Written by: Kenneth S. Risley
Constructing a Hangar Home
Designing and building a hangar home has several factors that are not encountered in routine custom home projects.One question of interest is properly determining the requirements for fire separation between the hangar and the dwelling. Understanding and preparing for this can help bypass some frustrating issues during plan approval and construction inspections.
The International Building Code (IBC), and the Florida Building Code (FBC), which is mostly derived from the IBC, clearly defines a “Residential Aircraft Hangar”. It is established that a Residential Aircraft Hangar shall have an area not exceeding 2000 ft.² nor a building height that exceeds 20 feet. The Building Height is defined as the vertical distance from the grade plane to the average height of the highest roof surface.
Therefore, there is a clear demarcation between hangars that meet those two criteria and those that don’t.
In my own hangar home design practice, about 50% of the projects have hangar areas that exceed 2000 ft.². This situation, in both the IBC and FBC, triggers more stringent requirements. Hangars that are not considered residential aircraft hangars fall into two broad categories: storage hangars and repair hangars. Both are considered Group S-1 which means that they are to be designed and built as though they will be storing moderately hazardous materials.
I will, first, present the exact requirements according to the letter of the code. At the end I will give you my personal opinion of the applicability.
Residential Aircraft Hangars
- If a residential aircraft hangar is connected to the dwelling it must be separated by a fire barrier having a fire resistance rating of not less than one hour. This separation must be continuous from the foundation to the underside of the roof and it may not be pierced by anything except doors between the hangar and the dwelling. Any such doors must be equipped with a self-closing device and must conform to other requirements of the code such as having a rating of at least 75% of the wall rating, in this case 45 minutes, and having a sill of at least 4 inches in height which must be noncombustible. Also, no opening from a hanger to the dwelling may go directly into any room used for sleeping purposes.
- Of additional interest, a residential aircraft hangar must have a smoke alarm. It must also have electrical, mechanical and plumbing systems independent from the dwelling. Smoke detector wiring and any electrical feed to the subpanels to the hangar are excluded from this requirement. Also any plumbing drains may utilize the same sewer system.
- A one- hour rated wall is a wall which is been constructed according to specifications established by Underwriters Laboratory (UL). They have established, through empirical testing, what systems comply with the requirements. One can find many wall (and other) details by visiting the UL website or by obtaining one of their catalogs. A one-hour rated assembly is usually rather simple to achieve. A couple layers of 5/8” type “X” gypsum will often do the trick. This detail is pretty straight forward for the partitions that separate the hangar from the home but since the rated wall must extend to the roof it can get a bit challenging up in the attic region depending on how the trusses and framing are running. The Designer Engineer needs to keep this in mind when suggesting truss layouts to help set up a simple surface upon which the fire rated drywall can be placed.
- Wires, pipes and ducting may not penetrate this barrier. Note, however, that in commercial building, it is common to have penetrations through fire walls and as long as the penetrations themselves are fire rated. Though not directly addressed in the Code for hangar homes, it is my opinion that any approved commercial type fire penetration would be completely acceptable to most plan reviewers.
- Though the code speaks only of doors through the firewall, generally, a window can be placed as long as it is fire-rated to a level of 75% the rating of the wall (ie. 45 minutes).
- If the hangar is not connected to the dwelling, and if the hangar is built of CMU concrete blocks, then the higher fire rating issue is essentially solved because the rating of CMU walls exceeds one hour.
Hangars Not Considered Residential Aircraft Hangars
- According to Table 707.3 .9 of the FBC (2010 edition) a Group S-1 usage must have a three-hour separation between itself and other areas of different fire ratings. In the case of a hangar home with an adjoining hangar, the requirement would be a three-hour fire separation between the hangar and the dwelling extending from the foundation to the bottom of the roof.
- A hangar not attached to the home, built of CMU materials, would by the nature of the concrete block exterior wall, be in compliance with this requirement.
- There is the question of whether or not an automatic sprinkler system is required for such structure. According to the code, Section 903.2 .9, a Group S-1 area does require an automatic sprinkler system however the exceptions tend to exclude most hangar home projects. These exclusions are: 1) The area must exceed 12,000 ft.²; 2) the area is located more than three stories above the grade plane; and a third one that as absolutely no applicability to hangar home projects. Therefore it can be deduced that an automatic fire sprinkler system is not required in any type of hangar home as long as the hangar is less than less than 12,000 ft.² in area.
- A system defined by a typical UL detail will have to be used for the three-hour rating. It is a good idea to build the walls between the dwelling in a hangar with CMU materials. The area above the ceiling, between the ceiling and the roof, can be a bit more complicated but there are several methods can be used to achieve that. A good designer engineer can work out that detail.
General Fire Wall Considerations
- There is another table in the code, Table 602, which is referenced to determine exterior firewall requirements for all types of structures. The parameters gives several requirements for fire walls on the exterior related to how close the structure is to the property line. The fire rating requirements reduce as the distance of the structure from the property line increases. These requirements range from zero to two hours for any type of hangar home. This assumes that no hangar would ever be closer to a property line than 5 feet.
- Given this argument, hangars build with CMU type materials are most recommended, not only for strength but also because they tend to exceed all fire separation requirements.
There Are The Facts. Here is my opinion.
Attempting to figure out building codes and applicability is sometimes similar to watching a dog chase its own tail. Codes have gotten vast today and can become complicated concatenations of cross referencing as well as a whole bunch of CYA. When I started in this business the Building Code (called Standard Building Code) was a single book about 2”thick. Today it is many large tomes – all of “equal” importance. Figuring out an applicable code, unfortunately, often becomes a matter of interpretation. I have seen areas of the code, especially in the ADA (codes covering the American with Disabilities Act) absolutely crash in conflict with themselves as Code writers attempt to comply with complicated mandates from Congress.
The good news is that saner heads have prevailed and, recognizing this possibility, have allowed local Building Officials to interpret the code and make the official call when necessary. A Building Official is one specific man or woman over a given building department and the buck stops with him or her.
However, we find codes being enforced relatively haphazardly throughout the United States. I have designed hangar homes in states where, while there is a code extant, there is no enforcement whatsoever. Many areas of the United States do not require building permits. I’ll bet they get along just fine.
In Florida, I have seen many hangar homes built with hangar sizes greater than 2000 ft.², with no particular attention being paid to fire separations beyond what is required for a residential aircraft hangar. So if you are looking to build a hangar home in Florida, or anywhere, it would be a good idea to speak to local builders, designers and engineers (as well as owners who have been through the maze) and determine for yourself part parts of the code will be strictly required.
But if it is to be, no fire requirements should exceed those I note above.