Bad roofs by design


The proof is in the puddles

Bad roofs by design

Mike Holmes explains how a roof that is poorly designed will leak no matter what products are used.

Photograph by: Handout , The Holmes Group


Think about it. We spend thousands and thousands of dollars on everything inside our homes. But what's protecting it all? The roof. If you have a bad roof it's only a matter of time before you have a bad house. It can lead to things like heat loss, mould, rotted-out structure and pests. These problems can travel to other parts of your home too, leaving a path of destruction.

Most homeowners will call a roofing company to reshingle their roof. But roofs are much more than just shingles. And homeowners need to know what they should be paying attention to if they want to do what's right for their home.

The most important thing when it comes to roofs is proper structure. If the roofline is wrong, everything else will be wrong too. You can have the best products and the best application methods. But if you're putting them over a roof with poor structure I guarantee it's going to leak.

I've dealt with roofs that seem like they've been designed to leak. It probably wasn't the intention of the people who built them - at least I hope not. But that's what happened. Why? Because the roof's structure was poor. What's poor structure when we talk about roofs? Those designed to slope or dip inward into the home. So instead of a pitch we get a valley.

Usually when a roof dips it's because the sheathing is sagging. Or because the roof joists are too far apart or OSB (oriented strand board) was used instead of plywood. But I have seen roofs where the structure was actually designed and built to have a slope right in the middle.

This doesn't make sense for a structure that's supposed to be directing water away from your home. These low areas create valleys that do not drain. And they're bad because they collect snow, rain, ice dams, and so on. Not to mention the heat loss. How do you get enough insulation if there's a low point designed into the roof? There's no space for insulation. So you're going to get heat loss, which is another big problem when it comes to roofs. Some telltale signs that your roof is losing heat include higher energy bills or a leak in your home.

If there's a low-lying area on your roof that collects snow and you also have major heat loss, what do you think is going to happen? You're going to get water pooling when that snow melts. And if the roof design doesn't allow for proper run off, or if the wrong materials were used on a low-slope roof, water will seep into your attic. It's inevitable.


Typically there should be roofing paper underneath the shingles to act as an extra layer of protection in case any shingles blow off. It's a preventive measure. But if a roof's structure is wrong what are the chances that everything else is right? I wouldn't count on it.

Roofing underlayment - which is an ice and water membrane - should be installed along the perimeter of your roof and in any run-off valleys. It's used in any areas on your roof where there's going to be extra water flow or drainage. But it can't protect an area that actively collects water. It's a preventive measure - not a direct line of defence.



Mike Holmes


Photograph by: Handout, The Holmes Group


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