Cellar insulation and ventilation query

[mb1]

Hi,

I purchased a Victorian terrace last year. We have a fairly large cellar under the hallway to the front door (inc an original coal chute at the end, connected to a small cover in the front path). At some point, insulation has been added between the floor joists to insulate the hall floor.

However, we have now realised that the cellar is pretty humid (I do recall from the viewing the prev owners had a dehumidifier down there, but had forgotten). Having examined more closely, I have realised that there is a ventilation grille (maybe called a daisy grate?) below the front door threshold, which connected directly to the cellar. However, it is blocked by the insulation - see diagram.

Rather than just buy a dehumidifier, I was thinking of installing a few of these S-shaped ducts to restore the air flow into the cellar from the grate while retaining the insulation at the front of the hallway: https://www.manthorpebp.co.uk/wall-...rfloor-ventilation/telescopic-underfloor-vent

Is this a good idea? Anybody see any reason this would not work? I plan to monitor the effect with a cheap humidity sensor.

Cheers in advance.

 

[Kearn]

You absolutely need ventilation, the more the better, and it must be cross flow, or at least have entry and exit points. It may be that you need some forced air movement across the space once you’ve cleared/created enough ventilation points. Or to pull in and push out of vents on the same wall if you can’t manage ventilation elsewhere due to the buildings orientation. Definitely get the chute open again.

Periscope style vents can work, the less sharp bends the better.

 

[Flyfisher]

I agree with all the above, but (there's always a 'but' ).

Is this a good idea? Anybody see any reason this would not work? I plan to monitor the effect with a cheap humidity sensor.

Yes, it's a good idea (plus the points made above), but whether it works or not depends on what's trying to be achieved.

I have a cellar that originally had a single small grating for ventilation to the rear wall of the house and was mostly blocked. The cellar had that damp and musty smell. I cleared the grating and added additional ventilation to the front wall of the house. I installed a half-decent dehumidifier and it pulled so much water out of the air that I got fed up with emptying the bowl so I bought a 'condensate pump' to collect a few pints at a time and then pump it up and out of the cellar (there being no drainage in the cellar).

All of this worked as far as reducing the musty smell but I don't recall my humidity meter ever dropping below 98%. Not entirely surprising when you consider the cellar is just a big hole in the ground with permeable walls surrounded by damp earth - an efffectively inexhaustible reserve of moisture.

I've considered adding some forced ventilation but I'm not convinced it would help a great deal. Also, without some form of humidistat control, it could make things worse by pulling warm humid summer air into the cool cellar below the dew-point, with the inevitable result.

So, did I waste my time? I don't think so, but only because I wasn't trying to reclaim the cellar as living space, only as a cool, dark storage space for items unaffected by damp, which in my case mostly means bottled items such as wine, home-brew cider and assorted pots of jams, chutneys and anything else that can be preserved in a jar or other airtight container. To that end, I can thoroughly recommend plastic shelving units designed for use in greenhouses etc. These can be found in most garden centres, are fairly cheap and are impervious to high levels of moisture.