How to Soundproof a Wall in a Semi-Detached House.

Quality townhouse soundproofing

This article is written for an owner of a semi-detached house, a semi-detached home, a townhouse or a row house, who is bothered by a noisy next door neighbour. The article explains how to soundproof a wall, the party (demising) wall between neighbours. You do not need to keep suffering; your problem can be fixed.


Yes, the problem can be fixed, but it needs to be done correctly in order for the soundproofing job to be effective, and the renovation worth its cost.

Planning to soundproof a wall.

The owner or his renovator should answer the following questions prior to undertaking the job to soundproof a wall:

  • Did you talk to your neighbour to try to address the noise or loud music issue?
    This is an obvious question, but some homeowners do not think of it, or are too timid to ask. Clearly, if the occupant disturbed by his neighbour’s noise can come to a reasonable accommodation with his neighbour, the noise problem can be solved most cost effectively. Addressing the source of noise is always cheaper than trying to block the path of the noise. Some of the measures that the noisy neighbour can take to reduce his noise are:
    - Stop playing loud music and use headphones instead.
    - Relocate TV or speakers away from the demising wall.
    - Place sound absorbing pads under loudspeakers, whether they are standing on the floor or on shelving.
    - Install carpet with thick under pad on all high traffic areas, particularly stairs. This will reduce footfall noise propagated by the building structure.
    It should be noted that in situations where the demising wall is very poor, these measures will not be sufficient. Just regular sounds of everyday living can be heard through a poorly soundproof wall and be disturbing a neighbour.

    Current version of the National Building Code that requires soundproofing between adjacent units was introduced only recently, in 2010. Any building built prior to 2010 may, or more likely may not have even the minimum soundproofing between adjacent units.
  • How many floor levels there are in the house, including basement?
    This is an obvious question, answer to which determines the scope of soundproofing work that needs to be done.
  • Are there construction drawings available for the house?
    Most homeowners do not have construction drawings, especially if the house is old, or most recent renovations were not done very professionally. However, if good drawings are available, then the scope of the required soundproofing addition can be established much easier.
  • What is the occupant’s major concern, loud music only or other types of noise as well (loud speech, banging, stomping, etc.)?
    Answer to this question helps in determining what kind of soundproofing is required to address the problem. Eliminating transfer of speech and moderately loud music is easier than damping loud music (particularly heavy base) and structure borne noise (banging, stomping, slamming doors, etc.). Different soundproofing measures need to be taken for different types of noise.
  • Are you disturbed in one floor or room in your house, or throughout the house?
    Answer to this question may help in determining the weak areas and to limit the scope of the required soundproofing renovations.
  • Does the house have a finished or unfinished basement?
    If your basement is unfinished it may be easier to inspect the wall structure and determine the soundproofing quality of existing walls without destructive inspections.

How bad is the existing demising wall?

If the existing demising wall is acoustically very bad, hollow, with no insulation in the cavity, with one layer of drywall or lath and plaster on each side, then soundproofing improvement is possible. By adding insulation to the wall cavity, and installing two layers of drywall on at least one side of the wall, soundproofing will be improved. The improvement will be modest, but noticeable. Residual sound transfer will now be mostly through horizontal wall/ceiling structure.

If the existing demising wall is already reasonably good, and the owner is still bothered by neighbour’s noises, the problem is more difficult to solve. As documented in a research paper by National Research Council of Canada [Ref. 1], significant noise path exists through the horizontal floor/ceiling junction between the adjacent units. The only way of reducing the noise transfer through this path in an existing building, is to add floor toppings on both sides of the demising wall. This is often not feasible in occupied buildings with different owners living on each side of the wall.

If the neighbour’s noise is noticed particularly on the top floor, then the attic space may be the path of the noise. The simplest method of attenuating this noise path is to add large amount thermal insulation in the attic over both parts of the semi-detached house.

Testing prior to soundproofing a wall

With adequate knowledge and experience in the field of soundproofing, and proper attention to detail, the problem of noisy neighbour can be resolved by soundproofing a wall. However, to find the acoustically weak points in the present structure is not easy and usually requires some destructive testing. The following items need to be checked:

  • How the demising wall is constructed and is it fire-rated or soundproofed?
    This usually requires cutting one or more openings in the drywall, or drilling thorough any masonry in the wall to determine its thickness.
  • How are floors/ceilings attached to the demising wall? Is the space between joists adequately filled and airtight?
    Answering this question usually requires removing some drywall on the ceiling at the demising wall and inspecting the structure. This is the area that is often overlooked by contractors who are not expert in soundproofing.

An illustration of a soundproofing job that seems to be done right is in the video by Mike Holmes:

Mike's approach to soundproofing, installing QuietRock drywall, is not the only approach, or even the best approach in all situations.  His claim that one layer of QuietRock is equivalent of 8 layers of drywall is a myth.  It is not substantiated by any documented tests and is by itself quite meaningless. More information about soundproofing myths is here. A soundproofing consultant knows facts and ignores myths and can select the best materials and the best assemblies for each problem situation.

Mike Holmes also demonstrates a crude test to verify the effectiveness (or lack of it) of soundproofing.

The author of this article has developed exclusive, sophisticated and inexpensive acoustic test procedure that will quantify soundproofing level prior to renovations and will also pinpoint noise leaks in the exiting wall. The test will also determine the relative levels of airborne noise and impact noise that is transmitted through the existing wall. This test will reduce the need for destructive inspections noted elsewhere in this article. The test can be repeated after the soundproofing job was completed to confirm and quantify the improvements that were achieved.

The author does the test routinely as part of soundproofing renovations his firm undertakes. He also provides the testing as a service to homeowners or other renovators. Please contact him through this website for a quote.

Renovation project to soundproof a wall

Here we are referring to doing the actual work to soundproof a wall, the demising wall. The answers to the questions listed earlier, and results of acoustic tests will provide input to determine exactly what needs to be done. There are many available approaches to the problem, and many materials and products that can be installed. A specialized soundproofing company, a soundproofing contractor, an architect experienced in soundproofing, an acoustical engineer or a soundproofing consultant will prepare a detailed plan outlining exactly what needs to be done to meet the client’s soundproofing objectives.

Reference 1: NRC Publications Archive; Guide for Soundproofing Insulation in Wood Frame Construction, Quirt, J.D.; Nightingale, T.R.T.; King F.

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About the Author Ivan Koval

The author is the publisher of the Soundproofing.Expert website. He is a soundproofing and building acoustics consultant working in Toronto and GTA, Ontario, Canada. Telephone (416) 471-2130

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