DIY – Pergola repair

The construction of the pergolas on our sun terraces is not great (…I am being kind here). Each pergola consists of four steel pillars supporting a rectangular steel construction that in its turn supports the wooden beams. Recently, one of the wooden beams came loose from the steel construction and fell down on the sun terrace. Fortunately, it caused no damage and it did not fall down two floors to ground level. It did however point out that maintenance was urgent due to the imminent danger of other beams falling and causing damage or worse – injury.

Analyzing the construction, it became clear that the long screws used to attach the wooden beam to the rectangular construction had rusted through leaving the beam no longer attached to the steel construction. The wind did the rest.

The rust is a result of the combination of using non-rust-resistant screws and the steel construction collecting rain and condensation water inside the steel beams. As a result of this, the steel construction rusts on the inside, and the screws corrode to the point where they are too thin to support the beam against the wind.

So we have a number of problems:

  • The steel construction collects water
  • Collected water remains trapped inside the construction
  • The screws that hold the beams are deteriorating

As usual, there are a number of solutions to any given engineering problem.

Water ingress and trapping:

On each of the standing pillars, you could drill a small hole to allow water out. This ought to be done as low in the construction as possible. But the fact that the tiling goes up a decimeter or so around the pillar limits how low one can drill. I drilled ours just above the edge of the tiles. Like so:

Remains the water collection in the upper rectangular construction. The internal void inside this part of the construction does not seem to be connected to the void in the pillars. Ideally, they would be connected in such a manner that any trapped water leads to the pillars and can be drained there. For this to work, on each corner, a vertical hole should be drilled through the rectangle into the pillar. In practice, this would require the beams on the corners to be removed and a vertical hole to be drilled using a long drill. This hole should not be too small so it clogs up easily, I’d estimate using an 8mm drill sounds reasonable, but bigger would be better. After drilling the vertical hole, the outer one on top of the construction has to be plugged.

Rusty screws:

In the simplest of worlds, the rusty screws would have to be replaced, preferably by a better solution. Where possible, you could try and get the rusty screw out and replace it with a stainless screw of similar dimensions.
Another solution would be to remove the screw, drill a larger diameter hole all the way through the steel rectangle and the wooden beam, and put in a steel bolt or threaded rod. This is the solution I chose for our pergola. It is also the solution that requires the most work.
A third option is to buy 90-degree angle brackets and mount these by screwing one part against the wooden beam and the other into the steel construction.

The state of the screws:

The threaded rod:

…M8, length 31cm.

Drilled and mounted:

…yes, the beam needs painting!

Be aware:

When I started removing screws, water trapped in the steel construction started pouring out. When I write pouring, that’s exactly what I mean. The water is mixed with rust and makes a mess of your sun terrace and the painted areas such as the pillars for the railing around your sun terrace. Once the rust water gets on the paint, it will not get off!

In the end, one of the beams contained 35 liters of water, at least half of it rust water.

To lead away this mess in a more controllable manner, I tied a small funnel under hole in the beam and attached a garden hose to it. The garden hose can lead to the sun terrace drain or to a bucket. Like this:

Tools and materials:

  • Ladder (see safety notice below)
  • Drill (electric or battery)
    • Drillbit 8.5mm
    • Drillbit 8mm, length 30cm
  • Hammer
  • Screwdriver with quality screw bits
  • Threaded rods: M8, length 31cm
  • Nuts m8, two for each connection
  • Washers 8mm, two for each connection
  • Proper shoes (see safety notice below)

Safety notices:

  • If you’re afraid of heights, do not embark on this endeavor!
  • When repairing your pergola, you will need a proper ladder (a suitable one can be found in the water meter room in the basement).
  • Don’t do any ladder work when there’s a lot of wind!
  • Once you do, I have to caution you to avoid flip-flops to dash up and down the ladder. Reminiscent of my youth (albeit a long time ago), I did not obey this rule causing an injury to my right heel. After a week or so on crutches, my foot was ok again, but I’ll be completing the work above next time instead of doing it all at once as I intended.