Black mould on inside of external corner and typical relative humidity of 75-88%!
Anonymous user 23/02/2024 - 3.42 PM
Hi all, I’ve a 1850’s end of Terrace town house. With high relative humidity (RH), I’ve 2 bedrooms in a half basement level, on a downhill slope, is kind of lower ground, not below ground some concrete steps covering side of corner bedroom (main issue one) perhaps 3 foot of other bedroom below ground.
Black mould problems on inside of external corner of wall of first bedroom, RH reaches 88% in that room, never below 65% even with dehumidifier full blast and raising temp by 2 degrees, so probably only really adjusting RH, it does take out a fair bit of water. 2 adults in room from 6:30pm each night until 7am-ish. Door left wide open to cold hallway from about 9pm.
£600 putting in a Dri Master ECO PIV installed it 2nd floor landing, runs at max fan 24/7, decreased condensation fair bit on living room large sash window, and RH of some of upstairs bedrooms a bit. Not overly impressed otherwise. Nearby ground floor extension pitched roof, would consider adding another Dri Master, if it would sort the problem, but spoke to them and they said not designed to get rid of RH, designed to reduce condensation. Appreciate condensation likely part of problem, but also aware that over 55% RH is mould growth paradise, so if the unit won’t bring down 88% RH then I can’t see it helping.
House has typical drafts from wooden sash windows in half of it +poor fitting internal doors, so not airtight.
Central heating off in summer and then on thermostat to 19 / 19.5 degrees.
External walls Cornish stone, about 27” deep though told there is a crap/rubble cavity in between where the Victorians dumped building rubble, so not technically cavity, but not solid either. Historically part rendered, 2nd and 3rd level (ground / upstairs). grade 2 listed.
£400 independent damp surveyor and recommend slate covering outside wall of corner with mould (listed, so no chance) also suggested ripping off plaster in corner, putting up Newton 805 or 803 membrane, plaster boarding and skim to stop damp coming in. Can’t help thinking problem may have a lot more to do with the RH of 88% which he gave no solution for. Asked about vent bricks (none on front side of house, where this bedroom is) or extractor fan, but said won’t help.
Suggested PIV may help, but Dri master said won’t help with RH.
I’ve would put pics in but can’t see anywhere to add them, it really is just that front external corner and coldest spot in room that suffers, but I would really like to get humidity down to sub 55% as well as fixing mould, though appreciate that fixing RH might cure mould. I have an old aluminium window in the corner, it’s not airtight and a little draughty, it has I’ll fitting secondary glaze that is not airtight, and the plaster all around the window has all fallen off, it’s probably lime plaster.
I need help I think in the first instance getting RH dealt with and think if that could be under 55% then I might see mould slow or go away.
Are you a tradesperson and able to answer this question?
This sounds like advice overkill...So with these humidity levels, you are dealing with warm air turning cooler and a combination of what you yourself are creating in the internal environment. We breathe out lots of moisture daily. I forget the average amount per adult a week. Then there's cooking, washing etc. Installing the Newton system isn't the correct advice as it's a very good ventilation system that you need. Not a PIV!!...
you need a system that will detect the humidity you are helping to create and bring in only dry air and not saturated air. The air in summer can be equally as moist as air in the winter. Look up a company called RHL direct. Very good ventilation system and they also design them for cellars etc. They are slightly nerdy so be patient. The temperature of your property should probably not exceed 17c during winter as these properties were never intended to be heated to temps like a modern house has. If you look up heritage house and peter ward he has further information regarding condensation and ventilation system. Good luck
Firstly your £400 survey missed the point and certainly ill advised you on treating the walls with any sort of waterproof covering .
Black mould is a sure indication that you don’t have a damp condition coming from outside.
The mould level is 65%RH not 55.
PIV is not the answer to your issues.
Humidity sensitive extraction is what you need ; in addition to that is air exchange.
You’re out a lot I guess so have a look at a HRV150-12 hour unit, absolutely brilliant for your circumstances.
Clean off the mould with distilled white vinegar or Ronseal 3in1 mould killer.
Given your description, the high RH is clearly a concern, especially with values reaching 88%. The mold growth is symptomatic of this high moisture content.
Immediate Steps:
Dehumidifiers: You mentioned using one, but consider purchasing or renting a larger capacity or industrial dehumidifier specifically designed for basements or damp spaces. Ensure the water collection unit is emptied regularly.
Ventilation: Improving ventilation can help reduce RH. Ensure vents are clear of obstructions, windows are occasionally opened, and consider installing more vents or an extractor fan, especially if the room is often occupied.
Long-Term Solutions:
Wall Treatment: As your damp surveyor mentioned, the Newton 805 or 803 membrane can help to prevent moisture ingress from the walls. This is a good approach, especially for older homes with unique wall structures.
External Factors: Check gutters, downspouts, and landscaping around the house to ensure they direct water away from the foundation. Given that one side of your house is below ground level, consider installing French drains to redirect groundwater.
Window Replacement: The aluminum window and ill-fitting secondary glaze might be contributing to the dampness. Upgrading to a more insulated, modern window can help reduce condensation and drafts.
Monitor & Adjust: Keep a digital hygrometer in the room to monitor RH levels continuously. This will give you a better understanding of the effectiveness of your solutions.
Lastly, consult with a specialist who understands historical buildings, given that your house is Grade 2 listed. Such specialists will be familiar with the restrictions and best practices for addressing damp issues in older structures.
The thickness and construction of the walls is what is causing the moisture within the room . with in the room this is then cooling and then it being turned to condensation so one waterproof the walls cavity drain membrane to insulate the walls so heating stays within the room and the Could stayed out you will also need to vent the and correctly I do suggest the whole house ventilation system it continuously changes the air
