- Understand that there is a difference between wind speeds and wind pressure on the roofing system.
- Taking a look at the differences and suggest ways in which specifications can be written to meet the local code requirement.
- What is the minimum wind speed coverage, required by the building code, for a commercial building?
- What building components are required to be covered with a warranty as mandated by the building code?
- What is the minimum tested and listed uplift rating?
5 BASIC FACTORS TO DETERMINE UPLIFT PRESSURES
The higher the building the greater the wind velocity.
This will affect the wind load on a building. More obstructions around the building will reduce the wind load, conversely the more open the area is the higher the wind load.
The more building openings, the greater the chance of internal pressure increasing during a wind event. It is important to know if a building is enclosed, partially enclosed or open.
This factor is based on how important the building is primarily for public safety. For example a hospital or emergency shelter is considered more important than a warehouse.
ASCE 7 includes wind maps so that the local basic wind can be determined.
The maps are based on a 3 second peak gust measured at 10 m above grade in
an exposure category “C”.
- Roof warranties, including wind speed coverage, started as a marketing approach to differentiate single plies from asphalt roofing.
- Wind speeds were and in some cases still are noted by description such as “windstorms”, “gale force” and such.
- Most roofing suppliers now offer a numerical wind coverage such as 50, 55 or 60 MPH, and will consider higher wind speed coverage with advance notice.
- Typically, when asked to provide a higher than normal wind speed coverage, the roofing supplier will require additional securement or enhancements to the system.
Upon determining the uplift requirements for the project, the designer should review roof assembly listings to confirm the assembly meets or exceeds the required uplift requirements through accepted testing.
Roof assembles may be tested in accordance with the following methods by an accredited lab.
- FM ANSI/FM 4474
- UL 580, 1895
QUESTIONS AND ANSWERS
For ASCE 10: Do the calculation by multiplying .6 then bring it to the allowable then it is building code. Now if using FM: you have to follow FM criteria. If FM using 0-5, they are following the allowable but they do add other safety factors on throughout calculation. One of them being automatic Sika factor of 2. If it is FM, calculate for FM and install for that. With the 7-10 version, because it is ultimate always bring it back to allowable.
This is the current issue with a vegetated roof. Vegetated roofs are strictly ballasted assemblies. The way to get around this is that we will actually install a roof system that has been tested and approved to pressure. We can install that however the vegetated part, the overburden, you can’t really test that but as long as the roof coverage itself is tested that is probably the safest approach to do. We have a document that talks about ballasting systems so you can follow the guidelines.
From the wind perspective, it’s almost exactly word for word. 2012 and 2015 are following the 7-10 version however anything earlier than 2012 version is using 0-5.
We test Rhinobond per difference densities or grid patterns. It is the same thing if we were doing an inseam fastening pattern or an adhered fastening pattern. When we build Rhinobond system, we have a 2x2 or 2x3 grid, we test that at a lab and that becomes an accepted system and we can codify that.
Basically, it's going to be an additional perimeter zone. It will be called a prime zone, more specifically a three prime zone. If you’re buying ASCE 17, please contact me for further details.
If you look at the system and pull out an insulation, there is a test program depending on the manufacturer’s design of the system. In the program, you will see that a lot of them will be from 1 to .06 inches but the most of the listings in this industry has insulation layers up to 12 and a half inches. So if it is a mechanically fastened system, we can count system fasteners and hope that they are setting fast, straight, and true. If adhering system, then it’s a workmanship issue and that is something we as manufactures should try to keep an eye on. Make sure everything is done right, work with contractor and train them but this is where those safety factors come in. You as the designer might think about increasing the safety factors if an assembly has layers of insulation to overcome the possible workmanship issues. But generally speaking if the problem that tends to be an installation issue more so than product, they always keep the safety factor at least 2.
ABOUT THE PRESENTER
VICE PRESIDENT, Technical Services
Mr. Schwetz is one of the most respected individuals in the roofing industry. He is currently involved with a handful of committees, and in 2015 he received the American Society for Testing and Materials (ASTM) International Award of Merit for his work with the E60 Committee.
Sika Roofing, a Division of Sika Corporation, is a Registered Provider with The American Institute of Architects Continuing Education Systems (AIA/CES). Credit(s) cannot be earned for the above webinar as the live event has concluded. However, we are happy to schedule a Lunch and Learn for your team!