How to Install Tapered Insulation and Crickets: Reading the Taper Plan, Layers, Joints and Fastening

Step by Step

1. 1Step 1: Prepare the deck and read the taper plan

   The deck must be sound, dry, clean and flat enough to receive boards. Fix loose fasteners, sag and damaged areas. Install the vapour control or air barrier layer if the design calls for one, and check the plan against the actual roof, since existing drains, curbs and walls sometimes sit in different places than the drawings show.

   A taper plan usually shows the roof divided into bays around each drain, with a numbered or lettered board for every area. Thicknesses at the high and low ends are noted, and the slope in inches per foot is given. Common slopes are 1/8 inch per foot and 1/4 inch per foot for the main taper, and steeper for crickets. Study the layout and find the thinnest point, which is at the drain, and the thickest, which is at the high points and ridges.

   Tip: Lay out the boards dry in one bay first. If the numbers do not meet up as the plan says, find the problem before the whole roof is committed.

2. 2Step 2: Install the flat base layer

   Most systems use one or two flat layers under the tapered layer. Place boards with the long edge across the deck flutes on a steel deck, and stagger the joints so end joints in one course do not line up with the next. Butt the boards tight, without forcing them. Gaps leave thermal bridges and a soft spot under the membrane.

   Fasten to the structural deck with the approved fasteners and plates, at the spacing the wind design gives. Fastener pattern is engineered for wind uplift, so do not guess. On a wood or concrete deck, the design may call for adhesive instead.

3. 3Step 3: Start the tapered layer at each drain

   The drain is the lowest point on the roof, so the layout starts there. The boards around the drain are usually the thinnest, and they slope down toward the drain body. Place the first board and check its orientation against the plan before fastening. A board turned 180 degrees slopes away from the drain.

   Work outward, matching each board number to the plan. Keep all the joints tight and check that boards meet correctly at the corners. At the drain, the insulation must be cut back to allow for the drain sump and clamping ring. See how to install a flat roof drain.

4. 4Step 4: Stagger the joints between layers

   Insulation boards shrink slightly and move. A joint that runs straight through two layers becomes a thermal channel and a place where the membrane can crack. Stagger both long and end joints between layers, offsetting them by at least 6 inches. Where the taper plan does not allow this, use the closest arrangement that does.

   Fill any gaps wider than about 1/4 inch with compatible foam or cut pieces of insulation. Do not leave voids under the membrane, and do not use a soft filler that compresses.

5. 5Step 5: Build the crickets

   A cricket is a pair of sloped planes meeting in a ridge that divides water. It is placed on the upslope side of a curb, at wall corners and between drains. Cricket boards are cut from tapered stock in the pattern shown on the plan, and are installed on top of the base and main taper layers.

   Crickets slope more steeply than the roof, commonly about 1/2 inch per foot, so that water always has a path around an obstruction. Check that the cricket edges meet the main taper surface cleanly, without ridges, and that the cricket ends at the drain side lead water toward the drain. See also how to flash a curb on a flat roof.

6. 6Step 6: Fasten or adhere the boards

   Fasteners must reach the structural deck at the required depth. With tapered boards, thickness varies, so fastener length changes across the roof. Check the plan for which length goes where, and use a depth-setting driver so plates sit flush without crushing the board.

   Perimeter and corner zones get more fasteners than the field, like the membrane above. See how to install mechanically fastened TPO for how those zones are defined. If the insulation is adhered, follow the adhesive manufacturer's ribbon or spray pattern and keep the boards in the open time.

7. 7Step 7: Add the cover board and check the slope

   Most membrane systems need a cover board over polyiso for puncture resistance, fire performance and a compatible surface. Stagger its joints away from the insulation joints, and fasten as specified.

   Check the finished slope with a long straightedge and a level, and check that no high spots lie between the drains and the water. If the roof can be wetted before the membrane goes on, a hose test will show where water runs. Correct any flat spots now.

Taper Rates and Minimum Thickness

Insulation Compatibility

Common Mistakes

• Boards in the wrong position. A rotated or swapped tapered board slopes water away from the drain. Match every number to the plan.
• Joints that line up between layers. Through-joints open up, and the membrane above cracks at them.
• Gaps left open. Voids under the membrane create soft spots and allow wind to work into the assembly.
• Fasteners that are too short or too long. Short ones do not reach the deck, and long ones can break through the ceiling below.
• Crickets forgotten. Water backs up behind curbs and between drains.
• Covering wet insulation. Trapped moisture ruins the new roof from the inside.