How to Install Synthetic Slate and Shake Roofing: Why the Manufacturer's Instructions Govern
Composite tiles look like slate or cedar but install by their own rules. Exposure, fasteners and sequence all come from the maker.
- Advanced
- 3 to 7 days for an average roof
- Updated
The short answer
Synthetic slate and shake tiles are made from polymer or composite materials, and each brand has its own installation system. In general, install a suitable underlayment, start with the manufacturer's starter course, lay tiles with the stated exposure and offsets, fasten with the specified corrosion-resistant nails or screws in the marked zone, cut with the recommended tool, and blend tiles from several bundles. The manufacturer's instructions override every general rule.
Synthetic slate and shake roofing is made from polymers, rubber or composite materials moulded to look like natural slate or cedar. The appeal is the look without the weight, the maintenance or, for many products, the fire and rot concerns. They are also more variable than shingles: each brand has its own tile size, exposure, fastener, starter and ridge system, and a different way of handling valleys and cuts.
That is why this guide is shorter on numbers than others. There is no universal exposure or nail position. Using the wrong fastener or the wrong position can void the warranty and cause tiles to crack, slide or lift. What we can set out is the general sequence that nearly every system shares, and the points where installers most often go wrong. Always get the current installation manual for the exact product and follow it.
If the synthetic roof replaces cedar, see how to install cedar shakes for what is being replaced, and how to plan a roof tear-off for the preparation.
Tools
- Tape measure
- Chalk line
- Fine-tooth saw or the cutting tool the maker recommends
- Hammer or pneumatic nailer with depth control
- Utility knife and straightedge
- Caulking gun
- Roofing harness, rope and roof anchors
- Safety glasses, gloves and dust mask
Materials
- Synthetic slate or shake tiles, blended from several boxes
- Starter and ridge or hip pieces from the same system
- Underlayment that meets the maker's requirement
- Fasteners specified by the maker, corrosion-resistant
- Ice and water membrane, drip edge and metal flashing
- Sealant approved for the product
Safety first
- Composite tiles are slippery, especially when damp, and they can crack under concentrated weight. Use roof jacks and boards or as the maker directs, and never assume the roof can be walked on like shingles.
- WorkSafeBC requires fall protection where a fall could be 3 metres (about 10 feet) or more. Most synthetic roofs are installed on steep, complex roofs, so anchors, harnesses and lifelines are the norm.
- Tiles are heavy in boxes. Stage loads over rafters and walls, and do not stack more than the structure can carry. See how to load and stage shingle bundles for the approach.
- Wear eye and dust protection when cutting. Cutting some composites produces fine dust.
Step by Step
Step 1: Get the installation manual and check the requirements
The manual gives the exposure, offset, fastener type and length, nail position, number of fasteners, starter and ridge details, cutting method and valley options. Minimum slopes vary, and some products need steeper roofs than asphalt shingles. Keep the manual on site. If you cannot find an answer in it, ask the manufacturer or the supplier before continuing.
Tip: Keep the lot or batch numbers of your boxes with your records. They help if there is ever a warranty question or a need to match tiles.
Step 2: Prepare the deck and install the underlayment system
Many makers require a particular type or weight of underlayment, and sometimes a high-temperature or self-adhered one, since tiles hold heat. Follow their requirement. See how to install ice and water shield and how to install synthetic underlayment. Replace any soft or damaged decking first, see how to replace roof sheathing.
Step 3: Lay out the chalk lines
Measure from the eave and divide the run so the last course at the ridge is not a tiny sliver. Synthetic tiles often come in varied widths, so the vertical alignment matters less than with shingles, but the horizontal lines keep the courses straight. See how to snap chalk lines for the technique.
Step 4: Install the starter course and first full course
Many systems use a dedicated starter strip or a turned first course to seal the eave. Follow the prescribed overhang at the drip edge. Check that the first course is straight, since every course above follows it.
Step 5: Blend tiles from several boxes
Colour and texture vary from tile to tile, and from box to box. Mixing as you go gives the natural look of real slate or shake. Installing one box at a time creates visible blocks. Step back and check from the ground every few courses.
Step 6: Fasten each tile in the marked zone with the specified fasteners
Fastener type, length and position are set by the maker, and are critical. Nails that are too high, too low or overdriven cause tiles to crack, slide or lift in wind. Some systems require a pneumatic nailer with depth control, and some forbid it. Use what the manual says, and adjust depth on a spare tile first. Check the wind rating and whether extra fasteners are needed in high-wind areas.
