Installation Guideline Tips For Modified Roofing Part III: Roof Recovery and Modified Technology
In Part I of this series, we covered an overview of the history of modified roofing membranes in the global market. In Part II, we focused on torch-applied roofing, also referred to as torch down in the industry. In Part III, we will discuss the considerations, evaluations, and procedures for a roof over an existing system left in place. We will also cover cap sheet reflectivity, ECO-friendly options, and a look into the future of laminates in modified roofing installations.
Below are some guidelines and tips from manufacturers, contractors, and my observations over the years to assure a successful and long performing installation.
Recovery is the application of a new roof over an existing roof. If a roof installation is a recovery, the existing roof assembly must be a suitable substrate for the application of a new roof system. Most codes limit recovers to one new roof. A structural engineer should only evaluate the combined live and dead loads before any application over an existing roof. Loading requirements may have changed since the original roof application increasing the live load requirements due to historical snow loading data in cold weather climates.
The existing roof should also be evaluated for moisture and adhesion to the underlying substrate. Proper adhesion can be assessed with either a bonded pull test or vacuum test as detailed in the FM Global Loss Prevention Data Sheet 1-52 or the vacuum test described in the ASTM E 9071 section. Moisture analysis can be performed with either a nuclear or infrared scan. You can also use a capacitance meter to verify moisture content in existing insulation. On-site core-cut verification is always recommended. All wet roofing materials must be removed before any recovery project commencing.
Should the existing roof be used as a bonding substrate, the surface must be prepared appropriately for the application of the new roof or insulating layer. Loose and large gravel shall be removed; blisters and splits shall be repaired, and existing flashings should be removed so that a clean bonding surface is created for the new roof system components. Where the new roof is to be mechanically attached to the underlying substrate, withdrawal resistance testing should be carried out to confirm the attachment values for each fastening point. Testing should be carried out in compliance with ANSI/SPRI FX-1-2006 or TAS 105. Copies of the test protocols are available from your manufacture as well. Fastener values should meet or exceed 325 lbf (440.64 nm) or as manufacture or code may require. Your manufacture will provide a fastening pattern needed based on code and testing requirements.
Areas of ponding shall be corrected before the installation of a recovery roof system. Fillers designed to fill low spots can be used to correct these conditions. Contact your Manufactures Technical Services Department for a list of approved products.
The following good roof practices, along with the manufacturer’s specific requirements, shall be used when installing a recovery system.
- Deck shall be dry, structurally sound and suitable for the application of the new roof assembly.
- Parapet walls, perimeter edges, equipment, and load-bearing supports, platforms, curbs, etc., shall be visually inspected to be structurally sound and suitable for the application of the flashings and terminations.
- Visual observations for wall cracks, membrane splits and other such condition are indicators of improper design expansion n original design and should be noted to building owner and designer if one is involved in the project
- The existing roof system shall be compatible with the new roof system, and the membrane shall also be dry and clean with all surface defects corrected.
- Remove all clamping rings from drains and clean to bare metal and refinished. Damaged drain components shall be discarded and replaced with new ones.
- All abandoned and non-functioning equipment shall be verified with the owner and removed. Make sure any opening is properly deck per code requirements.
- Any metal flashing trims that are not in reusable condition or up to the current local code, it will be replaced with new metal details.
- Flashing heights should be a minimum of 8″ from the surface of the roof membrane. If there are special conditions that prevent this, you should consult your manufacture for an acceptable solution.
- Base and wall flashing shall be removed to create a sound surface for the installation of new flashings.
- All roof penetrations require all new flashings in compliance with current Manufactures’ detailed specifications.
- HVAC condensate drainage, should not be allowed to drain onto the new roof. Install condensation lines piping fabricated from ultraviolet light-resistant materials. Lines should terminate at drains or scuppers.
- Masonry surfaces above flashings shall be tuck-pointed and sealed and sealed to adequately protected from the weather.
