Japanese knotweed
A new patio has been laid where knotweed was treated. Can the survey see rhizome through the slabs?
No. The survey cannot see rhizome through the new patio slabs. Rhizome is the underground growth. Slabs, bedding and a new surface hide it. A clear patio on the day of inspection shows the surface, not the ground beneath. Treatment beforehand does not make the buried plant visible, and it does not let the surveyor confirm that treatment worked. The report can say a patio is there, where you were told knotweed was treated. It cannot see through the slabs, and it should not be read as a clear test of what remains underneath.
Last reviewed 24 October 2026. Written for buyers in England and Wales unless this answer says otherwise. No named surveyor has signed this page. It is general guidance, not a report on your house, and not legal advice.
What is the fuller explanation?
Home surveys do not lift a newly laid patio to hunt for rhizome. Even a knotweed specialist would need a way of inspecting soil, not a glance across slabs. If shoots are absent above the patio, that is all you know about the surface. Dormant rhizome does not have to show on a Tuesday visit. Do not let a seller's treatment account, without soil evidence, become a finding that the ground is clear. The slabs are the reason the ground was not seen.
Ask what documents exist for the treatment: whose land, which area, and whether the patio was laid over the treated ground afterwards. A plan that stops at the edge of the slabs is not a view under them. GOV.UK expects knotweed not to be spread. Until someone inspects the ground properly, write that the rhizome was not visible because it could not be seen, not that it was gone.
What should you ask your surveyor?
- Did you see any growth at the patio edges, or only clear slabs?
- Were you told the treatment area, and does it match the new paving?
- What can you not say about rhizome because the surface was covered?
What are the typical next steps?
- State that the patio hides the ground where treatment was claimed.
- Do not read a clear surface as proof the rhizome has gone.
- Ask for the treatment papers before anyone lifts or moves that surface.
Costs vary with the building and with who you instruct. Where this page does not cite a published figure, ask the surveyor, a relevant specialist, or your solicitor for a written quote. Do not treat a forum average as the price.
Also asked about this
If the slabs look new and tidy, is the knotweed finished?
No. Tidy slabs do not show rhizome. The survey cannot see through them, so the ground is unconfirmed and treatment is not proved by the surface.
Can the surveyor scrape a joint and call that a rhizome survey?
No. A joint is not the treated ground. Rhizome under the patio stays unseen without a proper look at the soil beneath the slabs.