I'm not an expert but have done a lot of 'research' into my own situation.
It seems like a valid option. The reason I ask if the outdoor area is heated is that subfloor ventilation usually relies on dry cold air circulating in the winter so you would get a draft in the lean to area which would...
its a common problem where there ventilation to suspended timber floor blocks off ventilation.
The normal solution is to add more air bricks around the sides of the house - but this wouldn't be possible in a e.g terrace house.
New extensions may require laying of a vent and pipe to the subfloor...
I note that this is a subject that comes up now and again.
Bought a 1930s house early cavity wall which had new uPVC windows installed 5 years ago including two big L shaped bays downstairs and upstairs. They are offset so that the bottom floor has a little flat roof above.
As the house is...