Roofing Sheets Guide

There are a wide variety of roofing sheets that can be used for a garage or outbuilding. Generally, these sheets are corrugated as this improves the strength and durability, without increasing the weight. It also allows water to run off easily, providing that there is sufficient angle of inclination.

The main types of roofing sheet are:

  • Corrugated Bitumen Sheets
  • PVC Corrugated Sheets
  • GRP Polyester Corrugated Sheets
  • Polycarbonate Corrugated Sheets
  • Fibre Cement Roof Sheets
  • Corrugated Metal Sheets

Which type of sheet should I use?

The factors that determine what type of sheet you should use for a particular product include:

  • Price
  • Longevity
  • Weather resistance
  • Correct 'wavelength' for the application (see Figure: 1)
  • Aesthetic reasons
Figure 1

What are the key features of each type of roofing sheet?

Corrugated Bitumen Sheets

Corrugated Bitumen Sheets
  • Affordable
  • Can last for many years if properly installed
  • Watertight if installed with a small pitch
  • Lightweight but hard wearing
  • Dark colours can provide a heat sink
  • Easy to cut and shape
  • Available in a wide range of colours

Corrugated PVC Sheets

Corrugated PVC Sheets
  • Low price compared to other plastic sheets
  • Good transparency
  • Weatherproof
  • Lightweight and relatively easy to cut
  • Available in other colours (including bronze)

GRP Polyester Corrugated Sheets

GRP Polyester Corrugated Sheets
  • Mid-price (for plastic sheeting)
  • Translucent
  • Heavy duty
  • Good impact resistance
  • Excellent strength and durability
  • Less prone to flexing with 'wind uplift'

Polycarbonate Corrugated Sheets

Polycarbonate Corrugated Sheets
  • Highest visual clarity
  • Extremely tough
  • High impact resistance
  • Very high UV protection
  • Good fire rating

Fibre Cement Roof Sheets

  • Cost effective solution
  • Excellent noise and thermal insulation
  • Rot and corrosion resistant
  • Naturally breathable, improving ventilation
  • Highly absorbent, minimising condensation

Metal Sheets

  • Most hard wearing
  • Best resistance to high temperatures
  • Corrugated galvanised sheets have a long track record
  • Can be coated in different finishes to improve appearance & functionality

Installing Roofing Sheets

It is important to check the instructions that are provided by individual manufacturers for installing their roofing sheets. This is particularly relevant if a guarantee is offered, as it is generally mandatory to have followed the manufacturers' instructions correctly if you are planning to make a claim.

Step 1 - If possible, cut and prepare the sheets before starting the installation. This includes pre-drilling any holes that are required for fixing to purlins or the decking beneath.

Step 2 - Start laying the first sheet at the opposite end of the roof to the prevailing wind. Ensure that the eaves and verge are overlapped to prevent unnecessary exposure to the weather.

Step 3 - Ensure that you use 'capped' screws or nails to prevent water ingress and, where possible, fix through the 'crown' rather than the 'trough' of the corrugation (Figure 2).

Step 4 - Avoid the necessity for vertical cuts by overlapping roof sheets by more than two corrugations to match the dimensions of the roof exactly (Figure 3).

Step 5 - Use a foam eaves filler of the same profile as the sheet to prevent ingress by weather and insects. Ideally this should be sealed in place with a silicone sealant bead.

Step 6 - When applying ridges (with corrugated bitumen, for example), ensure that you start at the opposite end of the roof to the prevailing wind direction. Overlap the ridges and fix every two corrugations.

Figure 2
Figure 3