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Can You Put Metal Roof Over OSB? (How To)

Metal roofing looks great, and is easier to work with and install compared to some of the other options. OSB is a cheap material to use for a range of different purposes and is also more durable than plywood. In this article, I will explain if it’s possible to put metal roofing over OSB.

You can put metal roofing over OSB. OSB is commonly used as sheathing by professional roofers for roofs. Sheathing is the flat surface where you attach metal roof panels too. Before installing the metal roof it’s necessary to install an underlayment, this waterproofs the roof.

Metal roof top

Installing metal roofing over OSB is not super difficult, however, it’s important to ensure a few critical steps are done to ensure it’s waterproof, is building compliant, and lasts as long as it should. Below, I will cover everything you need to know about putting metal roofing over OSB.

Should You Put Metal Roof Over OSB?

Metal roof top

There are various materials that could technically be used under a metal roof. But, only some are recommended, and will work well. Here is if you should install metal roof panels over OSB, and if there is a better option.

As a general rule, you should put a metal roof over OSB. OSB is used by professional roofers as sheathing. Sheathing is a flat surface you attach to the framing for a roof, and provides a place to attach underlayment and the roof panels.

There are two types of materials that should be used as sheathing, these are OSB and plywood. OSB is preferred over plywood because it’s lighter, and is cheaper. This makes it easier to install, and in the end saves on the costs of materials and labor.

What Tools Do You Need to Put Metal Roof Over OSB

Metal roof top

All of the tools required to put metal roofing over OSB are commonly used in construction and are typically easy to source. Chances are, you may already have a lot of these, here are the tools you need to put metal roofing over OSB.

A power drill, hammer stapler (optional) or hammer, utility knife, metal shears or metal cutting blade on a circular saw, straight edge, pencil, chalk line, caulk gun, and sharp metal chisel are required to put a metal roof over OSB.

Below is a table that shows what each tool is used for. For some of the tasks required to install a metal roof over OSB a few different tools can be used. Also, some are optional.

Tool

What it’s used for

Power drill

To attach the metal roofing to the OSB

Hammer stapler or

Hammer

Nailing staples into the underlayment to attach it to the OSB

Utility knife

Cutting the underlayment and various other materials like the venting foam

Metal shears or

Metal cutting blade on a circular saw

Cutting the metal panels

Straight edge, pencil, chalk line (optional)

Marking out where to attach screws that go into the metal panels and attach it to the OSB

Caulk gun

For applying sealant around fixtures on the roof such as vent pipes

Sharp metal chisel

Making a hole for the metal shears to fit in to make interior cuts to the metal panels for fixtures on the roof such as vent pipes

What Preparations Do You Need to Put Metal Roof Over OSB

Metal roof top

Before installing metal roofing over OSB there are some preparation steps that are required. Doing these will ensure your roof is structurally sound, as well as waterproof. Below, is what preparation steps are required before putting metal roofing over OSB.

In general, you first need to install a drip edge (optional), then underlayment needs to be installed. If the OSB has not yet been installed, ideally the textured side should be facing up. The wooden framing, rafters and upper trussboard should also be checked to ensure they are in proper alignment.

Before installing metal roofing over OSB it’s best to check your local building codes to ensure your roof will be building compliant. Exactly how to do this is explained at the end of this article where there are step by step instructions for installing a metal roof over OSB.

How to Put Metal Roof Over OSB

confused man standing

The overall process to put a metal roof over OSB is fairly straightforward. In total there are 6 steps. Below are the instructions for how to do it, as well as some videos that show the entire process from start to finish.

First ensure the OSB is installed according to the relevant building codes and that you are aware of the relevant building codes for your jurisdiction. Then, install the drip edge (optional), the underlayment, the metal roof panels, the gable trim, and the pipe flashing, also called a boot.

Below are each of these steps in detail. As well as videos to show the entire process from start to finish.

1. Ensure the OSB is installed according to the relevant building codes

Every jurisdiction has a building codes office who you can contact. Typically over both phone and email. They can advise you of how the OSB needs to be installed, and what needs to be put over the OSB before the metal roof panels are installed.

The easiest way to find the office to contact is to do a Google search for ‘building codes office’ and the State that you are installing the roof in. For example, ‘building codes office Texas’. If you have yet to install the OSB over the roof framing, refer to the video below that shows how it’s done.

If the OSB has already been installed, then you should double check it’s up to the building codes.

2. Install the drip edge

The drip edge is optional. It’s a finishing that is installed along the outer edge of a metal roof. It helps control the flow of water when it reaches the edge of a roof, and helps prevent water from getting onto the waterproof underlayment.

3. Install the underlayment

The underlayment is rolled out and attached to the framing using staples. These are attached with a hammer, or staple hammer. How many staples you use depends on your jurisdiction but the video above gives an overall guideline for how many to use.

4. Install the metal roof panels

You’re now ready to install the metal roof panels. It’s best to start at one corner of your metal roof. Then install one more metal roof panel. These two are then used as a guide for where to put each additional roof panel.

These are attached using waterproof screws as shown in the video in step number 2. It’s common for there to be pipes and/or vents located on the roof. A piece of one or more of the metal roof panels will need to be cut out so that the metal roof panels fit around any vents.

Copyright protected content owner: ReadyToDIY.com and was initially posted on January 22, 2023.

Then pipe flashings, also called a boots, are then installed to make the areas around any vents waterproof. The boots can either be done as you go. Or at the end after you have installed the gable trim. Generally, it’s easiest to do it at the end, and the instructions for how to do that are in the final step – step 6.

5. Install the gable trim

The gable trim is a narrow piece of metal that finishes the roof, and is installed at the highest points on a roof. Similar to the metal roof panels, these are screwed into the wooden framing underneath. This is also shown in the video in step number 2.

6. Install any pipe flashings (also called boots) if required

It’s common for there to be vents located on the roof. These can be a toilet vent, or an exhaust fan for an HVAC/air conditioning system. As you install each piece of metal roofing you will need to cut out a piece of the metal roof panel so that it fits around these vents, prior to screwing the metal roof panel into place.

Exactly how this is done depends on where the vents are located in relation to a roof panel. You may need to do an interior cut, or cut a piece out of the side of two roof panels that join where a vent is. To make an interior cut a hole needs to be made in the metal panel so that a pair of metal shears can be poked into it and be used to cut it.

This can be done using a drill or a sharp chisel. After that the metal roof panels are secured in the same way as the other roof panels. Then a boot is put over the top of the vent.

Copyright article owner is ReadyToDiy.com for this article. This post was first published on January 22, 2023.

There are different sized boots. Some are universal and will fit a range of different vent sizes – such as 1 inch to 6 inch vents. Whereas, others are an exact size.

Apply a layer of silicone sealant on the underside of the boot, and then you slide it down over the vent and press it firmly to the roof panel. After that screw it in place.

Repeat this step for all of the vents on your roof. A video that shows how to do this can be found in step 2 above.

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ReadyToDIY is the owner of this article. This post was published on January 22, 2023.

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