The United States is now experiencing a new trend as vegetative roof coverings and waterproofing systems, otherwise known as green roofs, are increasingly being used by property owners. Environmental purists have complained about the term, but it is now widely used within the design and construction industry.
Benefits for the owner and benefits for the environment go much further than its aesthetic beauty. And that is precisely why the Environmental Protection Agency and the U.S. Department of Energy have decided to promote them as a way to lessen the impact caused by the urban heat island effect.
The U.S. Green Building Council are just one of many organizations that have taken up the challenge of maintaining optimal design standards and recognition points through the various LEED standards. In fact, these LEED standards are just some of the reasons why building owners are employing green roofs.
As they provide natural surroundings, health care professionals have particularly marketed these as the answer. The psychological advantages provided to patients just cannot be ignored. It is also part of the reason why Chicago have played a vital role in encouraging people to take them on, which had been compounded by a successful project in the year 2000.
Developers are being encouraged to use them when they submit projects for consideration, and they have taken it up as they are able to appeal to a wider audience, as well as enabling landlords to charge higher rent prices.
Roots in Europe
Green roof technology originally began in Europe. The U.S. construction industry has only recently taken on the idea of this technology, though, as new products and new designs have spread across the Atlantic Ocean. Waterproofing membranes and thermoplastic roofing are at the centre of this new technology.
PVC-based membranes have been in use throughout Europe for 35 years and North America for 25 years. These thermoplastic membranes have been partially supplanted by the new polyolefin thermoplastic membranes. Chemistry and experience are helping this prototype to take hold.
However, back to the PVC-based version and it is easy to see that the benefits are far-reaching. Here are just some of the advantages that they provide in the areas of installation and overall design:
•Flexibility for both flat and sloping roofs
•Proven track records
•Versatility for different types of green roofs
•Durability that will last for years to come
•Has passed tests as a suitable root barrier
•Forces water to disperse
•Allows detailing and heat welded seams
•Does not have to be installed in specific weather conditions
•Contractors have their productivity levels increased significantly
Adaptation is at the centre of the thermoplastic membrane systems. They are the most versatile green roof-type waterproofing that is currently on the market. In addition to this, they are available in a number of different versions, including containment grid, loose-laid, and adhered. Both extensive and intensive overburden on green roofs is accommodated.
Furthermore, they can be used on steel, wood, and concrete decks. Phasing has also played a crucial part in the appeal of this system as they can be installed over many years. Construction needs are met when using this type of product.
Conventional membrane systems are remarkably similar to the adhered and loose-laid types of waterproofing systems. An extruded polystyrene installation or a geotextile levelling layer can be utilised with a waterproofing membrane.
The adhered system involves the membrane being bonded to the substrate or another insulation layer, although the latter is definitely used less than the former. It is the loose-laid system, however, that has been shown to have the better economy, which is why extensive green roof installations tend to go for this option.
When it comes to vegetative coverings that are either semi-intensive or outright intensive, a containment grid system becomes the system of choice for installers. It utilises waterstops that can be found beneath the waterproofing membrane.
These integrated stops are used together with fully bonded grid strips that go under the concrete deck. This makes sure that the deck area has been compacted into various sliced up sections. Grid strips tend to be placed around the outside of the deck next to the base of the walls, as well as around any projections in the decking. High points of the drainage field slopes are also favoured locations. Either the insulation or geotextile has the membrane loose-laid over it before it is welded down to the grid strips.
It is not uncommon for leak detection devices to be installed inside each compartment of the overall grid. These leak detection devices will test the performance of the system over time. If there are any errors, then they can be repaired before any serious damage occurs. It reduces the risk of removal or replacement of the overburden.
New construction projects will benefit significantly from the grid system, particularly in the case of the winter months that make concrete deck curing an issue. Renovation projects can also benefit from the grid system as it is known to have a dramatic impact on the costs of preparing the deck. Removing the existing system can often mean that only the grid strip areas need to be targeted. For 25 years, this type of grid containment system has had massive success by reducing liability for all involved with its excellent protection.
