My planned underfloor insulation and airtightness work has stalled due to suspended wooden floor timbers showing high moisture readings, mostly in the front wall of the original parts of the house (which happens to be south facing).
I’m slowly addressing some of the problems identified, but improving airflow before insulating isn’t proving as simple as it sounds.
The house is detached with filled cavities on E/S/N walls. The W facing wall has a finger cavity. Joists run N-S along the longer walls. There are ample airbricks to 3 sides (E/S/W) of the house, and also several on the N facing rear extensions. There could be more added to the rear extensions but pretty sure they would have little bearing on the through airflow. from front o back of house.
All the 17? airbricks are almost but not quite 2 bricks above ground level and sit directly on the damp proof course, which is bitumen in original part of house and membrane in extensions. The top of the airbricks are lower than the tops of the joists but not below the bottom of the joists. Given that most of these are on E/W facing walls and that joists run parallel and generally quite close to these walls, the joists get in the way of any airflow, and it looks as they would make installing periscope type airbricks tricky.
There are signs of two or three partial openings between the old external wall at the back and the rear extension. These could in theory be opened up to provide effective airflow between the original building and extensions. Except that the rear extensions only have a void of 30cm, and less in places, rather than the 1m in the original building, so15cm clearance or less below joists! Which makes insulating to a sufficient depth tricky as well.
Various people have suggested various ways to insulate the extensions (two phases, one c 1990, and a second c2000) while maintaining airflow through from the original part of the house.
a) remove joists, put in pipes for through ventilation from main building to outside, pour in more concrete and insulate above that
Disruptive, higher embodied carbon, but well understood solution
b) put in pipes for through ventilation from main building to outside, put in thick layer of insulation below and between joists sitting on concrete base
Never heard of this method until today, so wary of implications
c) put in short pipes for through ventilation from main building into extension, insulate between joists as originally planned
Compromised airflow but straightforward and well understood
d) put in short pipes for through ventilation from main building into extension, install floating insulation above joists
Another option that’s new to me. I want to maintain level access throughout the ground floor and The costs and disruption would far outweigh any pros.
Does anyone have any experience of b) and d)?
And of directing airflow from airbricks under joists in tight spaces?