When a newly installed roof leaks, the homeowner's first reaction is to blame the tiles.
However, industry insiders live by a golden rule: **30% is the tile, 70% is the installation.** Synthetic resin tiles are co-extruded sheets with tight manufacturing tolerances and good flexibility; what truly determines whether the roof leaks-or withstands summer heat and winter contraction-comes down to the specific installation steps performed on-site.
This article won't cover material selection (we discussed that in our previous post); instead, it focuses on one thing: **how these tiles should actually be installed, and how you can judge on the spot whether the workers are doing it right.**
### I. Confirm these three things before starting work
Many people start laying tiles immediately, only to discover halfway through that the framework is unsuitable. These three items must be verified before the first tile is placed on the roof.
**1) Slope/Pitch**
Synthetic resin tiles are generally suitable for pitched roofs with a slope of approximately **15°–85°**. However, keep two boundary conditions in mind:
- **For roofs with a main ridge cap, the slope angle should ideally be kept between 15° and 30°**; a slope that is too steep increases the risk of the tiles sliding downward.
- Refer to the group standard **T/CADBM 19-2019** ("Standard for Installation and Quality Acceptance of Synthetic Resin Decorative Tiles"); this standard applies to cast-in-place reinforced concrete, timber, and steel-structure pitched roofs with a slope of **18.5°–60°**.
**For flat roofs with a slope of less than 15°, do not expect a tile replacement to solve leakage issues.** Drainage is inherently slow, and no type of tile can prevent leaks in such cases; you must first create a proper slope (grading) for drainage.
**2) Purlins: Material, spacing, and positioning-none of these can be wrong**
The purlins form the skeleton of the entire roof, while the tiles are merely the skin. Common Practices:
| Purlin Type | Standard Specifications | Treatment Requirements |
| ---- | ------------- | ----- |
| Square Steel Tube | 60×40×3mm | Anti-rust treatment required |
| C-Section Steel | 100×50×20×3mm | Anti-rust treatment required |
| Preservative-treated Timber | 60×40mm | Preservative treatment required |
Three Critical Measurements:
- **Main tile purlin spacing must not exceed 660mm** (for large-arc tiles or thick sheets, this may be relaxed to approximately 750mm based on the manufacturer's technical documentation). Excessive spacing leads to tile sagging and loose overlaps, ultimately resulting in "leaks despite correct nailing."
- **The uppermost purlin should be positioned approximately 150–180mm from the ridge line** to allow space for the main ridge tile.
- **The lowermost purlin should be positioned approximately 50–70mm from the eaves** to allow space for the eave trim.
Two additional scenarios requiring reduced spacing: **sheet thickness less than 2.5mm, or roofs on buildings with high internal temperatures (such as factories).**
**3) Complete Set of Accessories**
Main tiles, main ridge tiles, hip ridge tiles, three-way ridge connectors, eave trims, gutter drainage sheets, waterproof caps with washers, and neutral silicone weather-resistant sealant. **The roofing is a system; if a single component is missing, the joint becomes a potential leak point.**
### II. List of Tools and Auxiliary Materials (Use this list directly for material procurement)
**Tools**: Marking line (chalk line), tape measure, steel ruler, level, handheld electric drill (with specialized drill bits), cutting machine (with cutting discs designed for resin tiles), rubber mallet, wrench.
**Fasteners**: Must be **self-tapping screws specifically designed for resin tiles**; stainless steel (e.g., 304 grade) is recommended. Common diameter is φ6.3mm; lengths are selected based on the thickness of the purlins and roofing tiles, with 75mm and 110–150mm being the standard specifications. **Strictly prohibit the use of ordinary screws as substitutes.**
**Waterproofing Accessories**: Specialized waterproof cap + waterproof washer (or integrated fastener). **The waterproof cap must be made of weather-resistant material such as ASA; do not use cheap PP or PVC parts**-if the tile surface lasts twenty years without aging but the accessories become brittle in three, the installation is effectively wasted.
**Others**: Neutral silicone weather-resistant sealant (for sealing joints) and resin adhesive (for repairing incorrectly drilled holes).
### III. Construction Environment and Safety
- **Weather**: Avoid installation during rain, heavy fog, or winds exceeding Force 6; do not install when the ambient temperature is below 5°C or above 35°C.
- **Safety**: Hard hats and safety harnesses are mandatory; erect stable scaffolding or use non-slip ladders; **strictly prohibit stacking materials or standing on unsecured purlins**.
- **Wind Direction**: Install the main tiles **against the prevailing wind direction** to prevent wind from entering the overlap seams and lifting the tiles.
