Decking expansion gaps

Discussion in 'Carpenters' Talk' started by masonst0rm, Aug 3, 2006.

  1. masonst0rm

    masonst0rm New Member

    Putting decking down do I realy need to leave expansion gaps or will just butting them up be OK
  2. foxy

    foxy New Member

    You should have a gap. Most deck boards you buy will be fairly green and upon drying out will shrink across their width so whatever gap you leave will increase over the following weeks. So even if you butt them up you will end up with roughly a 3-4mm gap.
  3. Neil the Joiner

    Neil the Joiner New Member

    Hi mate, you need a gap. get 3 off cuts of joist or deck board about 200mm lond and put a 90mm paslode nail into each of then then use them as spacers, one at either end and one in the middle, that will keep you nice and uniform.
  4. Mr. Handyandy

    Mr. Handyandy Screwfix Select

    Think about it you lot.

    If your boards are fresh from the yard and recently dipped, they are likely to be at their widest, NOW.

    If you put these boards down now, with a 3mm gap, next summer you will have a 10mm gap.

    Freshly dipped boards should be put down tight.

    They may produce a small gap by the end of the summer. This winter, they will 'plim' up and be tight again. Next summer they will have a 4-6mm gap.

    Pre-weathered boards should be fitted with a gap.

    Mr. HandyAndy - really
    ANDY1409 likes this.
  5. The Hay

    The Hay New Member

    I only put down heartwood larch decking boards....freshly milled and cut to order.

    Therefore I butt them tightish (1mm if at all) as they are holding all the moisture that they ever will....a 3mm gap would soon be a great big gap if done that way.

    Pressure treated, imported softwood (the green **** that timber yards sell) will shrink like billy oh too. And next year it will probably rot too as the timber is cr*p to start with and it is often milled with the grain cupping up.

    All in all you really have to make a call on the timber as you are working with it....the first few screws (yes, screws....not paslode nails) will let you know.
  6. Neil the Joiner

    Neil the Joiner New Member

    Wrong, when you say "freshly dipped boards" what do you mean? Boards arent dipped there pressure treated and if you put down new boards now with a 3mm gap they wont be 10mm of a gap next summer, you wont get that much movement in a redwood board. you cant put boards down tight its not the correct way to do decking.
    Mr "Handy" Andy might do it this way but Neil the "joiner" does it the right way with a gap, the way any professional would.
  7. Mr. Handyandy

    Mr. Handyandy Screwfix Select

    Sorry, the opening poster is putting down redwood, is he ?
    Funny, I didn't read that. I didn't read softwood either, but hey, wood is wood, only separated by quality.

    Freshly dipped is just a way of saying treated(by any means) and so wet with the treatment.

    Why don't you accept that a board recently bought will be at it's widest now, than at any time in it's lifetime ?

    Therefore, if you put it tight, it will not get tighter, it will almost inevitably get looser(or gappier).

    I would expect you to know the properties of wood and it's reaction to weathering.

    Mr. HandyAndy - really
    norman fox likes this.
  8. audi-evo

    audi-evo Active Member

    "Why don't you accept that a board recently bought will be at it's widest now, than at any time in it's lifetime"

    don't know about decking but with wood flooring (if wood is wood) the expansion gap is there because you can't be sure that it has been at the highest temperature and the highest humidity of it's lifetime.
    If you fit the decking on a day at 18 degrees with a humidity of 40% it is very likely another day will be higher either in temperature or humidity or both, this must affect the timber.
  9. Neil the Joiner

    Neil the Joiner New Member

    The most popular deck board right now is redwood (red pine)and if you leave a 3mm gap it wont go to 10mm no way, not unless its real ****** cheap stuff.
    I dont know if i would say that its at the widest it will ever be ... ever when it get treated, I know where your coming from but maybe a bit more research on your parts needed. But maybe im wrong and youv been doing decks for years??
    Its not worth arguing about anyway.
  10. masonst0rm

    masonst0rm New Member

    Decking is pressure treated soft wood but alegidly guaranteed to last 10 years.... I hope as its not cheap. All comments welcome, you can see why I sort advise as the answer is far from clear.... I am going to screw them down and not nail them so it looks as if I half way there.
  11. Mr. Handyandy

    Mr. Handyandy Screwfix Select

    Take my word for it. I know it's difficult. You don't know me from Adam.

    As an example. I did my decking. All softwood. Medium quality.

    I fitted it in the summer. It was freshly treated.
    It was sold as 144mm wide. It was actually 147-148mm wide when it was delivered.

    I anticipated it would shrink. I fitted it as tight as I could and nearly broke my back forcing the boards togaether.

    Two years later, it is fine.

    There is now a gap of 6-8mm between all boards.

    I think I was right to force them together tight as if I had left a gap of 2-3mm, I would now have a 'hole' of 10-11mm between each board.

    In the winter, it fills up to a gap of only 2mm.

    Mr. HandyAndy - really
  12. !!

    !! New Member

    The hardwood and softwood deck boards I buy are air dried and stacked in sheds so they are pretty stable and around 16-18 % moisture content so I leave a 5mm gap between boards.

    The one bit of advice thats missing is that you should stain and seal exterior wood work, this reduces the amount of moisture movement, checks, splits, structure decay, cupping and all the other problems that result in a ear bashing from a grumpy customer
    ANDY1409 likes this.
  13. dunc

    dunc New Member

    It can often depend on the batch of timber and its subsequent treatment. I did my deck in 3 stages so I noticed the difference between each batch of timber. Some shrunk more than the others.

    One deck I did for a customer, I laid tightly together and its still a tight fit 2 years later. But hasn't caused any problems.

    I lay decks with a tight fit mainly because kids will lose all sorts of things down the wider gaps.
  14. Mr. Handyandy

    Mr. Handyandy Screwfix Select

    ...and my decking instructions said NOT to stain it for two years. But it did get lashed with Cuprinol. :)

    Mr. HandyAndy - really
  15. !!

    !! New Member

    don't stain for 2 years, I don't know anyone who likes that wankie green colour
  16. Mr. Handyandy

    Mr. Handyandy Screwfix Select

    It don't stay that colour for very long. Couple of weeks, it's tan/beige/buff colour.

    Mr. HandyAndy - really
  17. norman fox

    norman fox New Member

    No do not leave a gap.Handy Andy is correct.New boards will never expand they will only contract and leave you with a bigger gap.I have seen this happen so many times.They will look unsightly and expose the supporting timber.I have never seen a case where boards were butted up and then expanded and buckled.It's a fallacy.
  18. wuddy

    wuddy Member

    its not an expansion gap its a drainage gap
  19. norman fox

    norman fox New Member

    No it isn't.Every brochure published on decking installation says it's to allow the decking to expand and as most decking has grooves how could water run out of the grooves and go down the gaps.Think about it.
  20. stu1312

    stu1312 Member

    you've all worried me now that my gaps in my decking are going to be massive chasms in the next year!

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