Let’s strip away the needs of that sleek, beautiful roof
Some metal roofs require metal stripping to work efficiently.
Use the manufacturer's specifications as your guide.
Lack of wood stripping can cause condensation issues.
Specific batten techniques can increase ventilation in attics with metal roofs.
Wood battens can create problems with gutters, skylights, and chimneys.
If you are updating your home with a sleek metal roof, you may wonder, “Can you put a metal roof over shingles?” The best method to install a new roof is to remove the existing roof first, but in some cases you may need or want to install a metal roof over shingles without removing them first. Doing so can potentially reduce roof replacement costs, as well as spare you from having to deal with waste from the old roofing material.
If you do decide to install a metal roof over shingles, you should add wood stripping under the new roof. It is not recommended to install a metal roof over shingles without these strips, as condensation can build up between the roofing materials, causing moisture problems that may lead to mold, mildew, and structural damage.
Here is what to know when it comes to adding wood stripping under your metal roof.
Adding wood stripping to the existing shingles before you install metal roofing provides a place to attach the metal roofing. These strips also create space between the original roofing and the new roof. This allows more air to circulate, which can reduce the amount of condensation that forms. While it is not always recommended to install a metal roof over shingles, if you do go this route, installing wood stripping can help maintain the health of your roof.
Wood stripping on a metal roof is also referred to as battens, furring strips, or wood strapping. Typically, these narrow pieces of lumber run parallel to the eaves of the house, though they can also run perpendicular, following the slope of the roof to create a grid pattern. When you install a metal roof over shingles, furring strips act as purlins, providing a place to screw the metal roofing to. These battens also allow for the inclusion of insulation between the original shingles and the new metal roof.
It is important to understand the importance of wood stripping and how it functions. Wood stripping can bolster your new metal roof's performance in a number of ways. Mainly, it creates a thermal break that minimizes the transfer of heat from your new metal roofing material to the roof deck.
Wood stripping is especially beneficial in homes with poor attic insulation and ventilation. It is possible that you experienced poor ventilation with your asphalt roof without any condensation issues; however, the temperature changes that occur with the installation of a metal roof will remove that protection if it is installed directly on the shingles. That means that you could end up with a serious condensation issue that leads to moisture and mold problems if you are not using wood stripping with your new metal roof.
One of the pros of metal roofing is that, in some cases, you can install it directly over the existing shingles. If you are installing a metal roof over shingles, you should add furring strips at regular intervals. This gives you something to screw the metal roofing into, as well as provides space between the roofing materials to allow for air circulation. The furring strips should be added after the underlayment has been installed.
Before deciding whether or not to add wood stripping to your roof, it is important to talk with a local metal roofer about the best installation methods. If adding wood stripping is the way to go, here is a general overview of how to do it:
Assess the structure to determine if it can hold the additional weight of the underlayment, wood stripping, and new metal roof.
Determine if you will be installing stripping horizontally or vertically, or installing them both ways to form a grid.
Beginning at the bottom of the roof near the eaves, install the first row of wood stripping.
Install every 24 inches until you reach the peak.
If you are installing insulation along with the new roof, install it after all of the wood stripping is in place.
Make sure to cut metal roofing correctly so it overlaps the stripping in the right place.
Install the metal roof over the stripping using screws recommended by the manufacturer.
The answer to whether or not you need to install wood stripping under your roof comes down to the roof style you choose. Some metal roofs actually need to be installed over wood strips. This is common when you are using metal roofs with "tile" or "shake" aesthetics. Other styles should never be installed over wood stripping, though some are flexible enough to work with both strips and solid decking.
How do you know if your new metal roof requires wood stripping? This is where doing research is important. Follow the manufacturer's guidelines regarding installation requirements and recommendations.
If you are putting a new metal roof over old shingles or decking, consider an underlayment. Underlayments can be used with or without wood stripping using various installation techniques.
Installation techniques can impact your new roof's performance. One option for installing a metal roof over shingles without wood stripping is to use a cross-batten style. A cross-batten technique involves laying down vertical battens (or strips) first. Next, the battens attach through the roof deck to your rafters. Finally, your horizontal battens are placed.
The benefit of this technique is that the vertical chambers allow for better ventilation. While fresh air is drawn in from the bottom, the air is easily exhausted out the top. This can be extremely beneficial for getting heat out of your attic. It also achieves the reverse in the winter by preventing ice dams that can damage your roof's structure.
Yes, there are some potential downsides to a cross-battening technique. Your roof level will be raised significantly. This means that you may need to hang your gutters again if you are replacing an existing roof versus building a new home. It will also create a gap between the existing fascia and the roof material; you will either need to replace all the fascia, or use a wider drip edge on the roof to cover the gap. In addition, homes with skylights, dormers, or chimneys could encounter cross-battening issues. Getting advice from a local roofer is essential when you do not know if your new metal roof requires wood stripping.
It is not a good idea to install metal roofing over shingles without furring strips. Doing so could leave you with reduced insulation, noise reduction, and protection from the elements. While some homeowners do choose to forego furring strips when installing a metal roof to save on costs, it is not something that roofers typically recommend. Shingles by themselves, without furring strips, just do not offer as much insulation.
Roofers often install an underlayment under a metal roof to offer added protection. A common type of underlayment for metal roofs is made of either tar or asphalt felt, which is a more budget-friendly option. A metal roof underlayment made of woven polymers costs a bit more, but offers more durability and a longer lifespan.
