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Slate Roof Installation – Installing a Closed Valley

After finishing with the open valley, now we’ll outline the installation of a closed valley. A closed valley detail is when slates come together and meet so you cannot see any valley flashing underneath. Closed valley metal flashings are interwoven one piece at a time with each slate as it is installed.

Closed Valley Installation in Detail

Valley flashings may be rectangular, diamond or v-shaped. Their size will vary with the length, width, and exposure of the slate and the slope(s) of the adjoining roofs. Measure to see if an extra wide slate or “slate-and-a-half” is required to avoid nailing into any valley flashing. To measure your first slate to be cut, mark the bottom of the slate. Then mark the intersection point, by turning the slate over.

Trace a straight line between the two marks. Cutting the slate from the backside will give a beveled (chamfered) edge finish on the face of the slate. Install the slate into place. Drive the nail head down so that it’s cleanly set in the countersinks left by the punching in the slate. Nails should not be over-driven, nor under-driven.

Closed valley flashing should always be stepped up in pieces and not in long sections. Install the field slates as you approach the valley and cut slates immediately adjacent to the valley to align together. Drive 2 nails into the upper edge portion of the slate to avoid puncturing the valley flashing. You can use the point of your slate hammer to punch holes (from the backside) so that a countersunk hole is created on the front side of the slate. Repeat the same process on the other side so the adjoining slates butt together in the center of the valley.

Install the next piece of interwoven valley flashing with 2 nails. Line up your next piece of slate 180 degrees so that it can be marked, cut and fit into the valley. Transpose these marks to the backside of the slate. Lay the slate in the valley so that the intersecting spot can be marked for the correct angle. From both intersecting points, draw a line on the back of the slate so it can be cut with the beveled (chamfered) edge finish on the face of the slate.

Repeat this process up the roof, ensuring the bottom of the slates line up evenly.

I hope this has helped you understand the basics of installing a closed valley.

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Looking for a slate roofing contractor?
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The standard sizes for roofing slate start at 12″ in length and increase by 2-inch increments up to 24″ in length. Read More
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On average, North American produced S-1 rated roofing slate will cost $400 – $600 USD per square (100 square feet) or $4.00 to $6. Read More

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