I smell a rat!
8th October 2013
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Visit any high street DIY store and you will see an impressive range of vermin repellent products giving you an indication of a booming market and problem every building surveyor and property manager needs to be acutely aware of.

What is the problem?
Rattus Novegicus, aka the Norway or brown rat.
Rat numbers are on the increase as human population densities increase, warmer and wetter weather prevails and our nations increasingly slovenly refuse habits provide a constant food source. The presence of rats in types of properties from residential through to commercial can lead to very serious problems.  Property owners and advisors need to be informed of these risks and given the appropriate recommendation for resolution from their property and construction advisors.

Biology, life cycle and habits
Rats are active mostly at night. Although they have poor vision they have a highly developed sense of smell, hearing and touch. Unlike other rodents rats have a strong need for water.
Rat’s are inquisitive animals and love to explore and learn, memorizing the locations of pathways, obstacles, food and water, shelter, and features of their environment.
Rats can gain entry into buildings by climbing, jumping, or swimming and especially through sewers and entering through toilets or broken drains. Young rats can squeeze beneath a door with only a 13mm gap
Rats eat many types of food from cereal to grains, meats, fish, nuts, and rarely travel more than 50m from their burrows or nests. 

Structural and cosmetic damage
Rats have very hard front teeth that never stop growing and with their genetic compulsion to gnaw will cause damage to the fabric of any building they occupy.
This ranges from minor holes in walls, doors, furniture, cupboards through to structural collapse, flooding, electrical faults and fire (due to gnawing through cables).
The author has witnessed 3 core insulated lighting cable in suspended ceilings gnawed through to the exposed copper. There is some anecdotal evidence to suggest rats like the slight warmth given off by conductor cables from the current flowing through it.
It is estimated that 7% of house fires are caused by rats; yet very often traditional buildings insurance does not cover damage caused by vermin.

Things to look out for
  • Rat droppings are on average 12mm and spindle shaped.  House mouse droppings are much smaller, 3-7mm in length
  • Indoor Smears – grease marks from the rodent’s body as they repeatedly brush up against objects
  • Nesting material — shredded insulation, paper, cardboard, plastics, etc.
  • Digging scratching and burrowing marks
  • Blocked and sunken drains provide an excellent food source for the remarkably un-fussy rat though, not least before you consider who much fat and left over food is also flushed through our drainage system each day. Be particularly wary of drains running directly under properties
  • Similarly leaking water pipes provide the fresh drinking water rats have a high demand for
  • Unsealed penetrations into the property.  Holes into suspended floors and cavities provide a perfect route for rats to enter and nest within a property
Rats are incredibly resourceful and will eat pet food, feed from bird tables, burrow into compost bins, climb into dustbins (particularly as local authority refuse collections decrease in frequency), unsealed household recycling bins and generally feed on all edible street litter from take-away food restaurants etc.

Control measures
Despite the booming market of vermin deterrent products for sale on the high street, in most instances control should only be undertaken by professionals trained in the handling of poisons and dangerous and powerful rat traps that can cause very serious harm and or death to other animals and persons.
Rats are highly skilled at detecting and thus tend to avoid new objects and novel foods and they often avoid traps and baits set by the novice.  Any bait or traps that have come into contact with humans (by handling) will be immediately detected by a rat and very often completely ignored.
The most successful trap is the old fashioned “sprung / snap” rat trap. The recent proliferation of high street deterrents such as glue traps, sonic repellents etc are likely to be less effective than snap traps and are generally aimed at giving the general public some relatively safe options with varying degrees of success before more professional options are considered.
An alternative approach to traps is the use of Poisons. These range from fast acting highly toxic poisons to more slow acting (anti coagulant) poisons delivered over a number of days.
The rats’ adaptability to change though is highlighted by their response to Warfarin used as a rat poison but which is now declining, because many rat populations have developed resistance to it, and poisons of considerably greater potency are now available.
These poisons can be used locally for specific rat problems or placed over wider areas (usually by the Local Authority or Water Sewage Company) though baiting local sewers on a commercial scale.
The most successful deterrent is exclusion
  1. i.e. sealing all obvious holes, gaps and openings within a property. This includes all holes greater than 5mm in diameter and because rats are excellent climbers for the full height of the elevation of a building and especially at the roof line.
  2. Wire wool is useful for plugging many holes to deter rats and prevent gnawing
  3. Remove vegetation growth that can attach directly to the house such as climbing ivy or tree branches
  4. Place rat guards on pipes and gutters leading up to the house
  5. Place sturdy screen around vents and openings. The mesh size should measure no more than 5mm
  6. Repair gaps in sewer lines and other pipes leading to the house
  7. Place sturdy coverings on drain holes
Spencer Carroll MRICS
Lighthouse Chartered Building Surveyors
About the Author

Andrew M

Member since: 10th July 2012

The Best of Wimbledon and Merton helps to bring all the best local information to all local residents and businesses throughout Wimbledon and Merton. We also bring trusted businesses and the community...

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