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Terrace Wall Height

K

Kendra

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Joined
Aug 25, 2017
Messages
72
Location
Philadelphia
Hello

I am working with a client who is building an outdoor terrace with a wall around the perimeter. They want the terrace wall to be 20" high so that it can be used for seating. There is a drop at one point that is 48" to the ground from the top of the wall (on the side opposite the terrace). I think this is not allowed because of section R312 (see attached picture) in the residential code, but I wanted to see if there were any provisions if this area had trees and/or shrubs as an additional barrier.

If there is no provision for trees/shrubs to act as a barrier, it seems that the only way to do this is to grade away from the terrace with soil so that there is a section less than 30” measured vertically in the 36” measured horizontally adjacent to the terrace. Because in this condition no guardrail (36” high) is required.

The attached sketch shows what I mean. Thank you in advance for your help!
 

Attachments

Is this at a single family home?

If this project falls under the IRC, then you are beyond the scope of the IRC. In the IRC, there are not provisions that extend to the building site. Once you are outside the home, the IRC basically stops.

The IBC does contain requirements for building sites given the public access and generally lower level of familiarity people have in these spaces. Hence the increased scope that includes additional provisions for guards.

This is to say, I think you are aware of the hazard here. While the code would not stipulate a requirement to place a guard or other barrier, you obviously understand the risk. You can thereby make an informed decision.

Remember, the code is the minimum standard and not best practice.
 
Screen Shot 2023-12-11 at 9.20.53 AM.png

What you would like to do creates a 4’ drop from the seat to the ground. A person that falls from the seat will land on their head. A back rest is called for... if for no other reason than comfort.

As classic T mentioned, this may not be regulated by a code however, neither is common sense. They definitely should not go with the top drawing.
 
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classicT said:
In the IRC, where is it required?
Click to expand...
Here (maybe) if they happen to be on the 2012 IRC....:

R312.1.2 Height.​

Required guards at open-sided walking surfaces, including stairs, porches, balconies or landings, shall be not less than 36 inches (914 mm) high measured vertically above the adjacent walking surface, adjacent fixed seating or the line connecting the leading edges of the treads.
 
classicT said:
Is this at a single family home?

If this project falls under the IRC, then you are beyond the scope of the IRC. In the IRC, there are not provisions that extend to the building site. Once you are outside the home, the IRC basically stops.

The IBC does contain requirements for building sites given the public access and generally lower level of familiarity people have in these spaces. Hence the increased scope that includes additional provisions for guards.

This is to say, I think you are aware of the hazard here. While the code would not stipulate a requirement to place a guard or other barrier, you obviously understand the risk. You can thereby make an informed decision.

Remember, the code is the minimum standard and not best practice.
Click to expand...
Interesting point. If this were a deck rather than hard scape, is it part of IRC? Same geometry, same fall hazard, but - simplified - wood framed rather than dirt and masonry.

The role of seating in fall protection is interesting. Makes me wonder if the back should be 36" above the seating surface.
 
steveray said:
Here (maybe) if they happen to be on the 2012 IRC....:

R312.1.2 Height.​

Required guards at open-sided walking surfaces, including stairs, porches, balconies or landings, shall be not less than 36 inches (914 mm) high measured vertically above the adjacent walking surface, adjacent fixed seating or the line connecting the leading edges of the treads.
Click to expand...
I would say that the above does not apply to landscaping or elements of the property. It is outside the scope of the IRC. The above only applies to portions of the building/structure that are intend to be used as a walking surface.

This same thing is discussed often with relation to retaining walls. Does every retaining wall >30" tall require a guard?
 
classicT said:
I would say that the above does not apply to landscaping or elements of the property. It is outside the scope of the IRC. The above only applies to portions of the building/structure that are intend to be used as a walking surface.

This same thing is discussed often with relation to retaining walls. Does every retaining wall >30" tall require a guard?
Click to expand...
Hence the maybe....

And that depends....Do we know how far this terrace is away from the house? I do not believe that has been specified.

And here in CT:

R312.1.1.1 Retaining Wall Guards​

Retaining walls with a difference in height between the finished grade at the top of the wall and the finished grade at the bottom of the wall that is greater than 4 feet (1219mm) shall be provided with guards complying with Section R312 when there is a walking surface, parking lot or driveway on the high side located closer than 2 feet (610 mm) to the nearest side of the retaining wall. For the purposes of this section, grass, planting beds or landscaped areas are not a walking surface.
 
steveray said:
Hence the maybe....

And that depends....Do we know how far this terrace is away from the house? I do not believe that has been specified.

And here in CT:

R312.1.1.1 Retaining Wall Guards​

Retaining walls with a difference in height between the finished grade at the top of the wall and the finished grade at the bottom of the wall that is greater than 4 feet (1219mm) shall be provided with guards complying with Section R312 when there is a walking surface, parking lot or driveway on the high side located closer than 2 feet (610 mm) to the nearest side of the retaining wall. For the purposes of this section, grass, planting beds or landscaped areas are not a walking surface.
Click to expand...
I appreciate that amendment. Would be a nice section to have in the model code.
 
