Tools and Materials

Tools

Materials

Note

Product costs, availability and item numbers may vary online or by market.

How to Install Roofing Underlayment for a Shingle Roof

Here are general instructions for applying roofing underlayment for a shingle roof that you can use for planning purposes. Your project may vary greatly depending on the shape and slope of your roof, the type of products used and a variety of other factors. Always defer to the manufacturer’s instructions and local building codes for any roofing project.

Caution

Installing a new roof can be dangerous work. Make sure you’re familiar with the necessary safety protocols. If you’re inexperienced with major home renovations or you’re not comfortable working on tall ladders or from heights, contact a professional. Always wear proper work clothes and protective gear, and use fall protection.

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Instructions

Attach the drip edge flashing to the roof eaves. To attach the flashing to roof corners, cut the material at an angle then press it against the end of the eave. Snap a chalk line to use as a guide to ensure the flashing is straight before securing it to the plywood with roofing nails. Most professionals recommend leaving approximately one foot of space between each fastener, but check local building codes for additional guidance.

As you work, overlap the drip edge flashing by two inches or more to ensure a tight seam. When applying flashing to a hip or valley, cut it to create tabs. Then press the tabs neatly into the corners and secure with roofing nails.

Good to Know

The manufacturer of the roofing underlayment you choose may recommend installing it prior to the drip edge or even underneath the drip edge. Check the product instructions for details.

Using the chalk lines for guidance, either roll out or lay down sheets of underlayment, depending on which type of product you use. Be sure to smooth it out as you work to make sure it doesn’t trap air bubbles or wrinkle. If the roof has a very steep slope. It might be helpful to apply the bottom portion of each piece of underlayment first, then smooth the material upwards. This technique is especially helpful when working with a product that has a peel-off backing.

If your underlayment requires capped roofing nails, drive them according to the manufacturer’s recommended spacing. Some underlayment material may have dots or other markings printed on the surface to let you know exactly where to drive fasteners, which makes the work a lot quicker.

The manufacturer will also provide guidance for installing the underlayment product around chimneys, vents and corners. This may involve cutting the material to create tabs or layering the product a specific way to better fit around nonstandard shapes.

Good to Know

It may be recommended to install an ice and water shield underneath the roof underlayment material. Consult the manufacturer’s guidance and local building codes for details.

How to Install Underlayment for a Metal Roof

Installing a roof underlayment system is just as important when installing a metal roof as with a shingle roof. In many cases, you can simply follow the same general steps outlined above and use the same tools and materials. However, some types of metal roofing may require a special type of underlayment or an additional layer to be installed on top of the underlayment, such as a mesh layer. The roofing manufacturer may have specific guidance regarding whether the underlayment should be installed underneath the drip edge or over the top of it to ensure proper waterproofing. Also, pay attention to the manufacturer’s recommendations for applying the material around corners, seams and chimneys.

How to Install Roofing Underlayment