Which code applies, IRC or IBC?

[Jay Smith]

Thank you. It’s hard for me to tell. For GenieClip and other brands of isolation clips, how much space do you lose compared to screwing a layer of drywall directly into the stud?

Slightly less than 2 inches.

If the builder scaled down to the minimum they were required to do, the separation through the 3rd-floor truss cavity is acoustically doing little or nothing. Same thing in the attic, which is probably separated by only a draftstop. The floor cavity intersection detail shows three layers of gypsum board that were probably omitted. No insulation on the ceiling, gypsum underlayment on the subfloor, or sound isolation mat is indicated. No indication of continuing vertical wall board through horizontal cavities. No indication that I saw to avoid back-to-back penetrations.

 

[stillmand]

Slightly less than 2 inches.

If the builder scaled down to the minimum they were required to do, the separation through the 3rd-floor truss cavity is acoustically doing little or nothing. Same thing in the attic, which is probably separated by only a draftstop. The floor cavity intersection detail shows three layers of gypsum board that were probably omitted. No insulation on the ceiling, gypsum underlayment on the subfloor, or sound isolation mat is indicated. No indication of continuing vertical wall board through horizontal cavities. No indication that I saw to avoid back-to-back penetrations.

Thank you. As you know, we already discovered there is only one layer of drywall on each side of the common wall versus the 2 layers on each side indicated by the blueprint. What would you say are one or two other important components to preventing sound transmission between the two houses that we should check to see if the blueprints were followed, and could they be checked with out making holes in the wall?

 

[stillmand]

Thank you. As you know, we already discovered there is only one layer of drywall on each side of the common wall versus the 2 layers on each side indicated by the blueprint. What would you say are one or two other important components to preventing sound transmission between the two houses that we should check to see if the blueprints were followed, and could they be checked with out making holes in the wall?

Also, let’s say we’re especially concerned about the sound transmission across the master bedroom common wall and the loft common wall. Should we looking at blowing in insulation through the ceiling and floor within a certain distance of those walls? Or will just treating those wall areas themselves help enough?

 

[Mark K]

Thanks so much, happy to give a little more background.

Thanks for the answer and happy to provide more background. Blueprints called for “2-hour firewall” with 2 layers of 5/8” drywall on each side of the common wall. But in reality they only put in one layer on each side. Builder now claims that they really only had to meet a 1 hour firewall because they say building falls under IRC rather than IBC.

There is also no sound protection across the common wall. STC is in the 30s. Builder is willing to address but the question is whether they need to meet an IRC requirement of STC 45 or IBC requirement of STC 50.

This is in Ocean City, Md. The code and various ordinances are hard to decipher as to what is the true fire code and sound transmission code for this structure.

If the construction documents require something in excess of the code the contractor must provide what is in the construction documents. In such a situation what is required by the code is irrelevant.

 

[Genduct]

Thanks for this. My understanding is that if there are already insulation batts in the wall, you can’t blow in additional insulation.

If the batts are there then you have your STC value

 

[bill1952]

Rock wool is good but cellulose a lot less work in existing wall and pretty good. A combo that exceeded many walls was Fiberock abuse resistant drywall with dense pack cellulose.

 

[stillmand]

If the batts are there then you have your STC value

Not sure what you mean by that? There is 5.5” fiberglass batts in the wall. But the STC is still terribly poor based on the fact we can easily have a conversation with our neighbors through the wall. I’m told the fiberglass batts don’t really help to absorb much sound, and that Rockwool doesn’t much better for that.

 

[Jay Smith]

Thank you. As you know, we already discovered there is only one layer of drywall on each side of the common wall versus the 2 layers on each side indicated by the blueprint. What would you say are one or two other important components to preventing sound transmission between the two houses that we should check to see if the blueprints were followed, and could they be checked with out making holes in the wall?

I would be most interested in the separation of the bedroom floor cavity along the common wall. Maybe the builder would tell you how it was done. Even the three layers shown in the drawings would perform worse than the wall. The architect’s notes clearly present that separation detail with three layers as a fire-resistance measure, so it would seem very likely the builder omitted it or at least two layers of it when they decided to build a 1-hour assembly.

Also, let’s say we’re especially concerned about the sound transmission across the master bedroom common wall and the loft common wall. Should we looking at blowing in insulation through the ceiling and floor within a certain distance of those walls? Or will just treating those wall areas themselves help enough?

Aside from code compliance, I would think the acoustical solution is probably to (a) replace existing wall board on your side with resilient channel and two layers of wall board and (b) add insulation and wall board in the floor-ceiling cavity in line with the wall.

