Oak pergola?

[gasman]

SWMBO wants a pergola - big oak structure in the garden going down to an area where there are a couple of benches. She wants it a bit like this - quite simple but maybe with the horizontal cross pieces sticking out to the sides a bit more.

So I bought 16 x 3metre x 100x100mm green oak (about 20 cubic feet or so) from Venables in Shropshire for £400 + delivery £70. It is good quality, straight and true and seems a good buy
I plan to do pegged M&T joints, with 8 vertical pieces in 4 arches joined together longitudinally as well as cross-pieces
My questions are;
1. What do people think about putting the 8 vertical posts on 4 inch met posts rather than sinking them in concrete? I think it should be way strong enough and the whole structure should resist movement which I know is one drawback of metposts
2. Do I need the 45 degree bracing pieces? and if so do they have to be morticed and pegged as well/ If so that increases the amount of work dramatically.
Has anyone any experience of similar? It would be good to get some advice along these lines. Thanks a lot and regards
Mark

 

[blackrodd]

SWMBO wants a pergola - big oak structure in the garden going down to an area where there are a couple of benches. She wants it a bit like this - quite simple but maybe with the horizontal cross pieces sticking out to the sides a bit more.

So I bought 16 x 3metre x 100x100mm green oak (about 20 cubic feet or so) from Venables in Shropshire for £400 + delivery £70. It is good quality, straight and true and seems a good buy
I plan to do pegged M&T joints, with 8 vertical pieces in 4 arches joined together longitudinally as well as cross-pieces
My questions are;
1. What do people think about putting the 8 vertical posts on 4 inch met posts rather than sinking them in concrete? I think it should be way strong enough and the whole structure should resist movement which I know is one drawback of metposts
2. Do I need the 45 degree bracing pieces? and if so do they have to be morticed and pegged as well/ If so that increases the amount of work dramatically.
Has anyone any experience of similar? It would be good to get some advice along these lines. Thanks a lot and regards
Mark

Get the metpost that clamp at the base, in case of summer shrinkage.
To help prevent rot, I drill a sloping hole 12" up from the floor, around 1/2" bit and fill this up with wood preserver,twice a year, and whittle a plug to seal up the preservant "reservoir"
Yes, I would make and fix"Gallow brackets, you would only need a small stubby tenon on the post and a half lap and screw to the long rail each side.
As you will need to stiffen each post in this, or similar way below, the next pic from you'res
https://www.google.co.uk/search?q=oak+p ... B580%3B434
HTH Regards rodders

 

[woodfarmer]

In a crude fashion I have made pergola using 9 x3 inch timber. I installed 45 degree "knees" to brace the uprights and also across the corners. My crude "joint" was simple drill a countersink holle through and use 3/4 inch threaded rod. If I were to do it again, I woulds drill through with a big forstner bit and turn wooden pegs/dowels to fit say 2" diameter. You could literally use a small nails to hold the knee in place. drill through them both by eye and peg maybe using cascamite of similar, then remove the nails. Might even mini peg the peg.

If you are using newspeak

9x3 = 230mm x 80mm
3/4 inch = 20mm
2 inches = 50mm

 

[gasman]

Thanks gentlemen - that's very helpful
I think if I am going to use the 'gallow brackets' I should probably think about making them pegged M&T joints as well which obviously adds to the time because of having to hollow out the oddly-shaped mortices on the long pieces. I wonder if there's a quicker way of cutting them than chopping them out with a chisel
Thanks again
Regards Mark

 

[DTR]

I am watching with interest, I hope to put up a pergola this year

 

[turnamere]

I built a pergola last summer although I went with pressure treated timber rather than oak. For design inspiration I did a google image search for pergolas and then wnet through the results with SWMBO to settle on a design. I marked out the plot and dug holes for the base of each post about 8-10" deep and 10" square, pounded some stones into the bottom, formed shuttering from scrap timber then filled to a level with concrete. Metposts were then bolted down in line. I used mortice and tenon draw bored joints where the diagonal braces joined the uprights; the top joints were simply bolted between the paired long rails which sat in rebates on the top of the uprights. To prevent side to side sway diagonal braces at the front and back were formed with a face dovetail.

Mine is wider at the front than the back and the front right upright is further forward than the left, as a resulult I had to form a staggered front span to meet both the braces.

I used a spade bit in a drill stand to hog out most of the mortice and my router for most of the material on the tenon the final tidy up and tweak to fit done with chisels.

 

[blackrodd]

I like that! Very different, very nice.
There's a lotta work in that!
Rodders

 

[turnamere]

I like that! Very different, very nice.
There's a lotta work in that!
Rodders

Thanks Rodders, construction is probably a little OTT but it was as much about perfecting some techniques before I embark on a much larger pergola on the top garden with polycarbonate roof and some trellis walls; catch the prevailing south westerly winds and it will provide a nice sheltered area to make the garden more usable in the evenings.

