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Which code applies, IRC or IBC?

S

stillmand

Registered User
Joined
Apr 17, 2022
Messages
16
Location
Ocean City, MD
This duplex was built last year. The builder says that the applicable code is IRC. But my understanding is that IRC doesn’t apply to buildings more than 3 stories. And to me this is more than 3 stories (see picture:
https://imgur.com/a/yZTCERq
), which means that IBC is the required code. Note that the loft level is a livable space with a finished floor, bathroom, etc.

Would love any feedback on this.

Again, here is the picture:
https://imgur.com/a/yZTCERq
 
I think this may apply:

R325.6 Habitable Attic

A habitable attic shall not be considered a story where complying with all of the following requirements:
  1. The occupiable floor area is not less than 70 square feet (17 m2), in accordance with Section R304.
  2. The occupiable floor area has a ceiling height in accordance with Section R305.
  3. The occupiable space is enclosed by the roof assembly above, knee walls (if applicable) on the sides and the floor-ceiling assembly below.
  4. The floor of the occupiable space shall not extend beyond the exterior walls of the floor below.
 
Looks to comply with designing and building under the IRC 1 and 2 family dwelling code, with the little information provided.

My question is why are you asking what code after the project was built?
  • Are you questioning the Architect that drew it, noted the right code requirements
  • The builder submitted the wrong application for permit and;
  • That the Plan reviewer and building department missed the correct code on application
No offense but the question seems to be fishy with the amount of eyes and hands that had a part of the process before, during and up to the final certificate of occupancy was issued.

from where I am sitting on my chair anyway....
 
IBC for structural part of the structure. The columns supporting about 2/3rds of the structure are way beyond the IRC prescriptive requirements

R301.1.3 Engineered design.
Where a building of otherwise conventional construction contains structural elements exceeding the limits of Section R301 or otherwise not conforming to this code, these elements shall be designed in accordance with accepted engineering practice. The extent of such design need only demonstrate compliance of nonconventional elements with other applicable provisions and shall be compatible with the performance of the conventional framed system. Engineered design in accordance with the International Building Code is permitted for buildings and structures, and parts thereof, included in the scope of this code.
 
tbz said:
Looks to comply with designing and building under the IRC 1 and 2 family dwelling code, with the little information provided.

My question is why are you asking what code after the project was built?
  • Are you questioning the Architect that drew it, noted the right code requirements
  • The builder submitted the wrong application for permit and;
  • That the Plan reviewer and building department missed the correct code on application
No offense but the question seems to be fishy with the amount of eyes and hands that had a part of the process before, during and up to the final certificate of occupancy was issued.

from where I am sitting on my chair anyway....
Click to expand...
Thanks so much, happy to give a little more background.
tbz said:
Looks to comply with designing and building under the IRC 1 and 2 family dwelling code, with the little information provided.

My question is why are you asking what code after the project was built?
  • Are you questioning the Architect that drew it, noted the right code requirements
  • The builder submitted the wrong application for permit and;
  • That the Plan reviewer and building department missed the correct code on application
No offense but the question seems to be fishy with the amount of eyes and hands that had a part of the process before, during and up to the final certificate of occupancy was issued.

from where I am sitting on my chair anyway....
Click to expand...
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.
 
The extra layer of gypsum board on each side sounds like the way to achieve the STC.
 
STC numbers are not the best judge of an end result. I have been working through an old row home/ town home noise issue for about a year now.

I would be more interested in correcting the specific issue you have or goal than achieving a certain STC number.

The Town home I am working with was built in 1875, common wall is a single old school 2x4 turned on its face, so 1.75" thick. I went with 1.5" Safe & Sound and then Mass loaded vinyl barrier and two layers of 5/8" wall board. Since the neighbor is not into improving their side, I am only halfway to a reasonable level. I was not able to add another wall on the second floor because of the stair flight was on that wall, takes up 14 feet and there was no way to move it on a 12x28 floor plan.

I did however add a 2x4 gapped wall with staggered studs on the first floor, except on the stairwell going to the second floor level.

This with the 1.5" of safe and sound in the original common wall and then 3.5" of safe and sound in the new offset wall with the Mass loaded Vinyl and 2 layers of 5/8" wall board, has been a huge difference. But the lower base levels and the high pitches seem to just bleed through.

