Observations on a dampish cellar

[JohnArmer]

We have a cellar at the front of the house and it's not a dry one. In winter and times of heavy rain the floor gets damp and when it rains very hard there is a trickle of water that runs in from the bottom step. It's not a problem since 1. we know about it and keep everything down there up off the floor; 2. there's a 9" high concrete plinth at one end to keep stuff on if necessary; and 3. there's a drain in the far corner to let any water coming in escape. We've had it camera'd and its in good condition, connecting with the sewer in the road. The gulley's there for a reason and I guess that some underground rooms are wet.

However one thing I have noticed that while it tends to be dry in the summer, in times of very hot and very dry weather, like we're having now, it tends to get damp again. It's damp now. I can't for the life of me work out why this would be. It's usually bone dry when we have our normal damp summers, but I have noticed this dampness before when it's very hot and dry. Anyone with more experience that me have an idea why this might be?

 

[Gareth Hughes]

Just possibly, the very dry weather has led to an increase in the rate of evaporation through the cellar walls from the ground beyond? In a normal summer there's less 'incentive' for the ground moisture to go travelling.
I've noticed an increase in salt efflorescence on formerly damp masonry just recently.

 

[Lime]

Humidity in a cellar is always high no matter what the weather.
It is also very slow to warm up and can be relied upon to maintain a steady stable cool temperature.
In all likelihood the cellar is damp because the structure is much colder than elsewhere and the outside air, because it is much warmer than normal, holds a great deal more moisture than normal too.
That extra moisture condenses on the cellar walls and floor hence the extra damp.
Ventilation is the best answer.

I'd be concerned about the drain in the cellar if it were mine
If as you say it is connected to the main sewer then it is more than likely that your cellar will get inundated with sewage if the sewer backs up for whatever reason.
I'd want to fit a valve in the pipe to the sewer to prevent back-fill or fit a seal over the drain to prevent any flooding of the cellar.
https://www.plasticdrainage.co.uk/anti-flood-valve-spigot-socket-8732.html?gclid=EAIaIQobChMI86mOj5ej3AIVSLTtCh283AQ7EAYYAyABEgJ5IPD_BwE#fo_c=1765&fo_k=7487c908c1602c5fb926e76764bd0b3b&fo_s=gplauk
or
https://www.google.com/search?q=sewer+back-fill+valve&sourceid=ie7&rls=com.microsoft:en-GB:IE-Address&ie=&oe=

Remember the pressure from the sewer if blocked or flooded could be quite substantial.

 

[Easrow]

I guess it's an evaporation thing as we have similar with our blue lias flagstone floors. We notice they have more dark areas when it's hot and humid than when it's cooler. Or possibly a temperature difference is causing condensation. They are not wet to touch just change colour slightly. A cellar would probably be worse.

 

[88v8]

If you're in the country and on a slope, it could be an old land drain that's bringing in the water. When we water in the veg field, about 100ft away, the sump pump in the cellar starts up. So it seems we have working clay land drains that predate the cottage, two hundred years old.

Ivor