How to Properly Nail Slate

Nailing Slate

Proper nailing of slate shingles to the roof deck is critical to the long-term durability of a slate roof. It is a skill that is relatively easy to learn, but must be practiced to master. Slate shingles are intended to hang on their nails. This requires that the nails for each and every slate be set just right, with the heads of the nails cleanly set in the countersinks left by the punching of nail holes in the slate. The nails must not be over-driven and set too tightly, nor under-driven, leaving the heads of the nails projecting above the face of the slate. For more information nail holes in slate refer to Technical Bulletin #1.

Correct, Over-Driven, & Under-Driven – Figure 2.24

Figure 2.24 illustrates both the proper and improper nailing of slates. Nails set too tightly spring the slate into a slightly concave shape, thereby placing strain on the slate and subjecting the slate to cracking under direct load or movement of the deck under thermal or wind loads. Nails set too tightly can also result in blow-out on the back side of the slate, thereby reducing the holding capacity of the nail. Insufficiently driven nails can lead to cracking of overlying slates under snow, ice, and foot traffic loads, as the butt end of the overlying slate is lifted by the projecting nail head(s) (see Figure 2.25). Nails not driven far enough can, over time, also be forced through the overlying slate by pressure from above (see Figure 2.26).