DIY: Polycarbonate Roofing Projects

Whether you are building a car port, pergola or patio, the MODEK range of products is guaranteed to reward your choice of polycarbonate sheeting. 

Polycarbonate Roof Sheeting comes inso many options, in various colours and profiles, that the MODEK range of products has something for everyone. Choosing the right MODEK product and installing it correctly is vital to the success of your DIY project 

We have provided a guide below to assist you in choosing the right options:

Understanding Technical Terms
Cover Width

Roof Sheet Cover Width

Cover width is defined as the measurement across the sheet using the middle of each of the outer crowns and taking the distance between these two points. This will vary in some instances depending on product choice. (see Product Specification table below for details).

It is important to get correct cover width when calculating the amount of sheets required for any project.

Crown & Valley

The crown by description is the highest point of the roofsheet profile. The valley or trough is the bottom or lowest area between crowns on the roofsheet. Distances between crowns and heights between crowns and valleys will vary depending on the product choice. (see Product Specification table for details).Crown & Valley


Purlin Spacing

Purlin spacing is the distance measured between purlins from centre to centre. This will vary in some instances depending on product choice.

Purlin Spacing

Shading Coefficient

This is referred to as an indicator to how the roofsheet is thermally insulating (shading) the interior when there is direct sunlight on the roofsheet.

Shading coefficient is usually a value ranging from 1.00 to 0.00, where 1.00 offers the least amount of shade and 0.00 the most. This unit of measurement is particularily important for areas that will receive a high degree of sunlight that require light but not necessarily heat.

Light Transmission percentages will help you determine the amount of light desired vs amount of shade achieved from each particular colour in our roof sheet range.

Make the right selection

Selecting the correct sheet is important. Take time to examine the weather conditions vs. the desired end result before making a final decision on which product, profile and colour you are about to purchase and install. If you are unsure seek the advice of a professional, or visit for assistance.

Available Colours & Profiles

Measuring Up

Once you have selected your roof sheet profile & colour refer to the Product Specification table for the correct cover width. This is important as it will help determine how many roof sheet you will need for your project.

Measuring Up

Installation of Roof Sheets

Mark the crowns to be fastened. You will fasten every crown at both ends of the sheet, and alternative crowns on intermediate purlins.

If there are ends laps (overlapping sheets generally required when covering large areas), these will be fixed at every crown. (Note: Do not fasten through the valley of the profile).

Pre-drill the sheet at these points, allowing for a 1 mm – 2 mm clearance on GRP (Fibreglass) a 2 mm – 6 mm oversized on Polycarbonate to accommodate expansion and contraction.

Use a duck board (Piece of flat timber- to straddle purlin to purlin) on the roof to distribute your weight evenly when working.

Fix the started sheet down, leaving the side laps and end laps, (if using more than one sheet in length) to be fixed when the next sheet is in place. (Not: end overlaps should not be less than 300 mm)

Fasten the fixings, ensuring that the roof screw is not overtightend. The crown will now be held slightly in tension.

If waterproofing is a necessity, we advise to seal end laps on roof sheets which have a pitch of less than 20 degrees. Use a compatible sealant for Fibreglass and Polycarbonate roof sheets, only Sealing strips and neutral Silicone sealants are suitable.

Handling and Transport
  • Please tie your sheets down well when transporting on a rack or trailer. Ensure that the fronts of the sheets are well secured, as wind can lift the sheets and cause damage.
  • It is advisable to use lengths of timber (Your purlins) on top of the sheets when tying down for transportation.
  • This can also prevent sheets lifting and bending in the wind. It is common practice to roll sheets into tight bundles.(Polycarbonate only)
  • When loading and unloading be extra careful in windy conditions. A gust of wind can easily lift a sheet out of your hands or blow a sheet way, it left unsecured.
  • Edges of sheets are sharp and it is advisable to wear gloves to avoid possible cuts and grazes whilst handling sheets.
  • Avoid standing, or a walking on sheets; they are not designed to carry the weight of a person and could be damaged.
  • If you have long lengths (longer than 3,600m), support the sheets in the middle when carrying to avoid kinking.
  • If you need to store your sheets, pack them on pallets (off the ground), under cover, and avoid stacking higher than 700mm.
  • Polycarbonate sheets are not scratch resistant and extra care should be taken when handling.

Cleaning Polycarbonate Sheeting

Sheets may be washed using a mild soap solution with a soft cloth. Do not use abrasive cleaners such as thinners and acetone.