Building Design Advantages for Sprinklered One- and Two-Family Homes and Townhouses.
We are painfully aware of the difficulties we as an industry have faced in the effort to make residential sprinklers a reality nationwide. As many are aware, there are many design advantages that come with installing a sprinkler system. However, a lot of the time we only talk about the commercial side of the design advantages and very rarely talk about the residential advantages in the International Residential Code (IRC), specifically for NFPA 13D systems installed through IRC Section P2904.
The first several design advantages in the IRC to discuss are found in Table R302.1(2). This table provides the required ratings for exterior wall construction in relation to property lines. The minimum fire separation for non-fire-resistance rated exterior walls is reduced from 5 ft to 3 ft. Also, projections (eaves, decks, balconies, etc.) that are greater than 2 ft from the property line are not required to have a 1-hour rating on the underside, or heavy timber, or fire-retardant-treated wood. This is a helpful reduction for any projects with projections between 2 ft and 5 ft in width requiring to meet the same 1-hour underside protection. Additionally, it is permitted to have unlimited openings in walls when they are at least 3 ft from the property line. When no sprinklers are installed openings are limited to 25% of the wall area having openings. Lastly, for residential subdivisions where all dwellings are equipped throughout with an automatic sprinkler system, fire separation distance for exterior walls not fire-resistance rated and for fire-resistance-rated projections is permitted to be reduced to 0 ft and unlimited unprotected openings and penetrations shall be permitted where the adjoining lot provides an open setback yard that is 6 feet or more in width on the opposite side of the property line.
The next design advantage is found in Section R302.2.2. Common walls that separate townhouses are permitted to be reduced to a 1-hour-fire-resistance-rated wall assembly instead of the normal 2-hour requirement. A similar design advantage is found in Section R302.3. The separation wall in two family dwellings is reduced to a 1/2-hour fire-resistance rating in lieu of a 1-hour fire-resistance rating. Also, in Section R302.13 floor assemblies that are not required to be fire-resistance rated are required to be provided with a covering with an approved covering (½ in. drywall, 5/8 in. wood structural panel, or equivalent) on the underside of the floor framing. However, this is not required when an automatic sprinkler system is installed.
Section R310.1 provides a major design advantage, especially in renovation projects. The required emergency escape and rescue openings requirements change drastically for sleeping rooms in basements when an automatic sprinkler system is installed. An emergency escape and rescue opening are not required in each individual basement sleeping room. It is only required to provide one means of egress and one emergency escape/rescue opening for the whole basement: or two means of egress for the whole basement.
The next advantage can be found in R318.104.22.168. It provides alternative setback options for photovoltaic systems (PV)when an automatic sprinkler system is installed. PV systems are permitted to occupy 66% of the total roof area with only an 18 in. setback from the horizontal ridge, while increasing to a 36 in. setback when occupying more than 66%. The 36 in. setback is required at 33% coverage on a non-sprinklered dwelling.
The final design advantage can be found in Section R325.3, and it applies to the area limitations of mezzanines. Where a non-sprinklered dwelling mezzanine is limited to 33% of the floor area of the room or space in which it is located, a mezzanine in a building equipped with an automatic sprinkler system is permitted to be up to 50% of floor area. This is a significant increase that can aid in designing more dynamic spaces.
There are many advantages to installing a residential sprinkler system, on top of the already obvious life preserving advantages that they bring. Keep all these advantages in mind when designing, reviewing or bidding the next project. They may be able to give you a unique advantage.