2015 Home Builders' Jobsite Codes
352
2015 Home Builders' Jobsite Codes
352eBook
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Overview
Product Details
| ISBN-13: | 9780867187427 |
|---|---|
| Publisher: | National Association of Home Builders |
| Publication date: | 01/01/2016 |
| Sold by: | Barnes & Noble |
| Format: | eBook |
| Pages: | 352 |
| File size: | 10 MB |
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CHAPTER 1
Structural Design Criteria
The IRC establishes minimum structural design criteria necessary to accommodate normal loads placed on a building and, depending on a home's location, resist the forces of natural hazards such as snow, wind, earthquake, and flood. In most cases, the tried-and-true construction practices offered in the IRC incorporate these criteria, eliminating the need for an engineered design or complex calculations. For example, the code provides span tables for conventional wood framing elements such as joists, girders, headers, and rafters.
Construction must safely support all loads:
[] Snow, wind, seismic, and flood loads, which vary by geographic region
[] Live loads
[] Dead loads
[] Roof loads
Note The roof is designed for the roof live load (not more than 20) psf or the snow load, whichever is greater.
To correctly apply the values of the tables and the prescriptive methods of construction, builders must know the structural design criteria in the planning chapter of the code. Determining the appropriate live loads is fairly straightforward. However, seismic, wind, snow, soil, or flood area values differ by geographic location. In addition, frost depth, weathering severity, ice barrier underlayment requirements, and history of termite damage vary by climate and geography. Therefore, builders often must obtain information through the maps found in the IRC or through their local building departments.
Moreover, some structural elements still may require an engineered design. For example, the sizing of wide-flange steel beams commonly used in dwelling construction is outside the scope of the IRC. Instead, accepted engineering practices will determine their sizes.
Live Loads
Minimum required live loads for floors are based on the use of the space. Guards and handrails also must be secured to safely resist forces against them (table 1.1).
Deflection
Allowable deflection is a measurement of bending under code-prescribed loads to ensure adequate stiffness of structural framing members such as studs, joists, beams, and rafters (table 1.2). Although the prescriptive tables account for deflection in their values, builders must be familiar with deflection limits in order to choose the appropriate table for sizing a framing member. Allowable deflection is measured by dividing the span or length (L) of the member by a prescribed factor, such as 360 for floor joists (L/360). To determine allowable deflection for a certain span, convert feet to inches and divide the result by 360. The following example is for a floor joist with a 16 ft. span:
L = 16 ft. × 12 in. = 192 in.
Allowable deflection = 192 in. /360 = 0.53 in.
Allowable deflection for this floor joist is approximately ½ in.
Note: A 16 ft. span rafter with a 4/12 slope and no ceiling attached has an allowable deflection of L/180, which is twice the deflection allowed for floor joists.
Calculating Dead Loads
The prescriptive tables of the IRC detailing continuous footing sizes for conventional frame construction assume average weights of construction materials. Therefore, additional calculations typically are not required. The material and component weights (tables 1.3 and 1.4) may help builders correctly size an isolated footing, or another element not covered in the IRC tables.
Wind
The prescriptive structural provisions of the IRC are limited to those geographical regions with ultimate design wind speeds of 140 mph or less (130 mph in hurricane-prone regions) as defined in the IRC wind maps. Otherwise, the code requires a design in accordance with one of the referenced standards. In addition to an engineered design that complies with the International Building Code (IBC) and ASCE 7, the IRC includes references to ICC 600, Standard for Residential Construction in High Wind Regions and AWC Wood Frame Construction Manual (WFCM).
