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I’ve built my frame and my total areas is 3.46 x 3.0 metres.
Is it advisable to use whole length decking boards or is there a reason why not. e.g. I can get 3.6m boards and cut them all down to the 3.46 required but is there a reason why I shouldn’t, and use shorter lengths instead?
I’d use whole lengths.
If you cut it down then the (cut) end won't be treated. But that is easily remedied.
I'd avoid joints and short length when practical. The boards tend to warp, and a non-continuous length over a joist is harder to hold down. Also to get screws in without splitting you don't want them near the end, so you need to double up the joists at joints. In your case, you're only wasting 14cm per board, less than one whole board over the job, and you have the advantage that if any boards have minor damage on one end, you can cut that off.
What perchy says.
fit the whole boards and assuming you have an overhang trim the ends with a track saw.
Make sure you use some schaffer's Deck sealant
Make sure you use some schaffer’s Deck sealant
I'd keep their caulk out of it though.
Can you not revise the frame size to 3.6m to save cutting?
Just use whole boards. Its like 50p more for 15cm and you will have support at every end.
Make a planter or something from the offcuts
Can you not revise the frame size to 3.6m to save cutting?
I did actually design it to be 3.6 but miscalculated the height so had to add a bit by way of extra bearers. This means that although I’ve got a great surface for balustrade I’ve reduced the useable width by the width of my framework (70mm x 2). Bit annoying but hey ho, it’s easier to lop off 140mm from each plank than re make the framework.
Full length boards definitely. I'm not a joiner but I've built a couple of decked areas now and the idea of joining them mid way along gets an emphatic no thanks from me.
Also I used really fine (something like 3 or 3.5*70) torx headed deck screws and never had any issues with boards splitting at anything more than 20mm from the ends.
Ronseal and a couple of others make a deck board end sealant that you brush on. Always use that sort of thing after a cut, I've also painted the cut bits of the joists with it.