Can Rats Climb Walls? Brick and Pipes, Yes. Glass, No.

Yes — easily, on anything with texture. A brown rat can run up brick, breeze block, stone, render, stucco and timber cladding without slowing down, climb the inside or outside of a drainpipe, and cross a wire or a branch to reach a roof.

What stops them is smooth: glass, glazed tile, polished metal, clean uPVC.

What a rat can physically do

The 20mm figure is the one that matters for a house. The skull is the limiting dimension; if the head passes, the body follows. And a gap slightly too small is simply a gap they will gnaw larger.

Mice need about 6mm, so a house sealed against rats is not sealed against mice — and mice climb just as well, including up trees and into roofs.

Brown rats and black rats climb differently

• Brown rat (Rattus norvegicus) — the common one in most of Europe and North America. Heavy, burrows well, lives low: drains, foundations, decking, compost. Climbs competently.
• Black rat (Rattus rattus) — lighter, more agile, a genuinely excellent climber. Where present, this is the one in the loft, running along beams and cables.

Rats in a roof space are not evidence of a structural hole at roof level. They very often climb the outside of the building and enter under a loose tile or at a soffit gap.

How they actually get in

• Airbricks and vents without metal covers
• Gaps around pipework where it passes through a wall
• Under doors with a worn threshold seal
• Soffit and fascia gaps, and lifted roof tiles
• Drainpipes, climbed inside or out
• Damaged drains — a broken pipe in the garden is a direct route
• Overhanging branches and wires touching the roof
• Ivy and trellis on a wall, which is a ladder with cover
• Under decking, then up into a cavity

Sealing, so it works

Work through the building methodically:

1. Survey at ground level on hands and knees, all the way round. Most gaps are below knee height.
2. Seal everything over 20mm with steel wool plus mortar or metal sheet.
3. Cover airbricks and vents with fine stainless mesh — never block them, which causes damp.
4. Fit metal guards to drainpipes, or a smooth collar that removes the grip.
5. Cut branches back at least 4 feet from the roof, and remove ivy from walls.
6. Fit bristle strips or metal thresholds to door bases.
7. Check the drains. A cracked pipe or a missing rodent barrier is a common and invisible route.
8. Board or mesh the skirt of decking, buried a few inches into the ground.

The full set of measures, and what the evidence says about the repellents sold for this, is in rat deterrents for the garden.

Remove what brought them

Exclusion holds; food is what makes them keep trying.

Bird feeders are the most common single cause in a garden. Spilled seed under a feeder is a reliable nightly meal. Use trays to catch spillage, sweep underneath, and take feeders in at night if you have an active problem — the same discipline as squirrel-proofing, for a different animal.

Also: pet food left outdoors, unsecured bins, fallen fruit, chicken feed, and open compost with cooked food in it. A sealed compost bin with only plant material in it is not a rat attractant; an open heap with kitchen scraps is — see building a compost bin.

Shelter matters less than food but still counts: woodpiles against walls, dense ground cover, long grass and rubble.

On poison

Rodenticide without exclusion produces a temporary dip and then recolonisation, because the route in is still open and the food is still there.

It also carries costs worth weighing: secondary poisoning of owls, foxes, cats and dogs that eat a poisoned rat, and the near-certainty that at least one rat dies inside a wall cavity, which is a smell that lasts weeks and cannot be reached.

Traps are more controllable. Professional control is worth it for an established infestation. But neither is a substitute for closing the gaps, which is the only part that lasts.