Zero Leakage & Long Service Life

A practical guide to roof opening, concrete curb construction, frame fixing, waterproofing, drainage, and roof tile restoration.

KEY TAKEAWAYS
Correct roof opening • Stable concrete curb • Secure frame fixing • Multi-layer waterproofing • Bottom-to-top drainage • Proper roof tile restoration

Why Correct Installation Matters

Sloped roof skylights are widely used in residential villas, attics, and commercial buildings to bring in natural daylight, improve ventilation, and enhance indoor spaces.

Many long-term problems—such as water leakage, poor thermal insulation, weak sound insulation, and structural instability—are not necessarily caused by the skylight itself. They can result from non-standard or incorrect on-site installation.

This guide presents a standardized installation process and practical technical details to help builders and project owners achieve reliable watertight performance, stable structure, and better thermal and acoustic insulation.

1. Roof Opening: Measure and Cut Correctly

The roof opening is one of the most important steps in the installation process.

Some conventional installation advice recommends making the roof opening 1 cm larger than the skylight frame. For example, for an 80 cm wide skylight, the opening would be 81 cm. This method is technically incorrect and creates installation risks.

If the opening is larger than the frame, the skylight may be suspended in the roof opening. In that situation, only a thin waterproof membrane separates the indoor and outdoor layers. This does not provide effective support or sufficient thermal and acoustic insulation, and it may create hidden risks of water penetration and long-term material aging.

Standard construction rule:  Make the roof opening 2 cm smaller overall than the outside dimension of the skylight frame. This leaves a 1 cm supporting edge on all four sides, allowing the opening to fully support the frame and improving overall stability and tightness.

During cutting, workers must also account for the thickness of the cutting blade. This helps control dimensional errors and keeps the reserved supporting edges accurate.

2. Clean the Roof Base Surface

Before construction begins, completely remove the original roof finishing layer and any old waterproofing material around the opening.

A clean, flat base is essential for pouring the new concrete curb. It improves the bonding strength between the new concrete and the existing sloped roof and helps prevent hollow areas, cracking, and water seepage caused by poor bonding.

3. Build the Reinforced Concrete Curb

The concrete curb is the load-bearing foundation of the skylight system. It plays a key role in structural stability and long-term waterproofing.

The curb width can be adjusted according to site conditions. A 10 cm width is a practical standard size. The curb height should match the height of the roof tile batten so that the roof tiles can overlap correctly and press the drainage board, allowing water to flow smoothly.

Mandatory rebar anchoring:  Rebar implantation is necessary to help prevent concrete cracking. Before inserting the steel bars, clean and blow out all drilled holes to remove dust and debris. Clean holes provide better bonding between the rebar and concrete.

Pouring concrete on a sloped roof is difficult because fresh mortar naturally tends to slide downward. The standardized method is to start from the lower frame of the opening, install the formwork layer by layer, and pour the concrete gradually.

Continuously tap the formwork during pouring to improve compaction and reduce internal voids. The ordinary floor-concrete ratio of cement:sand:stone = 1:4:4 is not suitable for sloped roof construction. On sloped surfaces, the aggregate ratio should be reduced and small-size crushed stone should be used to help prevent mortar sliding and achieve a dense concrete curb.

4. Install and Secure the Skylight Frame

A skylight made from an aluminum alloy frame and double-layer laminated glass can be heavy. Installation should therefore be completed by 2–3 professional workers. This reduces the risk of frame collision, glass damage, and paint scratches caused by single-person handling.

Place the skylight frame flat and level with the finished concrete curb surface.

For each angle-iron fixing bracket, install at least two 304 stainless steel expansion bolts to provide stable load-bearing support. After fixing, cut and polish any protruding bolt ends so the installation surface remains flat and tidy for the next waterproofing stage.

5. Apply Multi-Layer Sealing & Waterproofing

The joint between the skylight frame and the roof structure is a common area for water leakage. A multi-layer waterproofing system is therefore a key part of reliable skylight installation.

Step 1 — Fill the gaps
Fill all gaps around the skylight frame with cement mortar. Allow the mortar to harden and cure completely.

Step 2 — Apply water-stop mortar
Apply two full coats of water-stop mortar to block fine pores inside the mortar layer.

Step 3 — Apply waterproof coating
Apply two cross-direction coats of weather-resistant outdoor waterproof coating. Exposed asphalt waterproof material is recommended. The second coat should be applied perpendicular to the first to form a continuous protective film.

Step 4 — Reinforce joints
Reinforce all structural joints with polyester waterproof fabric to improve crack resistance and tensile performance.

Step 5 — Install the waterproof membrane
After all coating layers are fully dry, install the waterproof membrane. Use a professional heating spray gun for hot-melt construction. Pre-position the membrane first, then complete the hot-melt bonding. Compact all edge flashing with a scraper.

6. Install the Drainage Board

Install the matching drainage boards using the same bottom-to-top construction principle.

The left and right side boards should overlap the bottom board, while the top board should cover the upper edges of the side boards. This staggered overlap creates a continuous drainage path, helps discharge rainwater quickly, and reduces the risk of water accumulation and infiltration around the skylight.

7. Restore the Roof Tiles & Complete the Finish

Reinstall and secure all original roof tile battens to restore the overall roof structure.

Keep a standard 5 cm drainage gap between the roof tiles and the skylight frame. This gap helps maintain smooth rainwater drainage.

Finally, inspect all joints and gaps on site. Add water-stop mortar and waterproof coating where potential seepage points are found, completing the overall closed waterproof system.

Conclusion: Build for Long-Term Performance

A durable and reliable sloped roof skylight system depends on more than simple glue sealing. It requires proper structural support, a reinforced concrete foundation, a scientific multi-layer waterproofing system, and correct drainage overlap.

Following this complete installation process can help reduce common problems such as water leakage, poor insulation, structural loosening, and premature aging, while maximizing the service life and overall performance of aluminum alloy skylights.

Installation Checklist

• Roof opening is correctly sized and provides a 1 cm support edge on all four sides.
• Roof base is clean, flat, and free from old finishing and waterproofing materials.
• Reinforced concrete curb is properly anchored and fully compacted.
• Skylight frame is level and securely fixed with 304 stainless steel expansion bolts.
• Waterproofing is completed in multiple layers.
• Waterproof membranes are overlapped from bottom to top.
• Drainage boards are installed with correct overlapping direction.
• A 5 cm drainage gap is maintained between roof tiles and the skylight frame.
• All joints and possible seepage points are inspected and reinforced.