IRC Height: unlimited?

[wtravisl]

Here's a fun one:

I've been commissioned to design a single-family residence in a floodplain near a lake. The 1st floor of occupied living space will be 2' above the flood elevation, which will place it approximately 30' above grade. With 2 stories, I anticipate a building height of 50', possibly a bit more. The builder is constructing something similar nearby, with typical wood framing for the elevated living spaces, over a concrete/metal deck, over structural steel columns down to slab-on-grade foundation.

I cannot find a 2021 IRC height limit. Only a story limit (3). Am I missing something?

If I were to classify this as 2021 IBC R-3, over a U private garage, Type VB construction would be capped at 40'. I'd need to use IIB (steel studs) or VA (rated assemblies over wood framing) to reach 50'.

Complicating matters is the fact that the client has mentioned this house could be used as an AirBnB rental in the future. To my thinking, R-3 Lodging House (transient) is a better fit for this type of occupancy than IRC dwelling.

Are any others out there designing 50' tall unrated wood-framed homes?
Does anyone have specific experience concerning AirBnB use causing problems for an IRC dwelling?
Any input is appreciated. Thanks-

 

[TheCommish]

I would like to see the designe for the foundation (stilts) under it and the switch back stairs to get u to it.

 

[wtravisl]

I would like to see the designe for the foundation (stilts) under it and the switch back stairs to get u to it.

Nothing has been designed yet. The at-grade foundation will be traditional concrete slab, steel reinforcement. Then steel columns & bracing (likely painted & exposed) up to the 1st floor of occupied space. The at grade slab will be used for 'private garage' with parking for 2 vehicles, and the only enclosure will be the elevator shaft and stair shaft - possibly a small storage area for lake toys. Elevator equipment at the top of the shaft, out of the flood zone. The stair will be concrete on metal pans. Both stair & elevator enclosures will be 1hr fire-rated.

 

[mtlogcabin]

If it was in my jurisdiction it will be engineered. What you are describing, steel columns, is not within the prescriptive requirements of the IRC

R106.1 Submittal documents.
Submittal documents consisting of construction documents, and other data shall be submitted in two or more sets with each application for a permit. The construction documents shall be prepared by a registered design professional where required by the statutes of the jurisdiction in which the project is to be constructed. Where special conditions exist, the building official is authorized to require additional construction documents to be prepared by a registered design professional.

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.

 

[classicT]

I too struggle to see how this is going to be entirely an IRC structure. I will concede that the interior environment can follow the IRC; however, the entire structural design will need to follow the IBC. That would include IBC Ch. 5 and 6, from where your construction types and rated construction requirements will originate from.

 

[tbz]

I have been on more than a few of these type projects after Irene and Sandy.

This is the closest I can come to theory off the top of my head, we worked on this property 3 times in 4 years.

Did the reno in the spring, then Irene messed up the original ground level home reno that fall.

Re-did the Reno the following spring

Then Sandy just hammered and left nothing standing but, the SAND that fall again, twice in the span of one year.

Then Client built this which sits 16ft up to the first floor level, then a second floor level.

Open parking under it with open stairway between elevator room and ground level storage room.

The first 2 reno's were IRC, this went IBC - R3

 

[Paul Sweet]

The building code might not have a height limit, but zoning probably will.

The IRC has wind load adjustments for mean roof heights up to 60 ft. Having to design part of the structure to IBC requirements doesn't kick the entire building out of the IRC.

 

[jar546]

The proposed design it outsider the prescriptive IRC and would then require IBC compliance for the structural components which includes height limitations. If you platform frame a home within the confines of wall height limitations, it is impossible to prescriptively exceed to the heights you describe.

 

[bill1952]

Humor me jar546. Is it the structural steel part or just the height that puts this outside IRC prescriptive design? For myself, with a steeply sloped site, I was looking for the IRC heigth limits of wood columns on piers, supporting a 2 story stick framed building, and found none. A very tall crawlspace. Now, probably 1st floor is around 20-25 ft high at down slope, and 10 or less at up slope side, with a short level bridge (deck?) from ground level to 1st floor.

