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Cantilever Code Update

By Glenn Mathewson

A new package of prescriptive deck code provisions—RB 264, which is partly based on the American Wood Council’s DCA 6—was approved at the final ICC code development hearing in early October and will be included in the 2015 International Residential Code (IRC). Among the provisions are updated span tables for decking, joists, and beams, which will help clarify the rules for cantilevers of joists and beams.

Joist Cantilevers

According to the new span tables and IRC provisions, cantilevers can extend up to one-fourth the backspan of the joist. This means that joists, such as southern pine 2x10s at 16 inches on-center, spanning 12 feet are allowed to cantilever up to an additional 3 feet (see illustration, below).

There are two sections in the new span table: one for joists with cantilevers, and one for joists without cantilevers. Cantilevering a joist produces greater stresses in the primary joist span (backspan), so the maximum span is often reduced. For cantilevers greater than the depth of the joist material (9 1/4 inches for a 2×10), you must use the span criteria for “joists with cantilevers.”

These joist span tables and cantilever allowances might be old news to those familiar with DCA 6 (awc.org), but there are a few differences. READ THE REST BY CLICKING HERE http://www.deckmagazine.com/codes-and-standards/cantilevers-in-the-2015-code.aspx

A Path to Safer Balconies

These tricky cantilevered structures demand careful framing and waterproofing details

By

Charles Bickford

On June 15, 2015, a group of 13 students in Berkeley, Calif., fell five stories when the balcony they were standing on suddenly collapsed. Six were killed, seven were critically injured, and the incident became the latest example of the often-fatal consequences of poor building practices. The 4-foot-5-inch by 8-foot-10-inch balcony wasn’t overloaded; it was designed to support combined live and dead loads of more than 100 lb. per square foot (the code requirement at the time it was built). Subsequent investigations revealed a number of problems, however, including a leaky walking surface and a non-ventilated deck soffit that trapped water inside the deck frame, causing the engineered (but not pressure-treated) wood framing to rot.It’s a sobering lesson for any builder who thinks a balcony is basically a cantilevered deck. Unlike a deck, which is supported by a ledger and a system of posts, beams, and footings, a balcony’s sole support derives from joists or beams that cantilever from the exterior wall. Its stability and longevity rely on the strength of the cantilever and a careful detailing of the exterior to protect the house and deck framing from water damage.

READ THE REST HERE http://www.deckmagazine.com/structure/a-path-to-safer-balconies_o.aspx

I found this table by the IRC for cantilever spans for floor joists…click the link to read the whole article!

TABLE R502.3.3(2) CANTILEVER SPANS FOR FLOOR JOISTS SUPPORTING EXTERIOR BALCONY^{a, b, e, f}

Member Size	Spacing	Maximum Cantilever Span (Uplift Force at Backspan Support in lb)^{c, d}
		Ground Snow Load
		≤ 30 psf	50 psf	70 psf
2 × 8	12″	42″ (139)	39″ (156)	34″ (165)
2 × 8	16″	36″ (151)	34″ (171)	29″ (180)
2 × 10	12″	61″ (164)	57″ (189)	49″ (201)
2 × 10	16″	53″ (180)	49″ (208)	42″ (220)
2 × 10	24″	43″ (212)	40″ (241)	34″ (255)
2 × 12	16″	72″ (228)	67″ (260)	57″ (268)
2 × 12	24″	58″ (279)	54″ (319)	47″ (330)

For SI: 1 inch = 25.4 mm, 1 pound per square foot = 0.0479 kPa.

a. Spans are based on No. 2 Grade lumber of Douglas fir-larch, hem-fir, southern pine, and spruce-pine-fir for repetitive (3 or more) members.

b. Ratio of backspan to cantilever span shall be at least 2:1.

c. Connections capable of resisting the indicated uplift force shall be provided at the backspan support.

d. Uplift force is for a backspan to cantilever span ratio of 2:1. Tabulated uplift values are permitted to be reduced by multiplying by a factor equal to 2 divided by the actual backspan ratio provided (2/backspan ratio).

e. A full-depth rim joist shall be provided at the unsupported end of the cantilever joists. Solid blocking shall be provided at the supported end.

f. Linear interpolation shall be permitted for ground snow loads other than shown.

http://publicecodes.cyberregs.com/icod/irc/2009/icod_irc_2009_5_par022.htm

CONSTRUCTION CONCERNS: CANTILEVERED BALCONIES

Article and photo by Gregory Havel Balconies and second-floor decks have been built on single-family and multifamily residences for hundreds of years. In earlier times, they were usually supported by simple beams, whose loads were carried by the wall of the building on one side and by a row of columns on the other.

