Composite deck expansion for walls

[Dylan T]

Hi all - I'm progressing through my composite decking project slowly but surely, and a new question has popped up regarding expansion gaps. The manufacturer instructions say to keep a 20mm expansion gap against any solid structure. However as I've started to lay the boards out I've realised how big 20mm looks, and you can see the ledger boards, the spacers against the walls (my ledgers are 10m off the wall as it is) and just looks way more than I remember seeing on other decks, and even more than their own website images seems to show. A search online shows that most manufacturers recommend 20mm although several say 10mm; but this is all coming from manufacturers so are they being over the top or is there really a reason to allow such a big gap? Visually 10mm looks more reasonable to me as this brings it in line with the ledger, would allow me to wash away any muck in the gap and isn't as big visually. Also I don't think my boards have much timber in the composition at all - they definitely seem more plasticy than some and were on the cheaper side so I'm not sure how they would expand that much.

Thanks!

 

[opps]

Our composite decking has 10mm expansion gaps where the boards meet the extension wall.

Horrible stuff to work with though. Hardwork on the saw blades. Ours was one of the more expensive ones (Trex).

Ours is like exterior MDF with a wood effect skin.

The best thing that I can say about it is that the dog pee doesn't soak in.

 

[Dylan T]

Our composite decking has 10mm expansion gaps where the boards meet the extension wall.

Horrible stuff to work with though. Hardwork on the saw blades. Ours was one of the more expensive ones (Trex).

Ours is like exterior MDF with a wood effect skin.

The best thing that I can say about it is that the dog pee doesn't soak in.

Thanks for the reply - have you notice the deck expand much at all?

 

[opps]

Thanks for the reply - have you notice the deck expand much at all?

No, I haven't but after 4(?) years, the sawn ends of the boards have expanded very, very slightly.

I built "boxes" where the stairs go down to the lower garden (either side), the mitres on those have opened slightly but I suspect that might be the result of the natural timber frames having expanded rather than the Trex decking.