That 2nd one would be tedious. You would have to cut into the living room ceiling and work between about 12 trusses in the bedroom floor.

 

[stillmand]

I would be most interested in the separation of the bedroom floor cavity along the common wall. Maybe the builder would tell you how it was done. Even the three layers shown in the drawings would perform worse than the wall. The architect’s notes clearly present that separation detail with three layers as a fire-resistance measure, so it would seem very likely the builder omitted it or at least two layers of it when they decided to build a 1-hour assembly.


Aside from code compliance, I would think the acoustical solution is probably to (a) replace existing wall board on your side with resilient channel and two layers of wall board and (b) add insulation and wall board in the floor-ceiling cavity in line with the wall.

That 2nd one would be tedious. You would have to cut into the living room ceiling and work between about 12 trusses in the bedroom floor.

Thanks Jay, appreciate this. Do you think we could address the master bedroom wall first, see if flanking is still significant enough of an issue, and if so then address the floor-ceiling cavity?

Also would there be an intermediate solution where we could cut small holes to blow in some insulation into the floor ceiling cavity and skip the addition of wall board there? Would that be less disruptive/expensive?

 

[Jay Smith]

Thanks Jay, appreciate this. Do you think we could address the master bedroom wall first, see if flanking is still significant enough of an issue, and if so then address the floor-ceiling cavity?

Also would there be an intermediate solution where we could cut small holes to blow in some insulation into the floor ceiling cavity and skip the addition of wall board there? Would that be less disruptive/expensive?

It does seem like addressing the wall first would be worth trying.

The blown insulation idea sounds plausible and helpful, and less disruptive/expensive. I just don’t know how to think about how effective it would be. With this idea of adding mass and resilience to an entire wall there are tested assemblies that can give us a goal like STC 50 and a means to try to achieve it.

 

[bill1952]

If adding drywall on resilient channels, I wouldnt remove the existing layer - just add the channels on top of it and add the new layer of drywall

 

[tbz]

This has become a very interesting topic, I guess since I am still battling the same issue in my place currently.

• As noted in my previous posts, not very specific, but as noted by Jay also, the floor cavity became like a bull horn for sound travel, at a minimum I would look at getting in there, the whole way and blowing or installing sound proofing, not just an insulation, for me this reduced a good bit of the sound transfer in the floor system.
• Common walls along stair flights, I will assume one of your common walls is along the stair flight and the side of the stringer sits flush with the face of the single sheet of drywall. Thus adding, like me a single layer of drywall is about the only option you have and that sets the issue for the rest of that exposed wall being uniform.
  • Hence adding a channel system or clip system to that existing wall, is not an option because it extends over the stringer and reduces the width of the stair flight. If your stair flight is wider, over 40", then this might not be a bad option, but I was already only 34" wide between walls.
  • I first did the green glue method and found the mids were affected, however the lows and some highs there was no difference at all to me, thus when they played music it was the same, except now I could not understand the words until they screamed in a high pitch and well, I got constant heavy base.
  • Thus, since I was only dealing with 10 sheets of drywall, I pulled everything down, on an internet whim, I put a layer of MLV ($700.00) and then did a 5/8" layer of drywall, taped and spackled and then applied a 2nd layer of 5/8 staggering the seams and then taped and spackled again.
  • This method for me did reduce the lows a good bit more and did reduce more mids, though both are still present. Not sure it was worth my time and effort, but I do hear a major difference than just the added 5/8 with green glue from before.
• As to the bedroom without knowing, and this becomes a personal choice, how much floor space you are willing to give up in the name of sound, well one can only speculate.
  • If you can give up the space, pull down the drywall remove the insulation, and install a system like Rockwools "Safe & Sound" or something better or equal in the existing cavity. Air-gap and then install another metal or wood stud wall, thickness could range from 1.5" - 5.5", depending on what you can give up and then sound proof with the same type of system in the first wall and then 2 layers of 5/8 following best practices with staggered seams and so on.
  • Being somewhat handy myself, I did all the work myself, thus reducing my costs to materials, and whatever time I had.
  • But, you need to also make sure they ceiling cavity above and floor cavity below are also done.
  • I did this on the first floor and I can't hear a thing coming through that wall when the neighbors are in the mist of who is cooking dinner tonight anymore... Very pleased with this, wish I could have done it along my stair flight.

The bottom line is, 90% of what is really going to work, will not be covered by anything your builder is probably responsible for.

