Can I replace my own roof? Ice and water shield . . .
The short answer is: Yes, you can replace your roof yourself.
And we’ll share a little bit about how. This post will help you understand ice-and-water shields, why you need one, and where you need it. Next week’s post will talk about the other elements of the underlayment and prep stage of installing a roof.
What is ice and water shield?
The roof of your home starts with an underlayment. It’s talked about as “dry-in" or “paper” or “felt.” It is a layer of waterproof material that acts as a secondary defense against moisture, which will inevitably get under your shingles at some point. Water that finds its way to your roof decking may not necessarily create a leak right away, or ever, but it can start to cause rot which will make for costly repairs down the road.
A critical part of that underlayment, particularly for those of us in snow country, like Bozeman, is the ice and water shield.
An ice an water shield is a form of underlayment made of self-healing material with an adhesive back. It is self-healing, meaning it will seal around nail holes from the shingles above, and the back is sticky so that it seals directly to your roof deck, preventing water from ever being able to get beneath it. You do not typically need to put ice and water over the entire roof. It has a specific purpose and only needs to be used in specific locations. Check with local building codes to see what those locations are, but typically: it needs to be applied at the eaves, and extend 24” beyond the exterior wall of the house, where the conditioned space begins. It looks something like this masterful illustration:
We typically use it a minimum of 36” beyond the conditioned space. How far along the pitch, or the roof deck, this means you need to go depends on the soffit size and the pitch of the roof, or how steep it is. Most of the time this means we need to use two rows along the eave. If you want to be extra careful and aren’t counting nickels and dimes, use it to line the valleys, as well as at any roof penetrations, chimney crickets, and low pitches (less than 4/12).
What does ice and water shield do?
If you are wondering when you need to use it, first, check with your local building codes and make sure you use it at least everywhere the code says to. Then, if you want to use it elsewhere, make the decision based on understanding what it does.
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The primary reason for ice and water shield, and the reason it is so critical in places with real winter, like Bozeman Montana, is to stop water from ruining your roof deck when it sneaks uphill under your shingles. And if you live in Bozeman, water will go uphill under your shingles. How? Let’s refer back to the brilliant drawing above.
When snow lands on your roof, it will melt. It will melt from sunshine and ambient temperatures, and it will also melt as heat from your home escapes through your roof. When it melts, it will flow downhill, as water does. It will flow down until it passes your conditioned space and runs out over your soffit at the eaves. In the winter, this part of your roof will be much cooler than the rest of your roof because there is no heated space below it. The water can freeze here, creating those ice-dams and icicles you can see as you drive around in February. As more melting occurs, that water will flow down and hit the ice dam, where it will begin to pool. It will creep up underneath the shingles, and it will sit on the roof deck. This is where the ice and water comes in. Waterproof, self-healing, and self-adhered to the deck, it is supposed to create a truly waterproof area that extends high enough that the water and ice-dam cannot reach the top of it and damage the roof deck.
Ice and water should be used anywhere you think an ice dam, or other causes of water getting below shingles, is possible.
