What Lies Beneath:
A Dry Rot Outbreak

Case Study

A severe case of dry rot (Serpula Lacrymans) was discovered within a suspended timber floor in a residential property. The dry rot was spotted as it breached the carpet and begun to creep up the skirting boards on one side of the room. However, it had been growing undisturbed for some time before it was discovered! The cause of the dry rot outbreak was a blocked external drain which had forced rainwater to flow into the sub-floor void and a raised ground level which had blocked airbricks. In order to solve the issue, we stopped the source of moisture, removed and disposed of the existing flooring, applied our specialist dry rot treatment and installed a new floor. This case of dry rot occurred in a detached property occupied by a small family.

dry rot

The Problem

The Dry Rot Outbreak 

The dry rot first reared its ugly head through the carpet in a spare room. It was poking up at the edge of the room and creeping onto the skirting board. At first sight it could have been mistaken for a small area of mould. However, upon closer inspection, it was clear this a much larger issue! We removed the carpet to expose the fungus and realised that this was quite a spectacular example causing extensive damage. The dry rot had spread its mycelium network throughout the timbers under the floor. Fruiting bodies were also discovered near joints between the wood and the wall. Reddish brown dust (spores) was also evident on the oversite underneath affected timbers. 


The Source of Penetrating Damp 

The dry rot fungus requires a source of moisture to grow and flourish. So our first job, after discovering the outbreak, was to locate the source of water.  After a little bit of investigation, we discovered that an external drain was blocked causing rainwater to flow undetected into the sub-floor void. The rainwater had overwhelmed the inner and outer brickwork, penetrating into the timber floor joist that abutted the exterior wall. This is where the dry rot fungus originally established itself. Also, the ground level outside the property had been raised when a new driveway had been installed. This work had caused an external airbrick to become covered with earth. Moisture from the soil was then able to penetrate into the sub-floor void through this route. Ventilation was also negatively affected creating the perfect conditions for the dry rot to flourish. 

The Solution

Stopping The Source of the Moisture – Repairing Rainwater Goods and Drying Out 

Before any treatment could be administered within the sub-floor, we needed to stop the sources of moisture and allow the area to dry. This is essential in preventing any future dry rot spores from germinating. We cleared the blocked drainage gully and removed any damp plaster from the affected internal area. Then we gave the sub-floor area time to dry before moving onto using our specialist dry rot treatment.


Stopping the Source of Moisture – Lowering Ground Levels & Replacing Airbricks 

We reduced the ground levels outside of the affected room to approximately 150mm lower than the damp proof course (DPC). We also installed a French drain, including perforated pipe and a loose stone covering. Four new airbricks were installed around the property. 


Removing Damaged Material  

Firstly, we removed and disposed half of the existing flooring in the affected room. This included all floorboards, joists and wall plates up to 600mm beyond the last evidence of the fungus. All dry rot (Serpula Lacymans) material was removed including clearing all traces of dry rot spores. 


Treating the Dry Rot 

Our specialist Dry Rot treatment began with scraping all mycelium from the brickwork and oversite. Next, we treated all the remaining exposed timbers in the sub-floor void using Safeguard* fungicidal fluid. Then we sprayed all exposed masonry and oversite areas with Safeguard dry rot eradication fluid.  


Replacing Timber 

The entire floor needed replacing so we reconstructed it using new pressure treated wall plate and floor joists. We then installed a floor covering comprised of moisture resistant chipboards and replaced affected skirting boards, which matched the original design.  


*Safeguard Europe are the leading manufacturer of specialist damp-proofing and water-proofing products. 

finished job
blocked airbrick

Our Recommendations

Regularly Check Rainwater Goods

As the cause of this dry rot outbreak was damaged rainwater goods and airbricks that had been covered with earth it is essential that the occupant now regularly checks and maintains their gutters and downpipes. This should be at least a bi-annual inspection to check that there is no damage or blockages which have a negative impact on their ability to remove rainwater effectively. 


Ensure Adequate Sub-floor Ventilation

It is also essential that any airbricks around their property are not blocked or covered in earth or debris. Sometimes future construction or landscaping works can result in the ground level being raised and ventilation being mistakenly obstructed (as was the case here). It is paramount that if this happens then any airbricks or other sub-floor vents are not covered. Airbricks are very important for allowing air to flow through the sub-floor voids in order to reduce humidity and remove stagnant air. Poorly ventilated and moist sub-floors are the perfect breeding ground for the dry rot fungus! 


Get In Touch With The Experts

If you think your property might be suffering from dry rot or any other damp problems get in touch today for friendly, expert advice and solutions! 

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About Insitu SCP

Insitu SCP are one of the most established names in building preservation in the South East of England, with over 40 years experience in the industry. You can be assured that we will identify potential issues, find the best solution and deliver long lasting results with minimal disruption. Please contact us to discuss your requirements and we will do our utmost to assist you.

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