Concepts of Thermoplastic Membranes
TPO and PVC thermoplastic membranes can be permanently fused without any caulking, adhesives, or primers to depend on. Alternatively, they can just be hot-air welded.
Permanent seaming of the laps and the flashings that end up covering the overburden after the project has been completed can be obtained due to its welding ability. These thermoplastic membranes are known for quality and have been praised for their abilities to defend against both root growth and ponds of still water that often form.
Although, every green roof should not be automatically paired with thermoplastic membranes as there are other options. Long term success comes as a result of proper planning and preparation, especially when it comes to subgrade waterproofing items.
All membranes should have an ASTM D 570 value of 3.0%, at its maximum, to fulfil the need for a low water absorption level. Membranes should also be engineered towards resisting the growth of algae, fungi, and any other damaging organisms. Dimensional stability is also something that has to be taken into account.
The linear dimensional change should be kept low at ASTM D 1204 2%. Also, it should be able to stand up to any cracks in the concrete or minor structural changes. Obviously, thicker membranes are a key benefit in this situation so 80 mil or 96 mil products should be used. A number of studies have demonstrated that they have a superior resistance to any abuse during construction.
Where Is The Insulation Under The Waterproofing?
A lot of different manufacturers have products available that can be placed directly onto concrete decking, along with extruded insulation positioned on top of the waterproofing itself. It is not something that can apply to all applications, however.
When it comes to semi-intensive, extensive, and certain other intensive systems pond designs are integrated into the design; which could be as a water feature or for the purposes of irrigation. These designs can sustain floating features and displaced items during particularly heavy rainfall. Extruded polystyrene is placed above the membrane itself to prevent displacement, though.
When it comes to zones with high wind, phased construction, and applications on steep slopes the insulation must be secured mechanically so it meets the requirements demanded by the manufacturers. Tapered insulation may also need to be implemented to influence certain water flows. Overall, these thermoplastic systems have a lot of flexibility and are able to adapt to a wide variety of situations; this is the reason they are so popular.
Root Barrier FLL Resistance Studying
20 million square feet of green roof are constructed each year, and that is just in Germany. Both the German and Swiss governments place heavy regulation on waterproofing products that are involved in the construction of green roofs. In fact, it is the Swiss Society of Engineers and Architects SIA 280 Standard that sets the standards and inspects each product based on its application to a certain field.
Four fields exist for waterproofing products:
3.Water vapour barriers
15 different testing methods are used to inspect each product. Water absorption, root resistance, and dimensional stability are just some of the things that are tested by the SIA 280.
When it comes to Germany, each green roofing membrane product is tested by the FLL, which in German is the Forschungsgesellschaft Landschaftsentwicklung Landschaftsbau of Essen. Root penetration and resistance are the main things that they test. It is considered to be one of the most stringent tests in the world, which is why it is so well-respected. The only way to pass is to make sure that the product can permanently protect against penetration by roots in any area.
Tests last a total of four hours using containers that measure 31 inches by 31 inches by 14 inches. Eight different containers of these sizes are used and are made of aluminium sheets. A glass bottom allows for the examiners to observe. Four containers are used as the control, and four for the material itself. Geotextile fabrics are used to cover wet clay that is layered over two inches on the bottom.
Pre-manufactured bitumen boards are used in the asphalt material that lines the control containers. These boards are incredibly robust at 31 x 31 x 0.5 inches. Any gaps are sealed with asphalt. The material’s containers utilise two different flat seams with a T joint running across the rest of the container.
The stipulations state that no membrane can have any herbicides or other slow growth products applied in order to keep the test fair. Furthermore, no treatments to the seams can be done at any point before, after, or during the testing process.
