Victorian terraced house - Please help! - Air vents, wall cavity, humidity & moisture advice

[GeorgeC]

Hello good people of this forum,

Please help! My bedroom is the at the rear of a ground floor flat in a London Victorian terraced house. The bedroom has very high humidity (80% overnight), even running dehumidifier all day i can only get it down to 60%. Last winter I had an outbreak of mould on the walls that I have sprayed with mould proof paint. I have asthma and allergies and as a result of humidity i've had constant sinusitis, so really trying to get to the root of this problem and solve it!

Given all the below information, what do you think needs to be done? I'm looking for a specialist who can come in and fix it, any suggestions?

Firstly, there is a hole at the base of the rear wall (see bottom left of photo attached) - Not sure if this used to be an air brick, but it's really deep, maybe 15-20cm. I noticed a lot of the skirting board was falling apart on the inside when i fitted a wardrobe a few months ago.



There's also an airvent at the base of the side passage wall (off right side of rear wall in photo).



A previous owner filled the room with concrete or scree, I believe in the 70s because the plug fittings date to back then (could tell from the cable colouring). Has this blocked the airflow and forced the moisture up into the walls?

Lastly, and I don't think it's related but I'm including just in case, there's a crack running up the wall from the old chimney stack. You can see the darkish patch of brickwork, the crack runs up the right side of that patch and then up directly above it towards the roof.




Any advice appreciated

Thanks so much,
George

 

[Stevers]

So, it looks like you now have a concrete floor with DPM pushing moisture into the walls due to an ineffective chemical injection DPC to aa solid wall. The UPVC windows will tend to keep it all in the building. No quick fixes to this one - everything that's been done to 'upgrade' your building will have made it worse. The damp 'specialists' will only do more of the same. Make sure all drains are working, including for all downpipes. The waterbutt has a divertor so just make sure that is working as it should. You'll need to check that ground levels are below floor level, and contemplate replacing that concrete floor with a suspended floor and restoring sub floor ventilation through plentiful and unblocked air bricks - it's how this building was designed to work. Internally you'll need to replace the 'new' cement and gypsum plastering (that I'm sure will be there) with lime.

Cooking and washing will introduce moisture so extract it at source. Warmth and ventilation will be your friend, so open those trickle vents and add a bit of gentle warmth all through the day with a smart heating system to keep things aired and avoid cold surfaces. You could do worse than try this first!

The black patch on the wall might suggest a problem with the gutter above, and if the white tidemark is salts and not 'street art' it's setting an altitude record for rising damp!

 

[GeorgeC]

Thanks Stevers for your time and help,
Interesting about the floor, I was worried it would be that. Thanks for the tip about warmth and ventilation, it definitely is worst when the temperature drops. The question I'm left with are:

1. Who would I speak to for replacing the concrete floor?
2. Should I open my windows and if so at what times of day?
3. What do you recommend I do about the cavity in the rear wall?

The white marks were put there by the kid of the previous owners! It's just chalk (i think). On an unrelated note, my partner's parents are from Compton Martin in Chew Valley at the base of the Mendips!

 

[Stevers]

That would be the posh side, we're on the sunny side!

A competent builder could put a suspended wooden floor in, but I guess building regs will come into play, (insulation etc.), so you'll probably need building control or a professional to spec. and sign it off. The void should have an air brick in it, but as there's nowhere for that air to go it's a little pointless. In the hope that that might change one day I'd still go down to a builders merchant and buy a clay one to fit.

I'd look at drains, moisture control at source (showering, cooking and laundry) and smart heating so that you can automatically vary the temperature through the day to avoid any room getting too cold when you're not using it. Leave the trickle vents open. A decent extractor fan on a humidistat could be useful for bathrooms, and the dry air that replaces the damp air will need to enter via trickle vents, as your building is probably pretty airtight otherwise. If you're in and it's a warm sunny day - open the windows. You need to eliminate all sources of moisture apart from breathing to see if you can get below the damp tolerance of the building which will be horribly low in it's current form.

I don't suppose any of this was flagged up by any survey!

 

[DaveG]

Stevers has it well covered above with having to address floors and walls.
Definitely replace the cover on that hole as it could encourage vermin into the building fabric.
With the windows, leave them open as often as possible (overnight is better during cooler temperatures as the air carries less moisture but appreciate from a security perspective you may have some limitations). Some windows have a secure catch that allows the window to be slightly ajar. The only time I’d close everything up is while running your dehumidifier as otherwise you’re wasting energy.
Any areas generating moisture like bathroom and kitchen try to keep those closed off and deal with those areas separately by opening windows in those rooms or even better running extractors if you have them.
Keep the bedroom door and wardrobe doors open as much as possible.
Finally I was going to suggest looking at thermal wall papers/covering purely as a temporary measure. You’ll obviously need to weigh up cost. It doesn’t fix things but it can help stop moisture from being able to condense on a cold external wall.
Unfortunately you’ll need to keep furniture away from those external walls and try to keep air moving with low speed fans. Damp, stale air that lingers is your enemy when it comes to mould