How to Build a Cricket Behind a Chimney

Written by paul massey
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How to Build a Cricket Behind a Chimney
(Jupiterimages/ Images)

A roof drainage diverter, or “cricket,” is a small, sloped area built-up behind a roof projection, such as a chimney or skylight dam, to insure proper shedding of rainwater. A simple and functional cricket can be made of plywood and covered with readily available metal flashing. The method can be adapted to a cricket of any width required by following this basic procedure.

Skill level:

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Things you need

  • Tape measure
  • Level
  • Hammer
  • Framing square
  • Circular saw
  • ½-inch plywood
  • 8d sinker or box nails
  • Caulking gun
  • Tube of construction adhesive
  • Tube of exterior-grade silicon caulking
  • 13.6kg. roofing felt
  • 4-inch “L” flashing
  • Metal snips

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  1. 1

    Use a tape measure to mark the centre line of the rear face of the chimney. Use a level to extend this mark from the point where the roof surface meets the base of the chimney to approximately eight inches up the chimney face. This will be the ridge reference line of the cricket.

  2. 2

    Layout a triangle shape on a piece of ½-inch plywood, with a baseline matching the full width of the chimney face marked in Step 1 minus two inches and the height of the triangle six inches perpendicular to the baseline. Use a circular saw to cut out the plywood triangle.

  3. 3

    Position the triangular piece of plywood cut in Step 2 where the roof line meets the back of the chimney and upright against the chimney surface. Attach the plywood triangle to the chimney with construction adhesive, making certain the centre point of the plywood aligns with the centre mark on the chimney. This is the cricket end support.

  4. 4

    Use a tape measure to get the dimension from the outer point of the cricket end support piece to the peak point at the centre.

  5. 5

    Use a framing square to mark a right angle on a piece of ½-inch plywood. From the corner of the square, mark a 12-inch pencil line on one side and a line on the other side to the dimension from Step 4. Use the edge of the framing square to connect the ends of these two lines.

  6. 6

    Cut out the triangle marked in Step 5. Use the cut out piece as a template to cut a matching piece. These two triangular pieces will form the cricket ridge and sloped drainage surfaces.

  7. 7

    Position one of the two pieces of plywood cut in Step 6 with the 90-degree corner at the peak point of the plywood triangle against the chimney and the side determined in Step 4 against the chimney surface, resting on the cricket support. Secure in place with 8d nails into the end support plywood and along the plywood edge that rests on the roof surface.

  8. 8

    Install the other plywood triangle piece cut in Step 6 to mirror the position in Step 7. Keep the plywood pieces tight at the ridge point of the cricket. Attach this piece as in Step 7.

  9. 9

    Seal the perimeter edges and ridge joint of the cricket with exterior-grade silicon caulking.

  10. 10

    Cut a length of 4-inch “L” flashing to the width of the chimney just above the cricket’s ridge plus 3-inches. Mark the centre point of the upright arm of the flashing and square the line to the bend. Use metal snips to cut the line to the bend on only the upright side. Center the “L” flashing on the cricket and fold it down to rest on the cricket plywood on both sides and against the chimney. Secure the flashing in place against the chimney with construction adhesive. Run a bead of silicon caulking around the upper edges of the flashing.

  11. 11

    Cover cricket assembly with roofing felt prior to installing roofing material over the cricket.

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