Kendra said:
Hello

I am working with a client who is building an outdoor terrace with a wall around the perimeter. They want the terrace wall to be 20" high so that it can be used for seating. There is a drop at one point that is 48" to the ground from the top of the wall (on the side opposite the terrace). I think this is not allowed because of section R312 (see attached picture) in the residential code, but I wanted to see if there were any provisions if this area had trees and/or shrubs as an additional barrier.

If there is no provision for trees/shrubs to act as a barrier, it seems that the only way to do this is to grade away from the terrace with soil so that there is a section less than 30” measured vertically in the 36” measured horizontally adjacent to the terrace. Because in this condition no guardrail (36” high) is required.

The attached sketch shows what I mean. Thank you in advance for your help!
Click to expand...
Kendra and the rest of you correct me if I am wrong here, but the If I minus the 20" seat height from the 48" drop height, I come up with 28" which is under 30", which is the trigger for a guard being required under the IRC from the walking surface.

Unless Philly adopted something specific and different, measuring from the wall is not in the code, I am pretty sure about it because I was one of the 2 authors that added Fixed Seating during the CTC hearings which was adopted during the CTC's proposals to the code cycles in 2006, 2009 & 2012. That stipulation was removed in the model code by the enforcement sector through proposals and is no longer in the model 2015 IRC and future additions currently.

So as long as the drop from the walking surface to the lower level does not exceed 30 inches within 36 inches, you are compliant per the state adopted and enforced code requirements currently. I would however not push it so close and try to stay under 26 inches from top of wall to ground below allowing more than just 2 inches for future erosion and landscaping, in other words give them more than 2 inches to work with. Just an opinion, not a requirement.

1702377706775.png

Additionally, based on my scaling the seat is about 15-16 inches wide, and thus
 
ICE said:
Well I suppose they had to come up with a dimension … 24” seems arbitrary and insufficient.
Click to expand...
ICE it is not an arbitrary number, it is the number that was published in multiple issues of the BOCA building code way before any IRC/IBC model code was published. As to being insufficient, well something is better than nothing I guess, so how insufficient can it be?
 
tbz said:
ICE it is not an arbitrary number, it is the number that was published in multiple issues of the BOCA building code way before any IRC/IBC model code was published. As to being insufficient, well something is better than nothing I guess, so how insufficient can it be?
Click to expand...
For sure I'll be surprised if you do not have an answer to this but.... what is the 24" based on? Published does not render it less than arbitrary. I met a man that claimed to have been part of the decision making that landed on the number 50 as as trigger for stuff in the building code. He was teaching a class and seemed legit. I asked him what the #50 was based on and he said nothing other than that's what the committee was willing to accept.

A 36"wide hallway... where did that come from? Eight inches above dirt for a mudsill.... six wasn't enough... why is it not ten? A great deal of the building code was pulled out of thin air.

Pay attention to the section that steveray posted:
Retaining walls with a difference in height between the finished grade at the top of the wall and the finished grade at the bottom of the wall that is greater than 4 feet (1219mm) shall be provided with guards complying with Section R312 when there is a walking surface, parking lot or driveway on the high side located closer than 2 feet (610 mm) to the nearest side of the retaining wall. For the purposes of this section, grass, planting beds or landscaped areas are not a walking surface.

"greater than 4 feet". Now about that, lets go with forty feet. There's nothing to stop that.

"parking lot or driveway" Did they forget runway? So there's the potential for a driveway forty feet above what exactly? I'm going with a daycare on this one. As long as your parking lot is twenty-four inches away from the edge of the retaining wall that's forty feet above a daycare I'm not supposed to loose any buttons?

"complying with Section R312". Well there you have it. A guard that will stop a fat puppy.

And none of that is arbitrary? None of it makes any sense... that's the signature of a committee.
 
TBZ is right. I glanced too quickly at the drawing and took the 4'-0" as the height of the terrace.

The code might not apply to a terrace located away from a house, but why would it apply to a deck attached to the house but not a terrace?

I would still recommend backrest as a safety measure. If the client refuses it, then tell the landscape architect to specify several soft bushes there to break a fall.
 
ICE said:
For sure I'll be surprised if you do not have an answer to this but.... what is the 24" based on? Published does not render it less than arbitrary. I met a man that claimed to have been part of the decision making that landed on the number 50 as as trigger for stuff in the building code. He was teaching a class and seemed legit. I asked him what the #50 was based on and he said nothing other than that's what the committee was willing to accept.

A 36"wide hallway... where did that come from? Eight inches above dirt for a mudsill.... six wasn't enough... why is it not ten? A great deal of the building code was pulled out of thin air.

