Outdoor Fixing for Green Oak

16 May 2021
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United Kingdom

I've bought some Eurpoean green oak timber and am now thinking about the best way to fix the crossbeams (2) to the 150 x 150mm posts (1). The decorative rafters (3) on top will also need fixing.

I know normal screws/bolts will rust so I should use stainless steel. Given the assembly I don't think dowels are an option.

Any ideas or recommendations?

Many thanks,


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Stainless steel is the best option for oak, especially green oak. If using long screws always pre-pilot (drill) for the screws and insert an equivalent size steel screw, swapping the steel screws out for stainless when you do the final assembly. This is because s/steel is soft and it is easy to chew up the screw heads by inserting and removing multiple times - and to snap very long screws if driven too hard into a pilot hole which is too small
Great suggestions thanks. Someone on another forum suggested sloping the top surfaces to allow water run off too. Not sure how that might look or be achieved yet.
So the timber is arriving next week and I've been thinking about how I'm going to secure the posts in the ground again. There seems to be a lot of conflicting information on the net.

Ideally I would build a concrete foundation and put the oak posts on top of that so they are well out of the way of the soil however due to the design I don't think it will be strong enough. It is not a traditional pergola an is more of a L shaped bit of screening/fencing so there may well be significant side loads. Therefore I have come to the conclusion that I will concrete about 600mm of the post into the ground with a footing about 400 x 400mm square. The posts are 150mm wide. I obviously want the timber to last as long as possible so have been researching the best way of minimising chances of rot. I will use gravel in the bottom of the foundation hole which will allow water to drain and will also be useful to get the post to the correct height etc. What about sealing/treating the bottom of the post? I have seen guidance that says do and also some that says don't as it can keep water in? Any advice?




  • Proposed Pergola-screen.PNG
    Proposed Pergola-screen.PNG
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Rawl bolt or epoxy fix these into the concrete, they are plenty strong enough.
Yes you bolt the bracket to the concrete and then the post goes on top. That way you have a strong fixing and are keeping the post out of the ground.
Yes you bolt the bracket to the concrete and then the post goes on top. That way you have a strong fixing and are keeping the post out of the ground.
OK, and you think it’ll be strong enough with the side loads. I suppose as it’s an L shape there will be some extra rigidity laterlly. I would prefer that solution but was worried it wouldn’t be strong enough when we have the July/august storms that seem normal now. :cool:
Hi everyone,

Well the installation seems to be going OK. I have 5 out of the 6 posts in the ground. I'm now thinking about the fixings (cross beam to the post). I'm going to use stainless steel screws and then use Oak dowels to cover them up. The question is what size screws should I use? An image of the two pieces to be screwed is shown below. Any recommendations greatly received.

Correct me if I'm wrong but I'm guessing I should drill the cross beam holes big enough so the screw goes through without biting? I will pre-drill the oak post with a pilot hole so it's not too hard for the screw thread to penetrate.


Screen Fixings1.PNG
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I would use an 8mm clearance hole in the beam and a 5mm hole in the post. Test in an offcut and adjust if necessary. You might need a 9mm clearance hole.

Personally I would bolt through rather than screwing. But unless you counterbore both sides the fixings will be visible.
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Thanks very much. Sounds good

I also need to attach item 3 to 2 (see drawing in my OP). One chap on another forum suggested screwing from the bottom of 2 by first counter sinking a large portion of it - see images. The benefit being there will be no fixings on top. Cam then dowel the holes.

Any other ideas? What size screws would you go for for this application?



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Yes, I’ve now corrected my previous post and added some pictures.

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