How to Measure a Sliding Gate on a Sloped Driveway

A sliding gate has to clear the ground the whole way it moves. On a flat driveway that is easy. On a sloping one, a gate that looks right when it is shut can scrape the moment it opens.

The fix is one trick: measure everything from a dead level line, not from the ground. This guide shows you how for the three cases you will meet on site. Flat ground, ground that slopes one way, and a gate whose top and bottom both slope. Drag the sliders in each picture to see what the numbers do.

Why does slope matter for a sliding gate?

Rake is just another word for slope. A swing gate hangs off hinges and swings through the air. A sliding gate slides sideways along the ground, so every bump and fall along its path matters.

There are two kinds of sloping driveway, and they are very different jobs:

• The driveway climbs away from the street. The ground rises as you walk in, but the boundary line where the gate runs is fairly level. This is a big problem for a swing gate, because it hits the rising ground as it opens inwards. It is a small problem for a sliding gate. That is why a lot of sloping blocks end up with one.
• The ground falls across the opening. One post sits higher than the other. Now the gate itself has to deal with the slope. This is the case the rest of this guide is about.

Most real driveways have a bit of both. Measure the fall across the opening first, because that is the one that changes the shape of the gate.

What is a datum line, and how do you set one up?

A datum line is a line that is perfectly level, flat like still water. You stretch it across the opening and measure every number from it. Up to where the top of the gate will sit, or down to the ground. The ground can be as bumpy as it likes. Your numbers still line up.

For a short opening, a string line and a spirit level do the job. Tie the string to both posts, then slide one end up or down until a line level sits dead centre. For a wide driveway, hire a laser level for the day. It is quicker, and you can take as many points across the opening as you like.

The dashed line in the picture is the datum. Everything else on this page is measured from it.

How do you measure a sliding gate on flat ground?

You need two numbers. The clear opening width, measured between the inside faces of the posts. And the height you want, from the ground to the top of the gate. In CAD60 this is Level mode.

Even on ground that looks flat, run the datum line and check a few points. A 15 mm dip in the middle of a 5 m opening is easy to miss by eye and easy to catch with a tape.

The gate is wider than the opening. It carries an overlap past each side so there is no gap when it shuts, usually 50 to 150 mm per side. Measure the opening, not the gate, and add the overlap on the drawing.

How do you measure a single rake?

A single rake keeps the top of the gate level and lets the bottom follow the ground. It lines up with a level fence top and looks tidy from the street.

Set your datum line at the height you want the top of the gate. Then measure from the line down to the ground at the left post and at the right post. Those are your two heights. On a slope they come out different, and the difference is the fall across the opening.

Drag the height sliders. The top stays flat and the bottom tilts. In CAD60 you type these two heights as measured, ground to top. The model takes the ground clearance off the frame for you, so the gate stands that far off the ground.

How do you measure a double rake?

A double rake is for when the top has to slope too. Maybe the fence on each side steps down the block, and the gate top needs to follow it. Now the top and the bottom tilt at their own angles.

You take four numbers, all from one level datum line. At the left post: up to the top of the gate and down to the bottom of the gate. Then the same two at the right post. That is it. The four sliders below are the four numbers you would write in your notebook.

Take the numbers at the opening edges, on the inside faces of the posts. CAD60 carries each slope out past the overlap on both sides, so the ends of the gate follow the same lines.

Here is the drawing CAD60 makes from a double rake example: a 4000 mm battened gate. Spin the 3D model and flip through the sheets. Every rail is cut to its slope and every length is on the cutting list.

Should the bottom be level or raked, and which way should it open?

A sliding gate runs on a level track. So the gate itself never rises or falls as it moves. It slides straight sideways. That has a catch people miss with a raked bottom.

A raked bottom matches the ground when the gate is shut, so the gap is even. Slide it toward the low side and the gap grows. Slide it uphill and the low end of the gate moves over higher ground. On a real slope it will hit.

So before you rake a gate, check where it parks. If it has to open uphill, you either cut the ground down along the run-back or keep the bottom level. Here is how the two options compare:

My rule of thumb: keep the bottom level unless the gap at the low end looks wrong. When it does, rake it, and make sure the gate opens toward the low side.

Is a tracked or cantilever gate better on a slope?

A tracked gate rolls on wheels in a track set into the driveway. The track has to be level along its whole run, or the gate rolls downhill on its own and a motor fights it every time. On a fall across the opening, that means a level track set into the concrete, deeper at the high end. The gap under the gate holds the wheels and track, so it is set by their size: about 60 mm for a 50 mm wheel on a 10 mm track.

A cantilever gate hangs from roller carriages beside the opening. There is no track across the driveway at all. Its bottom rail carries the cantilever rail, so it stays straight and level, and the gap opens up toward the low side. It does not care what the ground does underneath, as long as the high point clears. On a messy or steep slope it is often the easier gate. The cantilever vs sliding gate guide goes through the trade-offs.

In CAD60 the rake modes are on the tracked sliding gates. The cantilever and telescopic gates draw with a level bottom.

What mistakes do people make measuring on a slope?

• Measuring only at the posts. Two end points miss a hump or a dip in the middle. Take a reading every metre or so. The highest ground under the gate sets your clearance.
• Forgetting the run-back. The gate parks beside the opening. Measure the ground there too, from the same datum line.
• Measuring from the ground, not a line. Two heights taken off bumpy ground do not tell you the real fall. Always measure from the level line.
• Ignoring future paving. If the customer plans new pavers or a fresh concrete topping, the ground will rise. Ask, and leave room.
• Pouring the motor pad on the slope. The gate can be raked. The motor pad still needs to be poured level.

Measuring up the rest of the job (posts, power, access) is covered in how to measure up a gate job. When you have the numbers, the sliding gate shop drawing guide turns them into a drawing.

Common questions