Acoustic Flanking Strips: Where to use them?

[Dan F]

Hi,

 

I have a good understanding of the different way to mitigate noise transmission through walls usiing soundbloc, mineral wool and resilient bars, but I'm unclear on how to best use acoustic flanking strips and where they are really advantagous vs. not really needed.

 

Our architect has specified these under amost all internal stud walls, but when I speak to the product supplier they recommended using them both below and above internal stud walls and also where stud walls butt up to external walls.  Obvisouly we want to use these where it makes sense, but don't want to go overboard as it may drive our frame designer crazy and there is also obvisouly also an additional cost invovled.

 

My understanding is that these strips are mostly about avoiding the structure transmitting noise, but if you have well detailed walls, resilient bars on the ceiling, screedboard above the decking and you are as using the correct asositc sealant/strips at PB/skirting juntions, how important is it to use these strips between i) slab and studs ii) external wall and studs iii) studs and joists?

 

This is the product I'm referring to: http://www.cmsdanskin.co.uk/general-construction/acoustic-wall-solutions/regupol-acoustic-isolating-strips/

 

Thanks,

 

EDIT:  I should add that this is a MBC twin-wall build with 89mm internal studs and 253mm metal-web joists at 400mm centers.

 

Edited June 27, 2020 by Dan F

[Dan F]

@Moonshine Is this one that you can help with?

[ragg987]

What type of noise are you trying to reduce?

 

If you are using resilient bars to support the wall plasterboard, then I don't see why you would need the strips. If not then the pb will transmit the vibrations to the stud and hence into the structure.

 

Assuming you wish to keep noise inside the room from leaking out, e.g. home theater.

[Dan F]

7 hours ago, ragg987 said:

What type of noise are you trying to reduce?

 

Want to keep sound in TV room and teenagers bedrooms, but also have good noise isolation throughout the the between rooms in general.

 

7 hours ago, ragg987 said:

If you are using resilient bars to support the wall plasterboard, then I don't see why you would need the strips. If not then the pb will transmit the vibrations to the stud and hence into the structure.

 

Our current plan for TV room is resi-bars (on just one side), 2 layers of soundbloc each side and mineral wool plus the correct edge detailing. Most other internal walls between rooms in the house are the same, but just without the resi-bars.

 

8 hours ago, ragg987 said:

If you are using resilient bars to support the wall plasterboard, then I don't see why you would need the strips

 

We aren't using resi-bars everywhere (not currently) but I too was also wondering why/when you'd need both resilient bars and isolating strips.  That said, the supplier recommneds using the isolating strip even if you do have resilient bars and a lot of details online also show both.

 

Using the isolation strips in TV room just in case isn't a big deal and not going to cost a huge amount, what I'm trying to work out is it I should use them elsewhere in the house, where resi-bars aren't planned.  And also if I should be using below studs, or above and below as supplier suggests (they would though... as they sell more)

 

 

 

 

[Dreadnaught]

@Dan F, I wonder are planning using timber studs or metal framing for your internal walls? (I have chosen metal framing).

[Dan F]

1 minute ago, Dreadnaught said:

@Dan F, I wonder are planning using timber studs or metal framing for your internal walls? (I have chosen metal framing).

 

Timber studs because these come with the MBC package.  They can put the isolating strips in, no issue, I just need to decide where. Thing is I don't want to i) regret not putting them in when I could have (can't retrofit) or ii) put them everywhere if not needed due to cost implications and risk it doesn't go down too well with designer/installers if I put them everywhere just in case.

[Moonshine]

11 hours ago, Dan F said:

@Moonshine Is this one that you can help with?

 

From a quick scan of what you are trying to do they seem a bit redundant.

 

Have you got drawings you can share? Are these going at ground floor or first floor?

[Dan F]

8 minutes ago, Moonshine said:

Are these going at ground floor or first floor?

 

That's part of what I'm trying to work out.  This is our standard wall details (upstairs is 22mm caberdeck on metal-web joists, downstairs is concrete slab).  The TV room is the same plus a resi-bar on one side.

 

You can see that a strip is proposed below stud, but not above.  Yet the supplier says that to do the job probably you need to use it at the top of studwork and where it abuts external walls too.

 

 

[Moonshine]

You won't need them on the ground floor as the impedance mismatch between concrete and timber will do a fair bit of isolation for you.

 

At first floor I am not convinced they will make a bit difference as aren't the wall sole plates going to get screwed down to the joists negating the isolation provided by the pads.

 

Btw that drawing doesn't show resilient bars

[Dan F]

41 minutes ago, Moonshine said:

Btw that drawing doesn't show resilient bars

Currently we don't have resilient bars planned for anywhere apart from TV room.  The detail for TV room is the same as pasted with the addition of a resi-bar on one side (TV side).  It might make sense for us to use resi-bar detail slightly more widely though, e.g around bedroom/studies.

 

41 minutes ago, Moonshine said:

You won't need them on the ground floor as the impedance mismatch between concrete and timber will do a fair bit of isolation for you.

In laymans terms, does this mean that the type of sound/vibration carried by the slab isn't going to be transmitted easily by wood and vica-versa?  Also I assume that if you wanted to prevent sound (e.g. from a subwoofer) travelling through the slab, the best approach would be an acoustic mat in that specific room, right?

 

41 minutes ago, Moonshine said:

At first floor I am not convinced they will make a bit difference as aren't the wall sole plates going to get screwed down to the joists negating the isolation provided by the pads.

