217 Building Regs’ Guide to Sound Insulation

If you’ve ever experienced the stress of domestic noise pollution, you’ll understand why the Building Regs set out clear requirements for soundproofing. Paul Hymers explains what you need to know to keep you (and your neighbours) happy

A run-down of the best ways to decrease noise in your new home — and how to comply with the Building Regs in the process

Part E (Resistance to Sound) of the Building Regs sets out the soundproofing standards for new homes and conversions of barns, churches, etc into homes. It deals with dividing walls and floors

(and the measures needed to ensure these structures comply with a set level of soundproofing), and also requires some sound insulation internally to protect bedrooms from noise. It divides sound into airborne sound and impact sound.

l Airborne sound

The minimum level of airborne sound resistance for dividing walls or floors between homes is 45dB (decibels) in new builds and 43dB in conversion projects. This level should easily cut out normal levels of speech, TV and music playing.

Requirement E2 for internal airborne sound resistance inside any dwelling is a minimum of 40dB. It applies to walls and upper floors between bedrooms and other rooms (with an exemption for any wall that has a door in it and walls to en suite bathrooms).

l Impact sound

For impact sound (typically footsteps, jumping and dropped objects), a maximum of 62dB is required from floors and stairs in new builds. A maximum of 64dB is set for conversion projects.

The Problem of Sound

Sound, like water, is prepared to travel. And when it does it can be sneaky, looking for the path of least resistance. It can leak unexpectedly though tiny gaps and holes (such as service entry points for plumbing and electrics) or vibrate along fixing screws, bolts and nails; they are all pathways for sound transmission.

Even when you take care to build a sound-resistant wall or floor, noise can find a route around it. Sound can bypass a sound-resistant wall or floor via an adjacent one and this is known as flanking transmission — and it is more common than you might think. Given our fondness for timber frame and lightweight block walls for thermal insulation, the inner leaf of a cavity wall is an easy route for flanking

“If you value your privacy or your sleep, you might consider building in some external sound insulation”

transmission to bypass a sound-resistant wall or floor.

Overcoming it in timber frame homes usually means double lining the walls with heavier plasterboards internally, but the same can be needed for the super light blocks used on inner leaves.

The size and position of window and door openings can also contribute inadvertently to flanking transmission. Vibrations can be sent through the masonry wall between them, passing across the abutting sound-resistant wall. Here, the advice is to ensure the wall is short, no more than 700mm between the openings, because short walls don’t vibrate as much.

Upper Floors

The traditional upper floor structure, consisting of timber joists covered by chipboard boarding and a thin layer of plasterboard

ceiling, offers little sound resistance. By itself, it won’t achieve the minimal standard requirement of the Building Regulations for bedrooms, of 40dB. For that, you can either: l Add insulation material between the joists — 100mm of mineral wool of at least 10kg/m3 density l Upgrade to a heavier plasterboard of at least the same mass.

It’s a minimum for bedrooms only, but upgrading the whole floor structure is the easiest and most effective choice. It is possible to improve it more to achieve a desirable standard that will cut out airborne sound from a TV or music with just a bit more expense.

Unlike walls, floors can transmit impact sound as well as airborne sound. Although there is no requirement to deal with this under Building Regs, the best way to deal with it for your own

peace of mind is to provide some isolation between the joists and floor boarding. For instance, resilient layer materials that come on a roll can be pinned to the joists before flooring is laid. They simply float on top with the tongued joints glued into each board — no other fix- ing is required. To screw or nail it down would actually create a sound path!

These resilient layers vary in thickness but anything between 6mm and 12mm is common, depending on the material. Often it is foam plastic or rubber based. The skirting boards will pin it in place via an acoustic flanking strip, and this will avoid direct contact between the skirting and the floor boarding.

With the insulation between joists being denser than the thermal insulation quilt, it should tackle airborne sound.

To upgrade the performance, resilient layer materials can be supported on sound-quality plasterboard

planks that are themselves laid as shelves on battens fixed to the side of joists. The more you use in thickness terms of both plasterboard and insulation, the greater the density and the better the resistance to airborne sound.

If you can afford the headroom, a secondary suspended ceiling formed beneath the floor joists is ideal. This ceiling, supported by new timber joists that span from wall to wall, is not in contact with the joists above. A minimum gap of 25mm is advisable. Two layers of 15mm sound-quality plasterboard can amount to 26kg/m2, so check the joists’ size and spans.

Use acoustic silicone sealant or tape to seal around the perimeter edges to achieve airborne resistance of 45dB or more.

External Walls

Typically timber frame homes are insulated with PIR insulation foam boards between the timber studs for thermal insulation but these are poor sound insulators — so much so that I’ve been party to conversations in the street outside and arguments in homes on the other side of the road when carrying out completion inspections. If you value your privacy or your sleep, you might consider building in some external sound insulation. This isn’t a requirement of the Building Regs and although it appeared in a Part E draft it was dropped before it became law.

Using dense mineral wool slabs to insulate between the studs and an inner layer of thermal multi-foil laminate for thermal insulate before double boarding with a sound or fire-rated plasterboard lining will achieve high levels of both sound and thermal insulation. It also comes with great fire resistance.

Meanwhile, the Part Q security standards for windows and external doors can be met using laminated glass outer panes. By happy coincidence, these also provide better sound insulation by having a thicker outer pane than inner pane in double glazing, displacing sound waves.

Masonry Dividing Walls

Two skins of pointed-up dense blockwork in a 100mm cavity wall filled with mineral fibre will usually meet the airborne sound insulation requirement; adding a sound grade plasterboard will improve sound resistance to over 50dB. To achieve thermal insulation requirements, apply a soft thermal layer before plasterboarding.

Internal Stud Walls

In my opinion, stud walls seem to be the exact opposite of what you’re striving to achieve: a solid and robust separation with high levels of fire and sound resistance. Thermal relies on soft and squidgy insulation with air pockets to trap the heat in; sound relies on dense materials to add mass to the wall and air separation to keep airborne sound out.

If you can spare the space for a double timber stud compartment wall, use at least a 240mm cavity width. That is measured between the inner faces of plasterboard on both sides. So if you’re using 100mm deep timber studs, the distance between the studs will reduce the cavity here to 40mm.

Semi-rigid mineral wool insulation can then be installed between each stud and covered by two layers of plasterboard to each face. The first is a 19mm thick plank and the second is a 12.5mm sound-resisting plasterboard. Such constructions, with attention to detail and good workmanship, should offer good airborne sound insulation.

You might also use resilient bars (thin metal strips with rubber seating) to isolate the plasterboard from the walls’ timber studs. With the plasterboards fixed via these horizontal bars to the studs to isolate them, the first and last of should be 50mm from the ceiling and floor respectively.

NEXT MoNTH:

Part C — Site preparation and resistance to contaminates and moisture