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Understanding flanking transmission: the number one reason soundproofing fails

In the past, new homes were rarely built with any consideration for noise. Today, most of these properties are not fit for modern living. While new builds do have to pass a UKAS accredited sound insulation test, this test doesn’t take into account how people actually live. For example, the indirect noise path of children playing in an upstairs bedroom can affect the next-door neighbour trying to read a book in his living room diagonally below. A barrier on the party walls alone will not reduce this noise transfer. This is why so many new build properties will pass a sound test, yet the new homeowner complains they can hear conversation and TV noise from next door.

To truly make homes soundproof, one must consider how sound actually transmits through the house. With more flexible employment and irregular shift patterns, daily noise is higher than ever. Land shortages also mean we’re building nearer to busy roads.

Soundproofing: only as good as its weakest link
Noise in an upstairs room

The illustration shows how noise in an upstairs room transmits through the property via the party wall and flanking areas. In many cases the flanking paths (green arrows) are even louder than the direct transmission paths (red arrows). This means only soundproofing the upstairs rooms will not be very effective. You also need to treat the downstairs rooms and address the flanking areas.

Indirect noise paths are more complex and numerous. A party wall, for example, could have the floor, ceiling, window wall, and any wall perpendicular to the party wall as an indirect noise path. You might also have any of the following connected to that wall: 

  • uninsulated Rolled Steel Joist (RSJ),
  • a bay window ceiling,
  • chimney stack,
  • stud wall,
  • cupboard under the stairs,
  • en suite,
  • wall separating the front room from the back room.

A conflicting ceiling or flat floor will have the walls as indirect noise paths. There are reports now being published showing that “dot and dab” plaster boarded walls actually amplify the noise from neighbours above or below. This can result in noise being even louder than the direct noise path.

That’s why flanking transmission can be the “weakest link” in any soundproofing project. In many projects, the noise from neighbours is louder from those flanking transmission areas than directly through the party wall.

Flanking transmission – it’s worth getting right the first time round

Lynne loved her semi-detached house in Gloucestershire. She enjoyed the area and she knew all the residents in her street. The neighbours were a lovely, busy family who were there for her if she ever needed anything.

Unfortunately, an unexpected turn of events left her needing some peace and quiet – and the noise from the family next door was not helping. Lynne was woken up every day by slamming doors, TV, the sounds of plug sockets and light switches, and could even make out words from conversations. Lynne had to play music just to give the family their privacy.

She was determined to get her house back and embarked on some research into soundproofing, convinced that the noise was coming from the party wall alcoves and maybe the chimney stacks. She decided to get the whole of the party wall in all the rooms of her property soundproofed. Lynne ended up purchasing a top of the range panel system from a London company with glowing online reviews. They installed it in the alcoves and all the chimney stacks in the four rooms along the party wall.

Sadly, nothing changed. The noise remained. Lynne still felt uncomfortable in her own home.

She didn’t give up, however. She got back online and discovered Quietco, a domestic soundproofing company that specializes in reducing noise in homes. After being educated on how the noise was actually entering her house, she realized the flanking transmission noise paths were louder than the direct noise paths. She was advised that the flanking areas of her house had to be addressed, and the soundproofing re-attempted. This meant uninstalling built-in wardrobes and removing bespoke alcove shelving she’d just painted and decorated.

indirect noise in floorUnderstandably, Lynne was reluctant to go through the upheaval of another house renovation – she’d already spent thousands, how did she know it would work this time? Her concerns disappeared when she was shown the actual mistakes the London company had made, and precisely where the noise was getting into her house. After learning more and speaking with people who’d been through the same process, Lynne decided to invest in her house and make it a home, once and for all.

Quietco installed soundproofing to all the flanking areas of the property and made right the other company’s work. Lynne’s property before the sound insulation test was 39dB dntw+CTR. Afterwards it was 63dB dntw+CTR – a massive 24dB dntw+CTR reduction in noise.

Lynne doesn’t hear her neighbours anymore, even saying, “I think they were away over Christmas as I didn’t hear anything.” We had independent UKAS accredited engineers test the party wall to document the results, which is a valuable asset if Lynne ever comes to sell the property. We managed to speak with the neighbours during the sound testing, and they told us that they had had the whole family round for Christmas – completely unbeknownst to Lynne!

Lynne still lives happily in her semi-detached house and loves it more than ever. Read her full blog here: https://quietco.uk/domestic/soundproofing-semi-detached

A common story

Lynne ’s story is not unusual. We commonly find that indirect noses paths are louder than direct ones in semi-detached houses and new builds. It’s usually down to uninsulated RSJs running into the party wall, which can channel noise into every room along their path. Similarly, an uninsulated stud wall fixed incorrectly to the party wall creates an indirect noise path.

In both these cases, you can install the most effective barrier on the party wall possible, but unless you soundproof the flanking areas, you’ll still get unwanted noise.

Common questions
How do I know it will work?

This is a very common and justified concern. It can only be effective with an understanding of exactly how sound travels and how soundproofing actually works. The first thing you need to be aware of is soundproofing companies or installers who try to sell you a solution which only involves treating the party wall. Remember, when noise reaches a certain decibel (volume) it enters the structure of the building. The noise transmits through building materials faster that it does through air such as if we had a conversation in the garden. With concrete constructions, 50% of the noise you hear will be down to flanking noise which means only treating the party wall will be ineffective.

At Quietco, we understand this concern and go out of our way to offer reassurance. Most of our clients wish they had called us years ago. In fact, they are so positive about their experience that over 50 of them are happy for you to have their contact details, so you can pick up the phone and speak with them. They too have gone through the same decision-making process, wondering whether to move house or stay and invest in professional soundproofing. 

In addition, we developed our 4-step soundproofing method to ensure we treat all possible noise routes. Indirect noise paths is just one of these steps. This 4-step method means you don’t need to worry about whether our soundproofing will work or not.

For the last 15 years, Quietco has been reducing the noise for thousands of people. The success of our projects is due to our company values of TRUSTED PROFESSIONAL SOLUTIONS, underpinned by our unique four step soundproofing methodology. The culture of “The Quietco Way” is instilled in all our employees, partners, and suppliers, giving our customers peace of mind.

Seems like a lot of disruption…

Depending on which products you decide to have installed, the disruption can range from 2 days to 4 weeks. Which is a lot less disruption than moving!

If you:

  • want a completely discrete service, so no one knows what we are doing during the 2-3 week renovation
  • would love to make as much noise as you like without bothering your neighbours
  • are ready to  enjoy peace and quiet without having to wait for your neighbours to leave the house or go away on holiday…

Then Quietco can offer you all this. You can have the soundproofing you would normally only experience with a detached house.

Simply fill out the tabs on the contact us form or give us a call: 01926 658 638
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