We'd use "Regupol® 3D Isolation Washers" where mechanical fastenings are needed. So potentially still value in using tape at top of downstairs stubs and bottom of upstaris studs?

 

In you view, does the use of resi-bars reduce the need for isolation strips or are they two seperate complimentary strategies?

 

Edited June 28, 2020 by Dan F

[ragg987]

In my view adding the strips should help is you are not using resilient bar everywhere. And yes to above and below stud, though do not see the point of doing it adjacent to external walls, may as well use it on the internal wall boundary if that is the case.

 

FWIW we also have MBC timberframe build and have taken very few precautions for noise in most areas and I would say it is fine. The noisiest aspects are gaps under the door for MVHR and the sound of footsteps upstairs, none of the strategies you have mentioned will address those.

 

We did use single layer of fermacell on walls instead of plasterboard, plus sealed air gaps at floor and ceiling junctions.

 

I do have a basement home theater room, built as a room inside a room where the inner structure is sitting on an acoustic floating floor. Double skin of fermacell with green glue in between. The green glue binds the 2 sheets together and increases the effective mass, plus provided some resilience. Works really well, on this room I did not have any air gaps including for ventilation and used a muffler in the air ducts.

[Dan F]

I think I'm going to skip the isolating strips and use resilient bars more widely along with correct use of perimeter acoustic sealants etc.  My thinking is that this will reduce transmission to structure to the point that reducing transmission through the structure via these strips is less critical and wouldn't have much more additional impact.

[Ferdinand]

How is acoustic flexible sealant diifferent from non-acoustic flexible sealant?

 

My thought would be that it shrinks less to prevent gaps opening up.

 

Looking at it, I would say that the strips are designed to block noise transmitted through any air gaps.

Edited July 2, 2020 by Ferdinand

[Dan F]

1 hour ago, Ferdinand said:

Looking at it, I would say that the strips are designed to block noise transmitted through any air gaps.

 

Strip is to stop noise/vibration transmission from flooring to walls and vice-versa which can be an issue however many layers of plasterboard and rockwool you use as sound from foot-fall and other sources can be transmitted through structure.  What i've been told though is if you use a resilient layer under first floor flooring and resilient bars on ceiling below then this is isn't so much of an issue.  @Moonshine also made the point about it not being important on ground floor concrete->wood junctions.

[Dreadnaught]

 

On 28/06/2020 at 11:33, Moonshine said:

You won't need them on the ground floor as the impedance mismatch between concrete and timber will do a fair bit of isolation for you.

 

@Moonshine, I am using MF internal walls rather than timber stud. Is there still a sufficient impedance mismatch between concrete and steel/MF to make the use of acoustic-isolation strip largely redundant? 

 

(Mine is new-build bungalow and the reason I ask is that I am just now starting on my internal wall installation and wondering whether to order some acoustic-isolation strip.)

 

Sorry to resurrect an old thread.

[Mike]

I'm not convinced that they're going to do much in a new build bungalow, unless you have some room that needs to be acoustically isolated - in which case it will need more than just flanking strips. It's certainly worth considering the structure of the partitions and internal doors though, to reduce transmission through them between rooms.

[gc100]

We used res bars in our tv room and music/office room. They work very very well.

 

However

 

Think about the doors - sound will escape these and you need to pay attention to these to make a room more sound proof. I need to get around to doing something about it as it negates quite a lot the res bars. There are a few solutions like seals that come out when door closes etc.

 

I wasn’t aware of these strips but I think they would have been ideal to use in my house. It’s single story - the floor is self levelled screed (about 80mm) on top of 200m of insulation which in turn sits on top of a concrete slab (original barn). When my 5 year old runs down the central corridor the whole floor transmits this noise and I think these strips would have helps a lot at reducing this. 

[Dreadnaught]

3 hours ago, gc100 said:

Think about the doors

 

Good point. MVHR ventilation gaps under doors can undo a lot of good work. For the study/TV-room, I am going to move the ventilation gap from underneath the door to a new grill-vent through a cupboard in to a quiet neighbouring corridor. The door will be a snug fit.

[markharro]

On 28/06/2020 at 16:45, ragg987 said:

 

FWIW we also have MBC timberframe build and have taken very few precautions for noise in most areas and I would say it is fine. The noisiest aspects are gaps under the door for MVHR and the sound of footsteps upstairs, none of the strategies you have mentioned will address those.

 

We did use single layer of fermacell on walls instead of plasterboard, plus sealed air gaps at floor and ceiling junctions.

Hi @ragg987 we also have MBC and I am thinking of using fermacell with 75mm medium density rockwool. Are you completely happy or would you have changed anything? What do you mean by sealed air gaps?

[ragg987]

On 17/12/2023 at 21:13, markharro said:

Hi @ragg987 we also have MBC and I am thinking of using fermacell with 75mm medium density rockwool. Are you completely happy or would you have changed anything? What do you mean by sealed air gaps

I am happy with a couple of provisos, some I mentioned above. To summarize:

 

I would put a sound muffler in the MVHR flow pipe, or some other strategy to reduce impact of fan noise in bedrooms.

 

Increase the rigidity of the first floor pozi joists. I get quite a bit of floor bounce. Maybe even a concrete floor as used in some countries?

 

Do something to reduce the floorboards 'squeaking' when walked on. Perhaps related to above.

 

By sealed air gaps I mean caulk above at floor and ceiling level. This leaves air gaps under forests for MVHR.