Following these guidelines for SBS membrane recovery roof systems and referring to the manufacturer’s specification manuals, as well as always incorporating internal quality control measures in your installations, will give you a quality and long-lasting roof every time.
Since the implementation of California’s Title 24 legislation in October 2005, there has been significant growth in white or “cool” roof initiatives across North America and Europe The EU Cool Roofs Council (EU-CRC) was founded on February 2009. Other Countries have also embraced Cool Standards such as this stipulate levels of SRI or surface reflectance and thermal emittance for roofing material, pushing more people to adopt reflective roofing.
SBS-modified membranes offer many options to achieve high-reflectivity, including granule and film options. Coatings used in conjunction with modified membranes can also accomplish the desired reflectivity levels of your project. That being said, there are some factors to consider if pursuing a cool roof construction. Such as how much reflectance the surface will lose over time, what it will take to clean the membrane, potential consequences of that cleaning, condensation issues, or ramifications of deflecting so much radiation.
Some attractive possible alternatives to current reflectivity technology are being worked on by researchers at the Lawrence Berkeley National Laboratory. They are working on blue and red roof technology. They have determined that a pigment used by the ancient Egyptians known as “Egyptian blue” absorbs visible light, and emits light in the near-infrared range. It may be useful in roofing materials to keep roofs cool. They have also developed fluorescent ruby red coatings that have reflective properties similar to white roofs.
When your project does not allow open flames, kettles, VOCs, or strong odors where roofing needs to be applied, the use of zero-VOC adhesives and cement are a viable option with modified membranes. Solvent-free adhesives’ do not impact the environment like solvent-based products and need not be a concern with “greener” technology requirements.
Safety is always a principal concern in roofing. When your project does allow the use of a roofing torch or hot asphalt kettles or some circumstances that require a near odorless application, self-adhered membranes are the answer. Since the initial introduction marketplace, self-adhered membrane systems have come a long way with options that do not require a primer. Current film-surfaced sheets drastically increase adhesion and improved release films for both the backside and lap, are building a case for strong future growth for self-adhered membranes.
In the spirit of “going green,” there are now modified membranes that utilize entirely different chemistry—primarily thermoplastic polyurethane (TPU). TPU technology has been in the marketplace now for several years, and there a few companies that produce these materials.
These bio-based thermoplastic polyurethane elastomers, as a bitumen substitute, can reduce fossil fuel usage by up to 75 percent. They are also much lighter than traditional SBS-modified membranes, and they are inherently UV-resistant. There would not be a need to add granules or film to protect the membrane from UV rays. The performance test results on these membrane products are very favorable to outperform traditional membrane technology. Time will tell us how the marketplace and contractors accept this new advancement.
Laminated products in roofing are not a new technology; the use of implementing expanded use for labor savings is. Laminates account for one of the most significant advancements in SBS-modified roofing systems. Manufacturers offer products that utilize factory lamination of SBS-modified base sheets to various cover boards. This takes the process of applying the base layer out of the contractor’s hands and moves it into a controlled environment, ensuring a fully-bonded base ply to the substrate. They are also working on complete laminated systems that installed in a panel like puzzled interlocking configuration. We at CCG have not completed any production studies yet on these laminated systems. Still, the potential is there for up to 35% labor savings with a high-quality application in the field.
The modern roofing industry has evolved considerably since the birth of Coal Tar BUR systems in the 1840s. Modified bitumen products have a long history of proven performance and quality. Especially given new developments in modified material technology, we should expect to see modified roof systems in the marketplace for a long time.
John Kenney has over 45 years’ experience in the roofing industry. John started his career by working as a roofing apprentice at a family business in the Northeast to operating multiple Top 100 Roofing Contractors. As Chief Operating Officer, John is intimately familiar with all aspects of roofing production, estimating, and operations. During his tenure in the industry, John ran business units associated with delivering great workmanship and unparalleled customer service while ensuring strong net profits for his company prior to joining Cotney Consulting Group. If you would like any further information on this or another subject, you can contact John at firstname.lastname@example.org.