Survey says sub floor ventilation is inadequate and needs more airbricks. How likely is it that the timbers below have got dry rot and how much to rectify?

[what4your]

Particularly concerned that dry rot/any rot may have been caused by this lack of ventilation.

Is this likely? And if so, how much to fix?

Thank you.

1. you won't know until you look, but signs of rot should be evident in the floorboards and skirtings. Dry rot smells.

2. thousands

I have a feeling this is a house you are thinking of buying. Older houses usually have insufficient airbricks, and those they do have are often choked with cobwebs and dirt, so the surveyor could have inserted the standard text even before he looked at the house. If somebody has built an extension or porch which obstructs the original airbricks it will be even worse. One every two metres all along each external wall, so there is airflow, is about right. A builder or bricklayer can easily do it, but the floor needs to come inside up to make clear passage.