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Defect library

Ventilation defects in new builds

New homes are built to be airtight, so the ventilation has to work as designed to keep condensation and mould away. Check extractor fans run and that trickle vents open, and on homes with MVHR ask for the commissioning record.

Updated 19 October 2026

SiteSnag’s library has 6 entries under ventilation. They’re listed below with the most serious first. Each one gives the wording an inspector would put in a report and the trade that would fix it, and 4 carry a reference to the standard or guidance they relate to. The references help you look up the relevant section and aren’t a statement that a particular home does or doesn’t comply.

All 6 entries

  1. MVHR not commissioned / balanced

    Moderate

    MVHR system not commissioned or air flows unbalanced. Commission and provide records.

    Trade
    Heating engineer
    Reference
    Approved Document F

  2. Air bricks blocked / missing

    Moderate

    Sub-floor ventilation air bricks blocked or missing. Clear or fit.

    Trade
    Bricklayer
    Reference
    None listed

  3. Ventilation grille / valve missing

    Moderate

    Extract valve or grille missing. Fit and set.

    Trade
    Heating engineer
    Reference
    Approved Document F

  4. Extract rate insufficient

    Moderate

    Kitchen or bathroom extract does not clear moisture. Test flow rate and upgrade.

    Trade
    Electrician
    Reference
    Approved Document F

  5. Extract duct disconnected / not insulated

    Moderate

    Extract duct in loft disconnected, crushed or not insulated. Re-connect and insulate.

    Trade
    Electrician
    Reference
    Approved Document F

  6. MVHR filters dirty / not changed

    Minor

    MVHR filters dirty or not replaced. Clean or replace.

    Trade
    Mechanical contractor
    Reference
    None listed

Using these in a report

In the SiteSnag app, starting to type a defect title in the camera brings up these entries. Picking one fills in the description, severity, trade and reference, and you can edit the wording or add your own defects to the library. Every snag then goes into the branded PDF report with its photos and a numbered pin on the floor plan.

For a room-by-room walk-round, use the new build snagging checklist, or go back to all defect categories.

Other categories

Previous: General (9). Next: Insulation & damp (10).