Ventilation
Positive input ventilation
Whole-property ventilation that gently introduces filtered air to dilute and displace moist internal air.
What the issue is
A positive input ventilation unit is usually installed in the loft and introduces a controlled supply of filtered air into the property, encouraging moist air out through background ventilation paths.
Common symptoms
- Condensation in several rooms
- Mould in multiple locations
- Persistently high humidity
- Musty smell throughout
Likely contributing factors
- Insufficient whole-property ventilation
- Tightly sealed property with few air paths
- High occupancy and moisture production
Conditions that may be mistaken for it
- A localised leak causing damp in a single area
- Penetrating damp on one elevation
How the issue should be investigated
- Record humidity in several rooms
- Assess loft space and installation position
- Check available air paths and door undercuts
- Confirm electrical provision
Potential treatment or repair options
- Loft-mounted positive input ventilation unit
- Flat-specific hallway unit where no loft exists
- Improvements to internal air paths
- Combined localised extract improvements
When treatment may not be appropriate
- Where the moisture source is a single building defect
- Where the property has no viable installation position or air paths
Factors affecting the cost
- Unit specification and controls
- Loft access and electrical provision
- Ceiling diffuser installation
- Making good
What to expect during an inspection
A short survey of the loft, electrical supply and internal air paths, along with humidity readings.
Final recommendations always depend on the property, the inspection findings and the confirmed cause. Elevated readings alone do not confirm rising damp, not every mould problem requires extensive treatment, and damp-affected plaster does not always need replacing.
Frequently asked questions
Next step
Not sure which inspection you need? Start with a few questions.
Tell us what you are seeing and we will set out what is likely, what is uncertain and which inspection would answer the question. Speak to us on 0333 335 6152 if you would rather talk it through.