Once upon a remodeling project, a friend and colleague asked me to come over to help with a “small emergency.” As I walked into the newly remodeled garage living area, I looked up to find water dripping down the walls. While bolting down railings onto the rooftop patio, my friend was assured that he didn’t have to worry about puncturing any important membranes, but it turned out not to be the case. With a deadline in a few days and money on the line, I offered my help installing side mounted railings while my friend took the time to patch the holes he’d accidentally created.

Whether it’s a patio over a garage or a deck over any other flat roofed area, mounting a railing onto the surface of a roof can be a risky move, since you could be at risk of puncturing a hole and causing a leak. Instead, it’s generally better to anchor the railing into the side of the structure. Like with all building projects, there’s a time and place for everything, and the choice between fastening railing posts into the flooring surface or mounting the posts on the side of the roof (called fascia mounting) is no different.

When to Mount a Railing onto the Decking Surface

Fastening your railings using the normal old vertical method (screwing the railing posts onto the surface of the deck or porch) provides stability, especially when the fasteners are deeply inserted into a joist below the level of the flooring. When you are absolutely sure that the moisture barrier, or whatever structural element is working to keep water out, is well below the level of your screws, then feel free to drive the fasteners in with confidence.

Being certain here is important. When my friend drove a screw bolt down into his roof project, he was lucky to have a fairly easy patch job on his hands. Not everyone gets so lucky, and the ramifications of some botched jobs can be costly. How do you find out where your moisture barrier is? Ask the builder and/or the architect to chime in. If you can’t know for certain, I always counsel people to err on the side of caution.

When to Mount a Railing into the Fascia on the Side

There are two main reasons you’d choose to mount your railings on the side of the roof. The first one we’ve already mentioned:

• There’s a moisture barrier close to the surface: If the moisture barrier is close to the surface of the deck, then it’s time to screw or bolt the railing posts into the joists along the sides. Since the fasteners are in the sides, even though they are below the level of moisture, they will not allow significant amounts of water to enter the structure. Fastening the railings on the side of the roof is also pretty easy, as there is generally plenty of board. Most builders will be using two and sometimes three layers of 2 by 8’s or 2 by 6’s for the joists, an actual depth of 5.25 inches.
• Deck/patio space is limited: Maximizing a limited footprint is another excellent reason to attach the railings to the side of the structure. While gaining 4-8 inches of space all around the perimeter might seem trivial, in a smaller space, it can make a big difference in how large and open the space looks and feels. A fascia mount system is a good way to install a railing on a concrete porch, as well.

Clients frequently ask me if a fascia mount will be sturdy enough. The last thing anyone wants is a wobbly deck railing on an upper story space. If you share my clients’ concerns, relax. Almost all of us at one point have relied on the strength of that kind of join without knowing it. But it is true that it’s especially important, when you’re installing a fascia-mounted system, to choose a high-quality, code-tested system that can easily handle lots of lateral force.

The Ideal Railing for a Flat Roof

With the majority of flat roof projects, I like to choose a railing that I can mount on the side. Whether the moisture barrier is at risk or not, most of my clients want more space rather than less. Doing it this way makes it important to choose a sturdy material. Options like vinyl, wood, or composite really aren’t in the running here. My material of choice is steel, preferably from a manufacturer that uses more than one tough, corrosion-resistant coating on their steel in order to create a railing that doesn’t rust.

Whether you are concerned about creating a leak in the ceiling or simply want to maximize the space on your flat roof patio, side-mounted railing systems are a sturdy solution. Some of the most durable code-tested railings I’ve worked with are produced from Fortress Building Products. Their steel railings have several layers of protection, including an extra layer of protective zinc, an industrial grade e-coat, and a premium powder coat, making them some of the most durable and long-lasting railings on the market. They also come in a variety of colors and styles to complement different deck types and materials. And there’s a whole universe of other Fortress® products like fencing, decking, and ornamental hardware, which I’ve found useful when tackling all sorts of outdoor projects. If you look, you can find lots of ways to make your deck, fence, or outdoor structure just as good-looking and high quality as your railing.