Pay attention to the section that steveray posted:
Retaining walls with a difference in height between the finished grade at the top of the wall and the finished grade at the bottom of the wall that is greater than 4 feet (1219mm) shall be provided with guards complying with Section R312 when there is a walking surface, parking lot or driveway on the high side located closer than 2 feet (610 mm) to the nearest side of the retaining wall. For the purposes of this section, grass, planting beds or landscaped areas are not a walking surface.

"greater than 4 feet". Now about that, lets go with forty feet. There's nothing to stop that.

"parking lot or driveway" Did they forget runway? So there's the potential for a driveway forty feet above what exactly? I'm going with a daycare on this one. As long as your parking lot is twenty-four inches away from the edge of the retaining wall that's forty feet above a daycare I'm not supposed to loose any buttons?

"complying with Section R312". Well there you have it. A guard that will stop a fat puppy.

And none of that is arbitrary? None of it makes any sense... that's the signature of a committee.
Click to expand...
ICE,
  1. When I said the 24-inches was not arbitrary, I meant the reason that CT used it in their modified section of the IRC was because they had it in the BOCA building code for years before they adopted the IRC & IBC. Hence, that 24-inch number was not arbitrary for their adoption.
  2. As to the actual number being able to be called arbitrary, the 24-inches, I have looked for over 2 decades to find out were that number came from and have been unsuccessful in my research, though I can find it going back decades in the codes.
  3. When I authored the proposal which is now what the 30-inches within 36-inches is based on my first submittal, E97-06/07, in which I also used the 24" horizontal found in the Model BOCA Codes 93-99, as part of my reason statement for the 24" number.
    1. The committee asked me to work through my proposal within the CTC process since I was also attending those hearings and during those meetings the majority agreed on the 36-inches based on the minimum landing size in the IRC.
    2. I resubmitted the next cycle as E84-07/08 with 36-inches, and,
    3. E85-07/08 was the CTC proposal that had the same language and other changes that was adopted.
As thus, this is the best I can give you from my memory on the subject, and the so called 24-inch arbitrary number currently in the CT IRC.
 
Paul Sweet said:
TBZ is right. I glanced too quickly at the drawing and took the 4'-0" as the height of the terrace.

The code might not apply to a terrace located away from a house, but why would it apply to a deck attached to the house but not a terrace?

I would still recommend backrest as a safety measure. If the client refuses it, then tell the landscape architect to specify several soft bushes there to break a fall.
Click to expand...
Paul,

I agree with your backrest, and this is what we have done with clients in the past.

Fixed Seating 02.JPGFixed Seating 01.JPG
 
Much of the code - IRC - is somewhat (or totally) arbitrary. A lot seems to be based on common practice before there was a code. Some of it is based on old research possibly of questionable criteria. I thought the 22" which while not used a lot is still the basis for egress width. The type B handrail seems based on colonial practice.

I've always wanted to learn the basis for 30" before any fall protection is required. Bunch of people sitting around a table - no doubt all older white guys - thinking it was reasonable.

When I first got involved in code development, I was told if one code said 2, another said 4, and all the experts in the room said 10, the building officials might change it to 3.

It's a great process that makes buildings safer, just not at all perfect.
 
ICE said:
A 36"wide hallway... where did that come from? Eight inches above dirt for a mudsill.... six wasn't enough... why is it not ten? A great deal of the building code was pulled out of thin air.
Click to expand...

Not exactly pulled out of thin air, but you are correct that many of the numbers were chosen by consensus of what the members of [whatever committee] could agree upon as a baseline for safety.

Why is the minimum exit access corridor and stair width (excluding exceptions) 44 inches? Why not 48 inches? That seems arbitrary, but I'm old enough to remember when the BOCA codes didn't use a ratio of 0.2" or 0.3" per person for egress width. Those old codes used what was called "units of egress width." One unit of egress width was 22 inches, which was supposed to represent the shoulder width of a "typical" adult male. So 44 inches was picked because it would supposedly allow two adult males to travel in parallel. When the codes changed to the current system of calculating egress capacity, the 44-inch minimum width was retained because there was no evidence to support changing it.

Building codes are written using a consensus process. Other than things like span/load tables, which can be derived from actual testing to show at what load a particular member over a particular span fails, pretty much every number in the codes is an arbitrary number. Why is an exit access travel distance of 150 feet safe, but 151 feet isn't safe? Consensus. Somebody on that committee may have advocated for 100' or 125', and someone else may have advocated for 175' or maybe 200'. They settled in 150 as something all members of the committee could live with, and if there was an objection from the floor it wasn't strong enough to see the 150-foot distance get shot down.

The numbers aren't just pulled out of thin air. Many are the result of years of empirical experience. Some are certainly just codification of rules-of-thumb that have been handed down for generations, but they all get challenged from time to time and, if the challenge makes sense, the numbers get changed.
 
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