Updated: Feb 14
Knowing how many pounds per square foot a roof can hold is vital information for homeowners and business owners alike. It helps you to understand:
• Whether you can walk on your roof
• How much snow your property can withstand
• Whether you need to upgrade to a more sturdy material
• Whether it's safe for local roofing contractors to perform maintenance or emergency repairs
So how do you calculate how much weight the average roof can hold, and what measures can you take to improve this if necessary? Our guide answers all your questions.
How Much Weight Can a Typical Roof Hold?
As a general rule, roofing should hold about 15-20 pounds per square foot as a "dead load." The International Building Code (IBC) has more information about the general requirements, but it's worth noting that local regulations in areas like Maryland have independent restrictions.
It's also important to understand the difference between the "dead load" and "live loads" when calculating how much weight it can hold.
This is the amount of weight placed on the roof supported by materials used in its construction, i.e., shingles, underlayment, guttering, and any adhesive materials used to secure these materials in place.
A normal shingled roof supports 15-20 pounds per square foot, which is more than adequate to cover the weight of the shingles and other construction materials.
This weight of 15-20 pounds per square foot is still a guideline - while local regulations tend to vary more for live loads, you should always check your county regulations on dead loads.
The live load is calculated in addition to the dead weight borne: this means that the ratings are separate. Most roofs have a live weight capacity of 20 pounds per square foot on top of the standard weight they're expected to bear.
For example, if your roof was rated to hold 20lbs of dead weight and 20 pounds per square foot as a live load, you wouldn't combine your weight with the weight of the shingles. You'd ensure that the roofing material was properly held by the structure and then calculate whether you would be applying more than 20lbs per sq. ft. when you took a step.
However, live loads don't just include people. This measurement includes water, snow, ice dams, and anything else that burdens the structure.
It's extremely important to account for these additional weights to get a general idea of how much extra weight it can bear.
How Many Pounds Per Square Foot Can a Roof Support in Maryland?
Regulations in Maryland vary from county to county. Typically, an average roof in Maryland abides by the same 20 pounds per square foot live/dead rule as most modern roofs, although some counties have a higher minimum requirement.
This also depends on the type of roofing materials used. Asphalt shingles tend to be a lightweight, affordable, and popular option for residential properties. However, different roofing materials like metal and clay tile offer a higher rating (around 27lbs for a metal roof). Wooden roofs offer a similar rating to traditional asphalt.
The rating also depends on:
1. Whether your property is commercial or residential, and
2. The roof's slope (where snow is concerned).
Heavy snow is common in Maryland, which is why many counties ensure structural safety by mandating a higher minimum weight for commercial and residential roofs than other parts of the country. But how is the concentrated weight of snow calculated, and does snow count as live or dead in roofing?
Flat Roof Snow Loads in Maryland
Minimum standards for a commercial flat roof are often higher than sloped options. When calculating how much can a flat roof hold, it's important to remember that even light snow can accumulate dramatically over time. This can lead to roof collapse and endanger lives.
When rating flat roofs, a structural engineer will account for the huge range of climate variables that can accumulate on a flat surface. This is why some Maryland counties rate these options as 30lbs minimum, whereas sloped models might be rated lower.
Sloped Roof Snow Loads in Maryland
Maryland counties have individual regulations for snow loads on sloped models. Generally speaking, it's a good idea to choose a sturdy material (such as choosing clay tile over asphalt shingles or slate shingles) to ensure that your property can withstand the combined weight of snow and anyone who might need to perform maintenance.
Learn more about How Long Does a Metal Roof Last?
Can a Roof Support a Person?
Before performing services, professional roofers always need to know how much weight a roof can hold. This is why they always wear appropriate safety gear - a safety harness system, proper footwear such as wearing shoes with rubber-tracked soles, and knowing what makes a roof strong or weak in certain areas help keep professionals safe.
Unless your roof has been inspected recently and professionals have found no structural damage or unstable portions, it's inadvisable to walk on your roof. Consulting with professional roofers to check how much weight per square foot your shingles can hold and keeping hold of any structural documents is always advised.
Is It Safe to Walk On a Roof? How to Check
Here are a few tell-tale signs that your roof might not be safe to walk on.
The roof's interior structure is weak.
• This problem can come from inside your property. A poorly ventilated loft space can cause a huge range of roofing issues. Notably, it can allow unwanted moisture to promote rot and mold growth, forcing shingles apart in an outward direction. This could be a sign you need a new HVAC system, as mold also moves into your interior walls.
It sags when there's snow.
• Snow may feel light, but a cubic foot of snow makes a huge difference and places a lot of pressure on shingles. This is beginning evidence that you may have damaged shingles and that areas underneath are becoming weak, leading to serious problems.
• Leaking is never good, but it's essential to address the problem at the source rather than patching it up. Repeated leaks from weather damage can damage your roof's structural integrity.
Is My Roof Strong Enough to Walk? Tips for Improving Your Roof's Strength
Knowing how much weight your roof can hold is easiest if you work with local roofing specialists to strengthen it and prevent avoidable hazards. Here are some tips.
Trusses can easily be made to bear more weight by fortifying them. Attach additional wooden beams at an even horizontal distance to your existing trusses, ensuring they're properly secure.
This will increase how much weight your roof can bear, just as a double plank can hold more than a single plank.
Treating damaged shingles quickly will prevent ice dams from building up and reduce the risk of further weather damage to your property.
Your roofing is the first line of defense against the elements: keeping it intact makes your whole home stronger.
Attaching Trusses to the Wall
You can use hurricane tie-downs or other sturdy lashes to secure trusses to the internal walls of your property.
This can help fortify them and increase the number of pounds per square foot your roof can bear.
Learn more about Do Roofers Work in the Winter?
Maintaining Your Maryland Roof
Next time you're about to put the Christmas lights up, stop and think:
• Do I know the live load rating?
• Am I wearing proper safety equipment?
• Should I contact local professionals to arrange a roofing inspection and make sure my roof's weight rating is up-to-date and sufficient?
Knowing this rating keeps you and your property safe. Ensure your roofing is inspected regularly to comply with Maryland codes and protect your home and family.