 

[jar546]

First you have to get through zoning, if it exists, that most definitely will have a height limitation unless they are in the dark ages.
Next, this is not platform frame construction (not the whole thing). Show me the prescriptive requirements for 30' high concrete columns/pilings to a concrete deck on what is most likely going to be tie beams and I will assume there will be grade beams at the bottom. This is not masonry construction and the design is outside the scope of the IRC structurally. I am not sure why you are asking me to humor you.

 

[Mark K]

The IRC was not written with this type of situation in mind. The IBC should be used. ASCE 7 which is referenced from the IBC has provisions for flood loading.

The owner should find out the implications of the flood loads before proceeding.

You will need an engineer.

 

[jar546]

The IRC was not written with this type of situation in mind. The IBC should be used. ASCE 7 which is referenced from the IBC has provisions for flood loading.

The owner should find out the implications of the flood loads before proceeding.

You will need an engineer.

I absolutely agree with this.

 

[dancinbear]

100% this needs structural engineering. You indicate that floodwaters may be applying loads to the first 28 vertical feet of structure, which can create some tremendous loads. Add to this the wind loading of a structure this tall and the engineered foundation is going to be pretty massive. You need to review Section R322 Flood Resistant Construction and determine the wave height the structure may be subject to. Can be permitted as single family residential IRC with engineered construction as indicated by comment #4 and others above. We have 130 mph ultimate wind speed and plenty of flood zones in my area, we build similar (though not this tall) all the time here.

 

[bill1952]

I think you're all saying this could not be built under IRC? Basic post and beam with stick frame house. I couldn't find in IRC a height limit on the posts like It could stud walls, etc.

 

[classicT]

I think you're all saying this could not be built under IRC? Basic post and beam with stick frame house. I couldn't find in IRC a height limit on the posts like It could stud walls, etc.

Correct. That cannot be built per the IRC. Full structural engineering design required.

 

[steveray]

(Amd) R101.2 Scope. The provisions of this code shall apply to the construction, alteration, movement, enlargement, replacement, repair, equipment, use and occupancy, location, removal and demolition of detached one- and two-family dwellings and multiple single-family dwellings (townhouses) not more than three stories above grade plane in height with a separate means of egress and their accessory structures not more than three stories above grade plane in height.

R301.3 Story height. The wind and seismic provisions of this code shall apply to buildings with story heights not exceeding the following: 1. For wood wall framing, the story height shall not exceed 11 feet 7 inches (3531 mm) and the laterally unsupported bearing wall stud height permitted by Table R602.3(5). 2. For cold-formed steel wall framing, the story height shall be not more than 11 feet 7 inches (3531 mm) and the unsupported bearing wall stud height shall be not more than 10 feet (3048 mm). 3. For masonry walls, the story height shall be not more than 13 feet 7 inches (4140 mm) and the bearing wall clear height shall be not greater than 12 feet (3658 mm). Exception: An additional 8 feet (2438 mm) of bearing wall clear height is permitted for gable end walls. 4. For insulating concrete form walls, the maximum story height shall not exceed 11 feet 7 inches (3531 mm) and the maximum unsupported wall height per story as permitted by Section R608 tables shall not exceed 10 feet (3048 mm). 5. For structural insulated panel (SIP) walls, the story height shall be not greater than 11 feet 7 inches (3531 mm) and the bearing wall height per story as permitted by Section R610 tables shall not exceed 10 feet (3048 mm). Individual walls or wall studs shall be permitted to exceed these limits as permitted by Chapter 6 provisions, provided that story heights are not exceeded. An engineered design shall be provided for the wall or wall framing members where the limits of Chapter 6 are exceeded. Where the story height limits of this section are exceeded, the design of the building, or the noncompliant portions thereof, to resist wind and seismic loads shall be in accordance with the International Building Code.