Larch vs. treated softwood for fence?

[hugov]

I need to replace a short section of fence. There is a local sawmill (Bespoke Larch And Oak Cutting,Fencing,In CambridgeshireCladding http) that does larch, however it's only dip-treated rather than properly pressure treated. I've used their larch before (not for fencing) and been pretty happy with it, and it's much nicer to work with than treated softwood, and seems much stronger and harder. Larch has a reputation for being decently durable even without treatment, and that's been my experience above ground. What are you opinions on dip-treated larch versus proper incised and pressure treated softwood for fence posts? Or would it be better to combine concrete repair spur/stub posts or those concrete-in metal bracket things with larch uppers? (We don't want full length concrete posts due to aesthetics).

 

[J-G]

I've never used Larch so can't help on that score but if building a fence I would always use 'Godfathers' - those things you refer to as 'repair spur' or 'stub posts'. When I was in that business, I never considered them a 'Repair' option they were always 'original equipment' items.

 

[Jameshow]

I'd go larch every time. Nice to work with too.
Over order of course to keep some for the workshop!

Concrete stub posts would be best but ugly!

 

[recipio]

I have larch planks fixed between concrete posts and coated with Sadolins. I got about 25 years out of them before the ends began to rot. Next time I would find some way of sealing the end grain and they should last a lifetime. Not sure what to use - possibly a bitumen based compound ?

 

[Jones]

If it's going in the ground then class 4 treated will last alot longer than larch dipped in preservative or use concrete as suggested above.

 

[whereistheceilidh]

Larch for fence is very durable.....treated or not.... but it will go grey. Suggest you make sure that it is European Larch & not Japanese Larch as some ornamental stuff finds its way into sawmills & it is not durable at all. Also suggest you get envoronmentally acredited FSC timber.... & not Sberian larch.. for a variety of reasons ...although it is pleasant wood to work with.
Pressure trated posts/stobs.

 

[hugov]

Thanks everyone – I ended up going with untreated larch above ground, and concrete spur posts (bolted to larch upper posts). I've painted some Sika wood preserver on the larch with a foam roller, hopefully that'll help it last longer.

 

[hugov]

Obviously not rocket science, but for anyone reading this in the future, and like me not really knowing what you're doing, here are some design details and a rough drawing.

I used 3m 100x100m posts, cut in half at a 20 degree angle to shed water better, with three 75x43mm rails (I cut the top edge at a 15 degree angle on the table saw to help shed water), 1650mm feather edge boards, 150x25mm gravel boards, and a capping profile made from more 75x43mm rails (cut to shape on the table saw – two bevels on the top, and a rebate on the bottom to take the overlapping feather edge boards). The rails sit in shallow trenches in the posts (cut with multiple passes with a track saw, and chiselling out the waste), which really helped during assembly getting everything lined up.

In terms of hardware, I used 10x180mm Spax galvanised washer-head lag screws (with M12 Form A nylon washers) to hold the posts to the concrete spurs, 6x100mm Spax stainless washer-head screws for holding the gravel board and rails to the posts, 4x45mm Spax stainless screws for holding the feather edge boards to the rails, and 4x25mm Spax stainless screws for the capping profile.The posts are positioned on the concrete spurs so the end grain is 20~25mm above ground level, to hopefully reduce rotting over time.

Final result:

The capping profile: