🪵 A detection dog might one day help find hidden dry rot, but today the answer still comes from a proper timber survey that finds the water as well as the fungus.
Dry rot is the timber problem people dread. It hides behind plaster, under floorboards and inside walls, and by the time it shows itself it has often travelled a long way. So when a dog handler told us on The Healthy House Podcast that dogs can sniff out fungus, it was worth stopping to ask whether that could change how we find dry rot in homes.
In this week's episode of The Healthy House Podcast, Aaron Worrall talks to Kat, a detection dog handler, about what dogs can really smell and what that means for buildings. Aaron hosts the show and Weather Wise Solutions presents it. Dry rot only comes up near the end, but it is the part that homeowners with a worry under the floor will want to hear. This guide covers what she said, and then what we would do about hidden dry rot today.
🎙️ What Did Kat Say On The Healthy House Podcast?
Kat works with scent detection dogs. Her own dogs are trained to find Japanese knotweed rhizomes underground, and one of them is working on a project searching for a rare type of waxcap mushroom. Dry rot is not what her dogs are trained on today. What she shared about it is her view of the field and her plans, and we have paraphrased it here rather than quoting it.
Dogs have already been used on dry rot
Kat explained that dogs have been finding dry rot for a while. She described a friend's company that used dogs on large and listed buildings and found dry rot in places that were hard to reach, including behind marble in a bathroom (at around 1:01:48 in the episode). Kat added that where a marble bathroom is involved, working out roughly where the problem sits first is far less stressful than ripping it out blind (at about 1:02:38).
She is thinking about training dogs for it
Kat said she has been looking into dry rot as another area for her dogs, and that she thinks there is a big market for it (at about 1:03:01 and 1:09:03). She was clear that she would first need to understand the fungus much better. She also pointed out the practical side: a dog needs samples to learn from, so you have to keep some dry rot alive somewhere safe for training (at about 1:03:24).
Dogs would need proofing against other fungi
She said a trained dog has to be tested against look-alikes. In the same way her waxcap dog ignores the common meadow waxcaps and only responds to the rare family she has been trained on, a dry rot dog would have to be checked against other types of fungus so it doesn't respond to the wrong thing (at about 1:04:05 to 1:04:20).
Mapping the spread
Aaron asked whether a dog could map how far dry rot has travelled, because it can carry moisture through its own growth and reach places a surveyor can't see. Kat thought it should be possible as long as some scent can escape. If the timber were completely sealed in, a dog might struggle, because there would be nothing to smell. With even tiny openings, she thought the dog should be able to show where the scent starts. She compared it with how her dogs work on knotweed: they search from further away and move towards the plant, and the point where they start to follow a trail shows how far the roots have gone (at about 1:05:32).
Dogs are a help to surveyors, not a replacement
This was the part we liked most. Kat said dogs are very capable, but they are animals. They have better and worse days, and weather and soil can affect them. She described her dogs as an extra service that works alongside surveyors, not something that replaces them (at about 10:50). She also described a site where two experienced human surveyors had searched thoroughly and found no knotweed, and her dog found a piece within about 30 seconds (at about 12:14). Her point was that dogs don't rely on sight. They rely on scent, so they notice things eyes miss.
How to judge anyone offering dog surveys
Kat said the industry isn't heavily regulated, and her advice was to ask how the dogs are trained and how they are tested (at about 43:02). She would want a dog trained on one target, not twenty, and she would be wary of anyone claiming a dog is always right, because nothing in life is a hundred per cent, human surveyors included (at about 43:19). She said her own dogs are tested once a year, and the person who knows where the target is should ideally not be in the field during the test, because dogs pick up on human body language (at about 31:10 and 32:23).
We have not added anything to what she said. If you want to hear her explain it in her own words, the full episode is well worth the listen.
🔍 Why Is Dry Rot So Hard To Find?
Dry rot is a wood-rotting fungus. It needs damp timber to start, but once it gets going it can spread through masonry and across timber that isn't wet, which is why it has a reputation for causing more damage than wet rot. It likes still, humid, poorly ventilated places, such as sub-floor voids, the back of panelling, behind skirting boards and the ends of joists built into walls.
The trouble for a homeowner is that most of this is out of sight. The first signs you see may be a floor that dips or feels spongy, skirting boards that have shrunk away from the wall, paint that bubbles for no obvious reason, or a musty, mushroom smell. By then the fungus has often been growing for some time.
Signs that point to dry rot
- Timber that cracks across the grain into deep cubes and crumbles in your fingers.
- White or grey growth that looks a bit like cotton wool, sometimes with yellow or lilac patches.
- Flat, rust-red dust on nearby surfaces, which is the spores.
- Grey strands that spread across brick or plaster.
- A damp, musty smell that gets worse when a room is shut up.
- Floors or skirting that move, sag or feel soft.
None of these signs proves dry rot on its own. Wet rot, woodworm damage and ordinary damp can look similar to an untrained eye, so a proper look matters before anyone starts ripping things out.
🧪 Is It Dry Rot Or Wet Rot?
This is the first question a surveyor wants answered, because the two behave very differently and are dealt with differently.
Wet rot
Wet rot stays where the wood is wet. It tends to darken the timber, leave it soft and fibrous and crack it along the grain. Take away the source of moisture, let the timber dry and it generally stops. Our guide to what causes wet rot in floor joists explains how it starts.
Dry rot
Dry rot can grow beyond the wet area. It sends out strands that can cross masonry to reach new timber, which is why it can show up some distance from the original leak. That spread is what makes it harder to survey, and why the question of how far it has gone is so important.
You can read more about the difference in our guide what is dry rot, its causes, signs and treatment, and in our piece on early signs of dry rot in floor timbers.
💧 Where Does The Moisture Come From?
Dry rot doesn't start from nothing. Something has to wet the timber first, and a surveyor's job is as much about finding that source as it is about spotting the fungus. Common causes include:
- A leaking gutter, downpipe or roof junction soaking a wall and the timbers built into it.
- A slow leak from a pipe, radiator joint or waste, hidden under a floor or behind a bath panel.
- A bridged or failed damp proof course, or ground piled up against an outside wall.
- Blocked air bricks, so the void under a ground floor stays still and humid.
- Condensation in a poorly ventilated void or in a room that is rarely heated.
- Building work that traps timber in damp masonry, or a roof or floor left open to the rain.
Aaron touched on this in the episode. He said dry rot likes humid conditions and that the humidity this year has led to a rise in cases, and that people sometimes leave it lying dormant until it spreads quickly. That matches what we say to homeowners. Fix the water, and the fungus has nothing to feed on.
🛠️ How Do Surveyors Find Hidden Dry Rot Today?
You don't need a dog to get a good answer, but you do need someone who looks at the whole building rather than only the patch of damage you can see.
Start with the outside
We look at the gutters, downpipes, roof edges, ground levels, air bricks and the condition of the walls, because that is often where the water comes in. A dry rot problem under a floor frequently starts at an outside wall.
Probe the timber
Pressing a probe into skirting, joists, floorboards or window timber shows where sound wood ends. Dry rot leaves timber brittle and cuboid, and a probe tells you quickly whether the wood has lost its strength.
Take moisture readings
A moisture meter helps to map where the building is wet. Timber that stays above about 20 per cent moisture content is at risk of decay. Readings on the timber, the plaster and the wall behind all matter, because a dry timber surface can sit next to a wet core.
Look in the places you can't see
Where lifting a floor or opening a wall isn't allowed or isn't sensible yet, a borescope camera can be passed through a small hole to look into the void. Aaron described doing a dry rot survey like this recently, getting under a floor with a borescope when the owner wouldn't allow invasive work. It isn't perfect, because a camera only shows what is in line of sight, but it can save a lot of unnecessary damage.
Open up carefully when needed
Sometimes the only way to know the full extent is to take up a floor section or remove a patch of plaster. That is a judgement for the surveyor and the owner together. The aim is to open up as little as possible, and in the right places.
🐕 Where Could A Detection Dog Fit In?
From what Kat said, a trained dog could one day be a useful extra tool. It could help to narrow down where fungus is growing in a building where lifting everything isn't practical, such as a listed property or a room with expensive finishes. It might also help to work out how far a problem has spread before you open up.
There are limits, and she was open about them. A dog's performance changes with the day, the weather and the setting. The dog has to be trained and tested well, and you need to know what exactly it has been taught to find. A dog's signal also doesn't replace evidence. In Kat's knotweed work, the team confirms what a dog has marked by digging. For timber it would be the same: you would want to see the decay to confirm it before anyone started repairs.
We are not aware of a standard route for a homeowner to book a dry rot detection dog today, and Kat herself described it as something she is still looking into. So for now the practical answer is a surveyor with the right training, a moisture meter, a probe and a camera.
🧱 Can A Dog Tell You Why The Fungus Is There?
No, and this is worth saying plainly. Even a perfect method for finding fungus, dog or otherwise, tells you where it is, not why it grew. If you take out the rotten timber and leave the leak, the damp masonry or the blocked air brick, the problem comes back.
That is why a proper survey spends time on moisture sources as well as the timber. The fungus is the symptom. The cause is water, and ventilation that isn't doing its job.
🧰 What Does Dry Rot Treatment Involve?
The details depend on the building and the extent of the decay, and they are a judgement for a qualified surveyor after seeing the actual timber. In general the steps run like this:
- Find and stop the moisture source.
- Open up enough to see how far the decay and any fungal strands have gone.
- Remove the affected timber, cutting back to sound wood with a sensible margin.
- Deal with the masonry and any residue as the surveyor advises.
- Protect new and retained timber, and improve ventilation so the area can stay dry.
- Replace timber and finishes, once everything has dried.
You can read how we approach this on our wood rot and woodworm page and our wet rot treatment page.
🚫 What Should You Avoid If You Suspect Dry Rot?
- Don't rip out timber and carry on without finding out what is wetting it.
- Don't paint over a damp patch or spray a surface and call it treated.
- Don't bin the evidence. Take photos before anything is removed.
