Private renting, England
10%
of privately rented homes had damp in 2024.1
7% of social homes. 4% of owner-occupied homes.
Concept product · Manchester
Damp Diary
The tenant’s side of the story.
Warns you the night before. Tells you why. Keeps the record.
Planned price £29, one-off. Not yet for sale.
Damp is common.
So is the argument.
3%
of all homes had severe condensation, the most common form of damp.1
37%
of renters living with damp, cold or mould have never complained to their landlord. 51% of them cite fear of retaliation.2
Is it how you live, or the building?
That is the question every damp report turns into. The tenant normally has photos and nothing else.
The Chief Housing Ombudsman said the word ‘lifestyle’ should be “banished from the vernacular”.3
Image is a concept render.
One night in a Manchester bedroom
21:00
The night before.
Damp Diary compares tomorrow’s forecast with how your room usually behaves, hour by hour. If the coldest corner is likely to run wet, it tells you which hours and what to do. The ring pulses amber when a message arrives.
Example message
Tomorrow 6am to 9am, the bedroom’s coldest corner is likely to run wet. Keep the heating on low tonight, and open the window for ten minutes after your morning shower.
02:00
Close to condensing.
The light turns amber when the coldest surface nears the point where water condenses on it.
06:00
The corner runs wet.
Red when the coldest surface is wet. Every reading behind it is signed and dated in your log.
09:00
Back to green.
Window open after the shower, heating on: the room dries out and the light settles back to green. The log keeps the whole night.
Gen 1 · The prototype
Built from parts you can order today.
An off-the-shelf box, a light ring, two small boards and a battery. No wires on the wall.
- Frosted windowA frosted acrylic disc in a hole drilled in the lid. It spreads the light.
- LED ringTwelve LEDs: green, amber or red at a glance. £0.40
- SHT40 sensorTemperature ±0.2°C and humidity ±1.8% RH, typical (datasheet), by drilled side vents. £1.63
- ESP32-S3 boardReads the sensor and talks to the server over Wi-Fi. Module £2.46
- BatteryA 300 mAh pouch, so nothing is plugged in on the wall. £0.67
- ABS caseOff-the-shelf 36 x 36 x 20 mm wall box with four corner screws. £0.62
Concept model. Listed Alibaba.com prices for single parts, 15 October 2026, before shipping and VAT.10 Battery life not measured yet. Firmware written and compiling, not yet run on a real wall.
Gen 2 · The finished version
One soft square. One ring of light.
The same insides, designed as a product: about 40 x 40 x 18 mm, seamless, with a press button that sends a reading.
- Front shell and buttonSeamless matte shell with a press button in the middle. Press it to send a reading now.
- Light ringFrosted light guide: green, amber or red. An amber pulse means a new message.
- LED ringTwelve LEDs behind the light guide.
- Main boardShielded Wi-Fi module, USB-C, and the SHT40 sensor at the board edge behind a slot, away from the chip’s heat.
- BatterySlim backup battery for power cuts and moves.
- Back plateVent slits so room air reaches the sensor, and a keyhole wall mount.
Example message
Your bedroom’s coldest corner is close to condensing. Open the window for ten minutes.
Concept design, not final. Core parts £5.78 at listed Alibaba.com prices (15 October 2026), before the board, assembly, shipping and VAT.10
Gen 1 and Gen 2.
From a drilled box to a finished product.
| Gen 1 | Gen 2 | |
|---|---|---|
| Case | ABS project box, 36 x 36 x 20 mm, corner screws | Seamless rounded shell, about 40 x 40 x 18 mm |
| Light | 12-LED ring behind a frosted acrylic disc | Frosted light-guide ring over a slim LED ring |
| Brain | ESP32-S3 development board | Own main board with a shielded Wi-Fi module |
| Sensor | SHT40 board by drilled side vents | SHT40 at the board edge behind a slot |
| Button | On the board | A press button in the middle of the face |
| Power | Battery only, no wires on the wall | USB-C, with a slim backup battery |
| Status | Parts selected on Alibaba.com | Concept design |
What the light means.
On your phone.
- The night before. An alert with the hours your coldest corner is likely to run wet, and what to do.
- Live. The light’s colour and the room’s readings in °C and % RH, whenever you look.
- The record. The verdict, the signed diary and the landlord letter in one place.
App demo loading
App demo loading
Concept app (PWA, installs from the browser on iPhone and Android). Today the alerts arrive in a Telegram chat. Example data in the demo.
After 7 days, a reading every 10 minutes
Living, or the building?
It answers with numbers.
It compares the moisture in your room’s air with the air outside, and how often the room is cold. A lot of added moisture points to ventilation. A cold room with normal moisture points to the building.
