A concept more popular in the United Kingdom, semi-detached houses are two houses collocated and separated by a single wall or more complex designs.
Soundproofing between semi-detached houses is desired because there is no air gap which is separating the two. And you will learn how to do just that, in this post.
Just like in an apartment or flat system, you want that peace and privacy especially if any of the two parties play music or watch movies at loud volume.
For a person like me who likes to crank up the volume of the home theater, I would want to have a higher degree of soundproofing, especially for the low-frequency bass coming out of my subwoofer.
If you are looking at taming the mid and higher frequencies such as voices, then that much degree of soundproofing would not be required and you can cut on costs.
It also depends on the construction of the room, whether you have plaster walls, concrete or drywall or whether there are vents or ducts which need to be treated, etc.
Comparing Concrete, Plaster Walls And Drywall
Plaster walls are better than concrete for blocking sound. The problem with concrete is that it is a good transmitter of sound.
Drywall is good for low frequencies and is a poor transmitter of sound. However, drywall constructions are generally not as thick as concrete or plaster walls.
So, if you live in a North American house made of drywall, you will need to consider adding considerable mass to the wall that you want to soundproof.
For concrete and plaster walls, you would be trying to decouple more, to reduce the transfer of sound vibrations.
We will go over the various options that are available in order of cost (from low to high). Naturally, the highest costing option would give the best results.
Soundproofing Between Semi-Detached Houses
Before you spend your money, you should determine what is causing sound to transfer freely between the walls of the houses.
There may be sound leaks from vents, doors and windows which are causing sound to directly leak. It would not be advisable to assume beforehand that the wall is the culprit.
After you have taken care of the leaks and other weak points, you can go about treating that wall.
In most of the articles on this site, I talk about the four important elements of soundproofing and they are applicable to any soundproofing project. Here they are once again.
As we explore the options available to us for soundproofing between semi-detached houses, we will talk about these elements.
The first option would be to simply add mass to the existing wall directly. By adding a layer of thick sheetrock, you are taking care of the third element of soundproofing, which is mass.
When you add mass, you reduce the vibrations of the wall caused by sound waves which effectively reduce the amount of sound heard on the other side.
The second option is to make the wall thicker by adding a layer of wooden studs and drywall. The studs are not connected directly to the existing wall. Decoupling clips are attached at various points in the studs and it is these clips that are attached to the wall.
The aim of using decoupling clips is to reduce the amount of sound vibration transfer by limiting the number contact points.
After decoupling the studs and installing them, you add medium density insulation in between the cavities. The insulation will dissipate the sound energy but should not be too dense. The insulation is also required to prevent your walls from resonating.
After putting in the insulation, you add the drywall and what you have now is a thicker, heavier and decoupled wall.
In this option, three of the four elements of soundproofing are being taken care of – decoupling, absorption (by insulating material) and mass.
This option is significantly better than the first and would be good for mid and high frequencies and some lower frequencies.
The third option is mostly similar to the second one. The only difference here is that we add the fourth element also, which is damping.
As the name suggests, a damping compound dampens the sound and will reduce the vibrations of the walls. Less vibration of the wall means less sound transfer.
In the second option, we decoupled the wall, added insulation and one layer of drywall. In this option, we will install two layers of drywall with a damping compound in between.
The cheapest yet effective damping compound is Green Glue (not glue in the conventional sense).
Besides other very expensive solutions, this is closest to the best way to soundproof a wall. The amount of soundproofing can be further improved by adding other methods and layers of decoupling like resilient channels and whisper clips. You can even add more layers of sheetrock.
Remember, it is not possible to achieve 100 percent soundproofing, especially to cater for low bass coming out of your speakers.
Which Option is Best For You
This is a difficult question to answer correctly as only you would know best what issues you need to tackle.
Every room is different and unless you have an expert visually inspecting your house, it is really difficult to tell what is required.
As a thumb rule, if you have a limitation of space, then go for the first option. Some treatment is better than none at all.
If you have the space and budget, go for the second or third option if you feel that you need it. For home theater rooms, the third option is recommended.
What About the Windows and Doors
Windows and doors are weak links in soundproofing. Gaps and cracks in windows and doors need to be taken care first to stop sound leaking directly.
After you have sealed the gaps, you need to add more mass as doors and windows have less mass and transfer sound easily. A guide to soundproofing a window can be found here.
What About The Floor, Ceiling and Other Walls
The bad news is that treating only the wall between the semi-detached houses is not enough. The houses are built on a common floor which means that sound will be transferred through the walls from one house to the other.
Likewise, other walls of your room will also transmit sound to the other house even if you have treated the walls separating the semi-detached houses.
Bottom line is, that you need to treat all surfaces and the safest bet is to try to soundproof the room completely.
It would be better to have one room completely treated where you can have peace, privacy and play your favorite music and movies with no worries. Partial treatment or use of cheap and substandard materials will only lead to disappointment.
It is best to have an expert guide you through the process, even if it costs a bit. It would be worth it.
This site has dedicated articles on ways to soundproof floors and ceilings.
Soundproofing between semi-detached houses is very similar to that of an apartment where you are trying to block sound from the adjacent apartment.
Treating only the separating walls may not be good enough as sound will find its way through floors and ceilings.
If both sides can share the cost and work together, it can be a win-win situation for the two parties.