Case Study · Condensation & Ventilation
PIV Installation to Stop Condensation and Mould in a Home
Streaming windows, black mould that kept coming back and stuffy, humid air. Here is how a Positive Input Ventilation (PIV) unit fixed the cause, not just the symptom, in a residential property.
Written by Sam Fitzgerald, Founder & Surveyor
Residential home
Condensation & mould
Inadequate ventilation
PIV unit installed
Loft / central hallway
Fresher air, low energy
The Problem
The homeowner was dealing with condensation streaming down the windows, black mould appearing around the window frames and in corners, and air that felt stuffy and humid. Beyond how it looked, they were worried about the health side, mould spores are a known trigger for breathing problems, and about the damage the moisture was doing to the property.
The Diagnosis
On inspection, this was not rising or penetrating damp getting in from outside. It was condensation: too much moisture in the air, with nowhere to escape. Everyday living, cooking, washing, drying clothes, even breathing, all add moisture, and in a home without enough ventilation that humid air settles against cold surfaces like windows and external walls, condenses, and feeds mould.
The Solution: A PIV Unit
We recommended a Positive Input Ventilation (PIV) unit, a proven, low-energy way to fix condensation at the cause. Sited in the loft or a central hallway, a PIV unit draws in fresh, filtered air and gently pressurises the home, continuously displacing the stale, humid air that mould needs to grow.
We assessed the property to find the best position for the unit, installed it with its electrical connections and ductwork, fitted filters to clean the incoming air of pollutants and allergens, and set it up with simple controls so the homeowner could adjust it. The unit also tracks humidity, so they could see it working.
The Outcome
The change was quick and noticeable. Condensation on the windows dropped away, the mould was brought under control, and the air felt fresher and cleaner. Because a PIV unit runs on very little electricity, all of this came at a low running cost. We followed up afterwards to check the unit was performing and that humidity had settled where it should be.
“We are extremely pleased with the ventilation solution provided by Advanced Damp. The PIV unit has made a remarkable difference. We no longer get excessive condensation on our windows, and the air feels fresher and cleaner. The team was highly professional from the initial assessment through to the final installation.”
Homeowner
Why It Matters
Condensation and mould are almost always a ventilation problem, not a building fault. Wiping mould off the wall or painting over it only treats the symptom, it returns because the humid, stagnant air that caused it is still there. A PIV unit deals with the actual cause by keeping fresh air moving through the home and humidity down, which is why it is one of the most effective long-term fixes for condensation, and a core part of our condensation and mould work.
Frequently Asked Questions
What is a PIV unit and how does it work?
A PIV (positive input ventilation) unit is a small, low-energy unit, usually in the loft, that draws in fresh filtered air and gently pressurises the home. That steady flow pushes out stale, humid air and keeps humidity low, so condensation and mould cannot take hold.
Will a PIV unit stop condensation and mould?
In most homes where the problem is condensation rather than a leak or rising damp, yes. By lowering the overall humidity and keeping air moving, it removes the conditions mould needs. We confirm condensation is the cause with a survey first.
Where is a PIV unit installed, and is it disruptive?
Usually in the loft or a central hallway, with the air delivered through a discreet ceiling diffuser. Installation is typically completed in a few hours with minimal mess.
Does a PIV unit cost much to run?
No. PIV units are designed to run continuously on very little electricity, so running costs are low, and by reducing damp air they can even make a home feel easier to heat.
Battling Condensation and Mould?
These are the signs that point to condensation, which a PIV unit is well suited to fix:
A survey will confirm whether condensation is the cause and whether a PIV unit is the right fix.
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Struggling with condensation and mould?
Book a survey and we will confirm the cause and tell you whether a PIV unit or other ventilation is the right answer for your home.
Sam Fitzgerald is the founder of Advanced Damp and a working damp and structural waterproofing surveyor with over 12 years of experience diagnosing and treating moisture problems in residential and commercial properties across London and the South East. He is FODCS certified (a Federation of Damp Certified Surveyor) and a member of the Federation of Damp. His hands-on work covers rising damp, penetrating damp, condensation, basement waterproofing to BS 8102, and thermal imaging surveys, and he has personally completed over 400 damp surveys across properties of every type and age. Everything he writes draws directly from jobs he has carried out. He does not write about treatments, products or causes he has not dealt with first-hand in the field.
