How to Build A Zip Line
Whether you're looking to build a backyard zip line for do-it-yourself style or you're thinking about buying a kit you first need to understand the basics. It may seem daunting at first as there are so many factors; do I have to calculate slope and sag, what are the height requirements, can my home accommodate a backyard zip line kit. We will go into depth from start to finish on how you can safely and reliably come up with a zip line design that will satisfy your family for years to come.
Zip line Location
The first thing you need to do when installing a zip line is of course choose a location! Ideally in your backyard or on your property, you’ll need to find two trees that have a direct path towards each other. You might already have a spot in mind, but it is always good to have a couple different options. Check out this article if you want to install a zip line without trees. Measure and track these distances in feet. Most zip line kits go up from 50 to 500 feet, in 50 foot increments, so you’ll need to decide what cable length suits your scenario. Next we’ll talk about all the requirements for a safe install in the next section.
Zip line Design
Deciding on an anchor will help you secure the zip line firmly in position. I mentioned in the paragraph above to choose two trees. Seems pretty simple, but there’s more to it. These trees need to withstand a lot of horizontal force. Up to 3,000 pounds to be exact, which is more than a ton.
Let’s first start on what not to do. Do not choose trees that are rotten, old, have cracks or rooted in loose soil or sand. You cannot attach the zip line cable to a branch under any circumstances. Please use common sense or consult an engineer!
A safe zip lining tree has at least a 12-inch diameter around its trunk.
We recommend a 7ft clearance around the entire zip line, free from branches, rocks, or any other obstacle.
Cable Tension and Sag Calculation
Cable Sag is the amount the zipline drops when a rider’s weight is added. The simple formula is (Length of Zipline) x (.02). An example of this is a 100 foot zip line would have 2 feet of sag. You want to take this into consideration as you don’t want your rider’s feet to be dragging as they ride.
We recommend a 3% slope for zip lines will be only utilizing a stop block. This means there would be a 3 foot drop every 100 feet. If using a bungee braking system, the maximum slope is 6% or 6 foot drop per 100 feet.
We now have a few inputs. I’ll note them down below with an example of a 100 foot kit.
|Zip line Length
|Zip line Slope
3 feet (3% slope)
|Zip line Sag
We now need to find out 3 more inputs. Keep in mind anchor height refers to the height of where your zip line attaches to the tree or anchor.
Ending Anchor Height
Starting Anchor Height
I've created an easy to use calculator to help you calculate cable slope, sag, starting and ending anchor height.
|CABLE SLOPE & SAG CALCULATOR
|Length (Distance between start and end anchors)
|Zip Line Slope
|Zip Line Sag
|Calculate Elevation Change
|End Level Mark
|Start Sight Height
|Ending Anchor Point Height
|Starting Anchor Point Height
Elevation Change is easy if you are on flat land, it’s 0 feet! If you are on a slope or hill you may have to use a sight level to find the elevation change between the ground level of the starting anchor and the ground level of the end anchor.
Ending Anchor Height = (Zip line Sag) + 7 feet
Starting Anchor Height = (Zip line Slope) + (Ending Anchor Height) - (Elevation Change)
Did I lose you yet? Let’s bring it back all together with our example.
Zip line Length
Zip line Slope
3 feet (3% slope)
Zip line Sag
Ending Anchor Height
Starting Anchor Height
We highly recommend using Galvanized Aircraft Cable for zip lining. It is durable and flexible and you can find out more about all the cables here.
Cable clamps or U-Bolts are used to secure dead ends of cable. We recommend 15 ft. lbs of torque and 3 cable clamps, 1-2 inches apart.
A turnbuckle is a device for adjusting the tension or length of zip line cables. It is used to make adjustments to how much slack your cable has.
Cable Slings are designed to wrap around your anchor whether it be a tree or a pole. The two loops connect to the turnbuckle.
Thimbles help maintain the durability of a cable by preventing crimping. They should used in any sharp turns on a cable. In most cases you’ll use it near the cable clamps when the cable has to loop back around.
Installing the zip line
First we need to start at your starting anchor. Depending on what kind of zip line kit you have, the instructions may be a little different. Typically on the starting anchor you need to wrap the cable slings around your anchor to attach to a turnbuckle. The zip line cable will attach to the empty end of the turnbuckle and will wrap around the ending anchor, secured with cable clamps. Take a look at the pictures below.
The starting and ending anchor instructions might be vice versa depending on your kit’s instructions and there might be two turnbuckles (one on each end for further tensioning).
Next we will talk about the zip line equipment!
Zip line Equipment
With zip line accessories there will be cases where certain components have to have the cable fed through them, as opposed to being added on after the cable is set up. Be sure to check your individual parts!
There are trolleys where the end of the cable has to be fed through the trolley. There are others that are completely detachable. Please check out choosing a zip line trolley for more.
Being able to stop a zip line is a big concern for some! It’s a top priority for us too. There are a variety of braking systems that you can choose from. We do recommend having a Bungee Braking System, combined with a Stop Block. In some cases, a spring stop is acceptable! Or you can get creative. We go in depth into zip line brakes here.
In our opinion, this is the place where there is the most variation. Do you want a swing seat, disc seat, or harness? Do you have small kids and want to secure them? The installation is really simple as all of these attachments are secured using a carabiner attached to the trolley. We explore several options for you in our other blog post.
As a final note, once everything is installed, do a safety test and inspection. Use a test weight (bucket of water, weights, etc) to see if the braking mechanism, trolley and cable are acting as intended. Be sure to make sure the anchors are secure. One test is to sharpie where the cable clamps are before the test and see if they shifted during the test ride. If they shifted, it needs to be tightened.
If the cable shows signs of fraying, retire it immediately. Check the trolley for excessive friction or roughness. Make sure all carabiners are secured. Instruct your riders all of the dos and don’t before riding.
Above all else, have fun zipping!