Timber sub floor ventilation on only one side of house, install slab instead?

[AL_1234]

Hi,

I recently moved into a terraced house where there is a extension at the back covering the vents for the front and middle rooms so i only have 3 vents at the front of the property, there is no way to get vents at back any more. i have no damp problems at the moment (well none i know about yet), i know this lack of proper ventilation will eventually cause problems, better to act now.

I am about to renovate the rooms and they are being stripped back to brick.

Do i either put a concrete slab removing need for ventilation or do i use some form of ducting and a mechanical ventilator to force air to the back of the cavity. Doing either raises several questions

A) concrete slab
q1) if i put a slab down will this mean it just forces any moisture up into the walls as pretty sure old house has no DPC and relies on airflow to keep walls dry.
q2) what do i do with internal load bearing stud walls, they currently sit on dwarf walls and rely on ventilation, do i build mini foundations and a run of bricks with proper DPC that stud wall can go back on, this would mean holding up the studwall some how while that is done..and i am only removing plaster on one side of these walls so not easy
q3) how does the slab join into the wall to avoid damp coming up this boundary?
q4) do i need to inject DPC into all walls around this new slab to stop and damp being forced up thsi route?


B) Keep Suspended timber floor
q1) will a mechanical ventilator be good enough? what type should i use?
q2) am i just delaying the inevitable and i will need slab eventually.
q3) i haven't seen anyone in UK who offers such a service, know anybody?


really appreciate any view on this

A

 

[John D v2.0]

If you're lucky, the people who built the extension will have piped the existing air bricks out the new floor. These may well have been subsequently blocked by ground being build up behind the new extension, but check first.
I tested our air bricks by blowing a fan into the floor void and running round feeling the air bricks outside. I found the one that looked like it might have been piped through the porch was actually just for decoration. The conservatory ones were similar.

 

[AL_1234]

Sadly not, i have lifted the floor boards at the back of the house and the vent is directly sealed by the concrete of the extension

 

[endecotp]

You'll want some insulation under your slab. Celotex and/or kingspan have some docs about how to do this, which mention where polythene layers should go and what to do at the edges.