Soil mix and plants will then be installed. Soil mix consists of 70% light decomposed peat from North Germany. The other 30% is made up of volume billow clay. Scientists will spread the soil across a carefully measured area of 25cm on the waterproofing. Common fertilisers are used with the soil; however, the pH must maintain a standard 5.5-6.5 range or the test is invalidated.
Plants used for the standard tests include:
•Two two-year-old gray alders (alnus incana) that are between 60 and 100cm
•Two two-year-old trembling poplars (populous tremula) that are between 50 and 80cm
•Eight prickly field thistly seeds (cirsium arvense)
These plants are planted within each container and are fertilized and watered each spring. Any dead plants are replaced. Careful development is required, which is why these plants are regularly tested for diameter and height over four years. Root pressures must also be kept at a sustained level for both the control and the test material.
Twice every year the containers are inspected visually in October and June. When the test ends the waterproofing is checked. If there is any penetration within the roots, then they are catalogued and measured. However, the fact is that if there are any penetrations then it is automatically considered to be unsuitable for use.
When this test was carried out using the PVC membrane there were no root penetrations in any container. The test containers that held the asphalt had an average of one hundred different penetrations. A certificate of compliance is issued for the specific membrane to the manufacturer if the material passes. The FLL certification must be submitted by any contractors who are working on any project plans for an architect or a designer.
Despite the Benefits, Green Roof Growth has Been Limited. Why?
In the beginning, there was considered to be a lack of everything. From a range of products to people who had the skills to install them, there was very little choice. Nevertheless, all of that has been expanded in the past few years. RCI has been providing technical courses all across the U.S.
Increased technical expertise has been obtained as a result of the LEED standard. The only real issue is the CSI format as green roofs have yet to be changed from Division 2 of the green roof landscaping section to Division 7, which presents a variety of problems when it comes to planning, bidding, and other responsibilities relating to construction.
Other reasons include:
•No recognition as a method to reduce the current mandated stormwater infrastructure investment. Primarily, the success has come in Europe due to the tax reductions offered by governments. The pressure on the urban cities in the U.S. to construct larger treatment plants could have a positive effect on this issue.
•No well-respected testing methods in the U.S. that match the SIA 280 or the FLL-conducted root resistance test. It should be mentioned that ASTM E 06.71 is working towards constructing that.
•Vegetative covers are being installed over roof systems that already exist. Be careful of this as it could void a specific manufacturer’s warranty.
•Prices have been very high for installation, which has limited the amount of interested parties. At the moment, for each square foot it costs anywhere from $20 to $40, which is bumping up the price. There does look like there will be some changes as the installation techniques and cost reduction techniques are implemented, though. In many cases, a reduction to $12 per square foot has been achieved.
Summing Everything Up
A lot of momentum and interest has been garnered for the green roof system. What RCI needs to do is to focus on the roof in order to remain at the forefront of the industry. People need to understand that not every product can work together with the applications of green roof systems.
All waterproofing and roofing products have to be flexible, especially when it comes to preventing root growth and water gathering together on the roof. What RCI and its associates need to do is to learn from what the Europeans have done, whilst avoiding any possible problems. As of now, the only way to move forward is through strong leadership, and RCI should be attempting to do that.
Peter D’Antonio, for 23 years, has worked with Sarnafil Roofing and Waterproofing Systems. As of this writing, he is situated as manager of the Waterproofing Division in the U.S., along with acting as the national sales manager for various educational facilities. Alongside these activities, he has been on the boards of the Boston Chapter of the Construction Specifiers Institute and the Sealant, Waterproofing, and Restoration Institute. Furthermore, D’Antonio is a member of the ASTM Sustainability E.06.71 Green Roofing Committee. On top of this, he is the coordinator for Sarnafil as part of the U.S. Green Building Council and U.S. DOE Rebuild America/Energy $mart Schools Initiative. His education involves a BA awarded by the University of Massachusetts, which he has used to lecture and publish his work on a grand scale. Currently, he and his family live in the rural areas of New Hampshire.