What Are Bilco Stair Stringers Made Of? [And What Sizes Are They]

Thinking of what stair stringers to use for your basement stairs? You must have heard of how economical and durable Bilco stair stringers are. If you're curious as to what they're made of and what sizes are available in the market, you're on the right page. We've done the research to provide you with the best answer.

Bilco stair stringers are made of galvanized steel. They're available in sizes SL, O, B, and C.

Continue reading to learn more about Bilco stair stringers and the exact dimensions of their sizes. Additionally, we'll answer frequently asked questions about recommended stringer thickness, length, and support.

A steel plate cut in zigzag pattern for stair stringer fabrication, What Are Bilco Stair Stringers Made Of? [And What Sizes Are They]

Bilco Stair Stringer

Unlike the usual wood stringers, Bilco has created a basement stair stringer that can withstand heavy-duty loads, requires very minimal maintenance, is budget-friendly, and most of all will last for a longer period. Thanks to its galvanized steel material!

Consisting of a 14-gauge galvanized steel, the Bilco stair stringer lasts just as long as your Bilco doors.

The galvanized steel is quite versatile too as it is designed to have removable treads. This will help you move big appliances and furniture into the basement, like a king-size mattress, a pool table, a television, a big painting, a huge figurine, and a furnace.

You may have thought that because of its solid material, installing Bilco galvanized steel stair stringers is hard and requires great effort. Well, fortunately, it's quite easy and the steps are simple.

All you need to do is to nail them into the sidewalls of the areaway. Make sure that you cut the wooden treads into the required length based on the standard lumber stringer length which is 2" X 10". Next, attach or fix them in position with the nails provided.

If you want your stairs to match the color or concept of your house, the galvanized steel stair stringers, like wood, can also be painted for aesthetic purposes. You just only need to put on a metal primer before painting on your desired paint color.

Bilco Stair Stringer Sizes

Bilco has designed four standard stair stringer sizes that would best fit your basement door size.

Size SL

With a total length of 34 5/8 inches, the size SL Bilco stair stringer also has a total of four treads.

Size O

This Bilco stair stringer has a total length of 51 3/8 inches. The number of treads it can accommodate is six.

Size B

The size B Bilco stair stringer has a total length of 59 3/4 inches. And it can accommodate a total of seven treads.

Size C

This Bilco stair stringer has a total length of 68 1/8 inches. The total number of treads it can contain is eight.

Check this Bilco stair stringer on Amazon.

How thick should stair stringers be?

Stairs to the 2nd floor

Typically, stair stringers, especially those made of wood, are made of 2x10-inch or 2x12-inch boards that are at least 5 inches thick.

How far apart do stair stringers have to be?

According to the International Association of Certified Home Inspectors, the recommended spacing between stair stringers should not exceed 18 inches.

How do you join stringers?

Stair stringers for a backyard deck being cut into a piece of pressure treated wood

To join stringers, follow these steps below:

  1. The first thing that you need to do is to put up three parallel sawhorses and place them several feet apart from each other. Put the two stringers flat on the horses and make sure that the tread and riser notches face the same direction.
  2. Next, you need to measure the stair's run where you would install the stringers starting from the upper landing up to the deck or ground. To determine the length of each stringer, you should divide your measurement in half.
  3. Using a steel or framing square, mark each stringer on the face with cutting lines and make sure that they are perpendicular with the notches of the tread. With the use of a circular saw, cut each stringer. Adjoin the cut ends of the stringers and uniformly align their straight edges.
  4. Now, you need to measure the stringer's straight edge up to the inside corner of the riser notch and tread. This would usually range from 4-6 inches depending on the lumber size used for the stringers. Afterward, cut 3/4-inch thick plywood with a 48-inch length and a width that is the same as the measurement from the straight edge to the side or corner of the notch.
  5. Put the plywood flatly on the stringers. Align one edge of the plywood with the stringer's straight edges. Center each piece of plywood where the stringers adjoin.
  6. Next, drill through the plywood and stringers some pair of holes at 6 inches intervals from one end to another using a power drill and a 1/2-inch drill bit. Drill an extra pair of holes 2 inches on each seam where the stringers adjoin.
  7. Prepare 1/2" X 3" machine bolts with steel washers. Make sure that the steel washers are slid against the heads of the bolts. Put the bolts in each hole and install a washer at each end. For added security, tightly screw in a nut on each end using a ratchet and socket.
  8. To completely connect the remaining pairs of stringers, redo the whole procedure.

How far can a stair stringer span?

Newly constructed wooden deck to srew down the boards that have been placed across the stair stringers

According to the standards of practice of the International Association of Certified Home Inspectors, a closed stair stringer should not span exceeding 13 feet and 3 inches. On the other hand, a cut stair stinger should span, not exceeding 6 feet.

How do you strengthen deck stringers?

Deck and stair construction

There are various ways to strengthen deck stringers. However, the durability of a stringer also depends largely on the type of materials used to make it.

To strengthen deck stringers, especially those made of wood, you might as well follow these steps:

  • The first material or tool that you need for you to strengthen your deck stringers is an adjustable stringer connector made of stainless steel. You need to install a stringer connector on the upper end to support the entire structure and meet the resistance requirement for your staircase.
  • Next, you should also make sure that the lower part of the stringer is also secured. The bottom end of the stringer should be supported by a wood plate anchored to the footing with stainless steel heavy-duty screw anchors.
  • When fastening the stringer, use a stringer connector plate framing angle to securely connect the stringer to the wood plate.
  • To ensure that the staircase will be able to endure foot traffic and combined weight, you may add intermediate support. Support is usually placed at the center just underneath the staircase structure.

If you're a visual learner, watch this video for a demonstration on how to do the steps mentioned above:

In Closing

Most stair stringers are made of wood, however, Bilco was able to develop a more durable and cost-effective stair stringer that is made of galvanized steel. And it has four different sizes that could match your basement doors, namely, sizes SL, O, B, and C.

Before you go, check out these posts regarding Bilco basement doors:

How Much Does It Cost To Install Bilco Basement Doors? [Including New & Replacement]

Are Bilco Basement Doors Watertight?

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