Installing an ice and water shield is not especially complicated, but it does require precision. An ice and water shield is a roof membrane added to the decking of a roof to deter water from entering the structure. Ice and water shields can be used on any roof design, but they work best on the most vulnerable areas of a roof.
You can make this membrane from a number of materials, but it should almost always contain some form of rubber. This material ensures that the ice and water shield is flexible and water-resistant. Here’s everything you need to know on how to properly install an ice and water shield on your roof.
Why Is an Ice and Water Shield Important?
Some roof designs are steep, while others are flat or nearly flat. Your roof’s slope affects how efficiently rain or snow will slide off. On a shallow roof pitch like 3/12 or less, rain and snow exit the roof more slowly than on a steeper pitch. When ice and snow can’t exit the roof quickly, it accumulates near the bottom edge where the gutters are located.
That pooling water is the enemy of a shingle-style roof. An ice and water shield works in that vulnerable area so that slow-melting water can’t penetrate through the decking. Even tiny perforations like nail holes will leak if effectively submerged in water. The membrane seals the hole around the fasteners for an extra layer of protection.
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Tools for Installing an Ice and Water Shield
An ice and water shield typically comes in rolls from 2 to 4 feet wide and 50 to 150 feet long. To install it, you’ll need this relatively simple set of materials and tools:
- Tape measure
- Framing square
- Chalk line
- Utility knife with sharp blades
- Broom for cleaning the roof surface
- Sturdy ladder
- Nonslip shoes
- Fall protection gear
Remember that you’ll be working at heights when installing an ice and water shield. Only attempt the job yourself if you have experience working on ladders and roofs. Wear nonslip shoes and fall protection gear, and always watch your step to avoid injury. If you’re not confident doing the job yourself, contact a professional roofer for assistance.
Preparing for Installation
Before beginning the installation process, there are several important steps to take to ensure a successful outcome. These include the following:
- Inspect the decking: Thoroughly inspect the roof decking, remove any debris, and make sure the surface is clean and dry. Even a small amount of dust or moisture can interfere with the membrane’s adhesive backing.
- Measure and plan: Carefully measure the areas where the ice and water shield will be. This typically includes the first 3 to 6 feet from the roof’s edge and in valleys. Plan the layout to minimize seams and overlaps, which can create weak points in the water barrier.
- Consider weather conditions: It’s best to install an ice and water shield during moderate temperatures. Extremely cold weather can make the material stiff and difficult to work with. Hot conditions can make it too soft and sticky. A mild day is the best time to install an ice and water shield.
How To Install an Ice and Water Shield
Installing an ice and water shield requires patience and precision. Follow these steps for a proper installation:
- Measure and mark: Using a tape measure and chalk line, mark the area where the membrane will go. For eaves, measure at least 24 inches past the interior wall line. In valleys, extend the coverage at least 18 inches on each side.
- Cut the membrane: Use a square and utility knife or hook blade to cut the material off the roll. Don’t remove the protective backing until just before it makes contact with the roof. If the sticky side of the material contacts any other surface, including itself, it’s nearly impossible to attach. You’ll need to discard and replace it.
- Draw a reference line: Starting at the lowest portion of the roof, carefully position the ice and water shield. Measure from the left edge of the roof straight up and mark a chalk line all the way across. Then, find the middle of the roof and mark another chalk line a few feet long and straight up. These reference lines will help you keep the material straight.
- Install the membrane on the edge: If the reference lines are straight and level, flip the material over so the backing faces up. Remove about a foot of backing at a time. Lift the roll above the line on the roof deck, then very slowly and deliberately press the material onto the roof. Make sure the material follows the left-to-right line so no puckers or gaps can form. Keep removing only enough backing as needed and installing small sections until you’ve made it through the whole section.
- Install the membrane in the valleys: If the structure has valleys, you should install an ice and water shield there as well. Follow the same procedure, but install the material on one side of the valley at a time so air doesn’t get trapped underneath.
If you’re installing multiple courses of ice and water shield, overlap the higher course over the lower by at least 6 inches. In valleys, start at the center and work outward to overlap each side by 6 inches.
Avoid These Common Mistakes
Not all local codes require ice and water shields, but it’s a very smart idea—assuming you avoid these common installation pitfalls:
- Not applying the membrane firmly: Use a roller to help keep firm, even pressure across the surface as the membrane goes on.
- Improperly preparing the surface: Take the time to sweep off debris from your roof so the adhesive will stick as intended.
- Improper positioning: Misaligning the membrane can leave gaps or create wrinkles, both of which make for a less effective shield. Position each section correctly before you stick it to the roof.
- Not overlapping: Gaps without overlap can create weak points for water to get through. Always keep a minimum of 6 inches of overlap between courses of membrane.
- Not working with a partner: An extra set of hands can make the installation easier. Ice and water shield rolls can be large and bulky, and steep slopes aren’t safe to work on alone or without the proper gear.
- Not cutting relief slits: When you install membrane in roof valleys, cut small relief slits every few feet so the membrane will conform to the angles.
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