Example from simulated readings
Moisture added indoors, median
1.4g/m³
Normal living, not excess moisture.
Time below 16°C
42%
The room is often cold.
Coldest surface above 80% RH
37.5h
The usual mould-risk threshold.
Verdict
The building.
The fix is affordable heating and insulation, which is the landlord’s side.
| What the week shows | Verdict |
|---|---|
| Over 4 g/m³ of moisture added indoors, room not cold | Ventilation |
| Normal moisture, below 16°C more than 30% of the time | The building |
| Both | Mixed |
A log nobody can quietly change.
A letter that cites the law.
The signed log
Each reading is signed together with the one before it (HMAC-SHA256). Change or delete any old reading and the check shows exactly where. Export it as a file at any time.
Example rows
time temp RH signature
2026-10-14 06:00 12.8°C 85.7% sig e2b4…19c0
2026-10-14 06:10 12.8°C 86.0% sig 9f3a…c2e1
2026-10-14 06:20 12.7°C 86.4% sig 41b7…08da
2026-10-14 06:30 12.7°C 87.1% sig d05e…7b93
The landlord letter
If the verdict is the building, Damp Diary drafts a letter from the log: the dates, the readings, the hours of risk, and the law that applies.
“I am writing about condensation, damp and mould in the bedroom at my home in Manchester.”
The law it cites
Social landlords. Awaab’s Law since 27 October 2025, with phase 2 from 30 November 2026.4
Private renting. Government consultation on extending it, 9 October to 11.59pm on 18 December 2026.4
The letter is not legal advice. Shelter and Citizens Advice can help with that.
Three parts. Here is where each one stands.
Prototype
The sensor
Reads temperature and humidity every 5 seconds and reports every 10 minutes, or at once when the humidity jumps or the button is pressed. Firmware written and compiling. Not yet run on a real wall.
Built
The server
Signs every reading into the log, pulls 7 days of past weather and 3 days of forecast from Open-Meteo, estimates the coldest surface, and writes the verdict and the letter. 27 automated tests pass.
Built
The chat
Telegram today: alerts, the night-before warning, “why”, the letter, the log and “delete my data”. Nothing is stored before you say yes.
Not proved yet.
- No real home has been measured yet.
- The coldest-surface temperature is an estimate until a probe in the corner measures it.
- Whether councils, courts or ombudsmen accept a tenant’s own sensor log is untested.
Damp sensors exist.
Most of them work for the landlord.
In research on 15 October 2026, no product was found that turns a tenant’s own readings into a signed record, a verdict and a landlord letter.
| Product | Bought by | What the tenant gets |
|---|---|---|
| Aico HomeLINK, Switchee, FireAngel5 | Social landlords | Readings or alerts in an app. The record is the landlord’s. Aico separates structural causes from how the home is used (vendor-stated). |
| Cambridge Logic, Maple Diagnostics6 | Landlords and surveyors | Cause reports, written for the landlord or surveyor. |
| Breckland Council logger loans7 | One council, for local private tenants | Borrowed loggers. Council-owned. |
| Govee, SwitchBot hygrometers8 | Anyone, about £10 to £15 | Humidity alerts and history. |
| Airthings Wave Mini8 | Anyone, about £68 | A mould-risk indication from past readings (vendor-stated). |
| claim.co.uk app9 | Tenants | Analysis of photos, from a claims company. |
| Damp Diary | The tenant, £29 planned | A night-before forecast, a verdict with numbers, a signed log the tenant owns, and the landlord letter. |
Why I am building this
“Since finishing my master’s at the University of Manchester in 2025, I have moved house again and again. I lived with mould, and then with tenancy problems. Damp Diary is the device I wanted in each of those homes.”
- MSc Finance, University of ManchesterBicentenary Global Futures Scholar
- 19 months of cost-benefit analysisADB-funded infrastructure, DPM Consultants, Dhaka
- Venture Further Awards 2026Grand Finalist, Creative Excellence Award
- BAT Battle of Minds 2020National champion
Renting with damp?
Hear when Damp Diary is ready to try.
For the selection committee.
Everything behind this page, in one place.
Deck
The pitch deck, 15 slides
The problem, the product, Gen 1 and Gen 2, the evidence, the business and the road to the final.
App
The app demo
The night-before alert, the morning, the verdict and the letter, on a loop. Example data.
Plan
The plan
The business, the software and the hardware, with a Built, Prototype or Plan status on every part.
Drawings
Design drawings
Gen 1 and Gen 2 as views, dimensions and numbered parts.
Concept product. Renders and drawings are concept visualisations. The app demo uses example data.