Enclosures and Breakaway Walls Home Builder’s Guide to Coastal Construction FEMA 499/June 2005 Technical Fact Sheet No. 27 Purpose: To discuss requirements and recommendations for enclosures and breakaway walls below the Base Flood Elevation (BFE). Key Issues --Spaces below elevated buildings can be used only for building access, parking, and storage. --Areas enclosed by solid walls below the BFE (“enclosures”) are subject to strict regulation under the National Flood Insurance Program (NFIP). Note that some local jurisdictions enforce stricter regulations for enclosures. --Non-breakaway enclosures are prohibited in V-zone buildings. Breakaway enclosures in V zones must meet specific requirements and must be certified by a registered design professional --Enclosures (breakaway and non-breakaway) in A-zone buildings must be built with flood-resistant materials and equipped with flood openings that allow water levels inside and outside to equalize (see Fact Sheet No. 15). --For V zones, enclosures below the elevated building will result in higher flood insurance premiums. --Breakaway enclosure walls should be considered expendable, and the building owner will incur substantial costs when the walls are replaced. WARNING: Home builders and homeowners should consider the long-term effects of the construction of enclosures below elevated residential buildings and post- construction conversion of enclosed space to habitable use in A zones and V zones. Designers and owners should realize that (1) enclosures and items within them are likely to be destroyed even during minor flood events, (2) enclosures, and most items within them, are not covered by flood insurance and can result in significant costs to the building owner, and (3) even the presence of properly constructed enclosures will increase flood insurance premiums for the entire building (the premium rate will increase as the enclosed area increases). Including enclosures in a building design can have significant cost implications. This Home Builder’s Guide to Coastal Construction recommends the use of insect screening or open wood lattice instead of solid enclosures beneath elevated residential buildings. [End of Warning] Space Below the BFE — What Can it Be Used For? NFIP regulations state that the area below an elevated building can be used only for building access, parking, and storage. These areas must not be finished or used for recreational or habitable purposes. No mechanical, electrical, or plumbing equipment is to be installed below the BFE. What Is an Enclosure? An “enclosure” is formed when any space below the BFE is enclosed on all sides by walls or partitions. A V-zone building elevated on an open foundation (see Fact Sheet No. 11), without an enclosure or other obstructions below the BFE, is said to be free-of-obstructions, and enjoys favorable flood insurance premiums (a building is still classified free-of-obstructions if insect screening or open wood lattice is used to surround space below the BFE). See FEMA Technical Bulletin 5-93, Free of Obstruction Requirements for more information. Graphic: breakaway walls that failed under the flood forces of Hurricane Ivan. Enclosures can be divided into two types, breakaway and non-breakaway. --Breakaway enclosures are designed to fail under Base Flood conditions without jeopardizing the elevated building – any below-BFE enclosure in a V zone must be breakaway. Breakaway enclosures are permitted in A zones but must be equipped with flood openings. --Non-breakaway enclosures, under the NFIP, can be used in an A zone (they may or may not provide structural support to the elevated building), but they must be equipped with flood openings to allow the automatic entry and exit of floodwaters. The Home Builder’s Guide to Coastal Construction recommends their use only in A zone areas subject to shallow, slow-moving floodwaters without breaking waves. Graphic: open wood lattice installed beneath an elevated house in a V zone. Breakaway Walls Breakaway walls must be designed to break free under the larger of the design wind load, the design seismic load, or 10 psf, acting perpendicular to the plane of the wall. If the loading at which the breakaway wall is intended to collapse exceeds 20 psf, the breakaway wall design must be certified. When certification is required, a registered engineer or architect must certify that the walls will collapse under a water load associated with the Base Flood and that the elevated portion of the building and its foundation will not be subject to collapse, displacement, or lateral movement under simultaneous wind and water loads. (See the sample certification at the bottom of page 2 of Fact Sheet No. 5.) Utilities should not be attached to or pass through breakaway walls. Graphic: recommended breakaway wall construction. [diagram] Flood Openings Where permitted and used in A zones, foundation walls and enclosures must be equipped with openings that allow the automatic entry and exit of floodwaters. Note the following: --Flood openings must be provided in at least two of the walls forming the enclosure. --The bottom of each flood opening must be no more than 1 foot above the adjacent grade outside the wall. --Louvers, screens, or covers may be installed over flood openings as long as they do not interfere with the operation of the openings during a flood. --Flood openings may be sized according to either a prescriptive method (1 square inch of flood opening per square foot of enclosed area) or an engineering method (which must be certified by a registered engineer or architect). Details concerning flood openings can be found in FEMA Technical Bulletin 4-93, Openings in Foundation Walls. Other Considerations Enclosures are strictly regulated because, if not constructed properly, they can transfer flood forces to the main structure (possibly leading to structural collapse). There are other considerations, as well: --Owners may be tempted to convert enclosed areas below the BFE into habitable space, leading to life-safety concerns and uninsured losses. Construction without enclosures should be encouraged. Contractors should not stub out utilities in enclosures; utility stub-outs make it easier for owners to finish and occupy the space. --Siding used on non-breakaway portions of a building should not be extended over breakaway walls. Instead, a clean separation should be provided so that any siding installed on breakaway walls is structurally independent of siding elsewhere on the building. Without such a separation, the failure of breakaway walls can result in damage to siding elsewhere on the building. --Breakaway enclosures in V zones will result in substantially higher flood insurance premiums (especially where the enclosed area is 300 square feet or greater). Insect screening or lattice is recommended instead. --If enclosures are constructed in A zones with the potential for breaking waves, open foundations with breakaway enclosures are recommended in lieu of foundation walls or crawlspaces. If breakaway walls are used, they must be equipped with flood openings that allow flood waters to enter the enclosure during smaller storms. Breakaway enclosures in A zones will not lead to higher flood insurance premiums. --Garage doors installed in below-BFE enclosures of V-zone buildings — even reinforced and high-wind-resistant doors — must meet the performance requirement discussed in the Breakaway Walls section on page 2 of this fact sheet. Specifically, the doors must be designed to break free under the larger of the design wind load, the design seismic load, or 10 psf, acting perpendicular to the plane of the door. If the loading at which the door is intended to collapse is greater than 20 psf, the door must be designed and certified to collapse under Base Flood conditions. See the Breakaway Walls section of this fact sheet for information about certification requirements. Graphic: Siding on the non-breakaway portions of this elevated building was extended over breakaway enclosure walls and was damaged when breakaway walls failed under flood forces. [End of Fact Sheet No. 27]