Wind Exposure Category
In addition to the basic wind speeds for a geographic area, ground surface irregularities affect the wind's impact on a building. The IRC classifies wind exposure into three categories:
1. Exposure B — some wind protection with trees and buildings characteristic of urban and suburban settings
2. Exposure C — open terrain with scattered obstructions
3. Exposure D — adjacent to large bodies of water, including hurricane-prone regions
Exposure categories are important design criteria for engineering purposes. For many of the prescriptive methods of wood frame construction in the IRC, wind exposure category is not a factor. However, wind exposure category must be considered when applying the provisions for wall sheathing, wood wall bracing, roof tie-down, and exterior wall and roof coverings. The following components must be listed and installed to resist wind loads based on the wind speed and exposure category:
[] Siding
[] Roof covering
[] Windows
[] Skylights
[] Exterior doors
[] Overhead doors
Hurricanes
Hurricane-prone regions are the coastal areas of the Atlantic Ocean and Gulf of Mexico where the ultimate design wind speed is greater than 115 mph. The IRC wind maps identify the portions of hurricane-prone regions that require an engineered design or a design that complies with other referenced standards. Windows and other glazing require additional protection if they are in windborne debris regions — those areas within hurricane-prone regions as specifically defined in the code.
Storm Shelters
Storm shelters, sometimes called safe rooms, are not required by the code. However, they offer added protection from the destructive forces of high winds, hurricanes, and tornadoes. When installed within a dwelling or as a separate structure, storm shelters must conform to the requirements of ICC-500, Standard on the Design and Construction of Storm Shelters.
Earthquake
The IRC assigns a seismic design category (SDC) to building sites relative to the anticipated intensity and frequency of earthquakes. (For more details, see the seismic map in the code.) For buildings located in SDC A or B and constructed under the prescriptive methods of the IRC, there are no additional seismic requirements. One- and two-family dwellings in SDC C also are exempt from the seismic requirements. However, specific seismic requirements apply to townhomes sited in SDC C, and to all buildings in SDC [D.sub.0], [D.sub.1], and [D.sub.2].
The higher seismic design categories (SDC[D.sub.0], [D.sub.1], and [D.sub.2]) occur predominantly in western parts of the U.S., in the New Madrid area of Missouri, Illinois, Indiana, Tennessee, and Arkansas, and in South Carolina.
CHAPTER 2Fire Safety
Fire-resistant construction is required to separate dwelling units, for exterior walls located close to property lines, and on the garage side of an attached garage/dwelling separation.
This chapter addresses these requirements, as well as protection of floor assemblies and foam plastic insulation, fire sprinkler systems, smoke alarms, and emergency escape. Fire protection related to specific building components is addressed throughout the code and is detailed in this and other chapters of this book.
Location on Property
Exterior walls of dwellings and garages must maintain a minimum separation from the property line, measured perpendicular to the wall, or be protected for fire. For dwellings without fire sprinkler systems, walls less than 5 ft. from the property line must have a fire-resistance rating of one hour when exposed to fire from either side of the wall. The code permits a 3 ft. separation without a fire-resistance-rated wall when the dwelling has an automatic fire sprinkler system. A typical one-hour wall consists of ? in. Type X gypsum board or gypsum sheathing on both sides of a frame wall with insulation filling the cavity. However, a number of other approved designs are available.
The following fire-resistance requirements are based on distances to the property line (figs. 2.1 and 2.2):
For dwellings without fire sprinklers:
[] Less than 5 ft. — one-hour wall
[] Less than 5 ft. — limited area for windows and doors
[] Less than 3 ft. — no windows or doors
[] Less than 2 ft. — no roof overhang projections
Roof overhang projections less than 5 ft. from the property line require one-hour protection on their underside.
For dwellings with fire sprinklers:
[] Less than 3 ft. — one-hour wall
[] Less than 3 ft. — no windows or doors
[] Less than 2 ft. — no roof overhang projections
Roof overhang projections less than 3 ft. from the property line require one-hour protection on their undersides.
Note: Sheds and playhouses of 200 sq. ft. or less do not require fire-resistant protection regardless of their location on the property.
Dwelling Unit Separation
Fire-resistant-rated separations are required between dwelling units of duplexes and townhomes as follows:
Two-Family Dwelling Separation
[] One-hour fire-resistance-rated construction is required to completely separate dwelling units.
[] The separation may have a ½-hour rating if an NFPA 13 sprinkler system is installed throughout.
