Background
The property is an a semi-detached Victorian lower ground floor flat with a solid wall made of two brick widths (225mm). The front door faces north.
Changes to the property’s original design
Properties are not designed and built with damp problems. Understanding changes to a property since first inhabited is the starting point for tracing damp back to its root cause.
TIPS: changes since original design: conversion into flats, steel support, suspended timber floor replaced with solid floor, chemical damp proofing, damage to rear plinth, central heating, double glazing with no or insufficient trickle vents, bathroom and lifestyle changes including more frequent showers and clothes washing, including greater occupancy during the Covid pandemic..
Cause of damp
There was condensation and mould caused by thermal imbalance and insufficient use of ventilation.
Tips
The property has been damp proofed. However the issue is excess condensation through insufficient ventilation.
Illustrations
Holes at the base of the wall shows that the property has been damp proofed using chemicals.
Unfortunately the damp proofers have damaged the plinth, which should be reinstated.
Signs of dampness, surface salts and mould was found on front bay.
There are a number of damp issues in the property they all come down to one root cause.
The front Bay has mould and flaking paint from surface salts. FACT: white surfaces salts are typically calcium sulphate, a key ingredient in cement and other building materials. If diluted in water salts move to the surface. Use sandpaper to remove salts and decorate.
Mould was growing at the base of the wall next to the surface salts.
TIP: detecting surface damp. The wall surface was dry at the time of the survey there’s mould above surface salts. FACT: mould is inhibited by nitrates Groundwater is rich in nitrates. The presence of mould at the bottom of a wall eliminates rising damp as the root cause and points toward condensation from unvented excess vapour.
A sample of salts was collected to test for nitrates. The test came back negative for nitrates.
TIP: testing for nitrates. There were no significant quantiles of nitrates. If there are no nitrates, then we can eliminate rising damp as root cause of damp.
There is dampness deep within the wall.
TIP: dampness deep within a wall when there is no surface dampness is often a sign of moisture trapped by an impermeable surface replaced as part of damp proofing treatment.
I left a data logger to record relative humidity and temperature overtime.
TIP: dataloggers log relative humidity and temperature over time. They can be used to help determine the cause of damp, and sometimes if a wall is drying out.
I measured the temperature as 12.7°C this is compared to an ambient temperature of 16.4 °C.
TIP: measuring heat loss. Condensation will form on the coldest part of a property first.
There is damp at ceiling level underneath under a steel beam known as an RSJ.
FACT: RSJs are prone to condensation as they lose heat rapidly causing interstitial condensation.
Using a metal detector I determined that there was a large metal beam.
The discoloration is almost certainly rust under the condensation forming on the steel beam.
Mould is growing high up in the corner. At the time of the survey this wall was dry.
FACT: mould only grows where relative humidity exceeds 85%RH for 6+ hours. Excessive humidity results from insufficient ventilation, poor air circulation and a cold surface.
Mould is growing in the master bedroom on an internal wall.
I understand that the tenant had a lot of camera equipment stacked up against this internal wall reducing air flow he also turned the radiators off and the bedroom. FACT: airflow restrictions cause a built up of surface humidity creating the perfect environment for mould.
There are early signs of window rot.
FACT: single glazed windows are prone to window rot from condensation. FACT: window rot is common in period properties. TIP: cut out rot, apply wood glue, hardener and filler, sand down and paint with a gloss paint to protect timber from water (the cause of rot).
Mould is growing behind the bedroom cupboard.
FACT: cupboards by external walls are at risk of mould. TIP: insulated between cupboard and wall.
Calcium sulphate salt are appearing around the sides of built-in cupboards.
There are three interrelated causes of the disruption. 1) excessive vapour, 2) reduced air-circulation from furniture, thereby reducing the benefit from heating, increasing the relative humidity, 3) it is probable that an absorbent plaster or filler was used to complete the installation around the furniture and wiring.
There is mould and rust at the base of an internal kitchen cupboard.
FACT: plasterer’s beading increases the risk of condensation. Rust can be seen on the plasterer’s beading. again metal loses heat rapidly increasing the risk of condensation.
Dampness is high on an internal kitchen wall by the plasterer’s beading.
The floors are solid, probably made of a concrete screed. FACT: solid floors are prone to condensation as the ground is typically the colder than walls, increasing the risk of condensation. TIP: plaster should not touch a solid floor. The issue is
The bathroom extractor fan is running fast, but was set to stop after about 15 minutes.
FAFT: 90% of vapour remains in a bathroom after lights are switched off typically. TIP: bathroom extractor fan overrun. The blue dial in the above image, can be adjusted, clockwise to extend it, which I did during the survey. This alone could have stopped damp.
There is very little background ventilation.
TIP: keep windows open on the safety lock, it is as good as using a trickle vent.
Cracks to bathroom tiles could result in water being absorbed into the wall.
TIP: regrout tiles. TIP: silicone around the bath. TIP: seal shower panel gaps.
