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.
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
|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.
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.
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
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