When engineers and architects go about designing a home or commercial property, they take into account the fact that we experience potentially heavy amounts of snow during the winters. If a roof isn’t made to withstand certain snow load tolerances, the building can be deemed unsafe.
As with any structure, every building has its load limits. When it comes to roof loads, it can help knowing just how much weight your roof can shoulder before exhibiting signs of failure. A sagging, shifting, or settling roof is very expensive to fix, and property owners are wise to add reinforcements to weaker roofs at the earliest possible opportunity.
So, how much weight can a roof hold? The roofing experts at A-to-Z Roofing & Exteriors are here to help by definitively answering this question in this article.
Live Loads vs Dead Loads
When calculating the weight tolerance of any given roof, there are two different load types that are used.
Live loads are loads that vary over time. Examples of live loads are accumulated snow and ice, debris, and the weight of people who might be walking on the roof.
Dead loads are loads that are static and don’t change. Examples of dead loads are the weight of timber, rafters, and roofing material.
For normal, shingled or wooden roofs, a good estimate for dead load is about 15 pounds per square foot. This is the weight that comes from structural material itself. Stronger roof types including clay tile and metal roofs can have dead loads in excess of 25 pounds per square inch.
In order to arrive at a satisfactory answer to the question, “How much weight can a roof hold?”, we must add the dead load of the roof to any anticipated live load.
Regardless of how they’re constructed, most modern roofs can hold up to about ten feet of accumulated snow. And, because snow weighs about 20 pounds per cubic foot, it can be safely assumed that a structurally sound roof can withstand ~200 pounds of live load per square foot.
When we add the live load to the dead load using the above example, we get 215 pounds per square foot for a shingled or wooden roof and 225+ pounds per square foot for a metal or clay tile roof.
How to Tell If a Roof Is Losing Support
Now that we have some rough estimates for how much weight a roof can hold, let’s have a look at some of the signs that a roof is beginning to ‘give’ due to excess weight.
Here are some common symptoms of failing roofs:
- Sagging. It’s very rare for an entire roof to suddenly give out all of a sudden. What happens more often than not is the roof starts to sag in areas of the highest stress. Sagging roofs can take months or even years to become obvious, but when they do, it’s time to take action to fix them.
- Cracked ceilings, brickwork, or raftering. Another telltale sign that a roof is failing involves cracks that begin to form along load-bearing walls.
- Leaks. Sometimes, a roof that is under too much weight will start to leak. What might look like just a few faulty shingles could actually be a structurally unsound roof that is beginning to fail under excess weight.
- Strange noises coming from the roof. When walking on a roof, the only sound you should be hearing are your own footsteps. If there is creaking, moaning, or squeaking, it could be a sign that the integrity of the roof has been compromised.
- Uneven surfaces in the attic or crawl space. Where roofs might be weakening, it’s possible they’ll reveal themselves in localized areas where surfaces start to warp or divot.
If you notice any of these issues, it is highly advised that you contact a roofer immediately. If an unsafe roof is left to get worse, there is the possibility of structural failure which could result in serious injury or death.
No Matter the Scope, We’re the Roofers to Know!
Many older buildings have roofs that need to be 100% replaced in order to restore safety and functionality to the overall building.