What ho one and all,

Just asking because I am interested.

When a neighbour built their SIP house, they installed a treated timer patio decking at the back. Of course, all the decking is screwed to the under structure and looked good. But over the years, as with most externally used UK construction 'rubbish' timber, the unseen structure has rotted and as I write, they are having it all replaced.

My rhetorical question is, if installing timber decking, what is the best way to ensure that it lasts longer than 10-15 years? Or is it something that one has to bit the bullet and replace every X years?

Thanks and toodle pip

The substructure rots as it is almost permanently moist/wet. It you want it to last longer you need to construct in a way that allows it to dry out after rain.

As Jonti says, the supports stay wet for the best part of the year and unlike the decking, the purlins never get a refresh of the surface treatment

Extra treatment on stuff under the ground and as it comes out of the ground ?

About to put some stone down after 25 years of decking which lasted well.
Rat/s have been a slight issue recently, a lot of neighbours feed birds and they get into sheds where the feed is stored. It is also quite slippy for winter months. Would build in bait stations if doing again.

My decking is at end life now after 25 years probably more luck than judgement - simple redwood 20mm x 100 mm thick pressure treated but not stained. It was refurbed and treated once about 6 years ago.
Frames of 3x3 softwood treated posts sitting on breeze blocks and a bit of dampproof - have never rotted. Treat any cut ends with preserver. Rot on planks mainly around nails that were not treated.
Coated screws were used mainly and did not have same effect - so perhaps stopped water pooling under the wood as it held them tighter to frame ?

I am about to take out some 3x3 posts that were put in 25 years ago and are still rot free.
They were a swing an shelter at various times. Not special timber just treated soft from wickes.
Treat any cut ends with preserver.
I coated the timbers in bitumen underground, I am pretty sure they were wrapped in plastic too- advice from my Dad! Make sure any concrete slopes away from interface point on the post too.
Quite high water table - clay about 18 inches down.

No timber in the ground, whatever it is or however treated. Telegraph poles impregnated with the filfthiest old-style Creosote (coal tar based, carcinogenic, banned from retail supply (tho its same-name weedy substitute has same smell added) but still allowed industrially) still rot.

Design all timber to drain/ventilate/re-dry, not sit in a puddle, and use douglas fir, larch or other semi-durable-grade species. No 'treatment'. Should last forever then.