In modern lightweight-wood frame construction, these balconies and decks are often carried by cantilever beams, supported by the building wall on one side, unsupported on the other; and counterbalanced by an extension of the cantilevers to beams inside the floor-ceiling assemblies inside the building.

Photo 1 shows the framing for a second-floor deck on a house under construction. The cantilevered beams are dimensional lumber nailed together. Since this deck also serves as a canopy over the French doors on the first floor, it is supported on a beam of laminated veneer lumber (LVL) that is part of a load-bearing wall of 2×6 studs.

Second-Story Balconies

By Martin Holladay Issue 236 – June/July 2013

Returning home from a visit to France or perhaps from a local production of Romeo and Juliet, many romantics vow, “My next bedroom will have a balcony.” Builders with clients who request a second floor balcony have to figure out durable details that will support Juliet and her railing. For years, some designers have created second-floor balconies by cantilevering floor joists (or a floor slab) through the thermal envelope of the building. However, there are two serious problems that are associated with following this practice: thermal bridging and moisture management.

Thermal bridging and moisture risks

Some builders address the wicking problem by installing plywood on the exterior deck, followed by a waterproof surface material such as fiberglass. This works better than deck boards with drainage gaps, but it still leaves a tricky problem at the door threshold. Because the cantilevered joists guarantee that the interior flooring and the balcony deck are at the same level, it’s hard to prevent rain and snow entry. The best water-management details call for a balcony or deck to be one step lower than the interior flooring—an impossibility if the joists are cantilevered.

READ THE REST HERE http://www.finehomebuilding.com/2013/05/16/second-story-balconies

BUILD A DECK – FINE HOMEBUILDING

Cantilevered Balcony Safety

By Andy Engel Aug 06, 2015

Recently, a cantilevered balcony collapsed in Berkeley, Calif., killing six people. The evident reason was wood rot, caused either by poor initial construction or by a lack of maintenance. An article in the San Jose Mercury News suggests that, particularly with multifamily homes, similar problems abound in the Bay Area. There’s a move afoot to require regular inspections of such balconies on rental properties.

Although the issue in Berkeley was on a multifamily property, similar balconies are common in single-family residential construction throughout the country. I spoke with Glenn Mathewson, a building inspector in Westminster, Colo., and an expert on deck construction, to find out more.

FHB: Glenn, can you say a little about how cantilevered balconies are built? For example, do the joists have to be rot-resistant? Are the same flashing details required as with decks?

READ THE REST HERE http://www.finehomebuilding.com/2015/08/06/cantilevered-balcony-safety

Construction Concerns: Cantilevered Balconies

Modern balconies and decks may not be able to to handle the weights required for firefighting operations. Gregory Havel takes an in-depth look at this aspect of contemporary building construction.

Jan 8, 2009

Article and photo by Gregory Havel

Gregory Havel is a member of the (WI) Fire Department; retired deputy chief and training officer; and a 30-year veteran of the fire service. He is a Wisconsin-certified fire instructor II and fire officer II, an adjunct instructor in fire service programs at Gateway Technical College, and safety director for Scherrer Construction Co., Inc. He has a bachelor’s degree from St. Norbert College. He has more than 30 years of experience in facilities management and building construction.

Balconies and second-floor decks have been built on single-family and multifamily residences for hundreds of years. In earlier times, they were usually supported by simple beams, whose loads were carried by the wall of the building on one side and by a row of columns on the other.

CLICK HERE TO READ ALL OF THIS ARTICLE AT FIREENGINEERING.COM

CANTILEVERED DECKS – THE SERIES OF BUILD ARTICLES ON TIMBER DECKING CONSTRUCTION CONTINUES WITH THE REQUIREMENTS FOR CONSTRUCTING A CANTILEVERED SLATTED TIMBER DECK.

A DECK OR BALCONY CANTILEVERED from a building presents structural and weathertightness issues not encountered with non-cantilevered decks (see Figure 1). Construction consists of deck joists installed alongside and bolted to the floor joists extending over the external wall framing. The back extension alongside the floor joist must be at least 1.25 times longer than the length of the cantilever (see Figure 2). The finished level of a cantilevered deck with slatted timber decking must be at least 50 mm below the finished floor level or threshold of the building interior (from E2/AS1). Joist treatment and fixing Cantilevered deck joists must be treated to hazard class H3.2 and bolted to the floor joist with two M12 bolts and 50 × 50 × 3 mm washers at the innermost end of the cantilevered joist.

READ THE REST BY CLICKING HERE http://www.buildmagazine.org.nz/assets/PDF/Build-137-27-Build-Right-Cantilevered-decks.pdf