I've got an old semi-detached house with a suspended timber floor across most of ground floor (area in green on drawing), mainly 4x2" timbers across a maze of sleeper walls with about 250-500mm underneath them. I have all the timber floor up so I can replace a few rotted timbers. I will also insulate between the 4x2" with 100mm Celotex, and foam and tape all the gaps to create an airtight seal.
An extension at back with concrete slab means no through ventilation front-back. The airflow into the side airbricks is small as it's down a very sheltered side passage, and our neighbour's subfloor is full of rubble. So probably very little side-side natural airflow too. I have already put a couple of extra air bricks in where I can, but the damp smell in the heart of the house is still strong.
I think subfloor fans are probably the answer. But where should they go? And which direction should they push the air? I have labelled pink 1, 2, 3 as possible places:
- Positions 1 or 3 would be replacing air brick with an externally accessible trickle fan like WMF Mori. Should they push air in or suck it out?
- Position 2 I could create a hatch in the cupboard floor for maintenance and use a traditional inline fan. From there guess you would want to push air back towards the air bricks?
- Other option would be to put an external fan in 1 but duct it through to the heart of the unventilated space. But should it suck or blow?
Or does anyone think I should do something else; my only other ideas are:
- Just rely on the insulation to stop warm damp air from house coming down into the void, and hope this stops rot (once sealed up will be hard to know)
- Treat the timbers with something to prevent dry rot?
- Fill the void in some way? I don't think it would be worth paying for a whole concrete subfloor. But are there any expanding foam treatments that could exclude air from the subfloor permanently?
Thanks - bit stuck with this one. But I know doing something now while I have the subfloor up will be a lot easier than replacing a rotted floor in 10yrs time!
An extension at back with concrete slab means no through ventilation front-back. The airflow into the side airbricks is small as it's down a very sheltered side passage, and our neighbour's subfloor is full of rubble. So probably very little side-side natural airflow too. I have already put a couple of extra air bricks in where I can, but the damp smell in the heart of the house is still strong.
I think subfloor fans are probably the answer. But where should they go? And which direction should they push the air? I have labelled pink 1, 2, 3 as possible places:
- Positions 1 or 3 would be replacing air brick with an externally accessible trickle fan like WMF Mori. Should they push air in or suck it out?
- Position 2 I could create a hatch in the cupboard floor for maintenance and use a traditional inline fan. From there guess you would want to push air back towards the air bricks?
- Other option would be to put an external fan in 1 but duct it through to the heart of the unventilated space. But should it suck or blow?
Or does anyone think I should do something else; my only other ideas are:
- Just rely on the insulation to stop warm damp air from house coming down into the void, and hope this stops rot (once sealed up will be hard to know)
- Treat the timbers with something to prevent dry rot?
- Fill the void in some way? I don't think it would be worth paying for a whole concrete subfloor. But are there any expanding foam treatments that could exclude air from the subfloor permanently?
Thanks - bit stuck with this one. But I know doing something now while I have the subfloor up will be a lot easier than replacing a rotted floor in 10yrs time!
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