Loft and roof insulation against aircraft noise

When the noise comes from above, the roof is the part of the house nearest to it. Under a landing path the planes pass over the same streets at the same height every time: at 10 km from Heathrow's runways, over Kew or North Sheen, a landing plane is typically about 1,800 ft up. For a top-floor room, only the roof, the loft and the ceiling stand between you and it.

Why the roof matters when planes fly overhead

US guidance on insulating homes near airports, prepared for the Navy and hosted by the FAA, sets out how the roof behaves:

• Rooms under a loft are noisier than rooms with another floor above them.
• Sloping and vaulted ceilings are noisier still, and ceilings open to the roof timbers are the worst of all.
• Sound gets in two ways: directly, through vents and gaps, and by shaking the roof covering, which then passes the sound into the loft.
• A loft is a buffer. Sound entering it bounces around and loses energy before it reaches the ceiling, so less of it passes into the room below. That only works if the ceiling is sound and the loft is closed off from the rooms.

Keep it in proportion. Across the whole house, more noise usually comes in through windows and doors than through walls and roofs, so the windows come first. Our overview of soundproofing a home against aircraft noise sets out the order. The roof matters most for top-floor bedrooms, rooms in the roof and houses where the windows have already been dealt with.

What loft insulation does for sound

Three things decide how much sound gets through a roof and ceiling: weight, absorption and airtightness. Insulation mainly does the second.

Weight

Heavy layers block sound; light ones let it through, especially the low notes that make up much of aircraft noise. Glass wool and mineral wool are light, so a thick layer blocks very little. To keep sound out you need weight: a heavier ceiling, or a heavier roof deck.

Absorption

What insulation does well is absorb sound bouncing around the loft, or inside a cavity between two boards. For a low-pitched source such as a plane, thickness matters most: thicker layers absorb lower notes. US guidance for homes near military airfields asks for about 130 to 200 mm in moderate noise zones and 230 to 330 mm in the loudest, the upper figures for loose, blown insulation. The same guidance stresses that absorbing sound is not the same as insulating against it, and that insulation on its own has little blocking effect.

Airtightness

Any hole between the loft and a room lets sound straight through, however much insulation lies around it. The US guidance calls closing gaps the single most important step, and one that is sometimes overlooked.

Upgrading the ceiling

For a top-floor room, the ceiling is the real barrier. There are two ways to make it better:

• Add weight. A second layer of plasterboard, or a denser, damped board, makes the ceiling harder to shake.
• Separate it from the joists. Plasterboard hung on resilient bars, fixed across the joists, stops vibration passing straight from the roof timbers into the ceiling. In US guidance, doing this takes a typical roof and ceiling from about 45 to 55 points on the STC scale, a large gain. The screws must be short enough not to reach the joists; a screw that touches a joist carries the vibration straight through and undoes the work.

Insulation between the joists above the new ceiling then works as the absorbent layer in a proper double construction. Ask a builder to check the joists can take the extra weight. Heathrow's insulation scheme includes upgraded ceilings in eligible rooms.

Leaks into the loft: hatches, fittings and vents

• The loft hatch. A hatch in a bedroom or living room can be a significant leak; one in a landing or cupboard matters less. The US guidance replaces a hatch in a living space with a heavier board, around 19 mm thick, with a continuous rubber seal round the edge. A pull-down ladder needs a sealed cover.
• Holes in the ceiling. Light fittings, pipes and extractor fans that pass into the loft are all openings. Seal round them, and keep insulation clear of fittings that need it, such as some recessed lights.
• Roof vents. Vents that open straight through the roof towards the flight path let sound into the loft. They can be fitted with lined baffles or acoustic louvres, which the guidance prefers because they are less likely to cut the airflow. Vents under the eaves are shielded by the roof and can usually be left. Do not block vents: a cold loft needs its ventilation to stay dry.
• Chimneys. An open flue is a hole through the roof. A damper or a tight-fitting fireplace cover closes it.

Roof windows, dormers and rooms in the roof

A loft conversion puts a room right under the roof, with no loft space to act as a buffer. A sloping ceiling fixed to the rafters behaves like the vaulted ceilings the US guidance warns against. Where one is needed, it recommends a wider than usual insulated space between the ceiling and the roof, or a small void above a false sloping ceiling, and it strongly discourages open, vaulted ceilings wherever a lot of noise reduction is needed.

Roof windows face the sky and are often the weakest part of the room. The guidance suggests adding a second pane, of thick or double glazing, at the bottom of the window well, or fitting an acoustic unit. In the loudest zones it suggests removing them. The same principles as for any window apply, and our guide to the best windows for aircraft noise explains them.

Dormers usually have lightweight timber walls and small flat roofs. Treat their walls and ceilings like any other lightweight wall: an extra lining of plasterboard, ideally on resilient bars, with insulation behind it.

For a bedroom in the roof, see also soundproofing a bedroom against night flights.

What airport schemes include

Airport schemes treat roofs as part of the job, which shows what the professionals expect to work.

• Heathrow: its Residential Insulation Scheme includes acoustic quilts for roof spaces and upgraded ceilings in eligible rooms, alongside windows or secondary glazing, doors and acoustic ventilation. It funds up to 100% of eligible work, up to £34,000 a home. See our Heathrow page.
• United States: the FAA's guidance for airport programmes lists typical treatments by house type. For low-roofed houses that may have no loft, they include work on the sloping ceilings; for single-storey houses with a loft, sealing the loft openings; for terraced houses, loft insulation.
• Germany: the rules for airport noise zones count roofs and ceilings among the parts of a room that must meet the required insulation, alongside walls, windows and doors.

Our guide to airport noise insulation schemes explains who qualifies.

The limits

• The weakest part wins. A heavier ceiling does little if most of the noise comes through a single-glazed window or an open vent.
• No roof makes a room silent. A well-insulated house with the windows shut cuts outside noise by about 30 to 35 dB, and more than 35 to 40 dB is rarely practical.
• Safety and damp come first. Have old wiring checked before burying it in insulation, keep insulation away from fittings that get hot, and keep the loft ventilated.

Before you start, find out whether the planes actually pass overhead or off to one side, and how many are loud. If they pass to one side, the walls and windows facing them matter more than the roof.