Tag Archives: occupancy classification

Pole Barn Conversion, Condensation Concerns, and Setting Trusses

This week the Pole Barn Guru answers reader questions regarding converting a section of an existing building into living space, concerns about condensation in an insulated wall, and a concern about setting trusses too soon following a concrete pour.

DEAR POLE BARN GURU: Hello! We have a pole barn already built, 60×80, and we’ve decided to build living quarters in a 30×60 portion of the barn. We want to put a second level in the living quarters. We’ve done a 2ft monolithic pour that extends to the footings, around the exterior, 6-8inch thick concrete with steel grates underneath. We’ve done a 2ft by 3ft thick concrete footer underneath each pole. There are 16 total. Is this something that could be turned into engineered living space with a second story space (30×30)? Thanks in advance. KAITLIN in EDEN

DEAR KAITLIN: Most pole barns are built either without being engineered or to Risk Category I. For residential purposes, it would need to meet more stringent structural requirements of Risk Category II. You will probably have to add some perimeter slab insulation in order to meet Energy Code requirements. My best recommendation is to engage a Utah Registered Professional Engineer to do a physical evaluation of your existing building and to design needed structural upgrades.


DEAR POLE BARN GURU: Hello I recently built a post frame home and I have a question for you regarding the insulation on the walls. The exterior walls are 6×6 posts with 2×6 flat girts and a well-sealed WRB then steel. I used R-21 fiberglass with bookshelves girts on the inside of the wall then applied a 6 mil vapor barrier with acoustical caulk and tape to achieve a tight seal. Do you see any issues with this system in the long or short term as far as condensation and air sealing because of the lack of OSB or plywood sheathing on the outside? WESLEY in DULUTH

Installing a ceilingDEAR WESLEY: I have seen many far less well thought out wall systems without exterior sheathing not experience issues with condensation. As far as air sealing, you could get a blower door test done to find out exactly what your situation is. For extended reading, please see https://www.hansenpolebuildings.com/2020/10/blower-door-testing-your-new-barndominium-part-i/ and https://www.hansenpolebuildings.com/2020/10/blower-door-testing-your-new-barndominium-part-ii/


DEAR POLE BARN GURU: I am getting ready to pour my footing for my posts and am wondering how long I wait for the concrete to cure before setting the trusses, etc TRIPPE in NINE MILE FALLS

DEAR TRIPPE: We always suspend our columns eight (8) inches above bottom of holes and mono-pour footing and concrete encasement in a single pour (saves on paying for short haul charges). While concrete typically reaches 75% of compressive strength in seven days, when I was building we would pour one day and start building next day. For slabs on grade, it is recommended to not walk on them for 24-48 hours after a pour. Keep in mind, concrete compressive strength is in psi (pounds per square inch) and soil bearing capacity under footing is in psf (pounds per square foot). Most soil will support a maximum of 2000 psf or 13.88 psi, so your concrete (at 2500-3000 psi) is going to be much stronger, even after a very short time span, than soils beneath. You can increase concrete strength by ordering a higher cement mix and speed curing time by use of hot water (avoid use of chemical additives to speed curing).

Use and Occupancy Group Classification Part I

In life, most everything is given some type classification whether it’s objective, such as motor vehicle operators’ licenses (automobile, commercial, motorcycle, etc.), or subjective, such as social status (wealthy, middle class, poor). Then there are those who are in “a class all by themselves.” Buildings, like much of everything else, are classified, as well.

There are two elements of classification in the building code: occupancy and construction type. This blog is about the essential elements of determining a building’s classification based on its occupancy.

The International Building Code (IBC) establishes the requirements for classifying buildings based on occupancy. Essentially, an occupancy establishes how the building will be used, whether for business, residential, or one of the many other types.

The IBC states, all “…structures shall be classified with respect to occupancy…”. There’s no assignment of responsibility included. Therefore, the Registered Design Professional (RDP – either an engineer or architect) can “legally” determine a building’s occupancy; and the building official, will either concur or not concur with the RDP’s decision during plan review as a part of enforcing the provisions of the code.

As a potential owner of a new building, early discussions with the Building Department can avoid confusion as to which occupancy group will be accepted for the intended use.

The IBC has established 10 occupancy groups, with some having multiple subgroups. These subgroups are numbered with a purpose. The lower the number, the greater the perceived risk is for the occupants. For example, A-1 has large occupant loads in fixed seating. Whereas A-5 is includes seating of large numbers of people for viewing outdoor activities. Assuming the occupancies had equal occupant loads, the A-1 is indoors with fixed seats that reduce egress speed. The A-5 occupancy, although having fixed seats, is outdoors reducing the risk of smoke and heat buildup within the seating area.

The 10 occupancy groups are Assembly (A), Business (B), Educational (E), Factory and Industrial (F), High Hazard (H), Institutional (I), Mercantile (M), Residential (R), Storage (S) and Utility and Miscellaneous (U).

Most of the occupancies are assigned strictly on the building’s intended use, or uses, as most buildings have many spaces which can be classified under more than one occupancy group.

For example, a fire station may have sleeping quarters for the firemen (Residential), office areas (Business), vehicle and other miscellaneous storage areas for the fire equipment (Storage), and a training area (Assembly).

Buildings which can be classified with multiple uses are considered “mixed occupancies.” However, before calling a building a mixed occupancy, it needs to be determined if the additional occupancies can be considered “incidental use areas.” These are spaces which provide minor support to the building’s main occupancy. The IBC provides the criteria for incidental use areas, which typically include storage, mechanical, and other specialty spaces. If a space qualifies as an incidental use area, it will be classified as a part of the main occupancy it’s incidental to.

For example, if an office building (Group B) has a 200 square foot storage area (Group S) within the office area, then it could be considered Group B if it is separated from the office area by 1-hour fire barrier, or is provided an automatic fire-extinguishing system for the storage space only.

Most spaces can be classified solely on their intended use; however, some occupancy assignments are more objective. For example, a room may be used for assembly purposes, but if the space is equal to or less than 750 square feet, then its classification is considered a part of the main occupancy. Using the fire station example above, if the training area is 750 square feet in area, then it will be considered a part of the Business Group. If it’s any larger, then it would have an Assembly Group classification.

Why the 750 square foot limitation? It goes back to the basic definition of “Assembly” occupancy. If the occupant load is 50 or greater, and is used for the gathering of people for various purposes (such as civic, social, or religious), then it’s considered an Assembly occupancy. Taking 750 square feet and dividing by 50 occupants, gives 15 square feet per occupant, which equals the most liberal occupant load factor for an assembly use.

Your head hurt yet?  Don’t worry; your local building department will help you with the use classification of your building.  It will do you no good to “guess”.  My suggestion is to clearly list each “room” and describe what it will be used for, by how many people at any given time.  Then take your list to the building department for a “use category” assignment.  Come back tomorrow. There is more on this topic for discussion.