1. Assess The Underlying Roof Structure
Slate roofs are heavier than asphalt shingles and other types of roofing, like zinc and copper roofs. This means that, in some cases, the underlying home and structure may need reinforcement to handle the heavy weight of slate. The first step in the process is to assess the integrity and strength of the underlying structure, and ensure that the structure is strong enough to accept a slate roof. If not, extra steps must be taken to reinforce it before work can begin.
2. Install High-Quality Roof Decking
When properly installed, the lifespan of a slate roof is 100-150+ years – so the underlying structural elements must be built to withstand this duration. Because of this, the most commonly-used roof decking material is solid lumber that’s at least 2-3 cm in thickness.
Solid lumber is the best product to use for this, as other materials like gypsum and glued roof decking products will not withstand the elements, and could lead to premature failure of the slate roof.
3. Place Felt Underlayment To Protect The Roof
Slate roofs do not usually depend on an underlayment to remain watertight, but a felt underlayment should still be used to protect the roof structure while the slate tiles are installed. This underlayment will be removed when each row of tiles is completed, and the flashing for the roof is installed.
4. Begin Installation Of Each Course Of Slate Tiles
Each slate is nailed into place in a “course” using galvanized, copper roofing nails. 2 nails are used for each slate, with a vertical separation of about 3-4 cm. These nails are driven gently into the slate, and sunk until they are flush with the slate surface. Nailing the slate too deep can cause cracks and damage, so care should be taken during this step to avoid overdriving nails.
Each slate must overlap with the lower and upper course, creating “headlap.” The overlapping nature of slate tiles is what creates a water-tight roof – without the proper head lap and overlap, the roof will leak. That’s why slate roof installation is usually a job that’s best left to the professionals – even minor mistakes in installation can result in serious leaks.
5. Install High-Quality Flashing On Valleys, Gutters, Chimneys, Etc.
As each course of slate tiles is installed, copper flashing is placed in valleys in the roof, and installed near gutters and chimneys, and other gaps in the roof. Copper standing seam is preferred because of its long lifespan – because it can last over 100 years, it’s the perfect pair for slate tiles, which have a similar lifespan.
Once all of the flashing has been placed, courses of slate tiles are placed over the roof decking, underlayment and flashing, until the roof has been completely covered, and the project has been completed.