- Don't assume that no visible growth means no problem. Dry rot can hide for a long time.
- Don't move affected timber around the house or garden, because spores and fragments can spread.
- Don't rely on a single quote from someone who hasn't looked at the water source.
Aaron said on the episode that the biggest problem with dry rot is the cost people run into when they leave it dormant and it spreads. Catching it early, and finding the water, is the cheapest route.
🏠 Can You Check Anything Yourself?
There are a few safe checks any homeowner can do without a survey. Stay on the ground floor or the loft hatch, and don't take risks with ladders or loose boards.
- Walk across your floors. Note any that dip, bounce or feel soft, especially near outside walls and under windows.
- Look along the bottom of skirting boards for gaps, shrinkage, cracks or crumbly wood.
- Check the air bricks on the outside of the house. They should be clear, with no soil, plants or paint blocking them.
- Look at gutters and downpipes in the next dry spell for leaks, overflows and stained brickwork.
- Sniff the air in cupboards under stairs, in sub-floor hatches and in rooms that are rarely used. A strong mushroom smell is a warning.
- Take dated photos of anything you find, so you can see whether it changes.
❓ What About Mould And Leaks, Can Dogs Find Those Too?
Kat mentioned that detection dogs are being used in a range of other jobs. She said there are dogs trained to find mould, which can be a health concern because it can affect people (at about 1:07:16), and she described dogs trained to look for water leaks in pipelines (at about 1:00:58). She wasn't sure of the exact method used in the UK for the leak work, so we won't claim more than that.
It does show where the idea is heading. If scent training can find a pipeline leak or a particular fungus underground, it is reasonable to think it could help with buildings too. Whether it becomes common in homes is something we will have to wait and see.
🪟 What Else Can Look Like Dry Rot?
Several things get mistaken for it.
- Wet rot, which stays in the wet area and darkens timber.
- Woodworm, which leaves small round exit holes and fine dust, not cuboid cracking.
- Surface mould, which grows on damp walls and ceilings but isn't the same as a wood-rotting fungus.
- Efflorescence, the white salt deposits on damp brickwork, which can look like fungus growth.
- Old, dry decay, where rot stopped long ago when the timber dried out.
Reading the signs correctly is one of the main reasons the right qualification matters.
🎓 Why Does The Surveyor's Training Matter?
Telling dry rot from wet rot, working out how far it has gone and tracing the water behind it takes training and experience. Our surveying team includes professionals holding the Certified Surveyor of Timber & Dampness in Buildings (CSTDB) qualification alongside the Level 3 Award DMCB and City & Guilds-recognised FODCS qualification.
We cover this when we visit a property: the timber, the walls, the roof drainage, the ground levels and the ventilation, all in the same look. You can meet our qualified surveyors to see who does the work.
🧑🔧 How Do We Look At A Suspected Dry Rot Problem?
- We look at the outside of the building first, for the sources of water.
- We inspect the timber and the walls around it, probing and taking moisture readings.
- We check the ventilation, including air bricks and sub-floor voids where they exist.
- We use a camera where it can show us what is behind a surface without opening it up.
- We tell you what we have found in plain words, what is most likely, and what still needs to be confirmed.
- We explain what needs to be fixed first, and in what order.
If it turns out to be something simpler than dry rot, we will say so.
🎧 Hear More On The Healthy House Podcast
If you want the whole conversation, including the knotweed stories, the waxcap project and how Kat trains her dogs, listen to the full episode here. It is episode 10, released on Monday 5 October 2026. Aaron Worrall hosts The Healthy House Podcast, and Weather Wise Solutions presents it. What Kat says on the show is her own view and experience. It isn't a statement about our services, and she doesn't recommend or endorse us.
✅ Quick Answers
Can dogs find dry rot?
According to Kat, dogs have been used to find dry rot, including behind marble in a bathroom. She is looking at training dogs for it herself, but her dogs aren't trained on it today.
Could a dog tell me how far dry rot has spread?
Kat thought it should be possible if some scent can escape from the timber. If the timber is fully sealed, a dog might struggle.
Do detection dogs replace a surveyor?
No. Kat described her dogs as working alongside surveyors, and said they have better and worse days like any other tool.
How do I know if it is dry rot or wet rot?
Deep cube-shaped cracking, white growth, rust-red dust and a mushroom smell point to dry rot. Wet rot stays where the wood is wet. A survey is the only way to be sure.
What should I do first?
Find and stop the source of water, and get the timber checked before you pull anything out.
📞 Worried About Hidden Dry Rot?
If you've found soft timber, a musty smell or a floor that has started to move, and you want to know what is behind it, we can help. Read about our qualified surveyors, or get in touch.
Our services include:
- Damp and timber surveys
- Wet rot and dry rot assessment and treatment
- Woodworm treatment
- Condensation and mould control
- Ventilation advice
We're members of the Damp Proofing Association and the Federation of Damp. Our surveying team includes professionals holding the CSTDB qualification alongside the Level 3 Award DMCB and City & Guilds-recognised FODCS qualification.
Book your free survey with Weather Wise Solutions on 01782 901101, or get in touch online.