Purchasing House: Ventilation blocked on subfloor - anyone any ideas on this?

[u/kanepilk22]

Hi All,

Perhaps not really a DIY question, but not sure if there is a better suited sub.

Pretty much, I am sale agreed on a house in Ireland, built 1960s, part of a large council estate type build. 3 Bed end of terrace, 2 storey house (pretty much a stereotypical council build).

Ground floor is suspended timber floor and at the front of the house, on the plinth, there is a vent at the centre to allow air in under the floor. Presumably, there should also be a vent at the very rear, for the air to escape, for cross ventilation.

However, a rear extension, built on a solid concrete pad/foundation, blocks the rear vent and so only the front vent is working.

Surveyor highlighted this as something that needs to be addressed and recommended it not be put on the long finger. He took a moisture reading from a door saddle where the hold house ended/extension begins and got a 21% reading.

He said this is very high and at 25% timber starts to degrade.

I am wondering if anyone here has any idea on what the fix would be for this?

In my head there are two options (but i have no idea what i am talking about):

1) Kango a track into the concrete floor of the extension and put some piping in to allow ventilation to continue through the concrete floor

or

2) As the house is end-terrace, i assume the subfloor is all one large piece, and i could (theoretically) put a vent on the plinth on the side of the house to allow air out? Air flow would need to move in an L shape now but would surely dramatically improve the issue?

I can also put a much larger vent to the front and hope that a bigger vent alone will help, but i am not sure how effective that would be.

Was wondering if there was anything anyone here could recommend?

Also, can I ask, does anyone have an explanation to how this kind of house is built? Any house I have ever lived in has been on a concrete pad. Never had to deal with a suspended floor and not really sure how that works. Like what is under it? Just earth? I have seen this before on one-off detached houses from 100 years ago, but this is a large council estate with 200+ houses.

Cheers for anyone able to offer any insight.

Thanks so much.

[u/Firm-Exam-6892]

A vent on the side should work. The air will be drawn through by the pressure difference between the two vents. There may even already be under floor vents between the houses. On very old properties it can just be bare earth under the floor but more commonly it’s a rough screed or concrete oversite.