To really solve the issue, you will have to spend a good bit more than the code or the builder is responsible for.

Just getting to a higher STC is not really going to change what you personally have an issue with currently.

I could be wrong, but I would take a real hard look at it before just achieving a specific STC.

Good luck
 
So built last year, as in it's complete? Find the approved (stamped) construction plans and see what they show. If the plans were approved as it was built I don't think anything's going to happen. If the buildings were not built to plan then you might have some leverage.
 
Joe.B said:
So built last year, as in it's complete? Find the approved (stamped) construction plans and see what they show. If the plans were approved as it was built I don't think anything's going to happen. If the buildings were not built to plan then you might have some leverage.
Click to expand...
Thanks Joe, yes that’s right. It is complete. The blueprints on file with the city show 2 layers of drywall on each side of the common wall. But in reality only one layer was installed on each side.
 
tbz said:
STC numbers are not the best judge of an end result. I have been working through an old row home/ town home noise issue for about a year now.

I would be more interested in correcting the specific issue you have or goal than achieving a certain STC number.

The Town home I am working with was built in 1875, common wall is a single old school 2x4 turned on its face, so 1.75" thick. I went with 1.5" Safe & Sound and then Mass loaded vinyl barrier and two layers of 5/8" wall board. Since the neighbor is not into improving their side, I am only halfway to a reasonable level. I was not able to add another wall on the second floor because of the stair flight was on that wall, takes up 14 feet and there was no way to move it on a 12x28 floor plan.

I did however add a 2x4 gapped wall with staggered studs on the first floor, except on the stairwell going to the second floor level.

This with the 1.5" of safe and sound in the original common wall and then 3.5" of safe and sound in the new offset wall with the Mass loaded Vinyl and 2 layers of 5/8" wall board, has been a huge difference. But the lower base levels and the high pitches seem to just bleed through.

To really solve the issue, you will have to spend a good bit more than the code or the builder is responsible for.

Just getting to a higher STC is not really going to change what you personally have an issue with currently.

I could be wrong, but I would take a real hard look at it before just achieving a specific STC.

Good luck
Click to expand...
Thanks so much for this reply. Would be interested in any additional feedback. The situation is this. We can hear every word our neighbor says and they can every word we say with barely a raised voice.

While agree it’s the solution not the STC that matters, the fact is the matter is that based on how easy it is to have a conversation across the wall, the STC is somewhere in the low to mid 30s. The code requires an STC of 45, which would be a major improvement. Not perfect, and we’re not going for perfect, we (us and the neighbors) don’t think it’s acceptable for new construction that we can easily hear each other’s conversations, let alone kids screaming and dogs barking.

Again I agree it’s the solution that matters, but the builder is only going to feel obligated to meet the code required STC of 45. We can always offer to cover the cost of going above and beyond that value if we want to.

One thing I was thinking (and we’re working together with the neighbors by the way) is let’s say the builder agrees to add an additional layer of drywall on one side of the wall, and that they claim that will get us to STC 45. Could we then decide on our own to add an additional layer on the other side in targeted areas, say the master bedroom wall (the units are mirrors of each other), or the main level wall but not the adjoining staircase (since it is a lot more complicated and expensive to deal with stairwell walls), to add extra protection in those targeted areas. Or do have to the same to the whole wall to get any benefit due to flanking.

It sounds like from your description maybe you had done success treating one span of the wall but not the continuation of the wall into the stairwell? (Our stairwells are open, not enclosed)
 
The reason I was asking about the approved plans is they function as a contract. If the plans show two layers on each side and they only installed one then they did not build what was approved, regardless of whether they claim to "meet code". Even if what they built did meet code minimum standards it was not what was contracted to be built. Normally this should have been caught by inspections, and even if not the customer (the one paying the contractor) did not get what was agreed upon and they are the ones who have been "cheated." If you are the one who paid for this to be built then you may have a reasonable claim against the contractor.

Based on the tone of this thread I suspect that the one paying the bills was trying to pinch every penny and cut the corners by saying "well it only needs one layer by code so why should we pay for two?" or even worse (and maybe more likely) the builder is the owner. If this is the case and you're the tenant then you are in for an uphill battle.

