How to add roof onto wooden pergola?

kaushikmistry

Hello Community,

I am in need of help, to find out how I can put either a colour bond/trimdeck or corrugated  clear roof onto the pergola as per picture. 

I need to know what to do to create a fall for water run off , I understand it's should be 5 % fall.

The Dimensions are 2400mm x 3200.

Any advice would be very much appreciated.

MitchellMc

Hi @kaushikmistry,

Before getting started on your project, it’s really important to reach out to the manufacturer of your pergola to confirm whether the structure is designed to support a roof. Most prefabricated pergolas are engineered and tested to meet specific safety standards, including wind loads, based on their original open-roof design. Once you add a solid roof—whether it’s Colorbond, Trimdek, or clear corrugated sheeting—you’re significantly changing the way the structure behaves under load, which could compromise its safety or even void warranties.

You’ll also want to check with your local council, as approvals may be required for roofing additions to existing structures. If that’s the case, the council will likely ask for an engineering assessment of the pergola with your proposed changes, and the engineer would need to sign off before the project can proceed.

Assuming your pergola is suitable and approvals are in place, to create the required fall (a 5% gradient equates to about 5cm per metre), you’ll need to install roof rafters or battens at differing heights across the structure. One approach is to cut birdsmouth joints into the rafters—this allows the timbers to rest securely on the top plates of the pergola frame while stepping them down gradually to achieve your fall. For a span of 3200mm, you’d need around 160mm of total fall from high point to low point.

Given the structural nature of the proposed alterations, I would suggest reaching out to a builder or carpenter for their assistance.

Please let me know if you have any questions.

Mitchell