Every year there is one week where the phone changes. The ant and wasp calls stop. The rodent calls start, and they do not stop until spring.
It is the first properly cold week, which in the Lower Mainland usually lands in September. The activity curve on our rodent page peaks September through November, and that window is also when the fix is cheapest, because the population moving in is still small and the routes it is using are new.
Why this region is different
Rats do not get knocked back here. A prairie winter culls a rat population every year. A wet Fraser Valley winter sitting a few degrees above freezing does not, so the numbers going into autumn are roughly the numbers that come out of it. Mild springs and a long berry season do the rest. The pressure never really resets.
Geography then decides the route in. Richmond, Delta and Pitt Meadows sit on drained delta silt close to sea level, so a heavy week floods burrows and pushes Norway rats up out of the ground and straight into crawlspaces. Older stock in Newton and Whalley has crawlspace vents and service penetrations from an era when nobody screened them. New Westminster has century-old balloon framing, which gives a rodent a clear run from a basement to a top-floor ceiling without crossing a single room.
The number that matters is 6 mm
The HealthLink BC guidance is to seal any gap in the building exterior larger than 6 mm, about a quarter of an inch, and to cover crawlspace, attic and fresh air vents with 6 mm metal screening or steel mesh.
That is not a cautious round number. A house mouse gets through a gap a little over a centimetre. A rat gets through anything wider than its skull, which is roughly 20 to 25 mm, and it will widen a smaller gap by gnawing. Steel mesh matters for the same reason: rodents chew through plastic, rubber and expanding foam.
Where those gaps actually are, in the order we find them:
Almost none of that is about how old or how clean a house is. New builds in Surrey get rats through an unsealed gas line penetration in their first autumn. It is the state of the openings that decides it.
The poison you are picturing is no longer legal in a house
British Columbia made its restriction on second-generation anticoagulant rodenticides permanent on 21 January 2023, under a revised Integrated Pest Management Regulation. Those are the fast, potent products most people mean when they say rat poison.
They are now prohibited for residential use and for most commercial use. The exemptions cover organisations designated as essential services, which is a defined list including health facilities, food production, and water and power infrastructure, plus agricultural operators. A licensed company working for one of those still has to build a written rodent management plan on IPM principles, cap a baiting cycle at 35 consecutive days and 120 days in a year, and document all of it.
So if somebody offers to sort out the rats in your house by putting down the strong stuff, they are describing work they are not allowed to do.
The practical argument lands in the same place, and HealthLink BC puts it plainly: traps are the best way to get rid of rats or mice. A poisoned rodent walks off and dies somewhere you cannot reach. That is a smell in a wall cavity for weeks, and a secondary poisoning risk for whatever finds the body first, which in this region is often a neighbour's dog or an owl.
Sealing first, and why the order is the whole job
Rodent work that skips the sealing is a subscription.
You can trap out everything currently living in a crawlspace inside three weeks. If the dryer vent is still open when you finish, you have bought yourself until the next cold snap. So the sequence is find every entry, close it, then remove what is already inside.
Traps and tamper-resistant stations then go on the runs the inspection found, which is why droppings along one wall are worth photographing rather than sweeping. That line maps the route they use nightly, and a trap set two metres off the run catches nothing at all.
The other half is what is feeding them. Compost and green bins locked. Fallen fruit picked up. Bird seed and pet food out of the original bag and into metal or rigid plastic. Ivy and blackberry cut off the building, hedges cut clear of the roofline. A roof rat uses a branch as a bridge, and removing the bridge costs nothing.
What to do in the next fortnight
Walk the outside of the house with a torch before the weather turns, then go into the crawlspace and look for daylight. You want torn vent screen, a dryer flap that does not close, and any gap you can push a pencil into.
Fixing four of those in August costs you a Saturday. Finding them in November, after something has already pulled insulation into a nest beside the hot water tank, costs a good deal more than that.
If there is activity already, it is the same inspection either way. The rodent guide covers the species, the signs and how a treatment runs, and there is a separate post on telling a rat from a mouse if you are not sure yet which one you have.