Whether you’re a contractor or building owner, there’s one aspect of finding the right rooftop support that’s often overlooked — load distribution. Sure, modern roofs are designed to support an incredible amount of weight. However, this doesn’t mean much if the rooftop support system doesn’t distribute the weight across the rooftop evenly. The measurement of this effect is called PSI, or pounds per square inch. It indicates the weight applied to a square inch of space on a rooftop membrane. A high PSI would mean a greater number of pounds pressing down on a single point, and a low PSI would mean less pressure on a given point — and a lower likelihood of damage to the roof.
Why does PSI matter?
Imagine holding a tower of textbooks with two open palms. Now, imagine doing the same thing, but using the tip of one finger. Not only would that require some delicate balancing skills, but it would strain and possibly injure your hand. A similar thing happens with rooftop support structures. When an object on top of a support structure is too heavy in one area, this is called “point loading.” Point loading will crush the insulation and could even puncture the roof membrane and lead to serious and expensive roof damage. When combined with environmental factors like snow, it may even cause roof collapse.
What’s More Important: Max Weight or PSI?
Some rooftop engineers talk about max weight as if it’s the most important consideration in choosing a support structure, but it’s simply not true. A Civic Solar article gives a prime example, citing that a solar module and its racking system can weigh around 50 lbs. This would be fine if the solar panel and rack were sitting flat against the rooftop, but “the weight of the modules is actually distributed to a limited number of mounting points,” the article states. “Installers generally try to minimize this number…this strategy has a downside that it can create large point loads on the trusses that support the racking.” In short, the rack may be capable of supporting an impressive amount of weight — but if there are too few mounting points, the rack is essentially drilling down into the rooftop.
The Savings in the Science
As Ben Franklin once said, “an ounce of prevention is worth a pound of cure.” This is certainly the case when it comes to rooftop supports and PSI. Imagine this: you’ve chosen a rooftop support provider who advertises a greater max weight or competitive pricing, but makes no mention of PSI. You may have thought you purchased the right stand for the job. It may have even saved you a fair amount of money on installation, but six months later the supports have crushed the insulation and punctured the rooftop and now you’re being sued for the damage. It may seem extreme, but damage to rooftop areas is one of the most common sources of litigation. Similarly, if you’re the owner of the building and a disregard for PSI leads to rooftop damage, you may be facing up to tens of thousands of dollars to repair your roof — and that’s not counting leaks, lawsuits, and ensuing damage done to the building below. The bottom line: a support system with an appropriate PSI rating, paired with engineering built to withstand UV, extreme weather, and fluctuations in temperature, will provide a safer rooftop support than any other solution.
How to Find Rooftop Supports That Last
There are a few criteria you should consider in a rooftop support system if you want to avoid expensive and dangerous accidents. The ideal support system should provide:
● A base with a flat surface, or multiple mounting points. By spreading out PSI load across a flat
surface or multiple mounting points, the weight of rooftop objects is distributed evenly. This will help avoid weight being concentrated on smaller pressure points, which protects the roof from
● Support designed with a max of 2 PSI. This is the optimal load that should be allowed per square inch to avoid damage.
● More focus on PSI than max weight. Although max weight is important, the leading cause of damage is too much weight applied to the rooftop. If the PSI rating is too severe, the damage has already occurred to the roofing system (including the insulation).
● The ability to withstand other weight distribution challenges like extreme weather conditions. Uncontrollable weather conditions such as snow and ice can contribute to point loading and lead to roof collapse, and it’s even more damaging in areas where it can collect — like around pipes and air conditioning units. According to a 2015 AccuWeather article, “one inch of water weighs 5.2 pounds per square foot,” and wet snow can be four times heavier than powdery snow. That’s a lot of unplanned additional pressure bearing down on the rooftop and support structures.
● A significant warranty. If a company doesn’t offer a long-term warranty, that’s a red flag. It may indicate the product may be poorly engineered. For a comparison, MIRO rooftop supports offer a 20-year warranty — the longest in the industry. PSI is one consideration among many others when choosing a rooftop support product, but it’s an indispensable feature — one that could mean the difference between endless expenses, and a solid and safe rooftop for years to come.