Now here is the big question that those leaning on what the plans said to what is built.

• Did you and your neighbor hire a architect/design team to draw the plans and build it for your?
  • or did the builder, construct the property and sell each of you through a realtor a finished residence, separately?
• Because buying a floor plan from a builder and holding them to building it to the exact construction drawings becomes 2 separately different things.
  • If it's the later, the 2nd does not mean anything because the drawings are not part of the contract.
    • Only being built to the minimum code requirements does and that is why many states require New Home Warrantees as part of the sale of each new home constructed and sold, to the first owner.

The internet is full of suggestions I found more than a few websites on soundproofing apartments, condos and townhouse very interesting reads.

But this one helped me and I have another I used, just can't find the book mark at this minute, when I do I will post.

Soundproof Guide

If you're looking to soundproof your home then you've come to the right place. All you need to know for DIY soundproofing projects for step by step guides!

soundproofguide.com

The bottom line is, what's your goal and what's your budget, toss any thought of the original builder getting you to the level of quite you want, just not happening IMO.

 

[tbz]

As to your question about channel and clips systems, I have no personal experience with them and was told by those that did, that my situation, hanging kitchen cabinets and shelving to stay far away from it.

Thus, they all suggested the wall gapping method, being only 12ft wide with my space (Floor plan on that side 12'-2" x 28'-0" face of inside of balloon - framing built in 1875) I was only 140.5-inches between the inside of the framed walls to begin with.

So, giving up another 4" (1/2" gap & 3.5" stud wall) was huge on the first floor, I went from 140.5" to 136.5" minus another 1.75" of drywall, so face of sheet rock to face of sheet rock on the first floor is now 11'-2.75". But the layout works with the reduced space and I just ended up a much smaller door to the basement, which is not really useable. Low Ceilings and well.

Here is the floor concept floor plan I started with you can see the wall shift by the stair flight to the basement.

 

[Genduct]

Rock wool is good but cellulose a lot less work in existing wall and pretty good. A combo that exceeded many walls was Fiberock abuse resistant drywall with dense pack cellulose.

Personally, I prefer the INORGANIC fiber glass / Mineral type product. I have always been wary of the chemicals used to treat the ground up newspaper (cellulose) product. The concern comes from the potential of condensation in the wall cavity from air leakage or surface condensation of the sheathing of this porous product. IMHO

 

[Genduct]

Not sure what you mean by that? There is 5.5” fiberglass batts in the wall. But the STC is still terribly poor based on the fact we can easily have a conversation with our neighbors through the wall. I’m told the fiberglass batts don’t really help to absorb much sound, and that Rockwool doesn’t much better for that.

The sound also travels through the CRACKS AND GAPS as well as through the studs themselves ( hence the staggered stud design where Sound and STC is a real concern).
The density is not as high as mineral, that's true, but it would be much more if those batts were not there

With Acoustics there is no substitute for MASS for the STC values

 

[Genduct]

Since you are going to laminate another layer of gyp, why not blow in some insulation then cover the holes?

If this is a real concern, how about a layer of 1 inch, high density fiber glass insulation with the then the extra layer of drywall" There are electrical box extensions that can be added to outlets that might help this "FIX"

You'll want to calk those cracks where wall meets the ceiling. Just think about the "Cross-talk possibility if the wall intersects at the space between joists.
Commercial work often has the walls extend above the suspended ceiling to avoid this similar problem

 

[bill1952]

Genduct, on this issue, with sincere all due respect, just have come to different conclusions.

You pour a cup of water into a wall with fibre glass insulation, and you have a cup of water on the sill plate. Do same with cellulose, and it disappears, and can dry later.

Tested, for fire resistance, cellulose performed much better than fiberglass because it allowed less convection, which to me says it insulates better. That should improve acoustic performance as well.

Cellulose is more opaque than fiberglass, so better at preventing radiant transfer. Just put a flashlight behind each.

Some group studied it for mice and such, and mice don't like it as well as other insulation because the tunnels collapse.

As far as health concerns, Oak Ridge National Labs say no concern. https://timberhomesllc.com/cellulose-fire-safety-and-health-concerns-of-flame-retardants/

But either blow in has to be easier in existing wall compared to removing drywall.

 

[bill1952]

With Acoustics there is no substitute for MASS for the STC values

Basically agree, though physical separation - distance - is also very effective. Chorus and band room in a high school for instance, a double cmu wall with say a 8" air space between them and no physical connection works pretty good, but place a storage room between those two cmu walls, even better. (no doors or other penetrations.) Move those rooms to opposite ends of corridor, you can ditch some mass.

