Installation guide for multiwall polycarbonate sheets – a practical guide

A patio roof made of transparent multiwall polycarbonate sheets mounted on a wooden or metal structure is one of the most frequently chosen solutions in modern construction. This material is valued for its low weight, high durability, good thermal insulation properties, and very good light transmission. However, for the roof to remain durable, watertight, and aesthetically pleasing for many years, proper installation is essential. Below you will find a complete, step-by-step guide to installing multiwall polycarbonate sheets.

1. Preparing for the installation of polycarbonate sheets

The preparation stage has a direct impact on the durability of the entire structure and the comfort of later use.

Sheet dimensions and structural planning

Multiwall polycarbonate sheets are most commonly available in widths of 2.10 m and 1.05 m. With proper planning of the rafter spacing, these sheets can be efficiently joined without excessive material waste. A standard and proven solution is a rafter spacing of approximately 70 cm – this provides adequate support and stability for the sheets.

Rafter spacing and sheet thickness selection

With a rafter spacing of around 70 cm, 10 mm thick sheets work well. If the structure has larger spans (over 1 m), it is recommended to use counter battens or choose thicker material, such as multiwall sheets 16 mm or thicker. In such applications, multiwall polycarbonate for patio roofing works particularly well, combining lightness with sufficient rigidity.

Storing sheets before installation

Sheets should be stored on a flat surface and covered with a light, opaque material. Ideally, they should be kept in a dry place, away from direct sunlight, wind, and moisture. Improper storage may lead to deformation or damage to the protective film.

UV protection and sheet orientation

Each sheet has a protective film with markings indicating which side is protected against UV radiation. During installation, it is essential to ensure that the UV-protected side is facing outward.

Cutting the sheets

To cut the sheets, use a circular saw with fine teeth or a hand saw, cutting at a slight angle. The sheet should be supported as close to the cutting line as possible to reduce vibration. After cutting, thoroughly remove dust and chips (preferably with compressed air), and secure the open chambers with vapor-permeable tape.

2. Sealing multiwall polycarbonate sheets

Proper sealing of the joint between the sheet and the supporting structure protects against moisture, noise, and excessive material movement.

You can choose from several solutions:

• SD-12 rubber gasket,
• PE foam tape,
• EPDM tape.

The selected gasket should be attached directly to the rafters before laying the sheets. It separates the polycarbonate from wood or metal, compensates for temperature differences, and improves tightness. Only after this step should the actual installation of the sheets begin.

3. Installing polycarbonate sheets – step by step

3.1. Roof slope

Every roof should be designed with an appropriate slope to allow proper water runoff and to reduce the accumulation of dirt. The minimum recommended slope is 5%, although in practice better results are achieved with a slope of 10% or more.

3.2. Fixing the sheets to the structure

When installing the sheets, the thermal expansion of polycarbonate must be taken into account.

• Mounting holes: drill holes with a diameter approximately 2 mm larger than the screw diameter. This provides expansion clearance and prevents cracking. Holes should be drilled at least 40 mm from the sheet edge.
• Screws: use self-drilling roofing screws about 55 mm long, which ensure stable fastening without damaging the sheet.

3.3. Mushroom washers

In areas where the sheets are not joined with profiles, they can be fixed directly to the structure using mushroom washers. These ensure even pressure distribution and protect the material from cracking.

3.4. Fixing with aluminum profiles

An alternative solution is installation using top aluminum profiles. These profiles not only join sheets at their joints but can also be installed along the entire length of the sheet. They increase the rigidity of the structure and provide an aesthetic finish to the roof.

4. Joining polycarbonate sheets

The method of joining depends on the rafter spacing and the structural layout.

• Aluminum profiles: if the joint falls on a rafter, a top profile with gaskets is sufficient. For narrower rafters or transverse installation, it is recommended to use a complete system (top profile + bottom profile + gaskets).
• Plastic H-profiles: a simple and economical solution that ensures proper sheet connection and a neat appearance.

5. Closing the chambers of polycarbonate sheets

The chambers in multiwall sheets must be properly protected against moisture, dust, and insects.

• Chambers should always be positioned vertically, in line with the roof slope.
• Top edge of the sheet: secure with solid (closing) tape.
• Bottom edge of the sheet: use perforated tape to allow condensation to drain.
• Apply closing profiles over the tapes – aluminum F-profiles or plastic U-profiles – to protect the edges and improve aesthetics.

6. Maintenance rules for polycarbonate sheets

Regular maintenance significantly extends the service life of the roof.

• Wash the sheets with lukewarm water and mild detergents.
• Avoid dry cleaning – sand particles may scratch the surface.
• Do not use aggressive chemicals or solvents.
• Periodically check the condition of gaskets, profiles, and fixing points.

7. Most common installation mistakes – how to avoid them?

No expansion clearance

Polycarbonate expands with temperature changes. Allow approximately 3.5 mm of clearance for each meter of sheet length.

Insufficient slope

Too little slope leads to water and dirt accumulation. The minimum recommended slope is 5%.

Incorrect tapes and gaskets

Using random materials results in leaks and faster sheet wear.

Incorrect UV side orientation

Always install sheets with the UV-protected side facing outward – only then are they properly protected from sunlight.

Summary

Installing multiwall polycarbonate sheets requires precision, proper preparation of the structure, and the use of appropriate accessories. Correct rafter spacing, maintaining expansion gaps, proper sealing, and securing the chambers are the key factors determining the durability of the entire roof. Whether the project is based on systems made of multiwall polycarbonate or supplemented with elements of solid polycarbonate, it is worth choosing proven solutions and, when carrying out your investment, buying polycarbonate from us to immediately select the right material and parameters for your structure.