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?
During construction, one of the critical factors that engineers keep in mind is drainage because of its impact on buildings' performance. The effects of poorly installed drainage systems are very unpleasant, and repairs can run into tens and even hundreds of thousands of dollars. Not to mention the potential health risks of such failure — think mold growth and invasive plant roots.The consequences of poorly constructed drainage (negative drainage) range from damage to asphalt and concrete surfaces, damage to structural elements and foundation, accelerated deterioration of building materials, discoloration of walls, floors, and ceilings, and overflowing gutters and infestations.
Others include erosion, mold growth, wood rot, creating uneven surfaces, and turning your landscape into an ugly sight and eyesore. Having touched on the effects of negative drainage and why it should be avoided by every means possible, we can proceed to shed more light on positive drainage.
What Is Positive Drainage?
As you can imagine, positive drainage means making provision for water to get drained from surfaces within the shortest possible time. In roof construction, positive drainage are design considerations to curb loading deflection of the deck and provide adequate roof slope to ensure rainwater drainage within 73 hours under drying conditions.
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 can help with these challenges by ensuring water doesn't stand on your roof longer than it should after rainfall. Working with a professional roofing contractor will help you prevent further damage to your roof and prolong the lifespan of the roofing structure.