WATERPROOFING - Dr. Fixit Institute

1 Vol. 8 No. 1 (Jan Mar 2014)A Quarterly NewsletterWATERPROOFINGPART - 8 WATERPROOFING AND LOW ENERGY CONSUMPTION ROOFING SYSTEMSIt has been observed that in an average building envelope 23% of the heat is transferred through the roof, which is the highest percentage when compared to walls, windows, etc. It is often a challenge while contemplating a change from the traditional black roof system to an energy efficient one, or determining the savings when considering alternatives for a new building or the retrofitting of an existing building. While considering the energy efficiency of WATERPROOFING performances, the latest low energy consumption roofing system, popularly known as the LEC system, has gained momentum in various metros in India. Basically, the system consists of a mixture of multiple materials that are blended together. Though they bear different physical or chemical properties, when combined together they produce a system which is capable of delivering durable, energy-efficient, high-performance and sustainable roofing.

2 However, the following criteria need to be considered for calculating the energy efficient performance of vegetative roofs/roof gardens/green roof systems or energy efficient roofs: Climate and geographical location Building s intended use and design life expectancy Exterior and interior temperature, humidity and use conditions Type and condition of substrate Structural system Slope and drainage Roof WATERPROOFING membrane Type of vegetative roof system including overburden, if any Type and amount of insulation, protection and drainage needed Type of reflecting materialAs per the International Energy Conservation Code (IECC) 2012 and ASHRAE , Energy standard for buildings except low-rise residential buildings , the minimum thermal insulation requirement for roof assemblies may need significantly more insulation than previously required. Along with WATERPROOFING and thermal insulation, this latest LEC system can be applied to virtually any existing roof, so there is no tearing off the roof, rather it involves retrofitting it to green and satisfying the norms of the Green Building Council and Cool Roof Rating Council (CRRC).

3 Studies show that they lower roof temperatures by up to 40%, which decreases the amount of heat transferred into a building interior to dramatically reduce the cooling cost. So far a roof has been considered as nothing more than a blanket of protection for a building. This is true in most cases, but a commercial roof can also have a huge impact on the amount of energy that a building consumes. Usually commercial roofing systems are white which reflect the heat. In fact, a commercial roofing system can lower the temperature of a roof by as much as 30OC. The system reflects as much as 85% of the sun s solar energy away from the building. An often debated topic in the LEC system, whether the insulation will be kept over the WATERPROOFING membrane, or vice-versa. But it is desirable to keep the WATERPROOFING membrane over the insulation layer while retrofitting an old building with an LEC roofing system.

4 Both the systems have their own advantages and disadvantages. As such, no particular system is ideal and the system has to be tailor-made based on the client s requirement in a particular is very disheartening to find that most of our codes and specifications in the government sectors are still following 50 year old, traditional practices of tar felting for WATERPROOFING , which is brittle in nature and get damaged after just 2-3 years. Sometimes, layers of brickbat coba are laid on the existing surface, thus adding distress to already distressed structural members. With the technology-driven approach, following a 50 year old practice may cause huge loss to the state coffers. So adopting the latest LEC system would save a substantial amount and would also help the energy crisis being faced by the country today, to some collective approach of all the technocrats, builders, developers, architects, engineers and bureaucrats involves adopting this latest LEC system, which provides a guaranteed service life for 20-25 years, and energy efficient and sustainable roofing systems.

5 In fact, the dilemma of balancing between WATERPROOFING and thermal performance for roof assemblies has led to the need for further scientific research with the available materials and systems in the country, before finalizing the correct specification for the the issue is being dedicated to WATERPROOFING only, a combo system which deals with both WATERPROOFING and thermal insulation of the roof is most ideal in the present energy crisis era, for which we have given importance to the LEC system. We have covered various aspects of the system and tried to solve the dilemma of WATERPROOFING and thermal performances with their advantages and disadvantages through some selected articles in this issue. We will conclude our ongoing series of publications with the WATERPROOFING of an external facade in the next issue of theEditor s Desk2 Balancing between WATERPROOFING and Insulation of Vegetative Roof Systems[Excerpts from Professional Roofing of NRCA, November 2011,pp25-29, The dilemma of balancing WATERPROOFING and thermal performance for vegetative roof assemblies ] IntroductionGreen or vegetative roof systems perceived by many as durable, sustainable, energy-efficient and high-performing, comprise layered assemblies combining landscaping, thermal insulation, WATERPROOFING components and other elements to provide a functioning system.

