Are French Drains the Ultimate Solution?
French drains are a common method to manage water issues around properties. Designed to prevent ground and surface water from infiltrating building foundations, they are an effective alternative to open ditches or storm sewers in urban and rural settings. They are also employed in septic systems to distribute water or relieve groundwater pressure behind retaining walls. While French drains have a reputation for resolving drainage problems, they are not a one-size-fits-all solution.
At Leakbusters, our expertise lies in identifying and resolving hidden leaks. However, not all cases of damp or water damage are due to internal plumbing issues. Frequently, damp walls result from rising damp or external groundwater ingress rather than leaks in pipework. A French drain might address external water problems, but a thorough investigation is crucial to determine the root cause of the damp before committing to such a solution.
In January 2024, we investigated damp patches in a modern block of flats, around 25 years old. Employing advanced techniques such as thermal imaging and moisture mapping, alongside static and dynamic pressure testing of internal pipework, we confirmed the damp wasn’t caused by a leak. External factors, like groundwater ingress, highlighted the need for targeted solutions—such as French drains—tailored to the specific issues at hand.
French drains are invaluable in certain scenarios but should always be installed based on accurate diagnostics and expert advice. If you’re facing persistent damp issues, consult professionals to identify the cause and recommend the best course of action
Internal was 68% moisture – should be 0.5%
Outside wall 85% moisture content in brick
Outside wall 85% moisture content in brick
We discussed with all the issues with all the occupiers of the affected properties and locals who had lived there for some times. The feed back was the area was always water logged even when there hadn’t been ‘rain or heavy rain’.
Time to Play Detective
Our investigative approach combines meticulous data collection and the expertise of our seasoned engineers to craft a tailored treatment plan for each case. Sometimes, the solution is straightforward, requiring only minor adjustments. Other times, it calls for a more intricate combination of remedies. In the situation we encountered, however, there was a singular resolution: the installation of French drains around the building’s perimeter.
The challenge lay in the building’s location, nestled at the lower end of a natural slope. Over time, the natural flow of groundwater from the higher terrain had no proper outlet and pressed directly against the brickwork. Without adequate drainage systems in place, this led to consistent damp issues, leaving the internal walls prone to moisture buildup.
French drains provided an efficient and effective solution. By creating a controlled path for water to follow away from the building’s foundation, we alleviated the pressure and prevented further groundwater ingress. This case is a strong reminder that even the best-built structures require proactive measures to contend with the forces of nature.
Resolving Conflicting Diagnoses: The French Drain Success Story
When we initially quoted the installation of French drains to address persistent damp issues at a property, the client sought second opinions. Two other contractors offered differing diagnoses: one recommended injecting a damp-proof course (DPC) into the external brickwork, and the other suggested another leak detection survey, despite our thorough investigation having ruled out hidden leaks. The client faced a dilemma: three contrasting opinions with the French drain solution being the most costly.
Contractor 3 performed a second leak detection survey and, like us, found no leaks. Contractor 2 injected the external brickwork with DPC and monitored the walls for four months. Despite this effort, the damp worsened, with bedroom wall moisture levels climbing from 68% to 85%, coinciding with rainfall. Frustrated and out of options, the client returned to us, having spent additional money without resolution. Upon engaging us to install the French drain system, the damp issues were finally addressed.
The results were immediate and measurable. One month post-installation, the 85% moisture level dropped to 62%, falling further to 55% in the second month and 49% in the third. Over six months, the moisture levels continued to decline until the walls dried out completely. This case underscores the importance of accurate diagnosis and tailored solutions, highlighting how advanced knowledge and expertise can resolve even the most challenging property issues.
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