Best post stand-off for large pergola

[nakb]

I'm building an 80m2 paved terrace that will have a large oak pergola on it. Terrace construction will be calibrated Indian sandstone laid on 50mm of 8:1 moist mix bedding which will be on a 0/31.5 sub-base.

The oak pergola will have 150mm x 150mm posts, each supporting a static weight of up to 250kg. Green oak will be used so it can be expected to twist a bit over time.

I am planning concrete foundations (250mm x 250mm down to the bottom of the sub-base) under each pergola post.

My question concerns the best type of stand-offs (post bases) to use for the posts. Two specific questions:

1. Is it better to use stand-offs whose bases are cast into the concrete post foundations, or can I use the type that bolt on to the surface of the terrace (presumably with bolts extending down through the slabs and bedding layer into the concrete post foundation)?

2. At the top of the stand-offs, I have a choice of boxed, stirrup, blade or pin fixings. It seems to me that a central pin is better as this locates the post on the supporting plate but still allows a degree of twisting movement as the oak ages, whereas the other types of fixings might cause the oak to split. Is my thinking right on this?

Many thanks

Nigel

[lutonlagerlout]

Hi nigel we had the same thoughts on a green oak storm porch earlier this year
we use products from this company for the bases
http://www.canopyproducts.co.uk/product.php?hdnProductID=164

at the top the carpenters just formed cross halving joints and dowelled it for extra strength
I probably have a picture someplace but not to hand

cheers LLL

[Forestboy1978]

^We use the same company. Extremely expensive though I think.

I've been looking around for cheaper but can't find anything.

[lutonlagerlout]

IIRC the stainless steel ones for 6 inch oak posts were around £80 each

but proper kit for the job....

LLL

[Forestboy1978]

Oh I agree. They are accurately machined lumps of stainless steel and they are robust as hell. It's never nice adding £300 to a materials costing on a pergola or whatever just for feet though.

I've been doing a quote without and a quote with just so people know how much the damn feet cost and have the option.

[nakb]

Certainly look like what I need. But I'll want 17 so will be £1,000 plus VAT which makes me gulp a bit!

[lutonlagerlout]

problem is we will know that green oak splits and twists and if you concrete them in they will rot for sure

so proper job needs proper kit!!

LLL

[GB_Groundworks]

you can get cheaper ones that are painted that you set into a hole drilled in concrete but they arent adjustable and will rust and fail over time

im with tony if you were my client id be using these, do it right the first time and it should give decades with out hassle, nothing worse than having to try repair them in a few years false economy