Damp and moisture meters
A stain under a window lines up with a cracked sill and the floor is dry. Which defect should be read before any injection?
Read the cracked sill before any injection. The stain under the window lines up with that crack, so the defect in front of you is a sill that can let rain in at the opening, not a diagnosis that the wall needs a chemical damp course. The floor is dry, which does not fit a general rising path across the room. The survey has recorded the alignment of stain and cracked sill, and a dry floor. It has not specified injection. Treating the wall chemically while the sill still admits rain would ignore the defect the stain is pointing at.
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?
Rain hits a sill first. A crack through it, or through the joint under it, gives water a route to the wall beneath the window, which is where this stain is. That is penetrating damp at a defective sill. Injection is aimed at moisture rising from the ground through the base of a wall. A dry floor and a stain parked under one window do not describe that pattern. The survey saw the line-up. It did not specify a chemical, and it did not say the damp-proof course had failed.
Ask a builder to repair the cracked sill, and to check the joint under it, before anyone prices a chemical treatment. Tell the solicitor the stain lines up with the sill and the floor was dry. If a damp contractor recommends injection, ask them to explain the dry floor and the cracked sill in writing. The survey has not specified their product. Sorting the sill is the defect to read first. A chemical does not close a crack in the sill outside.
What should you ask your surveyor?
- Does the stain line up with the cracked sill?
- Was the floor dry, and has injection been left unspecified?
- Is the sill the defect to read before any chemical treatment?
What are the typical next steps?
- Read the cracked sill before any talk of injection.
- Ask a builder to deal with the sill and the joint under it.
- Do not accept a chemical specification this survey did not write.
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 sill is stone, does the crack mean the lintel has failed?
Not on this note. The defect to read is the cracked sill under the stain, with a dry floor. The survey has not said the lintel has failed, and it has not specified injection. A stone sill can crack on its own. Do not merge the sill crack into a lintel failure that was not written.
Does a dry floor mean there is no damp at all?
No. The floor being dry steers you away from a rising path across the room. It does not erase the stain under the window. That stain lines up with the cracked sill, which is the defect to read before any injection. Local rain entry at the opening can exist while the floor stays dry. The survey has not specified a chemical treatment.