6 But there are different approaches to vegetative roof system can be placed above a vegetative roof system s WATERPROOFING membrane to improve WATERPROOFING performance; this often is referred to as an inverted roof membrane assembly. With this construction, water flows through the insulation and compromises the insulation layer s thermal resistance at the membrane level. This often is recognized as an acceptable compromise to improve WATERPROOFING performance. However, the magnitude of the loss in thermal resistance is difficult to quantify and not Inverted Roof AssembliesDesign principles for building deck WATERPROOFING assemblies, including plaza systems, place the WATERPROOFING membrane on the roof deck with the protection and drainage layer(s), insulation and additional landscaping components above the WATERPROOFING membrane (see Fig.)

7 1). 3 The above layered system is referred to as an inverted roof membrane assembly because the insulation is located above the membrane whereas in conventional roof assemblies, the membrane typically is above the insulation. Building deck WATERPROOFING design principles apply to vegetative roof roof assemblies provide the following advantages: Fully adhered and loose-laid WATERPROOFING membranes can limit the horizontal migration of water, which assists in the investigation of leaks and subsequent repairs. Water that leaks through the membrane in a conventional roof system can travel variable distances over the roof deck and leak into the building s interior from the breach in the membrane. Conventional roof systems typically include polyisocyanurate insulation, which can deteriorate when exposed to moisture, further increasing the cost and extent of repairs to restore a failed roof system.

8 Insulation above the WATERPROOFING membrane reduces temperature cycling, which improves the membrane s long-term durability. Insulation above the WATERPROOFING membrane provides protection from construction activities, components above the membrane and live loads. The roof deck provides a rigid substrate to support the membrane; conventional roof systems have the membrane over the insulation or cover board, which is installed to improve the substrate s rigidity. Compression of insulation resulting from loads can deflect the insulation and cause the membrane to be unsupported. An unsupported membrane has decreased puncture resistance and is prone to seam failure. The WATERPROOFING membrane can act as an air barrier and vapour retarder for the roof assembly and is located on the warm side of the insulation, which generally is consistent with design practices to address moisture migration.

9 A conventional roof assembly that lacks an air barrier or dedicated vapour retarder is more likely to develop condensation at the membrane s underside because of air leakage and moisture migration from the building s interior. This moisture can cause roof system components to deteriorate; wetting of construction and finish materials that are susceptible to mold growth; and perceived leaks to the building s interior. These problems are exacerbated in high-humidity buildings (museums and natatoriums, for example).For inverted assemblies, insulation located above the WATERPROOFING membrane should have low moisture absorption and high compressive strength and resist freeze-thaw damage in climates where it s a concern. Extruded polystyrene (XPS) insulation is the most appropriate material for this application. XPS boards in buried applications show a loss of 5 to 10 percent in thermal resistance within three to five years that can be attributed to moisture 1 : A vegetative roof system with an inverted assembly (The position of the root barrier varies by Conventional Roof AssembliesAlthough generally in conflict with the preferred WATERPROOFING approach, insulation can be located below WATERPROOFING membranes in vegetative roof assemblies, particularly in retrofit and other applications where inverted assemblies may not be appropriate or desired.)

10 This approach is similar to the installation of a conventional roof assembly with the remaining WATERPROOFING and landscaping components placed above the membrane (see Fig. 2).Designers might choose this system because its base system is consistent with the design of a typical roof assembly and to avoid reductions in thermal performance that are anticipated when installing the membrane and a drainage layer beneath the insulation. Advantages of such systems for vegetative roof assemblies include: Improved thermal performance of insulation compared with that of an inverted roof membrane assembly. Drainage below insulation in an inverted assembly can contribute to a reduction in the insulation s thermal performance because of moisture absorption by the insulation and water and air flow below the insulation. The insulation separates the membrane from surface irregularities and roof deck movement.