I honestly can’t figure it out. There’s no manufacturer information available on this. I imagine the foundation on the side plates is important for lateral forces, but I can’t really assess how serious this is.
Background: the 91mm (3.6 inches) wide ones are €2.50 cheaper each (no idea why), and I might want to upgrade later if the pergola ends up becoming a full roof. In that case, the posts would be replaced with 100mm (4 inches) ones, and the side plates would be routed out. With 81mm (3.2 inches), that would mean quite a bit material removed when routing...
What do you think?
Background: the 91mm (3.6 inches) wide ones are €2.50 cheaper each (no idea why), and I might want to upgrade later if the pergola ends up becoming a full roof. In that case, the posts would be replaced with 100mm (4 inches) ones, and the side plates would be routed out. With 81mm (3.2 inches), that would mean quite a bit material removed when routing...
What do you think?
M
MachsSelbst10 Mar 2026 10:2491mm (3.6 inches) is more common than 81mm (3.2 inches), making it more cost-effective. I would avoid using posts that are either too large or too small. Of course, you can insert something or rout out a section, but in the end, these are always unnecessary weak points, especially when routing.
What speaks against using 91mm (3.6 inches) posts and 91mm (3.6 inches) post anchors?
What speaks against using 91mm (3.6 inches) posts and 91mm (3.6 inches) post anchors?
M
MachsSelbst10 Mar 2026 11:50What speaks against 81mm (3.2 inches) posts, and in favor of choosing the more expensive post anchors at 2.50 EUR each?
Shouldn't 81mm (3.2 inches) posts be sufficient for a roofing structure?
Shouldn't 81mm (3.2 inches) posts be sufficient for a roofing structure?
Budget
The budget for the project is basically zero. It wasn’t planned for this year, but now it needs to be realized quite soon. This year it will be a pergola with just a few fabric panels hung inside. With 8-10 posts, even a small amount of money already makes a difference.
Future viability – Load-bearing capacity / Stability
Later on (in 3-5 years), a proper roof will be installed that will likely hold photovoltaic modules as well as vertical, fixed wind and privacy screens. I think due to the increased weight and stronger wind loads, 80x80mm (3x3 inches) posts probably won’t be sufficient anymore, or I would need to plan for significantly more posts.
Do you really think that 5mm (0.2 inches) of play on each side weakens the structure that much? And if I use flat connectors to fill the gap (I still have some lying around), would that help?
The budget for the project is basically zero. It wasn’t planned for this year, but now it needs to be realized quite soon. This year it will be a pergola with just a few fabric panels hung inside. With 8-10 posts, even a small amount of money already makes a difference.
Future viability – Load-bearing capacity / Stability
Later on (in 3-5 years), a proper roof will be installed that will likely hold photovoltaic modules as well as vertical, fixed wind and privacy screens. I think due to the increased weight and stronger wind loads, 80x80mm (3x3 inches) posts probably won’t be sufficient anymore, or I would need to plan for significantly more posts.
Do you really think that 5mm (0.2 inches) of play on each side weakens the structure that much? And if I use flat connectors to fill the gap (I still have some lying around), would that help?
80 mm (3 inches) is completely sufficient for the pergola. Do it exactly like that. In a few years, if you add side walls, photovoltaic panels, or a fixed roof, I would then plan a budget to do it properly with bracing, carpentry work, maybe 100 mm (4 inches) timber and concrete supports, cross beams, etc. The pergola can then be moved to another nice spot in your garden or someone else’s.
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