How to Install Ice and Water Shield on Eaves, Valleys and Penetrations

Step by Step

1. 1Step 1: Prepare a clean, dry deck

   The membrane only sticks to a clean, dry, smooth surface. Broom off dust and grit, drive down raised nails and remove staples. Do not install over wet or frosty wood. Most manufacturers give a minimum application temperature, commonly around 5 degrees C (40 F), below which the adhesive is slow to bond. In cold weather, a primer or warm storage of the rolls may be needed. Always follow the manufacturer's instructions for your product.

   On OSB or dusty decks, prime where the manufacturer calls for it. Check the deck for damage first, using how to inspect a roof deck for rot.

2. 2Step 2: Decide how far up the roof it goes

   The BC Building Code's eave protection rule for shingle, shake and tile roofs calls for protection from the roof edge a minimum of 900 mm up the slope, to a line not less than 300 mm inside the inner face of the exterior wall. The same article lists exceptions: unheated garages, carports and porches, overhangs longer than 900 mm measured along the slope, asphalt shingles laid by the code's low-slope method, slopes of 1 in 1.5 (8/12) or steeper, and locations with 3,500 or fewer heating degree-days. The code also accepts materials other than self-adhered membrane, such as two plies of No. 15 felt cemented together.

   That degree-day exception matters here. The code's own climate table puts Chilliwack at about 2,780 degree-days, Abbotsford at 2,860 and Hope at 3,000, so on much of the valley floor the code does not strictly require eave protection. Do not read that as permission to skip it. Shingle manufacturers commonly call for a leak barrier at the eaves wherever ice dams or backed-up gutters are possible, the code requires their instructions to be followed, and a cold snap after wet snow will back water up at the eave anywhere in the valley. Many roofers in the region lay it on every shingle roof, and your local building department may have its own requirement.

   On a house with a typical overhang of 12 to 16 inches, the inside of the wall is about 2 to 3 feet up the slope from the edge, so the 300 mm rule usually means two courses of 36 inch membrane. Ice damming is worst where the roof is shallow, the overhang is long, the attic is warm, and at valleys, so those roofs deserve more.

   Tip: Measure from the inside face of the wall, not the outside. Get the real overhang and wall thickness, then snap a line and lay the membrane to it.

3. 3Step 3: Start at the eave and fit the drip edge order

   At the eaves the drip edge goes on the deck first, and the membrane goes over it, so water runs from the membrane onto the drip edge and out. At the rakes the order is reversed: membrane first, then drip edge over it. Details are in how to install drip edge.

   Set the first course so the lower edge sits over the drip edge flange, and trim so the membrane does not hang out beyond the gutter line. Cut the roll to length before peeling.

4. 4Step 4: Peel the release film and press the membrane down

   Cut a length of roll to the run, plus an inch or two for overhang. Fold it in half lengthways, peel a few feet of film, and position the membrane along the line. Press it down from the centre outward to avoid wrinkles and air pockets, and then peel the rest of the film as you go. Do not stretch it.

   Two people work better on long runs. Once it touches the deck it is difficult to reposition, and pulling it up tears the membrane and the top layer of the plywood.

5. 5Step 5: Roll or press every inch firmly

   Adhesion depends on pressure. Use a J-roller or a stiff broom and work across the width, not just along the length. Pay extra attention to laps and to edges, where lifting begins. Wrinkles and fish-mouths at edges are channels for water, and are cut and patched before shingles go on.

6. 6Step 6: Lap each course correctly

   Most manufacturers mark the roll with a selvage line for the side lap, commonly 3 inches. End laps are commonly 6 inches and should be staggered from one course to the next, so two end laps do not stack. Upper courses lap over lower ones so that water sheds over the joint. Confirm the lap dimensions against the product's instructions.

   If you need to install a second course above the first, it laps onto the first by the side lap width, never under it.

7. 7Step 7: Cover the valleys and other high-risk areas

   A strip of membrane in the centre of the valley, then the shingles or metal over it, is standard. See how to prep a roof valley. Low-slope areas below about 4/12 pitch and areas where a shingle manufacturer requires full coverage need it across the whole slope. Wall junctions get a strip turned up the wall, as in how to install step flashing, and penetrations get membrane sealed tight around them.

   Fold the membrane into inside corners and press it in well, so there is no bridging gap.

8. 8Step 8: Finish edges, nail the top and cover with underlayment

   The top edge can be tacked with a few nails just above the lap line so it does not slide before the next layer goes on. The field underlayment then laps over the top of the membrane, in shingle fashion. Finish with shingles promptly. Most membrane products carry an exposure limit, and UV over a long exposure can harm the adhesive and the surface.

Where Ice and Water Shield Goes

Hot Weather, Cold Weather

Common Mistakes

• Stopping at the outside wall line. Water from ice dams backs up past the eave and into the wall. Go at least 300 mm inside the inner face of the wall.
• Installing over wet or dusty wood. The adhesive does not bond, and the membrane slides or lifts.
• Wrinkles and fish-mouths. They make channels for water, and have to be cut out and patched.
• Wrong drip edge order. At the eave the drip edge goes under the membrane, and at the rake it goes over.
• Short laps or stacked end laps. Laps under 3 inches at the sides or 6 inches at the ends leak, and stacked end laps make a weak line.
• Leaving it exposed too long. UV and foot traffic degrade the membrane.