Just needs to weather in a little and for the clematis and roses to climb up and soften the top.

 

[Paul200]

Have you considered other ways of fixing the posts to the ground Mark? I only ask because I built a pergola in my garden in Somerset and used Metposts and always regretted it. Without wanting to detract from the beautiful workmanship that others have posted here - I personally hate the things.

There are some more subtle (and very expensive) options available, such as:

Dissatisfaction with my own work in the past had me wondering if something cheaper but just as effective could be fashioned from stainless threaded bar, nuts and square plate washers. The bar could either be set in the concrete direct or set in a bolt anchor (rawlbolt, sleeve anchor or surface anchor) into the concrete.

Just throwing a thought into the mix.

Cheers

Paul

 

[graduate_owner]

Regarding wood preservative - Sovereign Chemcals from Barrow in Furness make (or used to) a product called deep kill paste. This stuff is the consistency of mayonnaise so you can slap it on and it won't run off. It really does penetrate (as in ends of joists in walls which can't be reached. Not cheap at £100 or so forma 10 litre tub but if you need this sort of penetraton it's worth it. Good for woodworm and rot in your attics too.

K

 

[Random Orbital Bob]

I also don't like metposts at all. Invention of the devil and in my experience work for a limited time only. Particularly the pointy ones you hammer into the ground to avoid the faff of digging concrete holes. The problem with metposts is of course the wood is in considerable contact with mother earth no matter what you do and as such it accelerates the rotting time no end. If you're leaving in 30 minutes and don't care then fair enough but if you plan to actually use the garden and like the fence to be there then I would bite the bullet and get digging. To be honest, with modern quick drying cement post setting isn't that much of a chore and the solution is heaps better.

Turnamere's solution which is a compromise between the two ie enough concrete to provide a foundation for boltable metposts is better for rot reduction because he's shuttered them above ground level. The trouble is (no offence meant Turnamere) they're well above ground and a bit ugly in my view. I don't want a pergola with concrete welly's at the end of every post and if you were going to go in that direction then I would be inclined to build a brick pillar and set the post into that. Then the aesthetic is maintained.

If it were me (and it was about 3 years ago) I just got on and dug 21/2 foot holes and postcreted the posts in. To aid the digging I bought an inexpensive hole digging spade which really helped.

 

[turnamere]

Turnamere's solution which is a compromise between the two ie enough concrete to provide a foundation for boltable metposts is better for rot reduction because he's shuttered them above ground level. The trouble is (no offence meant Turnamere) they're well above ground and a bit ugly in my view. I don't want a pergola with concrete welly's at the end of every post and if you were going to go in that direction then I would be inclined to build a brick pillar and set the post into that. Then the aesthetic is maintained.

No offence taken, I literally got the pergola completed as guests were arriving for my Birthday BBQ last year, probably not obvious from the phots but there is a considerable slope accross the run of the pergola and one of the jobs on my TUIT list is to level and re seed that area leaving the very tops of the concrete piers above ground. I may also clad outside the Metposts with timber to give the base of the posts an aparent thicker section and hide the galvanized fitting but I'm hoping that the greenery will soon hide the lower part of the posts.. Regarding the brick pier suggestion, don't see many bricks in Cornwall and I'm not sure how accurate the results would be with granite.

For concreted in posts I have read somewhere that placing a layer of gravel in the bottom of the hole for the post to sit on and then concrete around will provide drainage and allow any water that gets down between post and concrete to drain away rather than soaking in to the endgrain. This combined with the preserver reservoir idea should give a good long life.

 

[graduate_owner]

If you intend digging holes where there may be tree roots then a good tool is one of the roughneck post hole diggers, but they do cost a bit, over £50. I was going to buy one but then I broke the shaft on my axe, so I welded the head onto a thick steel bar to make my own alternative version. It worked a treat. Just like a 5 foot long, 4" wide, heavy wood chisel

K

 

[blackrodd]

When setting posts in the ground, with or without concrete the ground is always soaking or at least wet.
This is why I put a decent bag wrapped around the post base to try and keep the post base dry.
Remember most posts fail in the area just above ground.
I agree that metposts do look ugly but when used in the right place, they can help in a difficult fixing situation,
When building timber structures retrospectively
The idea of the drilled resovoir filled twice a year, is to keep the preserver in place and working within the wood.
Regards Rodders

 

[Alex H]

I'm in the process of constructing an oak veranda - the common method of supporting the posts over here is these

Not as ugly as a metpost, and not really noticeable at all until you look closely (the base is covered by the patio tiles)