Whether you are building or doing a makeover for a residential or commercial building, top on the list of factors you should consider in your design is the functional requirements of the structure. It should provide adequate protection from the elements — wind, sunlight, snow, and rain, among others. Having mentioned rain, we can kickstart our discussion on positive drainage and why it is causing so much buzz among contractors, plumbers, roofers, and other construction industry stakeholders.
Yes, engineers, architects, and contractors have been designing and constructing flat roofs for ages. However, not many contractors and roofers are familiar with the concept of positive drainage and how it impacts the sustainability and longevity of structures and the well-being of inhabitants.
To set the foundation for our discussion, it would help if we took a second to understand the difference between positive drainage and negative drainage systems.
What Are the Dangers of Negative Drainage?
Effective drainage is a critical consideration during construction, as it significantly impacts the performance of buildings. The consequences of inadequately installed drainage systems are far from desirable and can result in exorbitant repair costs. Furthermore, the potential health hazards associated with such failures, such as mold growth and invasive plant roots, cannot be overlooked.
The detrimental effects of poorly constructed drainage, commonly known as negative drainage, manifest in various ways. These include damage to asphalt and concrete surfaces, compromised structural elements and foundations, accelerated deterioration of building materials, unsightly discoloration of walls, floors, and ceilings, as well as overflowing gutters and infestations.
Moreover, negative drainage contributes to erosion, fosters the growth of mold, promotes wood rot, creates uneven surfaces, and transforms once-pleasant landscapes into unsightly eyesores. Having highlighted the adverse consequences of negative drainage and the importance of avoiding it at all costs, let us delve deeper into the concept of positive drainage, shedding light on its significance and benefits.
What Is Positive Drainage?
Positive drainage is a crucial aspect of water management, ensuring efficient water runoff from surfaces in a timely manner. In the context of roof construction, positive drainage encompasses specific design considerations aimed at preventing excessive deflection of the roof deck and providing an adequate slope to facilitate rainwater drainage within 72 hours, even under drying conditions.
By implementing proper positive drainage measures, such as optimizing roof slope and incorporating appropriate drainage systems, the risk of water accumulation, structural damage, and related issues can be effectively mitigated.
Achieving positive drainage is vital in every flat roof design. While this may seem like a piece of cake, it requires the expertise of contractors, architects, and engineers who know their stuff to handle — and, of course, roofers and plumbers to execute the design. Traditional flat roof designs feature roof drains located at the lowest points of flat roofs. They leverage gravity to push the water to the roof drain, from where it will be transported to a designated disposable point via the roof drain piping system.
With the "positive drainage" trend gaining popularity and throttling at full steam, innovative technologies designed to get water off roof decks faster are taking center stage and yielding positive results.
How To Achieve Positive Drainage in Buildings?
Aside from the age-long time consuming, laborious, costly, and less effective practice of using wood sump boxes to drain flat roofs, new technologies like sump receivers and tapered roofing systems have proven to be effective roof drainage systems that are capable of achieving positive drainage on new construction projects and revamping old projects.
Positive drainage transcends designing roof slopes to ensure fast water drying after rainfall and preventing loading deflection caused by pooling on roofs. It extends to getting water far away from building foundations and walls. The last thing every homeowner and contractor wants is to have water sitting on surfaces (puddles) around their property. When pooling occurs around foundation walls, excessive moisture causes repeated upheaval and settling in the soil, weakening the foundation.
To prevent or mitigate such nerve-wrenching and spine-tingling experience, it is always best to work with professional excavation contractors experienced with land grading. Effective land grading allows smooth water runoff — Thereby directing water to lower elevations and far away from structures.
Is Positive Drainage the Best Solution to Flat Roof Ponding?
The speed of constructing flat roofs, with their pocket-friendly installation cost and less risk to roofers, makes them an economical roofing system. However, flat roofs are synonymous with ponding issues, which is reflected in frequent repairs and high maintenance costs.
Even though flat roofs are applauded for their excellence and performance (primarily) in commercial buildings, it is almost impossible to lose sight of how they are prone to water ponding because of the absence of pitch—hindering water runoff. When water remains on your roof 48 hours after rainfall, it is usually a sign that you have a ponding problem on your hands, and it won't take long before it compromises the roof's structural integrity.
Even flat roofs with some level of drainage also experience ponding at some point during hail, windstorms, and snow — causing water to sit on rooftops for a more extended period. When this happens, moisture begins to seep through roof coating and membranes (rooftop aggregates, asphalt, and polymeric materials) and eventually causes severe damage to roof felt.
Positive drainage is a vital solution to combat the challenges posed by water accumulation on roofs following rainfall. By promptly draining water away from the roof surface, it helps prevent potential damage and prolongs the lifespan of the roofing structure. Collaborating with a knowledgeable and experienced roofing contractor is essential to ensure the implementation of effective positive drainage measures tailored to your specific needs. With their expertise, you can safeguard your roof against unnecessary risks, maintain its integrity, and optimize its longevity in today's dynamic roofing landscape.