How to Install Metal Roofing over Plywood


How to Install Metal Roofing over Plywood

How to Install Metal Roofing over Plywood

February 2021

By adminconstrux

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When it comes to roofing, a sturdy substructure is vital to offer the support that the roof needs. This is important, especially when you choose to upgrade to metal roof in your home, by installing it on top of the old roof structure. A good substructure provides the necessary structural support system. It also serves as the base for attaching the roof’s fasteners. A proper substructure is going to support the weight of the building adequately and keep your roof rigid and sound. If you need to install a metal roof over plywood, you need to ensure the underlying structure is secured.

Plywood boards are large boards attached to the purlins and rafters of your roof. They serve as a support to the building structure. They are also barriers between the lower part of the substructure and the roof and are materials that you bond your underlayment to. Using the right plywood for the job is as important as the metal roofing itself. It is recommended that plywood that is at least 15/32 inches thick be used. The span rating should also match your other plywood boards. This span rating is important if you are carrying out replacement or repairs. Also, you should ensure that the plywood is clean and free of dirt and dust.

Installing Metal Roofing over Plywood

As time goes on, the roofing material of your home will become old and break down. This is not a favorable condition, and so, you may need to replace the roof. You should know how to install metal roofs over plywood. Proper installation will offer adequate outdoor elemental protection even in harsh weather conditions. In planning for installation, following these tips will make your work easier.

1. Inspect the condition of the old plywood

Inspect the condition of the old plywood

You should properly inspect the condition of your aged roof’s plywood before you start any work. While trying to install metal roofing over plywood, you will have to also check whether to replace roof sheathing (roof sheathing is produced from wood, an organic material). This is because you will have to tear off the sheathing first. With a proper guide, you will have little or no problem tearing the sheathing off your roof. It is also important that you check if the existing sheathing is safe to walk on. If it is not, you will need to get a scaffolding built around the edges of the roof. Then start by replacing the panels on the lower levels of the roof that have been torn off before pulling off the next higher row of panels.

2. All unused roofing structures should be removed

When the roof of your home was built, it was done together with structures such as vents, chimneys, and skylights. Regrettably, all these have to be removed before installing the metal roof over plywood. You will need the right and proper tools to pull them out without breaking them apart.

3. Clean your working area properly

You will need to replace the old roofing material or sections of the rotten plywood after you have removed them. Installing plywood before your metal roofing panels is an easy and straightforward process if you follow the appropriate guide. As soon as that is done, make sure that your working area is cleaned. You reduce the likelihood of the materials corroding when you do so. Also, you get to make measurements that are more accurate upon installing your roof.

4. Install the felt underlayment properly

Install the felt underlayment properly

To ensure that the new plywood installed is not drenched by any gaps or leaks caused by your metal roof panels, you should properly install the felt underlayment. An error can occur when you try to install the felt underlayment properly. For example, screw gaskets may become loosened, and this may lead to leaks. This problem can also happen over time. So, knowing how to properly lay the felt underlayment is an important part of installation of metal roof over a plywood roof. To lay the felt underlayment properly, you can follow the following steps:

1. Apply the roofing felt in the layers that overlap. 2. You should start work from the bottom of the roofline. This is to ensure that any water that gets through the material is shed down the tar paper and goes under it. 3. To ensure that the paper does not get blown away as you work, tack it to the center. 4. Adjust the paper with the chalk line as you arrive at the rake. Staple the paper every 3 to 4 inches across. 5. At the end of a roll and the beginning of a new one, overlap two rolls by 4 inches. 6. Let there be a 6-inch overlap for ridges, hips, and valleys.

5. Use the proper tools

It is very important to use proper roofing tools such as hammers, measuring tapes, metal snips, and right-sized nails.

6. Use chalks

Chalk is an important tool you will need for installing your roofing. They can be used to put a mark on areas that are meant for panel installations. You can also use them to indicate areas where the screws, nails, and other vital accessories will stay.

7. Take note of the overlaps

Ensure that your metal roof panels overlap the previous one by 12 inches as you do the installation. You reduce the possibility of leaks in doing so. Also, screws are easily and effectively fastened to the roof when this is done.


In many instances, installing a metal roof over plywood can be challenging. Areas in the roof that are already rotted or sagging should be replaced before installing metal panels. Doing this will help you avoid costly repairs in the future. Do ensure that roof’s plywood panels are sturdy enough and capable of withstanding the metal panels’ additional weight. To provide a consistent deck structure for the metal, thoroughly clean the plywood. Also make sure that there no raised or jutting nail heads. For added protection against moisture, you should install waterproof felt over the plywood. It is a good choice to choose metal roofs; they are energy efficient, and they come in a variety of colors that will give your home added value.

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