 

[stillmand]

This has become a very interesting topic, I guess since I am still battling the same issue in my place currently.

• As noted in my previous posts, not very specific, but as noted by Jay also, the floor cavity became like a bull horn for sound travel, at a minimum I would look at getting in there, the whole way and blowing or installing sound proofing, not just an insulation, for me this reduced a good bit of the sound transfer in the floor system.
• Common walls along stair flights, I will assume one of your common walls is along the stair flight and the side of the stringer sits flush with the face of the single sheet of drywall. Thus adding, like me a single layer of drywall is about the only option you have and that sets the issue for the rest of that exposed wall being uniform.
  • Hence adding a channel system or clip system to that existing wall, is not an option because it extends over the stringer and reduces the width of the stair flight. If your stair flight is wider, over 40", then this might not be a bad option, but I was already only 34" wide between walls.
  • I first did the green glue method and found the mids were affected, however the lows and some highs there was no difference at all to me, thus when they played music it was the same, except now I could not understand the words until they screamed in a high pitch and well, I got constant heavy base.
  • Thus, since I was only dealing with 10 sheets of drywall, I pulled everything down, on an internet whim, I put a layer of MLV ($700.00) and then did a 5/8" layer of drywall, taped and spackled and then applied a 2nd layer of 5/8 staggering the seams and then taped and spackled again.
  • This method for me did reduce the lows a good bit more and did reduce more mids, though both are still present. Not sure it was worth my time and effort, but I do hear a major difference than just the added 5/8 with green glue from before.
• As to the bedroom without knowing, and this becomes a personal choice, how much floor space you are willing to give up in the name of sound, well one can only speculate.
  • If you can give up the space, pull down the drywall remove the insulation, and install a system like Rockwools "Safe & Sound" or something better or equal in the existing cavity. Air-gap and then install another metal or wood stud wall, thickness could range from 1.5" - 5.5", depending on what you can give up and then sound proof with the same type of system in the first wall and then 2 layers of 5/8 following best practices with staggered seams and so on.
  • Being somewhat handy myself, I did all the work myself, thus reducing my costs to materials, and whatever time I had.
  • But, you need to also make sure they ceiling cavity above and floor cavity below are also done.
  • I did this on the first floor and I can't hear a thing coming through that wall when the neighbors are in the mist of who is cooking dinner tonight anymore... Very pleased with this, wish I could have done it along my stair flight.

The bottom line is, 90% of what is really going to work, will not be covered by anything your builder is probably responsible for.

Now here is the big question that those leaning on what the plans said to what is built.

• Did you and your neighbor hire a architect/design team to draw the plans and build it for your?
  • or did the builder, construct the property and sell each of you through a realtor a finished residence, separately?
• Because buying a floor plan from a builder and holding them to building it to the exact construction drawings becomes 2 separately different things.
  • If it's the later, the 2nd does not mean anything because the drawings are not part of the contract.
    • Only being built to the minimum code requirements does and that is why many states require New Home Warrantees as part of the sale of each new home constructed and sold, to the first owner.

The internet is full of suggestions I found more than a few websites on soundproofing apartments, condos and townhouse very interesting reads.

But this one helped me and I have another I used, just can't find the book mark at this minute, when I do I will post.

Soundproof Guide

If you're looking to soundproof your home then you've come to the right place. All you need to know for DIY soundproofing projects for step by step guides!

soundproofguide.com

The bottom line is, what's your goal and what's your budget, toss any thought of the original builder getting you to the level of quite you want, just not happening IMO.

Thanks so much for this. Indeed, we did not hire an architect. We put a reservation on the house as it was being built, and then purchased final product. That said, we believe the blueprints represent a contract, such that the builder should be accountable for 2 missing layers of drywall that are on the blueprints, which were approved by the city, but weren’t actually installed.

We also believe the builder is obligated to cover the cost of bringing the common wall up from the current STC that an acoustical engineer has estimates as 32, to the STC of 45 required by IRC, which is the applicable code. We realize that an STC 45 still won’t be good enough (although a heck of a lot better than 32). But let’s just say, making up numbers, it would cost $30,000 to get the common wall to an STC 45 and $40,000 to get to an STC 52. If we can compel the builder to cover the $30,000, then the additional $10,000 split between us and our neighbors, who want to solve the problem as much as we do, is potentially doable. Again, making up numbers here, although they may not be far off.

