When working with construction materials and systems, there are a number of things you need to be aware of. These pertain not only to rooftop safety, but also to the materials themselves.
Accessing the Roof
Even before we think about our rooftop objectives, we have to get up there. The best, most secure access is through a roof scuttle (hatch). This may be located in a custodian’s closet or some other obscure location, so a sign ought to be posted that this is the roof access point.
Outside ladders, permanently fixed to the structural wall, are also relatively safe. On grounds that are not secure, a locking cage will discourage vandalism. The ladder should extend well above the roof height so that you can step directly onto the roof.
When there is no permanently mounted access to the roof, a movable ladder may be necessary. The ladder must be in good condition, have no broken rungs, and be tall enough to extend well above the roof edge. Raising the ladder means being aware of electrical hazards overhead. Once the ladder is placed, the slope should be such that if you stand at the base with hands extended, they just reach the side rails. Bring cord along to tie off the ladder, and leave the tie-off in place until the last person is leaving the roof.
Tools of the Trade
Many roof inspectors have found that a canvas carrying-bag saves time and effort. Tools and small repair materials can be placed in the bag, which is lifted to the roof by rope (not by carrying up the ladder with one hand). Depending upon your needs, the bag might contain work gloves, eye protection, a trowel, a sharp roofing knife, a spudding bar or straight-claw hammer to chip adhered gravel away, spray paint or chalk to mark defects, treated glass mesh (6- to 8-inch-wide woven fabric), a screwdriver or pail opener, and trash bags for debris.
Preassembled kits like this are available from several roofing materials distributors. Moisture meters, coring tools, and more advanced tools may be desired as well.
Several previous columns in this series discussed the importance of knowing what roof system is overhead, the status of warranties, and the nature of repair materials and tools.
For bituminous materials, the most useful and versatile repair material is a bucket of asphalt roof cement. From a safety and accountability viewpoint, you should be aware that many of today’s mastics still contain asbestos fibers. The bitumen-encapsulated asbestos fibers are not a hazard, and are no longer controlled by EPA or OSHA regulations. The asbestos-containing mastics are good-performing products for general patching, and have over 100 years of experience. However, if you feel that you want to avoid this issue, then specify and purchase asbestos-free products.
The solvents in asphaltic mastics are relatively mild petroleum products, with a flash point high enough so the pails do not require a red label. They are designated paint thinner or mineral spirits, but you should be aware that they have an odor, and might be detected within the building if repairs are being made right at an air intake for the HVAC system. Problems can be avoided if a notice is posted that roofing repairs are under way, and that some odor may be detected. An alternative is to either shut off the HVAC or to fabricate a temporary plywood chimney to draw fresh air while the mastic cures.
The asphalt mastics do not have a limited shelf life, and can be thinned by adding additional mineral spirits when needed. However, pails that have been opened should be resealed as with any solvent-based paint.
Aluminized roof coatings: For smooth-surfaced built-up and modified bituminous roofs, asphalt-aluminum roof coatings have served the dual purpose of lowering roof temperatures and screening harmful ultraviolet light that embrittles bituminous materials. You need to know that when a pail of coating has been opened, it should not be resealed and stored. Moisture entering the pail will react with the aluminum flakes and generate hydrogen gas that can bulge the pails and explode if the gas finds a spark. Even the new water-based aluminum roof coatings will generate hydrogen, so watch the shelf life on these and store in a spark-free environment.
Rubberized Mastics and Mastics for EPDM Roofing
These materials require stronger, more aromatic solvents than those for simple asphalt mastics. The products may be low-flash aromatic materials, so when you see that red label, you should carefully read the warnings on the pail and obtain a copy of the MSDS (readily available online). Storage needs to be smarter, away from boiler room heat, sparks, and the like. It is probably best to discard the remaining material once a pail has been opened, as the materials generally have a shelf life of less than one year anyway. Cautions about the work area need to be taken more seriously, too. Workers must not smoke anywhere near the fresh mastic, and sparks or static electricity can cause fires or an explosion. Some primers and splice washes for EPDM have contained isocyanate or other toxic ingredients, so proper chemical-resistant gloves are needed.
Use of Torches, Kettles, and Mops
Asphalt and modified bituminous roofing systems are generally applied and repaired with hot techniques. A conventional built-up roof will use a kettle and/or tanker to provide hot bitumen to the repair point. The tankers and kettles should be far enough away from the building so that if they catch fire, they do not burn down the building. Kettles now use LP gas for fuel, and these pressurized containers need to be properly stored in a vertical configuration, chained so that they cannot topple over. When hoisted to the roof, they should never be lifted by the regulator, but in an appropriate sling. As a building owner, you should establish the maximum quantity of LP that you will allow on the roof.
When LP gas is used for torching, the roofer must have a certified torch applicator doing the work. Verify this with your insurance agent, and perhaps with your local fire department as well. They will have advice for you, such as on the use of a fire watch at the end of the day, and how to properly shut down the torch system. (Shut off the fuel at the cylinder, and burn off the gas in the line.) By the way, you should do this with your home barbeque as well, as a pressurized line can leak overnight. If you are planning to allow your own crews to do hot repairs, plan on having at least one supervisor obtain the certification from the National Roofing Contractors or Midwest Roofing Contractors Associations.
We mentioned mops. Hot bitumen, in a mass like a roof mop, may result in spontaneous combustion. A prudent roofer knows to work the mop against the roof surface to remove as much leftover asphalt as possible.
We mentioned in a previous article (See November 2003 issue, Being Prepared) that heavy wet snow can cause roof collapse, and that the owner/manager needs to have an emergency plan. Looking at the tool and safety side: Metal shovels on a roof will cause considerable harm, even with the most careful worker. It is far better to have plastic shovels that are dedicated to the snow operations. The snow should only be removed down to the last inch or so, not to the roof surface. If snow blowers are to be used, don’t set them so low that they scrape up roof aggregate or ballast. Also, you may want to put warning flags on low roof vents, jacks, and gas lines, which may become buried under a snowdrift.
We also mentioned that you need to have some place to dump the snow. In a blizzard, vehicles are likely to park anywhere they can. You need to block access to areas where you plan to dump the snow.
Blocked Drains and Roof Collapse
One of the important goals of a periodic roof inspection is to verify that the roof drains are working and free of debris. In a heavy storm, low slope roofs will deflect if the drains are plugged. When ceiling tiles start falling in due to deck deflection, it is too late for maintenance. The area must be evacuated and the fire department called to pump off water before collapse occurs. If the storm has toppled trees and power lines, they may not get there in time. Knowing the structural system overhead might make it feasible for you to cordon off only the areas affected within a particular bay, i.e., a 40- by 40-foot section of the building.
Current plumbing codes require that every roof have two independent means of drainage. When the roof slopes toward an outside wall, the back-up means might be a roof scupper. For larger buildings with internal drains, a duplicate drain, set a couple of inches higher than the primary drain, takes the overflow water away and dumps it into the parking lot or retention pond. The code requires that the under-deck plumbing be independent, so that if the primary downspouts are blocked, the blockage does not affect the secondary system as well. If your building does not meet these requirements, insist that they be included in your reroofing plans.
Contact NRCA at www.nrca.net, MRCA at www.mrca.org