### IV. Eight-Step Installation Process
**Step 1: Layout and Positioning**
Mark longitudinal reference lines (eave line, ridge line) and transverse control lines based on roof dimensions. **Do not skip this step**-if you install without marking lines, the tile alignment will inevitably skew, resulting in a mismatch of the corrugation pattern at the ridge, necessitating disassembly.
**Step 2: Install Eave Purlins and Eave Closures**
Install the eave closure and the bottom section of the main tile simultaneously; secure them to the purlin using self-tapping screws that fasten through both layers at the end of the main tile.
**Step 3: Lay the First Tile (The Most Critical Tile)**
Begin installation from one side of the roof (usually the bottom-right corner). **The bottom edge of the first tile must be strictly aligned with the eaves line, and its side edge aligned with the vertical reference line.** After alignment, drill a hole at the crest of the lowest purlin to temporarily secure it. If the first tile is crooked, all subsequent tiles will be misaligned.
**Step 4: Horizontal overlapping and staggered interlocking**
The second tile overlaps the first by **one corrugation crest** (approximately 90mm for the 1050 model; 80mm for the 880 model). To ensure the roof surface remains straight, use a **staggered "over-under" arrangement**: the second tile overlaps the first and third; the fourth overlaps the third and fifth; and so on. A simple unidirectional overlap sequence will cause the entire roof surface to gradually tilt.
**Step 5: Longitudinal overlapping**
Overlap the upper and lower rows of tiles longitudinally by **one tile pitch** (commonly 220–250mm; refer to the technical specifications for your specific model and follow the manufacturer's guidelines).
**Step 6: Fastening with screws**
This is the most critical step in the entire process.
- **Position:** Screws must be driven into the **center of the corrugation crest**; driving them into the trough or the transition slope is strictly prohibited. Driving into the trough allows rainwater to flow down through the screw hole, almost guaranteeing a leak; this is the primary safeguard against water ingress.
- **Pre-drilling:** The hole diameter should be **2–3mm larger than the screw diameter** to allow for thermal expansion and contraction. This step may be skipped if using self-reaming screws, but **forcing the screw in without enlarging the hole is strictly forbidden**.
- **Sequence:** Place the waterproof washer and protective pad first, then drive the screw vertically into the purlin.
- **Tightness:** Tighten until the waterproof washer deforms slightly and the tile is secure but not loose. Overtightening restricts expansion and contraction, causing the roof surface to buckle or crack in summer; undertightening fails to create a tight seal, leading to water seepage. - **Density:** Approximately 4–5 self-tapping screws per square meter; install a fastener assembly at every other corrugation peak.
- **Synchronized Installation (Dual-Slope Roofs):** Installation should proceed symmetrically upwards from both sides, finishing at the ridge to ensure the corrugations align correctly.
**Step 7: Installing Ridge Tiles**
Install main ridge tiles first, followed by hip (diagonal) ridge tiles, and finally the three-way ridge tiles.
- **Main Ridge Tiles:** Install along the ridge line, overlapping adjacent tiles by one corrugation. **The overlap point of the ridge tiles must not align with the overlap point of the underlying main roof tiles**; otherwise, a four-layer overlap will occur, preventing a tight fit or proper seal.
- **Hip Ridge Tiles:** Install along the sloping edges of multi-slope roofs; align the centerline with the hip line and overlap adjacent sections by approximately 30mm.
- **Three-Way Ridge Tiles:** Use at the vertex where three roof planes intersect; position one side to overlap beneath the main ridge tile, while the other two sides overlap above the hip ridge tiles.
**Step 8: Detailing and Edge Finishing**
These details are critical to the success of the waterproofing system:
- **Gutters:** If the roof features diagonal gutters, install a galvanized steel sheet or resin drainage board of appropriate width before laying the main roof tiles, ensuring an **exposed width of approximately 200–300mm**.
- **Flashing (Gables, Chimneys, Pipes):** Use custom metal or resin flashing sheets; secure one end to the wall or structure and tuck the other end beneath the corrugations of the roof tiles.
