Tips on dealing with subsidence, rising damp, and dry rot

Subsidence in an old building can be indicated by long, wide cracks.

Rising damp will make other damp problems worse — and mould is a key indicator.

Dry rot can take hold in warm, unseen parts of a building and can be difficult to see for some time.

Subsidence, rising damp, and dry rot are the big three when it comes to bad news about your home, but there are some cracks that you should simply never paper over. Let’s stare these villains down and take a look at the options in dealing with such daunting challenges.

SUBSIDENCE

Subsidence is downward movement in the supporting structure of the house, its walls and foundations. With even a slight sag below ground, small signs become apparent above ground, and they can be discreet. The earth under the house may have slightly given way because of the soil make up, or because of underground water activity from drains or subterranean streams.

Trees with roots too close to the foundation may be leeching the moisture from clay soils around the foundation, causing the earth to shrink and become unstable. Sometimes the removal of a tree can also alter the amount of water held below ground. Most apparent indications of subsidence turn out to be natural settling cracks, seasonal changes or shoddy workmanship, but don’t ignore that sinking feeling.

Signs:

* Cracks in the render or brickwork more than 3mm wide.

* Discreet cracks in plaster indoors 1mm wide or more, that may get wider over time or creep in lightning bolts up the walls.

* Doors to rooms, built-in cabinets and windows sticking for no obvious reason, floors lifting or skirting popping off.

* Floors appearing uneven to the eye (roll a marble across the floor if you think it’s just that last glass of Merlot). Solutions: The buildings section of your house insurance should cover you for ‘subsidence, land heave or groundslip’, and once informed, insurers will send a chartered surveyor and structural engineer, if needed, to assess the situation. Historically, subsidence is hard to prove and a chartered loss adjuster or experienced structural engineer can help to fight your claim. It’s vital that underground repair work is carried out, rather than damage being superficially patched up on the house. Most proven subsidence can be dealt with by strengthening the ground with mass concrete underpinning or what is termed ‘pressure grouting’ as well as dealing with leaking subterranean drains. Keep all certificates following works with your essential paperwork. Insurance claims for subsidence generally carry an excess that’s higher for buildings over 10 years old. If the area is known as a black spot for subsidence, or a former claim was made, insurance companies may exclude this in the cover offered to you.

RISING DAMP

Penetrating ‘horizontal’ damp through a leaking gutter, a thoughtlessly buried floor vent, a slipped tile or a broken shower tray — a competent handyman will be able to sort these damp squibs. However, rising damp is something of a mystery. Modern houses have a horizontal damp proof course (DPC) and membrane (DPM) under the floor. This is an impermeable layer of plastic or a slate strip that stops ground water rising vertically from the wet earth below. If this layer is compromised, allowing the wet to jump to the unprotected courses and render, the DPC is broken or just not there, and moisture can be pulled up the walls by capillary action.

There’s a lot of debate as to whether rising damp is the main culprit in a damp house. As a contributor, rising damp will make other damp problems, caused by penetrating damp and inadequate ventilation, (condensation, cold, poor air quality, and ruined finishes), worse. Rising damp, other than repair after flooding, is not covered by home insurance.

Signs:

* Damp patches on walls close to the floor. This may appear as a tide mark.

* Paper on walls lifting, paint powdering off. These are soluble salts pulled up by capillary action out of ground water and left as the damp evaporates. nBlack mould, fungus-like growths.

* Damp patches on exterior walls where the DPC has become buried under ground. nSkirting and flooring warping and lifting. Solutions: If it’s just a matter of a buried DPC, a local builder will be able to dig it out to 150-200cm or deal with a minor ground drainage problem. You may even find one spot causing issues indoors and spade it out yourself. If the DPC is non-existent or compromised, a damp proof silicone cream can be injected through regularly spaced drilled out holes in the exterior leaf by a reputable, specialist company. Quotes are by the metre plus some decorative repair inside and possibly out. Get independent advice, as it’s too easy for a remedial contractor in these straitened times to get you on the back foot with a bleating moisture meter on a cold wall and a firm assertion that “yes, it’s rising damp, you need a new DPC”.

Damp issues may be resolved by a visit from the plumber, improving insulation in the walls, or through fixing, say, pointing problems on the roof, (gaps between tiles), or in the flashing, (where the roof meets the chimney). Ensure you are not paying for more than you need. Proven rising damp that comes straight up through flooring will demand a dedicated DPM.

DRY ROT

Wood rot is a terrifying prospect to all but the stoic period property dweller, immersed in issues of decay all their lives. Even in a stone or concrete building, wood forms a vital part of floors, partitions, and the roof. Rotting timber must be dealt with immediately whatever the cause. Oddly, wet rot is less invasive and less serious than dry rot. Both are caused by a fruiting fungus that lives on decaying wood, pushing their thread-like mycelium through the timber’s fibres, softening and destroying its structural integrity. Neglected wood windows and doors will rot, this is standard wet rot and you’re faced with replacing parts of, or the entire element.

Dry rot tends to get hold in the warm, unseen parts of an older building, inside walls, beneath stairs, in roofs and under floors. It requires at least 20% moisture in the timber for Serpula lacrymans to have a party and dry rot has a particularly sinister talent for jumping across other materials blocking its advance to more wood.

Signs:

* Wood that crumbles on poking.

* Matted whitish growth with lilac and yellow strands.

* Pancakes of fungus- nasty stuff developed over a long time.

* A thick, mushroom smell.

Solutions: Now you’re faced with two challenges. First of all, dry rot needs wetness to thrive, so the damp must be followed to its source and resolved. Secondly all the infected timber must be removed, destroyed, and replaced. This will generally demand wood coming out at least 60cm either side of any signs of rot. If this is a joist for example, the whole joist is probably doomed. Timbers close by will be treated with a fungicide to ensure their protection from any lingering spores. Dry rot is not covered by house insurance as it is considered a ‘gradual cause’. The price of treatment and repair by a specialist will depend on location and spread.