RETROFIT BUSINESS
Roo RTheetrofi tfi ng Game: A Fit-for-Usepplications
Acoustic and wood decking require a thorough inspection to determine the amount of deterioration from moisture infi ltration. You will fi nd these roof systems in warehousing, schools, commercial/retail and industrial facilities. Depending on the type of new roof geometry (hips, valleys, gable, etc.), a typi- cal zee-shaped purlin and cee-shaped post system is the best choice for the retrofi t framing.
timber and glulam systems. They are common in school gymnasiums and other facilities that require clear-span framing without intermediate supporting columns.
• Concrete roofs typically are retrofi tted similarly to bar joist systems. Concrete roofs can include structural, poured-in-place concrete decks; factory-
Images courtesy of McElroy Metal
This retrofi t system is best known as “Post & Purlin.” Base member type will depend on the geometry and the orientation of the joist spans relative to the new roof slope direction.
By Mark James
• A roof system of dimensional lumber with wood decking can be challenging because of its inability to receive concentrated positive loads from the retrofi t system, plus its exposure to moisture deteriora- tion. You will fi nd these in offi ces, lodging and light commercial buildings. The retrofi t framing for these will include components similar to the steel-framed roof, except the base member will be continuous and vertical members should be spaced no more than two-times the spacing of the existing joists.
formed concrete planking over steel or concrete beams; pre-cast concrete tee construction or even intermittent tees with acoustic decking. Concrete systems are found in schools, warehousing, lodg- ing and high-rise buildings. The retrofi t system for structural concrete decking often will be limited by the amount of point load it can impose on the concrete deck. It is always best to locate your verti- cal supporting members directly above the existing beams instead of on the deck itself.
• The best way to enter the retrofi t roofi ng market is to start with pre-engineered metal buildings. These roof replacements usually do not include removal of the existing metal roof and they utilize the simplest type of retrofi t sub-purlin members similar to those manufactured by Roof Hugger, Lutz, Fla.
This month, we will discuss the different types of conventional roof construction and how each of these infl uence the type of retrofi t framing system that best suits the project. Believe it or not, conventional roof construc-
tion hasn’t changed much over several decades. It utilizes a structural grid of primary supporting members such as girders and a secondary joist. There are exceptions to this, but the basics stand true for the majority of buildings. Existing roof construction typically includes
wood, steel or concrete framing. The following are the most common systems that have been retrofi t- ted over the years:
• The most common roof system to retrofi t is open- web steel bar joists with a decking material that will range from: rigid insulation over ribbed metal, lightweight concrete over metal deck, acoustic decking such as Tectum, and even wood on much older buildings. Most of these will support the posi- tive loads imposed by the new retrofi t system, but they should still be analyzed by a qualifi ed engineer.
10 METAL CONSTRUCTION NEWS September 2012
For example, if the joists are spaced at 16 inches, then the vertical retrofi t member would be spaced at 32 inches maximum.
• Heavy timber and glulams will usually require a special framing system due to the distance between the beams. These beams commonly are spaced from 10 to 15 feet on center. Also, such a roof’s structural wood decking is not intended to receive concentrated loads. Therefore, the retrofi t framing must distribute its roof loads back to the existing beams. The new framing will consist of vertical framing directly above the existing beams with deeper zee-shaped purlins because of the inherent spans.
• Steel or wood trusses found in fl at and barrel- shaped roofs are framed very similarly to heavy
If you are considering retrofi t as an alternative to
your current construction skills, you will surely be exposed to very different roof framing systems. Some will challenge the design of a conventional retrofi t framing system, and a few will not be suited for retrofi t. The retrofi t roof game is always fi lled with surprises because in renovation and remodeling you never know what is behind that wall. Unfortunately, it is never that long-lost box of money the original building owner left behind. Next month, we will discuss the retrofi t sys-
tems themselves and what programs are available to help you.
Mark James has more than 40 years experience in the retrofi t and metal construction markets, work- ing for leading manufacturers and executing great projects. Currently, he is president of RetroSpec LLC, a consulting company offering direction and deep knowledge of the retrofi t business for manu- facturers and contractors. James can be reached at
mark@retrospecllc.com.
www.metalconstructionnews.com
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60