soundproofing a brick party wall -- avoiding 'triple leaf effect'

10 years ago

I live in an old rowhouse and the party wall is two layers of brick. I'm wondering what kind of interior wall to construct to reduce sound coming from the neighbors, and also lessen any noise I send their way. If I build a stud wall on my side, I don't know if there's any danger of creating a "triple leaf effect", since there is a stud wall on my neighbor's side: neighbor's drywall -> brick party wall -> my drywall. Is that a triple leaf?

In the party wall, there is a slight gap between layers in most of the brick courses. This photo shows the gap between layers -- you can see it back behind the bottom of the outlet where the bricks are missing:

Every 15 courses or so, the bricks are turned lengthwise so that they span the width of the wall. See the course in the middle of this photo where the mortar joints are closer together:

So, is this brick wall two leaves or one? Or maybe it is, effectively, not a leaf at all, since there are holes that go through the mortar in places?

If my neighbor has a 2x4 frame wall on the other side (with drywall), what should I build on my side for noise reduction purposes?

Many thanks

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Comments (8)

renovator8
10 years ago
The triple leaf effect is for drywall on studs so it would not apply to a brick wall.

Your minimum goal should be an STC rating above 50 and if the voids and penetrations in the brick wall are filled and sealed you will already have exceeded that rating.

One layer of 5/8" drywall on wood stud walls on each side of the brick wall with fiberglass thermal insulation will probably get the STC rating above 60, possibly 65.

If you want it higher try more drywall and/or resilient channels, IsoMax clips, or Green Glue but seal the perimeter and penetrations well.
worthy
10 years ago
One layer of 5/8" drywall on wood stud walls on each side of the brick wall with fiberglass thermal insulation will probably get the STC rating above 60, possibly 65.

The STC of a standard double brick wall is 42+/-. I would be curious to see any lab -tested results that bring the suggested extra 2x4 wall with insulation up to STC65.

But even if it does provide that result in a lab test, in practice you will notice very little difference, as bulking up the walls does nothing for flanking transmissions in the floor and ceiling.

I lived in and owned many such 19th Century/early 20th Century homes with exactly that construction. Old rowhouses are notorious for noise transmission--let alone the common attics that turn a fire in one unit into an inferno consuming the whole row at once.

Here is a link that might be useful: Technical Literature on Sound Transmission
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renovator8
10 years ago
Just something I found on the internet.

Here is a link that might be useful: masonry STC info
worthy
10 years ago
So, according to the linked item, steel studs on fiberglass and 8" modern block yields STC 59. No mention about flanking transmission.

I've added resilient channel and fg on several century homes converted to multiple-family dwellings. But without making improvements to ceilings and floors--let alone crawls and attics--there was little noticeable difference.

If I were doing the job, I'd suggest Renovator8's approach as a start and with the caveat not to expect a great improvement. Paying special attention to every crack, crevice, pentration and passageway between the units will help.

Source: Noise Control Manual, City of Vancouver, British Columbia
renovator8
10 years ago
I lived in a townhouse separated from it's neighbors by old double wythe brick walls with no finish. The sound separation was very good but if you were standing near a crack or some bad mortar you could put your ear to it and hear normal conversations next door.
brickeyee
10 years ago
Bewitching to steel studs (even on the flat to reduce thickness build) increase the STC rating over wood studs.

Two layers of 5/8 drywall on steel studs with sound insulation is probably a very reasonable approach.
tedwhite
10 years ago
Just a few points here.

A triple leaf is defined by three layers of any mass, not just drywall.

The brick wall you have is simply a poorly sealed single leaf. Despite the bit of air in the current wall.

You will have some vibration flank under, over and around that wall.

Having said that, you can certainly improve your situation.

Build a new wall in front of the old masonry wall. Leave a 1" gap. You can use wood or steel studs, doesn't matter, since the final assembly is not a single stud wall. Also, could be 16" or 24" at this point. Again, doesn't matter.

Use simple R13 fiberglass, no more. I'd avoid spending more than you have to on the insulation. Cheap fiberglass will work as well as anything.

Make the new wall as heavy as practical, so I'd recommend double 5/8" drywall. Damp the drywall with a quality damping compound.

Here is a link that might be useful: Soundproofing Wall Information
worthy
10 years ago
[Switching] to steel studs (even on the flat to reduce thickness build) increase the STC rating over wood studs.

Yep. Moves STC from 36 to 47 (See table in earlier link.)

With space at a premium, a layer of sound damped drywall such asQuiet Rock or regular drywall adhered with Green Glue could be effective.