Note: NFPA 13R and 13D systems do not satisfy this requirement.
[] The separating wall assemblies must extend from the foundation to the underside of the roof sheathing and to the exterior walls (fig. 2.3). There is one exception:
• Wall assemblies need not extend through the attic if 5/8 in. Type X gypsum board is installed on the ceiling of the living space and an attic draft stop lines up with the separating wall.
Townhome Separation
The fire-resistance rating of the common wall separating townhome dwelling units depends on the presence or absence of an automatic fire sprinkler system. Townhomes without sprinkler protection require a 2hr. rated separation whereas the rating is reduced to 1 hr. for townhomes with sprinkler systems (fig. 2.4). Additional requirements follow:
[] The common separation wall cannot contain plumbing, mechanical equipment, vents, or ducts.
[] The separation wall must be continuous from the foundation to the underside of the roof sheathing.
[] Parapets are not required when certain fire-resistant protection is provided for the roof for 4 ft. on both sides of the separating wall.
Fire-Resistant-Rated Penetrations
When items such as pipes or ducts penetrate one or both sides of the fire-resistant-rated wall or the floor/ceiling assemblies separating dwelling units, both the penetrating item and the space around it must be protected to maintain fire resistance. In general, penetrations by steel, ferrous and copper pipe, tubing, and conduit require only that the space left around the pipe be filled with approved materials to limit the passage of fire. The material, such as a listed fire caulk, must be installed according to the manufacturer's instructions to provide a fire-resistant time rating equivalent to that of the construction being penetrated.
Other penetrating materials, such as plastic pipe or metal ducts, (not permitted for the common wall separating townhomes), must be protected further by approved means, such as a listed firestop assembly or a fire damper, to maintain the fire-resistance rating of the wall or floor/ceiling assembly. Steel electrical boxes up to 16 sq. in. and listed electrical boxes of any material are permitted if they are separated by approved means when they are located on opposite sides of the wall. Wood blocking or applying listed putty pads to both boxes are two means of separating them.
Garages
Attached garages and detached garages within 3 ft. of the residence require protection to resist the spread of fire to the dwelling, but not the same protection as required between dwelling units (fig. 2.5). The separation does not require an assembly with a fire-resistance rating as in the case of dwelling unit separations. The prescriptive requirements are as follows: [] o provide complete separation of the garage from the dwelling, ½in. gypsum board must be installed on the garage side.
[] If habitable rooms are located above the garage, 5/8 in. Type X gypsum board must be installed on the garage ceiling and ½ in. gypsum board must be installed on the walls supporting the floor/ceiling.
[] Doors between the dwelling and garage must be self-closing and one of the following types:
• 13/8 in.-thick solid wood
• 13/8 in.-thick solid-core steel
• 13/8 in.-thick honeycomb-core steel
• 20-minute fire rated
[] Ducts in the garage as well as ducts penetrating the walls or ceilings that separate the dwelling from the garage shall be of a minimum No. 26 gage sheet steel. The ducts shall have no openings into the garage.
[] Garages cannot open into a sleeping room.
[] Garage floors shall be noncombustible and sloped to a drain or the vehicle entry door.
Fire Protection of Floors
For certain types of floor framing such as open-web trusses and I-joists, the IRC requires application of a membrane to the underside of the framing to provide limited fire protection and delay collapse of the floor in a fire. The membrane must be one of the following materials:
[] ½ in. gypsum wallboard
[] 5/8 in. wood structural panel
[] Other equivalent material
[] Protection is not required for floor assemblies:
[] Over a space protected with automatic fire sprinklers
[] Over a crawl space not intended for storage or fuel-fired appliances
[] With unprotected portions not greater than 80 sq. ft. per story isolated by prescribed fireblocking
[] Of 2 × 10 or greater dimension lumber or structural composite lumber
Foam Plastic Insulation
A thermal barrier of ½ in. gypsum board or equivalent must separate foam plastic from the interior. The following exceptions are permitted:
[] In attics and crawl spaces entered only for repairs or maintenance, foam plastic may be covered with one of the following ignitionbarrier materials:
• 1½ in. mineral fiber insulation
• ¼ in. wood structural panels
• 3/8 in. particleboard
• ¼ in. hardboard
• 3/8 in. gypsum board
• 0.016 in. corrosion-resistant steel
• 1½-inch-thick cellulose insulation
• ¼-inch fiber-cement panel, soffit or backer board
[] Foam plastic may be spray applied to a sill plate and header (rim joist area) without the thermal barrier when the foam plastic meets the following requirements:
• No more than 3¼ in. thick
• Density of 1½–2 lb. per cu. ft.