If the property owners are willing to do a little work to try to make you a little more comfortable then a second layer of drywall will help. A layer of soundboard in-between the two layers of drywall will help a little bit more. There's a product out there called "Green Glue" that is designed to go between two layers of drywall and I've heard first hand accounts that it actually works really well. Here's a link if you want to check that out:

Noiseproofing Compound

Noiseproofing Compound Fast, simple, and effect are the best descriptors of Green Glue Noiseproofing Compound. Green Glue Noiseproofing Compound is a unique damping product that is ideal for new construction and renovation projects. As the most cost-effective soundproofing material on the...
www.greengluecompany.com www.greengluecompany.com

Good luck and let us know how it goes.
 
The green glue with another layer of 5/8" will reduce the noise level, but it will not solve it to the level you would be happy with if the clarity of the speak is that clear in my opinion.

Without knowing the exact wall insulation / sound proofing between the 2 units, and truly knowing if it is gapped double wall or if it is a single wall with 2 layers of 5/8" drywall, one on each side you can't even begin to comprehend how well sound travels through a floor system. The place I am in is one single deck with the 5/4 x 6 floorboards (construction today uses plywood) running from the unit next to me into my unit. Next door they just refinished the 145 year old floors, and I did the same, when you drop something on the floor like a quarter, sounds just like it was in the same room.

I hate carpet, so I installed a padding with an engineered flooring on top, the difference in massive, another reason people like carpeting for the sound deadening.

But sound will also travel through the wood studs, thus gapping and breaking the bridge is important. All the times I have used Green glue, it worked ok for the mid tones, but nothing on lower base tones and some higher tones, thus you still heard everything, just not so precise.

I got my best results with gapping and safe and sound from rockwool, and then the Mass loaded vinyl barrier before sheet rock, the Mass loaded vinyl barrier breaks the path of travel from the wood and dulls the sound passing through the voids (insulation zones) besides the wood studs, then 2 layers of drywall.

If the sound is that clear with a STC of 30, getting to 45 might be an improvement, but the STC is mainly the mid tones, so the highs and low are normally still pretty clear when sitting near the wall or rooms without carpeting.

That is what happens when your neighbors are that close and the architectural plans are figured for the basic minimums.

Not sure what your options are, but I would look at all of them before pulling the trigger and not being afraid to try and work out getting a better level for more money, I have never been happy with STC 45 levels.

Then again I like it quite.....
 
I've spent 40+ years as a consultant on design of performing arts facilities and noise isolation was always a key part.

Look for flanking paths. No doors or other such openings, basement floor to roof. As I understand the code, that sheetrock should be continuous, not just floor to ceiling. And to roof deck and exterior sheathing. If two layers, that too. So try to figure out if the did that. No back to back electrical openings, at least a stud bay away. For sound, they should have been sealed with acoustic (butyl) caulk. Ditto any pipe penetrations and actually no ducts or pipes passing through wall (for acoustical). After all those paths are stopped, if the wall is not insulated, I'd blow cellulose into each cavity. Without flanking paths, drywall on both sides with cellulose does a pretty good job empirically.

If adding drywall, not sure it meets fire resistance but putting it on resilient channels and acoustic sealant at edges will get a lot of isolation. Use 5/8 if possible. Lot of work resetting trim, electrical, etc., but it will be major improvement. I don't know how well the green stuff does what the resilient channels do.

The acoustical consultants I worked with - the top firms in US - all just about dismissed the leaded vinyl material. It's heavily marketed and costly, much more costly than drywall or plaster pound for pound - and mass is a key. YMMV.
 
Resilient channels and similar are effective. Loading them up can even improve them. One acoustical consultant I worked with a lot did this on his grandson's room - gluing scraps of gwb to the back of the panels to be mounted on the channels, between channels.
 
stillmand said:
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.
Click to expand...
"This is in Ocean City, Md."
Before I read this, the design seemed to me to be a Shore Home.
At the end of the day, I think you need to approach these kinds of questions in the light of INTENT and Not look for little pieces of Code to hang your Hat On

So, the lower level ENTRANCE area could be considered Habitable area, but in the context of the Shore Home, it is not really just and enclosed Porch ? ( that could get flooded)

So with that in mind, would that kind of thinking not better way to the approach the question
 
tbz said:
The green glue with another layer of 5/8" will reduce the noise level, but it will not solve it to the level you would be happy with if the clarity of the speak is that clear in my opinion.