There are render cracks around the property. These are probably the freeholder’s responsibility.
FACT: penetrating damp where water travels through bricks or timber normally leaves a brown stain. FACT: dampness in bricks reduces insulation by about 50%, increasing the risk of condensation and mould. FACT: horizontal cracks cause more ingress than vertical cracks. FACT: render cracks suck in water, but render stops water from evaporating out.
Gaps in the surface above the kitchen should be filled in.
The down pipe from above the bay appears to be undrained. There are cracks in concrete base.
This is presumably a freeholder responsibility. The drain should be cleared. Make sure it is effective. Cracks should be filled with a similar cement-based mortar. Check slope to drain.
TIP: Observe and film around the property during a rainstorm to see where water flows, making sure water flows/drains away from the building. Check every 6 months.
Cracks around drains should be filled. Underground drains should be checked with a CCTV camera for cracks.
FACT: drain leaks are often misdiagnosed as rising damp. Given the state of the drains and the previous damp proofing treatment, the freeholder should commission a CCTV drain survey.
Timber is at risk of window rot if it is not regularly painted.
TIP: check for unpainted timber, gaps around windows and render cracks, fill and paint as required.
Datalogger
This is a graph from your datalogger and a comparison to external temperature and dew point.
Relative humidity
Relative humidity is a measure of how much vapour is in the air compared to air’s capacity to hold vapour. It is a function of vapour pressure (quality of vapour) and temperature. As temperature rises, air can hold more vapour. Conversely as temperature drops, air holds
Dew point
Dew point is the temperature where condensation takes place. It is also a proxy the vapour pressure. Comparing the dew point of one area to another makes it possible to see where vapour is being generated or conversely removed (normally through ventilation).
In conclusion from the dataloggers
- During the 5 days under observation the relative humidity is constantly below 50%RH, too dry for condensation or mould.
- The temperature is being held very constant, which is excellent, and will reduce the risk of condensation.
- The dew point is consistently at or below external dew point, suggesting adequate ventilation in its current unoccupied state. However, I don’t believe ventilation is sufficient when occupied.
- I measured about 1°C temperature difference between the datalogger and external wall. For each 1°C the relative humidity will be about 5%RH higher. The temperature difference increases as the temperature difference between inside and outside increases such as on a cold winter’s night.
See surveyor.tips/datalogger-examples
RECOMMENDED REMEDIAL ACTIONS
Remedial actions necessary to keep the property dry and mould free
TIP: datalogger. Monitor humidity and temperature against wall or ceiling, to see effects of improvements, such as ORIA Wireless Thermometer Hygrometer (20m (2 Packs)) |
TIP: monitor dampness. Monitor dampness with simple damp meter, logging at the same time and position every week. |
TIP: drying-wall. Use at least two fans to speed up process of drying out damp wall. |
TIP: speed up drying out process further. Depending on external temperature, either keep windows open, or close windows, put heat on constantly around 16°C (the higher the better) and use a dehumidifier. If using a dehumidifier, see Which! Guide; https://www.which.co.uk/reviews/dehumidifiers/article/how-to-buy-the-best-dehumidifier such as Inventor EVA II Pro 20L R290; £179 ideally buy one with a continous function draining into a sink or drain. |
TIP: fill bathroom cracks. The bathroom tile cracks should be seal and or grouted. |
TIP: freehold property management. There are some external issues that are probably freeholder issues and shared costs, such as draining out the front down-pipe and area in front of the bay, filling cracked render, making sure there are no gutter leaks and broken or blocked drains and to rear reinstating the cement mortar plinth to the ground, with run off. It is difficult to estimate the full cost, but it is probably 2 – 3 days work at about £300 – £400 per day, split by the share of costs. |
TIP: property management. Observe and photo or film around the property during a rainstorm to see where water flows, making sure water flows/drains away from the building. |
Optimal actions to improve the home environment
TIP: continous flow fans. I encourage all landlords and owners of properties with damp issues to install continous flow fans such as Elta Mori dMEV in the bathroom(s). The thermal cost of continually extracting air is an estimated £50 per year. |
TIP: kitchen extractor fan. Consider instructing general builder to duct out kitchen extractor fan – using rigid ducting. Hoover HGM600X (£149) has a Which! Best buy. |
TIP: remove mould. Consider sanding down mould and removing it with either bleach or anti-mould foam. |
TIP: anti-condensation paint. Consider painting anti-condensation (e.g. DryZone by Safeguard on Amazon 5L £53.70) or anti-mould paint onto walls vulnerable to condensation or mould (top coat only). |
TIP: dehumidifier. Consider using a dehumidifier, see Which! Guide; https://www.which.co.uk/reviews/dehumidifiers/article/how-to-buy-the-best-dehumidifier such as Inventor EVA II Pro 20L R290; £179 ideally buy one with a continous function draining into a sink or drain. |
TIP: monitor dampness. Consider monitoring dampness with simple damp meter (£10), logging at the same time and position every week. Monitor humidity and temperature against wall or ceiling, to see effects of improvements, such as using a Govee hygrometer datalogger (£42 – Amazon) – see surveyor.tips/datalogger |
TIP: WIFI thermostat. Consider installing a modern WIFI connected thermostat, with multiple heat settings, so as to ensure the wall temperature doesn’t drop below the dew point. With Nest you can pick up humidity readings remotely, but need to use a laser thermometer to measure the temperature difference between the thermostat and cold wall, adding approximately 5%RH per 1°C difference. |
TIP: trickle vents. Consider instructing general builder to install trickle vents (approx. £30 each), see surveyor.tips/trickle_vents. |
TIP: solid floor plaster. Many solid floor are build with plaster touching the ground, this causes upward absorption. Consider removing the ground floor skirting board, cutting base of the plaster by 10 – 20mm back to brick (chisel, grinder or better still Oscillating Multi Tool, such as Bosch). Run a bead ~10mm of a absorption reducing Thixotropic cream such as DryZone by Safeguard (Amazon etc), along the exposed brick. Replace the skirting board. |
A general builder can complete most work. CheckaTrade.com, trustatrader.com and trustedtraders.which.co.uk are good sources of general builders. Once the recommended remedial actions are completed and the walls allowed to dry, dampness will not have a material impact on the value of the property.