 

[Genduct]

Genduct, on this issue, with sincere all due respect, just have come to different conclusions.

You pour a cup of water into a wall with fibre glass insulation, and you have a cup of water on the sill plate. Do same with cellulose, and it disappears, and can dry later.

Tested, for fire resistance, cellulose performed much better than fiberglass because it allowed less convection, which to me says it insulates better. That should improve acoustic performance as well.

Cellulose is more opaque than fiberglass, so better at preventing radiant transfer. Just put a flashlight behind each.

Some group studied it for mice and such, and mice don't like it as well as other insulation because the tunnels collapse.

As far as health concerns, Oak Ridge National Labs say no concern. https://timberhomesllc.com/cellulose-fire-safety-and-health-concerns-of-flame-retardants/

But either blow in has to be easier in existing wall compared to removing drywall.

Bill, I like the fact that you too believe: Without the Data, You are Just someone with an OPINION"

But perhaps I am old enough to remember that Cellulose was, and perhaps still is Not Allowed Or discouraged to be used to retrofit old work where knob and tube wiring still exists.
Perhaps not the issue it was a number of years back, but there was and perhaps still is a concern about the chemicals used to "Fire Proof" ground up newspaper"

I also am old enough to remember the misinformation that the Cellulose people put forward in the late 70's that used efforts like "Victims of Fiber glass" to try to link Fiber glass with Asbestos. This effort lead to Prop 65 in California. So the Cellulose Industry's track record is somewhat suspect in my mind

Perhaps we can agree to disagree and respect each other's right to follow our preferences

 

[bill1952]

I agree, do not blow in cellulose where there id k&t wiring. Seems unlikely in a house new last year.

I recall (the much better funded) fiberglass industry casting aspersions on cellulose as flammable news paper and it was not safe. That led to the cellulose industry producing

 

[tbz]

Thanks so much for this. Indeed, we did not hire an architect. We put a reservation on the house as it was being built, and then purchased final product. That said, we believe the blueprints represent a contract, such that the builder should be accountable for 2 missing layers of drywall that are on the blueprints, which were approved by the city, but weren’t actually installed.

Without knowing the contract you signed, most builders today building spec or base homes, tend to contract on the floor plans and note someplace that the blueprints and construction documents are not part of the contact, just a code compliant home. Haven't a clue nor do I want to know, but that is the majority of the business, as this allows them the ability to change things and only be focused on delivering what is based on the floor plan and amenities stated and minimum code compliance.

If your contract is locked into the blueprints that they submitted, then all means, open season. The STC verified number is stating not 45 but 32, as thus, that is a code compliance issue and is justified requesting that the issue be rectified, my concern would be, will adding the 2 layers of 5/8" take you to a 45? Good chance maybe, but is that the result you are going to be satisfied with? I am thinking not so much

Only the acoustical engineers have the knowledge and expertise to speculate.

I guess my point is that if your main concern is the noise level and not the 2 hour fire protection in the IBC, then focus on working with them to get to a result of what you want, better sound proofing.

Hence maybe you pay to have the walls opened and sound proofing added, and the builder then takes over to install 2 new layers of 5/8 staggered seams with spackling in between, and painting.

Because, if they just add the additional layer they will still need to spackle and paint. You negotiate for them taking on the cost and redoing the new 1st layer 5/8".

From where I sit, your hanging your hat on double layer drywall and a STC number. and from my personal experience, I am guessing when the sound tech says yes it meets the 45 STC and there are 2 layers on each side, your still not going to be happy. But done with the builder...

 

[Genduct]

I agree, do not blow in cellulose where there id k&t wiring. Seems unlikely in a house new last year.

I recall (the much better funded) fiberglass industry casting aspersions on cellulose as flammable news paper and it was not safe. That led to the cellulose industry producing

To be fair, I believe they have info that strongly supports the notion that with the cycles of the cellulose absorbing then shedding moisture, that, over time, the fireproofing chemicals migrate and concentrate in the lower level, thus leaving less fire-resistant cellulose on top of attic / ceiling application. Or so it has been speculated!

The Victims of Fiberglass was a shameless and self serving attack that they knew was a LIE when they did it

 

[Genduct]

Basically agree, though physical separation - distance - is also very effective. Chorus and band room in a high school for instance, a double cmu wall with say a 8" air space between them and no physical connection works pretty good, but place a storage room between those two cmu walls, even better. (no doors or other penetrations.) Move those rooms to opposite ends of corridor, you can ditch some mass.

Bill, give me a call sometime, 267 784 2401