- **Expansion Joints:** Leave a gap of **10–15mm** between the tile ends and the wall, and 8–10mm at lateral overlap joints; **do not butt them tightly against the structure**. ### V. Quick Reference Parameter Table (Can be screenshotted and sent to workers)
| Item | Control Value |
| :--- | :--- |
| Applicable slope (general) | 15°–85° |
| Recommended slope for roofs with ridge caps | 15°–30° |
| Standard applicable slope (T/CADBM 19-2019) | 18.5°–60° |
| Main tile purlin spacing | ≤660mm (can be extended to approx. 750mm for large-arc/thick tiles) |
| Distance from top purlin to ridge line | 150–180mm |
| Distance from bottom purlin to eaves | 50–70mm |
| Lateral overlap | One corrugation crest (approx. 90mm for Model 1050 / 80mm for Model 880) |
| Longitudinal overlap | One tile pitch (typically 220–250mm; refer to manufacturer specs) |
| Fastening position | Center of the crest; fastening in the trough is strictly prohibited |
| Pre-drilled hole diameter | 2–3mm larger than the screw diameter |
| Screw density | 4–5 screws per square meter |
| End expansion gap | 10–15mm gap between tile end and wall |
| Maximum single tile length | Recommended not to exceed 6.5m |
### VI. The 6 Most Common Mistakes
1. **Driving screws into the trough.** The most critical and common error; rainwater flows into the screw hole, inevitably causing leaks.
2. **Forcing screws in without pre-drilling.** Lack of expansion allowance leads to buckling or cracking in summer and joint opening in winter.
3. **Tightening screws excessively ("dead tight").** ** Workers often have a habit of driving screws all the way in, believing that "tighter means more secure"-but the exact opposite is true; fully compressing the washer effectively locks the tile in place, preventing necessary movement.
4. **Skipping the layout and alignment step.** This results in tiles tilting individually and the ridge corrugations failing to align, requiring half the roof to be dismantled for rework.
5. **Overlapping the ridge tile joints directly with the main tile joints.** This creates a four-layer stack that cannot be pressed down firmly or sealed tightly.
6. **Installing new roofing directly over old tiles or color-coated steel sheets.** Uneven old tiles can deform the new ones; color-coated steel is thermally conductive, exacerbating temperature fluctuations and causing the tile surface to buckle. ### VII. Owner's Acceptance Checklist (Check these 8 items on-site after installation)
| # | Inspection Item | Acceptance Standard |
| --- | --- | --- |
| 1 | Roof Sheet Straightness | Straight and level both horizontally and vertically; no obvious tilting or misalignment. |
| 2 | Screw Placement | All screws located at the center of the corrugation crest; none driven into the trough. |
| 3 | Screw Tightness | Washers slightly deformed and compressed but not crushed; roof sheets remain secure. |
| 4 | Overlap | Horizontal overlap of one crest; vertical overlap of one pitch; tight fit with no curled edges. |
| 5 | Ridge Tiles | Main ridge tile overlaps staggered to avoid aligning with main sheet overlaps; hip ridge tiles aligned at the centerline. |
| 6 | Joint/Edge Finishing | Flashing and sealant at gables, chimneys, pipes, and gutters are intact and continuous. |
| 7 | Site Cleanup | No drilling debris, offcuts, or leftover materials on the roof or surrounding area. |
| 8 | Water Test | Smooth drainage after pouring water; no pooling, backflow, or signs of leakage. |
If incorrectly drilled holes are found, they can be sealed with a mixture of resin glue and resin powder; however, **sealed areas require a follow-up inspection**.
### VIII. Post-Installation Maintenance
- Clear fallen leaves and debris from the roof 2–3 times a year to ensure unobstructed drainage.
- Regularly inspect screws and waterproof caps; replace them promptly if loose or aged.
- Inspect and re-apply sealant every 5 years.
### A Word of Truth About Lifespan
The industry generally cites a lifespan of **20–30 years**, provided that: virgin materials are used, the ASA surface layer meets standards, **and installation follows specifications**. If any of these three conditions is missing, the quality of the first two factors becomes irrelevant. **Don't buy into the "50-year" or "70-year" marketing hype.** Figures that exceed industry consensus are a sign that the supplier is just spinning a story.
### What We Deliver
- **Construction Briefing Materials**: We convert the parameter quick-reference chart from this article into a construction briefing sheet, included with the shipment so workers can follow the instructions precisely.
- **Complete Accessory Kits**: We supply a full set of components-main tiles, ridge tiles, eaves trim, gutters, waterproof caps, and washers-tailored to your roof's actual dimensions, ensuring the installation team doesn't have to improvise on critical details.
- **Testing First**: Backed by [Insert Report Name, e.g., "Artificial Weathering Test Report"]-we let the data speak for itself.
- **Written Warranty**: We provide a formal written warranty for [Insert Warranty Period], with clear and detailed terms.
---
### Want a printable construction manual?
Reply "**Construction**" in the comments section and include your region and roof type (e.g., self-built home, factory, or flat-to-pitched roof conversion). We will send you the **complete technical parameter charts for the 1050 and 880 models**, a **printable construction briefing sheet**, and an **acceptance checklist**.