Are brick walls soundproof? Important facts

Brick walls provide good soundproofing and reduce noise. Good soundproofing relies on high mass to block noise, bricks are a high mass material. External brick walls are double skinned, and these will provide a higher level of soundproofing than internal, single skinned, brick walls. For brick walls to provide the best soundproofing, cavities should be filled with acoustic insulation to increase mass further.

What is the sound reduction index of a brick wall?

photo of a bare brick wall living room with text reading: sound reduction index brick wall no plaster 42dB

The sound reduction index of a single brick wall is around 40dB. The sound reduction index of a single brick wall with both sides plastered is around 45dB. The sound reduction index of a brick wall with cavity is about 50dB.
The exact figures will vary depending on the type of brick used and surrounding structures. In general, expect a brick wall to achieve a sound reduction index of 45dB.

The sound reduction index is a measurement of how much sound can pass to the other side of a partition. Under laboratory setting, a partition is erected in a frame to create a wall sealed in the middle of a room. On one side, a loud noise is generated, on the other side the level of decibels is measured to establish the transmission lost.

Is a double brick wall soundproof?

A double brick wall is the most soundproof wall in a house. Double brick walls with a cavity can achieve a sound reduction index of 50dB. Double brick walls are external walls and have a higher mass than internal brick or internal stud partitions. There are other ways to make your brick wall soundproof which are explored below.

Older buildings may have solid brick external walls. The soundproofing quality of a solid stone wall will vary with the material used as some stone is more porous than others and the thickness. Also, if a wall is old, the mortar may need repointing. Any gaps and cracks in the mortar will let sound travel through easily and reduce the soundproofing ability of your wall.

Is plaster over brick good for soundproofing?

Plaster over brick is good for soundproofing as it seals gaps and cracks in the wall. A brick wall with plaster also has more mass which is essential for good soundproofing. Sound can use the medium of air to travel through, plaster seals passages and reduces the transmission. Plastering one side of a wall will increase the sound reduction by up to 3dB^[1] because mass is increased and the brick wall is less porous.

Acoustic plasterboards are a different type of soundproofing solution. Soundproof plaster also increases the noise reduction of a wall, however, this is a dry applied material and will not seal porous brick in the same way. Acoustic plaster is a different material to normal plaster as it has a higher mass which reduces more noise for space used. Acoustic plasterboards can be installed directly to a brick wall to increase the mass and airborne resistance.

Brick wall v/s stud wall soundproofing

A brick wall vs a stud wall is better for soundproofing as brick has higher mass. Both brick and stud walls can be soundproofed but a brick wall has a naturally higher resistance to sound. To improve the resistance to the passage of sound, the mass of each wall needs to be increased. Increases in mass are significant to soundproofing when they are large compared to the overall mass of the structure. Walls with a high mass are harder to meaningfully increase relative to the overall mass.

Infographic explaining how decoupling works as a soundproofing technique. The diagram shows a Newtons cradle with a ball missing

The third soundproofing technique is absorption. Sound absorption reduces reverberation which can lead to amplification as sounds are repeated. Poor wall soundproofing can be caused by empty cavities as sound can travel easily through open air. Stud wall cavities should be filled with acoustic grade mineral wool to increase resistance to sound. If I knock a brick wall, the sound is a low thud. But if I knock on a stud wall, it sounds much louder and goes through to the other side more easily.

Infographic explains how adding mass will improve soundproofing as sound waves cannot transmit easily,

For this reason, stud walls are easier to make initial soundproofing improvements to as the starting mass is low. Other methods are used, alongside increasing the mass, to save space and ensure structural integrity. Decoupling is a high performing soundproofing technique used to separate structures. Reducing points of contact between an existing wall and the new partition reduces channels for sound vibrations to pass through. This makes soundproofing panels more effective as they are not in contact with the existing wall transmitting sound.

Infographic explaining that sound absorption works like a ball hitting a pillow as it will not bounce off.

Why can I hear neighbours through a brick wall?

photograph imagined of a lounge with brick wall and a hole showing neighbours on the other side being noisy

You can hear neighbours through a brick wall when the mass of the wall is low and gaps create flanking transmission. Some walls are made of porous bricks with more air gaps, this reduces the mass of your wall and increases the ability for sound to travel through. To improve the soundproofing quality of porous bricks, a wet plaster should be applied which helps seal the wall. This only needs to be done on one side for good effect.

To increase the mass of your wall and improve the soundproofing, additional layers are installed. Brick walls can be soundproofed in different ways, including:

Direct to wall acoustic plasterboard
Direct to wall soundproofing panels
Isolation clips for decoupled partition
Additional independent stud wall

You can also hear neighbours through a brick wall when flanking transmission occurs. Flanking transmission sounds find alternative routes over or around a partition. Common flanking issues include:

Wall mounted TV
Holes for fixings, like pictures and shelves
Back to back sockets or cupboards
Pipes passing between two rooms (floors and ceilings too)
Poor insulation around the edges of a wall

To reduce flanking transmission, gaps and cracks can be sealed with masonry fillers. It is best to avoid placing two sockets back-to-back on a wall, too, as this creates a thin partition with air gaps. If pipework runs under or over both rooms, acoustic pipe wrap can be added. This will decrease the ability for sound to travel along the pipe between the rooms.

I can hear my neighbours through our party wall because they have a wall mounted TV, which has made the wall weaker to sound. We also have several electric sockets on our party walls, so sound can travel trough more easily. To add to all of that, our floor structures are continuous between the properties! This means that I can hear thudding and footsteps from next door easily as the vibrations travel along the whole floor.

How to soundproof a brick party wall

To soundproof a brick party wall, the mass must be increased and the wall should be airtight. Party walls with a high mass will better resist airborne noise, which is the most common complaint. An airtight brick wall can also resist sound better and reduces flanking transmission around the perimeter.

The cost of soundproofing a brick party wall starts at £34 per m² for a budget friendly solution. Depending on your budget, noise complaint and space available, a reduction of 19dB can be achieved which will make your room far quieter. To understand more about decibels and how soundproofing is measured, read our guide to soundproofing.