Without knowing the exact wall insulation / sound proofing between the 2 units, and truly knowing if it is gapped double wall or if it is a single wall with 2 layers of 5/8" drywall, one on each side you can't even begin to comprehend how well sound travels through a floor system. The place I am in is one single deck with the 5/4 x 6 floorboards (construction today uses plywood) running from the unit next to me into my unit. Next door they just refinished the 145 year old floors, and I did the same, when you drop something on the floor like a quarter, sounds just like it was in the same room.

I hate carpet, so I installed a padding with an engineered flooring on top, the difference

I got my best results with gapping and safe and sound from rockwool, and then the Mass loaded vinyl barrier before sheet rock, the Mass loaded vinyl barrier breaks the path of travel from the wood and dulls the sound passing through the voids (insulation zones) besides the wood studs, then 2 layers of drywall.

If the sound is that clear with a STC of 30, getting to 45 might be an improvement, but the STC is mainly the mid tones, so the highs and low are normally still pretty clear when sitting near the wall or rooms without carpeting.

That is what happens when your neighbors are that close and the architectural plans are figured for the basic minimums.

Not sure what your options are, but I would look at all of them before pulling the trigger and not being afraid to try and work out getting a better level for more money, I have never been happy with STC 45 levels.

Then again I like it quite.....
Click to expand...
Thanks you, these are great insights. The common wall is single
tbz said:
The green glue with another layer of 5/8" will reduce the noise level, but it will not solve it to the level you would be happy with if the clarity of the speak is that clear in my opinion.

Without knowing the exact wall insulation / sound proofing between the 2 units, and truly knowing if it is gapped double wall or if it is a single wall with 2 layers of 5/8" drywall, one on each side you can't even begin to comprehend how well sound travels through a floor system. The place I am in is one single deck with the 5/4 x 6 floorboards (construction today uses plywood) running from the unit next to me into my unit. Next door they just refinished the 145 year old floors, and I did the same, when you drop something on the floor like a quarter, sounds just like it was in the same room.

I hate carpet, so I installed a padding with an engineered flooring on top, the difference in massive, another reason people like carpeting for the sound deadening.

But sound will also travel through the wood studs, thus gapping and breaking the bridge is important. All the times I have used Green glue, it worked ok for the mid tones, but nothing on lower base tones and some higher tones, thus you still heard everything, just not so precise.

I got my best results with gapping and safe and sound from rockwool, and then the Mass loaded vinyl barrier before sheet rock, the Mass loaded vinyl barrier breaks the path of travel from the wood and dulls the sound passing through the voids (insulation zones) besides the wood studs, then 2 layers of drywall.

If the sound is that clear with a STC of 30, getting to 45 might be an improvement, but the STC is mainly the mid tones, so the highs and low are normally still pretty clear when sitting near the wall or rooms without carpeting.

That is what happens when your neighbors are that close and the architectural plans are figured for the basic minimums.

Not sure what your options are, but I would look at all of them before pulling the trigger and not being afraid to try and work out getting a better level for more money, I have never been happy with STC 45 levels.

Then again I like it quite.....
Click to expand...
thank you for these insights. The common wall is a single wall 2x6 wood studs, 16” OC, with 5.5 inch fiberglass batts (yes, a terrible acoustic design). Let’s say we add an extra layer of 5/8” drywall to one side of the all for the whole common wall, except for the master bedroom to master bedroom wall, where for more privacy we decide to spend the money to tear down the existing wall and put up a new one with resilient channel or isolation clips for decoupling. Will that have the intended impact of providing an extra meaningful reduction in sound across the master bedroom wall compared to the rest of the house?
 
bill1952 said:
I've spent 40+ years as a consultant on design of performing arts facilities and noise isolation was always a key part.

