Ventilation Solutions & PIV Systems in North London
The permanent fix for condensation and mould isn't cleaning — it's air movement. We arrange PIV systems, extraction upgrades and whole-home ventilation design across North London.
What is positive input ventilation (PIV)? A PIV unit is a quiet fan system, usually loft-mounted (or wall-mounted in flats), that continuously draws in fresh filtered air and delivers it into the home at a gentle rate — slightly pressurising the property so stale, humid air is pushed out through natural leakage paths. Running costs are typically a few pence a day, installation takes about half a day, and installed prices in North London run £800–£1,500. For whole-home condensation and recurring mould, PIV is the most effective single retrofit available for typical houses and converted flats.
Understanding the problem
Modern refurbishment made North London's older homes airtight without making them ventilated. Double glazing without trickle vents, draught-proofed doors, sealed chimneys and insulated lofts all cut heat loss — and trapped the moisture that used to leak out. The building's air-change rate collapses, humidity climbs, and every cold surface becomes a condensation plane feeding mould.
Ventilation design puts the air-change rate back deliberately: extract at the wet rooms, supply fresh air to the habitable rooms, and keep a background flow the occupants don't have to think about. Done properly it's silent, automatic and cheap to run.
Signs your home is under-ventilated
- Condensation and mould recurring in multiple rooms
- Stuffy, stale air; smells lingering long after cooking
- Windows streaming despite wiping and airing
- No trickle vents on double-glazed windows
- Bathroom fan absent, broken, or venting into the loft
- Converted flat with single-aspect rooms and no cross-flow
What good ventilation looks like
- Kitchen extraction 30–60 l/s ducted outside (Part F)
- Bathroom extraction 15 l/s, humidity-controlled, with overrun
- Background ventilation in every habitable room
- Whole-dwelling air movement — PIV or equivalent — so no room stagnates
- Ducts that actually reach outside, not loft or void discharge
Getting the diagnosis right
We start with a ventilation audit: extraction flow measurements against Part F rates, duct checks (a shocking number of fans discharge into lofts, causing loft condensation), background provision per room, and humidity logging. The output is a ranked plan — often the first fix is embarrassingly simple, like a blocked duct — with PIV specified where whole-home air change is the gap. Use the free Ventilation Audit Checklist to see where your home stands.
Treatment
- PIV installation — loft unit with ceiling diffuser for houses; wall-mounted through-flow units for flats. Filtered supply, optional gentle heating of incoming air, near-silent operation.
- Extractor upgrades — humidity-triggered fans with overrun timers in bathrooms; ducted hoods in kitchens; rigid ducting to outside with condensation traps where needed.
- Background ventilation — retrofit trickle vents, through-wall vents with acoustic baffles on busy roads, door undercuts for cross-flow.
- Special cases — MVHR advice for well-sealed refurbishments; subfloor airflow via subfloor ventilation; loft airflow via eaves and tile vents.
What does it cost in North London?
| Item | Indicative range |
|---|---|
| Ventilation audit | £120 – £250 |
| PIV unit installed (house, loft-mounted) | £800 – £1,300 |
| PIV unit installed (flat, wall-mounted) | £900 – £1,500 |
| Humidity-controlled extractor, installed | £250 – £450 |
| Trickle vents, per window | £60 – £120 |
PIV running costs are typically £10–£30 per year in electricity — often offset by reduced heating of damp air. Figures are indicative for North London (2026) and vary with property, access and scope — written quotations follow a survey. See the North London Damp Cost Guide or try the Damp Proofing Cost Calculator.
Our process
Tell us the problem
Call or use the contact form — describe what you're seeing and where. Photos help.
Survey & diagnosis
An independent qualified surveyor inspects the property and identifies the true cause, with a written report.
Clear written quote
You receive a costed scope for exactly what the property needs — no more, no less.
Treatment & verification
Works are carried out by vetted independent specialists, with guarantees where applicable and verification that the fix worked.
Frequently asked questions
In North London, £800–£1,300 for a loft-mounted house installation and £900–£1,500 for a wall-mounted flat unit, including electrical connection. Premium models with integral heaters sit at the top of the range.
Yes — wall-mounted and cupboard-mounted PIV units are made specifically for flats without loft access. Converted Victorian flats, with their single-aspect rooms and sealed windows, are among the strongest candidates for PIV in the whole housing stock.
Modern units run at very low sound levels — normally inaudible from living rooms — and supply air at a trickle rather than a blast. In winter, models with a small integral heater temper the incoming air so the diffuser doesn't feel cold.
PIV ventilates the whole dwelling continuously for pence a day and needs no emptying; a dehumidifier treats one room, needs power, emptying and filter care, and does nothing for air quality. For an ongoing condensation problem, PIV is the structural fix; a dehumidifier is a short-term aid.
PIV removes the humid conditions mould needs, so regrowth stops in the large majority of condensation-driven cases. Existing growth still needs proper removal — see black mould removal — and mould fed by fabric damp needs that damp fixed too.
Worried about damp, mould or a wet basement?
Speak to us today or book a survey — we'll arrange the right independent specialist for your property.