Should I choose a water shedding or a water resistant roof?

Water is the fundamental ingredient in order for life to exist but when it comes to our homes and buildings – too much of it in the wrong place can do a great deal of damage. The roof is the first line of defense when it comes to protecting against the elements and as such – understanding the ‘how’ of how your roof protects you is important.

One of the most important distinctions we can make is between a water resistant (or hydrostatic) roof and a water shedding (hydrokinetic) roof. The first kind of roof is a low-sloped roof that doesn’t rely on secondary membranes to prevent leakage into a building. The second has a steeper slope, moves water faster but has to rely on a secondary membrane to resist water entering a building.

That being said, the differences are a little deeper – and its those differences that we’re going to discuss today. Let’s jump right in.

Water shedding roofs

The physics of water and roofs is super simple. The steeper the slope, the faster the water moves off your roof, pours into gutters, shoots thought downspouts and enters your drainage system.

3:12 isn’t a time or a regular number. It’s an important benchmark in the pitch of your roof. In this particular case, anything greater than this number is considered a steeper slope. Roofs with steeper pitches need a little help to make sure that water doesn’t enter a structure. So regardless of the material – in this case metal, decking and underlayment are a required ingredient in order for them to work.

Steeper pitch means water moves faster – and when water moves faster, it can tend to wear down on the surface and quickly dart into any gaps in your roof. With some materials, it can even create it’s own entrance. So that in mind, you’ll need some sort of solution to keep water out – and that’s usually some sort of membrane cover.

Water resistant roofs

Anything below a 3:12 pitch is a roof without a steep pitch. This means that water moves more slowly into the drainage systems we mentioned before. The problem with these roofs is less that they have water that runs and wears down long areas so much as they usually tend to attract standing water – especially in areas where there’s a greater variance to the pitch of the roof.

With metal roofs, fasteners will be a requirement, but it’s important to understand that these are merely an element of the roof and may not last the life of the roof and may have to be changed now and then – as they take a great deal of wear and tear.

Materials will be needed to better manage these roofs as well – but instead of adding simple membrane add ons, they’ll need things like closures, fasteners and sealant.

So what’s the real difference and what can I do to keep the water out?

Steel roofs are usually your answer here because the investment returns itself over time. Steel is environmentally friendly and is resistant to a lot of weather elements, but also bugs, pests and other invaders.

When it comes to a major difference between the two – one will require simple adhesives, while the other requires adding multiple insulative elements to ensure proper function. The good thing about a steel roof is that it creates and transfers heat quickly in the absence of insulation and can dry out a lot of the water. While in some models, this can lead to an increase in condensation, for the most part it will burn it off and protect against rust and the like.

When designing a metal roof – choosing which brand of roof comes with certain advantages, benefits and deficiencies, so it’s best to consult a pro. Regardless of the option you choose – it’s important to read blogs like this one so that you know the basic differences and can take them into consideration when making your decision.


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