Advice on ventilating and drying a cellar

[Relicah]

Hi all,

Although I have spent hours reading your collective insight, this is my first post - thanks in advance.

I’m looking for advice on how to properly ventilate a damp cellar.

For context we have a relatively small (picture attached) cellar with an open sump at one end and what I presume to be an old coal shoot at the other.

There is a ducting pipe in the coal shoot which runs to a vent on the external of the house but with no cross flow I think I need some mechanical help for the air flow in the ducting.

The cellar entrance is a trapdoor under our stairs with the RH in the cellar itself being 99% and 80+ in the cupboard (tools etc rusting in the cupboard air)

My questions are:

- should I be extracting air from the cellar to the outside via the duct (creating a negative pressure) or should I be inputting a positive pressure by pulling fresh air in through the vent

My concerns with either option are:

Will the positive pressure force stale/damp air into my property via the trap door and as we’re close to a road will I just be drawing in poor quality air into my house

Or will the extraction method pull warmth from the house and also pull more ground water from the walls on account of the negative pressure

And secondly

- there is always standing water in the sump, I believe we’re below the water table and the pump works on a float switch which doesn’t engage until there’s a fair amount of water in the hole - can I just fashion a plastic manhole cover with a rubber gasket to cover this standing water to stop it working it’s way into the air or is there a better way to limit the affect of this water?

We’re under no allusion about wanting to use this space for anything other than plastic box storage but I want to address the airborne moisture to avoid it increasing the humidity in the main property

Again, I really appreciate everyone’s advice here, it’s an invaluable resource. Thanks!

Pictures:

Front of cellar with stairs going up to cupboard (wood has been since removed)


Rear of cellar with chute (taken from stairs)



Sump and pump, located at the base of the staircase

 

[Relicah]

Hi again, or have I just overcomplicated my post and I should just run a small dehumidifier down there?

Any help much appreciated!

 

[Toby Newell]

Hi

Welcome and I will try and address all your questions.

1. Your ducting isn't doing much on it's own, yes you require mechanical extraction (negative pressure) to change the air.
2. The extractor will require a vent in the trap door or in the blocked coal shoot cover to allow fresh air to be brought in or your fan will not be very efficient.
3. Run the fan on a timer for a few minutes each day to change the stagnant air. Running longer just brings more moisture into the area, especially on humid warmer days which will condense on the colder cellar surfaces. Thus setting the timer to run at night, especially in the summer months, when it is cooler will bring in less moist air. Something like 20 minutes should be enough.
4. The ventillation will have little to no effect on the RH and may even increase it in the summer, although at 99% it is already saturated. It may slightly reduce the musty smell and is generally healthy removing heavier gases that can stagnate.
5. Yes, your sump should have a cover but this is unlikely to reduce your RH level either.
6. Your cellar is surrounded on exposed elevations by decompacted excavated soil which is less dense than the surrounding virgin unworked soil and thus acts like a sponge. The high RH is caused by this hydrostatic pressure (of probably several tons) forcing water through the walls. You will never stop this unless you excavate and tank the exterior and the floor.
7. The room is very small so your options are limited. In general you would fit an internal perimeter french drain with a perforated drain pipe falling towards your sump which would periodically drain the water.
8. In larger rooms you could use a trickle drain membrane on the walls and batten and plaster over the top. In your case you could just fit a waterproof membrane.

9. Nothing you do will reduce the RH levels that much unless you tank the outside and the floor, the best option is to allow for maximum drainage, waterproof the walls and run an extractor once a day. Fit a cover to the sump, or replace with a plastic bucket type sump (which come with cover)

10. Running a dehumidifier in a 99% RH cellar is akin to making forward progress running on a treadmill.

11. Your cellar may be great for making cheese.

 

[Feltwell]

All sounds sensible from Toby. Forget the dehumidifier, you're just pulling more moisture in from the near limitless supply behind the walls.

Make sure drains nearby are OK, I had one that was not ( https://www.periodproperty.co.uk/forum/threads/happy-but-not-so-happy.17864/ ) New tarmac has faded in beautifully since I posted that!

Fluorescent yellow drain dye is great stuff, very useful to let you know if drain water is leaking into cellars.

If you want to store things down there, Solent Plastics do airtight archive boxes.

 

[Toby Newell]

All sounds sensible from Toby. Forget the dehumidifier, you're just pulling more moisture in from the near limitless supply behind the walls.

Make sure drains nearby are OK, I had one that was not ( https://www.periodproperty.co.uk/forum/threads/happy-but-not-so-happy.17864/ ) New tarmac has faded in beautifully since I posted that!

Fluorescent yellow drain dye is great stuff, very useful to let you know if drain water is leaking into cellars.

If you want to store things down there, Solent Plastics do airtight archive boxes.

Ha! Have been using Solent Plastics for almost 20 years and have thousands of pounds worth of their boxes, excellent company. They also are big suppliers to industry and sometimes do buy backs and then offer secondhand resale in as new condition for discounted prices. Mind you, if you have a box fetish, you might wear out your credit card.

 

[Relicah]

@Toby Newell @Feltwell

Thank you both for your replies, it seems like the reply notifications were going into my junk so i missed them until now,

Good news on the cheese I guess, in contrary to my partners opinion; I can always have more hobbies.

Few follow up questions if you don't mind;

1. Seems like you're suggesting extraction of air out of the coal shute is better than a PIV inputting outside air, this is good news as i imagine a extractor fan is a lot cheaper than a wall mounted PIV - will this however not just pull warm humid air from my house to condense on the cellar walls?
2. tanking or waterproofing the walls seems to be considered death to old houses in most contexts so i hadn't really seen it as an option in my uneducated opinion but i presume this is conventional wisdom in areas where there is a smaller supply of available water, so should i be looking to coat this wall in a tanking, watertite style, paint? Or will this just rapidly decrease the life of the bricks/cause other issues?
3. Ill definitely be buying some of those solent boxes, thank you!
4. Im comfortable with having a damp, properly drained, cellar - but my area of concern is the under stairs storage cupboard in which the cellar trap door lives - i foolishly put some racking units in the cupboard for tool storage with cheap MDF inserts to find later find the shelves covered in mould and some of my carbon steel tools beginning to rust, along with this the walls have salts creeping up which i presume is because the cellar below is saturated- this cupboard would be difficult to extract to outside, do you think the periodic extraction/replacement of air from the cellar and covering of the sump would be enough to reduce the humidity in the cupboard above the cellar or should i be also venting this cupboard to the living room provided the musty smell decreases?

Now to research some cheese making,

Thanks again!

 

[CliffordPope]

Now to research some cheese making,

Or growing mushrooms?

 

[LadyArowana]

Your cellar looks exactly like our under pavement vaults. We run a dehumidifier which keeps it a little bit more comfortable, no mushrooms growing, cheeses ageing or wine gathering dust.

 

[KarlB]

How did you get on with your cellar ventilation project? It looks nearly identical to mine except I don't have a sump, I have 2 vent pipes running out to grates on the road, but they're blocked up and of questionable design (I suspect they drain water into the basement in heavy rain). Interested in what difference negative ventilation made, if any?

 

[chrisfraser05]

Another customer of Solent here.

I designed my workshop around the size of ISO stackable boxes and spent thousands on them over a few years. Really does make life easier.