Watch out: Fasteners outside the marked zone are the most common reason for warranty disputes. Follow the diagram exactly.
Step 7: Cut tiles with the recommended method
Some composites cut with a utility knife scored and snapped, and some with a fine-tooth saw or a wet or dry blade. Cutting the wrong way can chip or crack. Wear eye and dust protection. Do not leave very small cut pieces at edges, and cut from tiles that can be blended into less visible places.
Step 8: Flash the valleys, walls and penetrations, and finish the ridge
Valleys are often open metal valleys on synthetic roofs, since tiles cannot be woven. See how to install an open metal valley. Walls and chimneys use step and counter flashing, see how to install step flashing. Ridge and hip pieces are part of the system and are fastened as specified.
What Varies Between Products
- Exposure and tile size: set by the maker and usually marked on the tile or the manual.
- Fastener type and position: nails, screws or clips, in a marked zone, sometimes with a required nailer setting.
- Underlayment: some require a high-temperature or self-adhered type and a minimum performance.
- Minimum slope and wind rating: differ by product, and affect the number of fasteners.
- Cutting method and tools: knife, saw or shears, depending on the material.
Maintenance in the Fraser Valley
Synthetic tiles resist rot, but moss and needles still collect on the surface in shade, and debris in valleys still causes leaks. Clear them gently with a soft brush or blower, and check the maker's advice before using any moss treatment or pressure washing. See how to clean debris off a roof.
Common Mistakes
- Using instructions for another product. Every system is different. Use the manual for the exact tile.
- Fasteners outside the marked zone. Tiles crack, slide or lift and the warranty is at risk.
- Overdriving or underdriving. A crushed tile cracks, and a proud nail lifts the tile above. Set the nailer on a spare tile first.
- Not blending boxes. Colour blocks and stripes show from the ground.
- Wrong underlayment. Some tiles need high-temperature or specific underlayment, and standard felt may fail.
- Walking carelessly. Tiles can crack under point loads and are slippery when wet.
When to Call a Professional
Synthetic slate and shake is usually installed on steep, complex roofs, and the work is tied to warranty conditions, so it is often best left to a roofer who knows the system. Call one if the roof is steep, has many valleys, chimneys or skylights, or if you want the manufacturer's warranty to apply.
If you have an existing synthetic roof with cracked or slipping tiles, a roofer can check the fastening and the underlayment before replacing individual tiles, since the cause is often installation.
Fraser Roofing does free roof inspections across the Fraser Valley, from Hope to Abbotsford. See our Roof Repair service or the towns we cover.
How to Install Synthetic Slate and Shake: Questions
How are synthetic slate roofs installed?
They go over a sound deck with the underlayment the maker specifies, starting with a starter course at the eave and laying courses at the stated exposure. Each tile is fastened with the specified corrosion-resistant fasteners in a marked zone, tiles are blended from several boxes, and valleys, walls and ridges use the system's flashings and pieces. Follow the manufacturer's manual exactly.
What is the exposure for synthetic slate?
It depends entirely on the product. Different tile sizes and systems have different exposures, often printed on the tile or in the manual. There is no single figure that applies to all synthetic slate or shake, so use the manufacturer's installation instructions for your exact tile and confirm with the supplier if anything is unclear.
Can you walk on synthetic slate roofing?
Only as the manufacturer allows. Many composite tiles can crack under concentrated weight or scuff, and they are slippery when damp. Some makers require boards, roof jacks or a specific walking technique. Fall protection is needed on steep roofs regardless, and WorkSafeBC requires it where a fall could be 3 metres, about 10 feet, or more.
Do synthetic shake roofs need special underlayment?
Often yes. Many makers call for a particular underlayment, sometimes a high-temperature or self-adhered type, because tiles can hold heat. Ordinary felt may not meet the requirement and may affect the warranty. Check the installation manual for the underlayment type and any requirement for ice and water membrane at the eaves and valleys.
Why do manufacturer instructions matter so much for synthetic roofing?
Each system is engineered as a whole, with its own tile size, exposure, fastener position and underlayment. Using the wrong fastener or position can cause cracking, sliding or wind damage, and usually voids the warranty. Generic roofing rules from asphalt shingles do not apply, so the manual is the authority.
Related Guides
All Specialty Roofing guides|The full How-To Library
This guide is general education. Always follow the product manufacturer's installation instructions, the BC Building Code and WorkSafeBC requirements, which take priority over anything written here.
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