• Flame-spread index less than or equal to 25 and smoke-developed index less than or equal to 450
Other types of insulation and insulation facings or vapor barriers also may require covering with ½ in. gypsum board or other approved materials, depending on flame-spread and smoke-developed properties of the exposed material.
Automatic Fire Sprinkler Systems
A dwelling unit fire sprinkler system helps to detect and control fires and is meant to prevent flashover in the room where a fire originates to allow time for occupants to escape a building. The code requires an automatic fire sprinkler system in new townhomes and new one- and two-family dwellings.
The sprinkler system must conform to one of the following:
[] IRC sec. P2904, Dwelling Unit Fire Sprinkler Systems or
[] NFPA 13D, Standard for the Installation of Sprinkler Systems in One- and Two-Family Dwellings and Manufactured Homes
A dwelling unit fire sprinkler system requires less water compared with NFPA 13 and 13R systems. It may be either a multipurpose or stand-alone system. The code permits connection to many types of water supply systems to meet the required fire sprinkler system capacity. Generally, a dwelling unit fire sprinkler system does not require sprinklers in the following locations:
[]Closets not greater than 24 sq. ft. with a depth of 3 ft. or less
[] Bathrooms no larger than 55 sq. ft.
[] Open porches
[] Garages
[] Attics without a fuel-fired appliance [ ] Crawl spaces
[] Concealed spaces
Dwelling fire sprinkler systems also do not require a fire department connection.
Note: The IRC requires a single sprinkler above fuel-fired equipment installed in an attic.
Smoke Alarms
Dwelling units require smoke alarms as follows:
Required Locations
In new homes and dwelling units undergoing remodeling, the code requires a smoke alarm in the following locations:
[] Each sleeping room
[] Outside of and in the immediate vicinity of each separate sleeping area
[] On each story, including basements and habitable attics
Required Clearances
To prevent nuisance alarms, the code requires the following minimum clearances for smoke alarms:
[] 3 ft. horizontally from a bathroom door
[] 20 ft. horizontally from a cooking appliance for ionization smoke alarms
[] 10 ft. horizontally from a cooking appliance for ionization smoke alarms with an alarm-silencing switch
[] 6 ft. horizontally from a cooking appliance for photoelectric smoke alarms
Installation Requirements
The smoke alarms must meet the following installation requirements:
[] Hardwired to the building power with no disconnection switch
[] Battery backup
[] Alarms interconnected
Note: The code allows listed wireless alarms in place of physical interconnection. All alarms must sound upon activation of one alarm.
(Continues…)
Excerpted from "2015 Home Builders' Jobsite Codes"
by .
Copyright © 2019 Steve Van Note.
Excerpted by permission of National Association of Home Builders.
All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.
Excerpts are provided by Dial-A-Book Inc. solely for the personal use of visitors to this web site.
Table of Contents
List of Figures,
List of Tables,
Acknowledgments,
Introduction,
1 Structural Design Criteria,
2 Fire Safety,
3 Safe and Healthy Living Environments,
4 Foundations,
5 Floors,
6 Wall Construction,
7 Wall Covering,
8 Roof Framing,
9 Roof Finishing,
10 Chimneys and Fireplaces,
11 Energy Efficiency,
12 Mechanical Systems,
13 Fuel Gas,
14 Plumbing,
15 Electrical Systems,
Epilogue,
Notes,
Glossary,