Look for flanking paths. No doors or other such openings, basement floor to roof. As I understand the code, that sheetrock should be continuous, not just floor to ceiling. And to roof deck and exterior sheathing. If two layers, that too. So try to figure out if the did that. No back to back electrical openings, at least a stud bay away. For sound, they should have been sealed with acoustic (butyl) caulk. Ditto any pipe penetrations and actually no ducts or pipes passing through wall (for acoustical). After all those paths are stopped, if the wall is not insulated, I'd blow cellulose into each cavity. Without flanking paths, drywall on both sides with cellulose does a pretty good job empirically.

If adding drywall, not sure it meets fire resistance but putting it on resilient channels and acoustic sealant at edges will get a lot of isolation. Use 5/8 if possible. Lot of work resetting trim, electrical, etc., but it will be major improvement. I don't know how well the green stuff does what the resilient channels do.

The acoustical consultants I worked with - the top firms in US - all just about dismissed the leaded vinyl material. It's heavily marketed and costly, much more costly than drywall or plaster pound for pound - and mass is a key. YMMV.
Click to expand...
Fabulous feedback, thank you. If you’re able to take a look at the blueprint and provide any more fine tuned advice based on it, I would be grateful. The one caveat being that while the blueprint shows 2 layers of drywall on each side of the common wall, in reality there is only one layer on each side. Here is the link. Sometimes you have to reload it a few times:

http://weblink.ocgov.org/Weblink/ElectronicFile.aspx?docid=271878&dbid=0
 
Though a great sound barrier, remember to take a good look at what you are planning to hang on a wall with resilient channels, if it is nothing more than pictures and some other things its a great choice, if you are planning on hanging any millwork, cabinets or entertainment systems, make sure to plan the mounting locations to support those items and sound proof them.

I can't say enough about ROCKWOOL Safe & Sound, if it is an option to remove and install new insulation between, I found it to be worth the cost.

Here is a demo video -

This with the resilient channels and double drywall will drastically improve the current STC i would think.
 
stillmand said:
Thanks you, these are great insights. The common wall is single

thank you for these insights. The common wall is a single wall 2x6 wood studs, 16” OC, with 5.5 inch fiberglass batts (yes, a terrible acoustic design). Let’s say we add an extra layer of 5/8” drywall to one side of the all for the whole common wall, except for the master bedroom to master bedroom wall, where for more privacy we decide to spend the money to tear down the existing wall and put up a new one with resilient channel or isolation clips for decoupling. Will that have the intended impact of providing an extra meaningful reduction in sound across the master bedroom wall compared to the rest of the house?
Click to expand...
Since you are going to laminate another layer of gyp, why not blow in some insulation then cover the holes?
 
tbz said:
Though a great sound barrier, remember to take a good look at what you are planning to hang on a wall with resilient channels, if it is nothing more than pictures and some other things its a great choice, if you are planning on hanging any millwork, cabinets or entertainment systems, make sure to plan the mounting locations to support those items and sound proof them.

I can't say enough about ROCKWOOL Safe & Sound, if it is an option to remove and install new insulation between, I found it to be worth the cost.

Here is a demo video -

This with the resilient channels and double drywall will drastically improve the current STC i would think.
Click to expand...
Thank you for this. I’m not an expert and honestly not very handy at all; so i don’t know exactly what I’m saying here, but do you know the difference between resilient channel versus isolation clips? I read that isolation clip method is a little more expensive than resilient channel but doesn’t fail as often as resilient channel, which it sounds like has to be installed perfectly to work and, as you say there are limits to what you can hang on the wall, otherwise it fails. Do you know anything about this?

And again I have the question, let’s say for the whole common wall we only add a layer or 2 of drywall on top of what’s already there. But just for the master bedroom wall, we demo one side of it, replace the fiberglass batts with Rockwool, decouple with isolation clips or resilient channel, and put back up one or two layers of regular drywall (or one layer of QuietRock and green glue?). Will we realize the benefit of significantly lower sound transmission across the master bedroom wall? Or will flanking negate the extra mitigation?

What I’m getting at is, we’ve got long stretches of hallway and stairwells along the common wall where it’s not as important to reduce the sound transmission, and where the expense and disruptiveness of demolition will really pile up, whereas we’ve got a few rooms like bedroom and loft, and half of the main level, where we need more strongly block the sound.
 
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