated with mudslides after heavy rainfall.

Landfill

Much depends on the quality of the landfill. All sorts of problems have been reported, from sudden subsidence to underground explosions of decaying matter. These are impossible to predict. There is also the possibility of toxic substances percolating up through the soil.

SUBSIDENCE AND SETTLEMENT

All buildings settle in response to movement in the earth and expansion and contraction of their own structure. This can produce sloping floors with doors, windows—even walls—out of alignment. Many old buildings survive like this for centuries—think of the Leaning Tower of Pisa.

Any new or sudden movements, generally indicated by a crack of growing length or width, or creases or splits appearing in wallpaper at corners, should be investigated. Recent very dry, hot summers in temperate countries have dried out soils and greatly increased the number of properties affected by subsidence damage.

Any crack, especially a new one, should be investigated—or even monitored over a period of weeks or months to ascertain the cause. Don’t assume that the building is falling down—but don’t ignore the cracks either. Monitoring may involve marking the crack in some way to work out the direction of movement. A crack in an external wall will let in damp and this could lead to further problems.

Consult an expert such as a surveyor or a professional builder. Your insurance company may be able to advise, but many policies do not allow for the effects of subsidence and settlement.

WARNING

Climbing plants, particularly ivy, should not be allowed to scramble unchecked over the outside of a building. If the walls are in good condition or the bricks and mortar are new, there should not be much problem. The aerial roots will invade bad joints or cracked rendering, expand and severely weaken a wall. Eventually, the weight of old plants (stems can grow as thick as your neck!) could pull a wall down.

Care should be taken to avoid ivy invading the spaces around the eaves of the house, spaces between slates, tiles, flashing and weatherboarding. As the roots and stems expand they will open up any crack they can find. Remedial treatment may be difficult if the situation has got out of hand.

OUTSIDE CHECKS

Take a critical look at your home from outside and in. Make use of a neighbour’s upper windows to help you see the roof. Use binoculars if you can. The most serious damage could lead to collapse of all or part of the building, but anything which lets in rain or damp can start a chain of problems. Paint and other decorative treatments have a vital function in protecting wood and other materials, and require regular upkeep.

Roof

No roof covering is expected to last forever. The effects of the weather and conditions inside the roof space will take their toll. Look for sagging (drooping) roof lines. This may only indicate that, over a long period of settlement, the external walls have stood firm while the internal structure has ‘sunk’ slightly. This may not be serious. However, timbers may be decaying because of inadequate weatherproofing, condensation in the roof space or even infestation of wood-boring insects. Sometimes a new roof covering may be too heavy for the old timbers, or new work—such as a loft window—may be inadequately braced.

From the outside, try to find a good vantage point such as a neighbour’s upper window—use binoculars from the ground. Look for deformation of the shape and slipped tiles or slates. The latter may be due to failure of the nails holding them in place and could be progressive.

From the inside, working with a good light (and strong boards across the joists when there is no attic flooring) look for damp and rot. Its location may help pinpoint external problems. It may also be due to condensation in the roof space. All roofs are designed with some ventilation, usually at the eaves, to allow the space to ‘breathe’.

Wood-boring insects can do very considerable damage if allowed to colonize the roof space. Badly-infected timbers may have to be cut out and replaced. However serious the infestation, all internal timbers should be treated.

Lead roofs are vulnerable to the extremes of climate. Repeated expansion and contraction will crack the lead, resulting in further problems. Avoid long runs of lead which accentuate the problem.

All flat roofs must have good drainage. Most felt roofs will blister and trap water, but more damage is done by walking on them, or resting ladders on them, than is done by the weather. Cracked or leaky felt may only need to be painted with a new protective coating. Consult a local supplier.

WARNING

When insulating the loft space, do not carry the insulating material too far into the eaves. The loft needs to ‘breathe’ and you must not cut off or restrict its air supply. To do so could result in a build-up of condensation, which could lead to rot. This problem is particularly aggravated by ‘magic’ roof paints, used to seal and secure old slate roofs. This thick coating seals in the slates (trapping moisture which was present at the time of application) and could lead to far more serious problems than those you were trying to solve.

Chimneys and flashings

Flashings round roof edges and the base of chimneys always cause problems, but chimneys are at risk from inside as well. The soot contains acids, which eat away at the fabric of the stack. Pots on the top are set in mortar (known as flaunching). This may break up over the years, allowing pots to fall. Chimney stacks have been known to fall, sometimes onto the roof and thereby down into the house. Check your chimneys!

Gutters and downpipes

Leaks are easiest to see when it’s raining—you may be able to use a hose to produce the same effect. Look for stains on the wall, algae growing round brackets and joins. Plastic guttering is notorious for drooping or failing if the runs between retaining clips are too great. Drooping can cause otherwise secure seals to fail. Cast iron and aluminium guttering are subject to rust and corrosion (respectively).

EFFECTS OF CLIMATE

Pay particular attention to the sides of your house which face the prevailing wind or receive the severest ‘baking’ from the sun. Heavy rain, driven by strong winds, will find its way into all sorts of cracks and crevices. Flashings may be lifted by particularly strong gusts. Rain may be driven underneath roof coverings.

Strong sunlight gradually cooks paint and breaks it down. You will always have the worst problems with woodwork on the ‘sunny’ side of the house. Black and dark paints suffer most, because they absorb the heat.

The weight of a heavy snow fall may be too great for weak roofs and gutters to bear. Freezing temperatures will freeze water which has penetrated cracks and crevices, causing them to expand and let in more water. Remember, water bursts a frozen pipe indoors and can do the same to blocked downpipes outside.

Blockages, such as leaves, twigs and birds’ nests can cause water to sit in the gutters for long periods of time instead of racing away as is intended. Settlement of the house may mean that gutters, originally sloping to allow water to escape, no longer do so.

Leaky overflows, if they have persisted for a long time, will usually make a stain on the wall or the ground below. In winter a leaky overflow may produce a deadly patch of ice. Check the tank!

Walls

Look for horizontal or vertical distorting, eroded mortar between brickwork, cracked rendering, missing tiles or other cladding, soil or other obstructions covering the damp-proof course, blocked airbricks. Sulphates in some kinds of brick (and in chimney soot) can cause mortar, rendering and concrete to expand and crack. Areas looking damp when the rest of the wall has dried may indicate where old bricks, which have become porous, are located.