Japanese knotweed
Decking covers the spot where a knotweed crown was previously drawn. Has this survey lifted the boards?
No. This survey has not lifted the boards. Decking covers the spot where a knotweed crown was previously drawn, and the boards stayed down. The crown was not exposed on this visit. An earlier drawing is not an excavation done today, and it does not prove the crown is still there or has gone. The survey records the covering. It has not seen the ground beneath, has not dug for rhizome and has not decided what remains under the deck.
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?
Decking hides soil. A crown marked on an old plan may sit under a board, may have been removed when the deck was built, or may never have matched the ink. None of that can be settled while the boards stay down. The survey does not lift decks in an ordinary inspection and did not lift this one. What the earlier drawing marked is unverified. The covering is the whole of the finding.
Tell the solicitor about the old drawing and that this survey did not lift the decking. Ask the seller for any management plan or guarantee that mentions this spot. A knotweed specialist can advise whether the boards should come up. The survey has not instructed that and has not told a lender the crown is absent. Do not describe the deck as clearance.
What should you ask your surveyor?
- Who drew the earlier crown, and is that drawing in the pack?
- Was any board already loose so the soil could be seen?
- What specialist look would be needed under the deck?
What are the typical next steps?
- Tell the solicitor the boards were not lifted.
- Ask the seller for any knotweed plan that mentions this spot.
- Do not describe the covered ground as clear of a crown.
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
Does the old drawing prove the crown is still under the deck?
No. A previous drawing shows where someone marked a crown then. It does not prove the crown is still there, and this survey did not lift the boards to check. The deck covers the spot. Treat the drawing as history. The ground underneath was not seen, so presence and absence are both unproved.
Can a herbicide log replace a look under the boards?
No. A log records treatment visits, if you have one. It does not show the soil under decking this survey left in place. Treatment paper and a covered crown are different evidence. The boards were not lifted, so the log cannot stand in for that look. A specialist would have to deal with what is hidden.