It is the client’s responsibility to check that a contractor has sufficient insurance and competence to undertake any work that we recommend.
FINDINGS
Symptoms of main issue: mould and condensation.
Profile of main issue: mould condensation profile.
Visible effects: mould and condensation, mould to all corners.
Conditions during survey
Relative humidity: 57%RH Temperature: 16.2°C
Mould point: N/A Dew point: N/A See mouldpoint.co.uk
Temperature of damp wall: 12.7°C Relative humidity of wall: N/A
Weather: dry
External low at night: 8°C, low night-time temperature could result in mould or condensation without sufficient ventilation.
About the property
The property is an a semi-detached Victorian lower ground floor flat with a solid wall made of two brick widths (225mm). The front door faces north.
Changes to the property’s original design
Properties are not designed and built with damp problems. Understanding changes to a property since first inhabited is the starting point for tracing damp back to its root cause.
Key changes are: conversion into flats, steel support, suspended timber floor replaced with solid floor, chemical damp proofing, damage to rear plinth, central heating, double glazing with no or insufficient trickle vents, bathroom and lifestyle changes including more frequent showers and clothes washing, including greater occupancy during the Covid pandemic..
Ventilation assessment
Bathroom extractor (nearest damp wall) The extraction rate was 14.3 l/s (the Building Reg. minimum is 15 l/s). The extractor overrun was 15
minute(s) after the light was switched off. It should overrun for at least 30 minutes.
I extended the bathroom extractor fan overrun to 30 minutes. Note is slightly noisy and in my experience probably resulted in the tenant turning the fan off on the isolator.
Kitchen ventilation
The kitchen does not have an externally ducted extractor fan.
Thermal imbalance
The main source of unvented vapour appears to be the bathroom, kitchen and from drying clothes internally.
Ventilation improvements
Keep the bathroom door closed. In addition, dry clothes in a vented room or vented tumble drier (externally ducted). Install an externally ducted extractor fan to the kitchen. Keep heat balanced across the property and across the day and night so that the wall temperature doesn’t drop below the dew point. Consider retrofitting trickle vents into double glazed windows.
Ventilation overall
The main source of unvented vapour appears to be the bathroom, kitchen and from drying clothes internally. You should consider upgrading your ventilation. In the meantime, keep a balanced heating system and wipe away mould and condensation as soon as it appears.
Penetrating damp assessment (rainwater)
The drains seem to function correctly.
Timber assessment (structurally significant rot and woodworm)
There are no suspicions of significant timber decay.
Leak assessment (mains and wastewater)
There are no obvious signs of a significant mains or wastewater leak.
Rising damp assessment (groundwater i.e. water under the water table)
Elevation: 103M above sea level. Flood risk: no risk.
Sub-soil rocks: Rocks with essentially no groundwater.
Signs of groundwater: rising damp is not of concern.
Therefore risk of rising damp is highly unlikely, see a good explanation by
Dr Robyn Pender of Historic England https://youtu.be/Jo8oF9ubvtI
Despite the low risk of rising damp, there has been an attempt at treating the building with chemicals to stop rising damp.
Other matters
The property was reasonably uncluttered, which improves the distribution of warm air currents, but is unlikely to have been when tenanted.
Savings
By taking a root cause approach, rather than a focus on blocking the symptoms of damp the savings are likely to be around £5,000.
Outstanding matters
There are no outstanding matters. The remedial actions should resolve the highlighted damp issues. If they don’t, and the wall is given sufficient time to dry (6 – 10 months for any form of remedial treatment).
Video Link
Video to help understand damp issues.