Within Tolerance
A double-glazed window, one pane misted between the glass, with a cracked seal at the corner.

Windows and doors: locks, seals, glass and fire doors

The checklistThe detail

Open, close and lock every window and door, and check the keys are there. Look at the glass from 2m in daylight for scratches, and check sealed units for mist between the panes. Try every trickle vent. If you have an integral garage, the door into the house should close on its own. Report anything that sticks, leaks air or won't lock.

On the day

17 checks

Do the every-room checks first: Every room. These checks go through the whole house.

If something fails, add it to your snag list and report it to the builder. How to report a snag

Next: Heating and hot water

The detail, for reading before you go

Opening, closing and locking

Every window and door should open and close without catching, with handles, stays and catches working and fitted square. Stays are the arms that hold a window part-open. Keys should be there for every lock. LABC Warranty's checklist also asks whether windows and doors shut properly against their weather seals.

NHBC's standards say locks should turn easily, with keyholes properly lined up. A key that needs jiggling, or a handle you have to lift hard before it locks, is worth reporting.

Some stiffness is normal at first. The NHQB says windows and doors can feel stiff as materials dry out, especially south-facing ones in direct sun, and should ease with use. Don't force them. If one stays hard to use, doesn't close properly, or looks out of line, contact the builder.

How do I check windows for draughts?

Start by feeling. Clearview, a secondary glazing firm, suggests running your hand slowly round the inside edge of the frame. Any breeze, however small, usually means a draught.

A trick we used a strip of paper shut in the window, then pulled. Try the same strip in several places round the frame. If it slides out easily in one spot and grips in the others, note that spot.

The frame should have a seal all the way round it, inside and out. The NHQB lists draughts or cold air coming through closed windows and doors as a snag.

Scratched or misted glass

Check glass in daylight, from inside the room, standing at least 2m away. NHBC allows some small marks if they aren't obtrusive or bunched together. That includes fine scratches up to 25mm long, small bubbles and tiny particles. The outer 6mm of each pane, by the frame, isn't judged.

For toughened, laminated or coated glass, the distance is 3m.

Report scratches straight away. NHBC's Buildmark doesn't cover cosmetic damage, such as scratched glass, reported more than seven days after completion. The NHQB says light scratches can sometimes be polished out, but deeper ones may mean a new pane.

Mist or condensation between the two panes of a double-glazed unit is a different problem. LABC Warranty's checklist asks you to look for it. Condensation on the room side of the glass is common in a new home, where warm, damp air meets the cold pane. The year one page covers that.

What are trickle vents for?

They are the thin slots in the window frames that let a little fresh air in when the window is shut. Where a home relies on trickle vents and extractor fans, building regulations guidance says every room with an outside wall should have one or something similar. Homes with whole-house heat-recovery ventilation (MVHR) shouldn't have them. NHBC's standards say a window's "night vent" position doesn't count instead.

Slide each vent open and shut. It should move freely and close fully. Then leave them open. The NHQB says keeping trickle vents open helps a new home dry out.

Door gaps: how big is too big?

For internal doors, NHBC's standards allow a gap of up to 4mm at the top and sides, and it should be even. A door frame can be up to 5mm out of upright over its height. LABC Warranty uses the same 4mm limit.

The gap under an internal door is meant to be bigger. NHBC allows 10mm to 22mm above the bare floor, partly for ventilation. You choose a floor covering to suit, or have the door adjusted. So don't ask for that gap to be closed up.

A trick we used a £1 coin is about 3mm thick at the edge. If it slides easily into the gap at the side of a door, measure that gap.

Do I have fire doors?

You may. Building regulations guidance has two common cases in houses.

  • An integral garage. The door between the house and the garage should be a fire door with a self-closing device. Its opening should be at least 100mm above the garage floor, unless the floor slopes away to the outside.
  • A storey more than 4.5m above the ground. One option in the guidance is a protected stairway, with fire doors onto it. Inside a house, these don't need self-closers. If you have three storeys, ask the builder whether this applies to you.

The official checklist says fire doors should have gaps of 2mm to 4mm at the top and sides, no more than 4mm at the bottom, undamaged intumescent strips (the strips round the edge that swell in a fire), and an ID label on the top edge. A self-closer, where fitted, should work. Don't prop fire doors open.

Upstairs windows and restrictors

Restrictors limit how far a window opens, to reduce the risk of falls. The NHQB says to use them as intended.

Some upstairs windows are also your way out in a fire. The guidance says an escape window should open to at least 0.33 square metres, at least 450mm high and 450mm wide, with the bottom no more than 1100mm above the floor. It should stay open without being held. Locks and stays with child-resistant catches are allowed. If a bedroom has an escape window, check it stays open on its own.

From our own build

Our windows have a second latch that locks them slightly open, to let a little air in.

On three of them it didn't work.

Where this comes from

Every fact on this page comes from the documents below. Anything marked ‘a trick we used’ is our own.

Official and industry guidance

  1. New Homes Quality Board, Pre-Completion Inspection Checklist: House, Version 2, March 2026, p.5, p.17
  2. LABC Warranty, Snagging checklist for new build homes, undated (PDF metadata January 2016), retrieved 9 October 2026, Windows and doors
  3. NHBC, NHBC Standards 2024, Chapter 9.1: A consistent approach to finishes (copy published by New Build Inspections), 2024, 9.1.4, 9.1.6
  4. Ministry of Housing, Communities and Local Government, Approved Document F: Ventilation, Volume 1: Dwellings, 2021 edition, 2021 edition, in effect from 15 June 2022, 1.52, 1.72
  5. Ministry of Housing, Communities and Local Government, Approved Document B: Fire safety, Volume 1: Dwellings, 2019 edition incorporating 2020, 2022, 2025 and 2026 amendments, 2019 edition, September 2026 amendments, 2.2, 2.5, 2.10, 5.7, C5
  6. NHBC, NHBC Standards 2026, Chapter 6.7: Doors, windows and glazing (copy published by New Build Inspections), 2026, 6.7.9, 6.7.11.4
  7. New Homes Quality Board, A guide to settling into your new home, June 2026, p.7, p.8, p.9
  8. New Homes Quality Board, A homeowner guide to snagging, May 2026, Other possible snags and defects, Common snagging issues
  9. NHBC, Buildmark policy booklet (homes registered from 1 April 2025), April 2025, 2.1.2
  10. LABC Warranty, Technical Manual Version 11, Section 20: Tolerances, 2023, 20.1.6
  11. NHBC, Cracking in your home, November 2025, p.3

Snagging firms and buyer guides

  1. Clearview Secondary Glazing, How to Test Your Windows for Draughts in 4 Simple Steps, 15 March 2018, updated 15 January 2024, Get hands on

Last checked 15 October 2026

For general education only. It isn't legal or surveying advice. Always check your own warranty documents and Code version, and speak to your housebuilder, your warranty provider or a qualified snagging inspector before relying on it. Read the disclaimer.