We have had a mauldy smell in the house for some time.
A surveyer representing a damp company visited he sugested more air bricks to better ventilate the wood floor and alco advised installing a ventilation fan into the kitchin and bathroom.
I am considering this at the moment, however he only spent five minutes in the house.
Points that may help diagnosis.
The house is mainly cavity brick with a render, this does sound hollow in places when tapped.
We had double glazing installed two years ago and this does not have any ventilation vents fitted.
We have arranged cavity wall insulation to be fitted next week
The main problem seems to be in the kitchin.
We have just been away for three daya and the smell "hit-us" as we entered the house it was terrible all on the ground floor
contact the people who fitted your windows and ask if they can install trickle vents in the kitchen windows.
These vents will air the room and is quite an easy job to fit rather than installing clay vents in the wall.