Laying wooden decking - how much movement?

#1
I'm about to lay some wooden decking (pressure treated pine) on my patio. I've been recommended to leave about 6-8mm between the planks to accommodate the movement of the wood due to climatic conditions. How much vertical movement should I expect though?

The problem is that the height of the decking is limited due to a door which opens onto it. So if I am to avoid digging out the entire 50m2, I've only got about 6mm of space between the top of the planking and the bottom of the door. Is this going to be enough, or should I be spending my Sunday removing 1cm of dirt from my entire patio area?

Cheers
T_T
 
#2
Don't worry it won't expand that much. Think about old doors... Did they leave a cm under on all sides? As long as you have a couple of mm for thermal expansion you will be fine.
 
#3
The decking wont expand up by 6mm. Dont forget the 6mm gap between the boards is in practice 3mm per side. A spacer made from a suitable bit of ply makes that bit easier btw. Dont forget to put a 1% slope on the deck to keep it dry, and a good quality membrane/pea gravel layer underneath.
 
#5
Can I swap my decking for your patio?

There is decking out our back garden from when we moved in and it's shit. I cleaned it off last year, and put a couple of coats of stain on it. Already in some places the stain has worn off. And it gets slippery in winter when it's soaking wet.

Give me a concrete slab patio anyday of the week.

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A2_Matelot

LE
Book Reviewer
#6
Concur with Miner - we have a victorian house and as a consequence (around here) they have quite small rear courtyards so when the children were small we decked over ours as the previous tenants has concreted it. It's just a nightmare to maintain, gets wet over winter, traps all organic debris, gets slushy and slimy, needs powerwashing and scrubbing all the time. If you want I'd lay stone down, will last longer and is easier to look after.
 
#7
Its not that decking is a bad product, but people try to use it as a cheap alternative to masonry in the wrong situations. Wet decking is normally due to it being laid level in a north or south facing location. Any patio laid like that is going to get wet and slimy.

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#10
Problems you might encounter in the future with your decking include warping across the grain (due to the grooves),lifting of edges (especially if nails are used instead of screws),very slippy mould growth (especially when wet in the colder months),rats and mice making a home under decking (try to encourage a fox to live underneath instead),future maintenance (I built mine when I was much younger now the annual painting/cleaning is a nightmare).

Still when completed it should give you lots of pleasure,good luck with your project.
 
#11
The pressure washer obliterates the treated surface of the timber, leaving an abraded layer of untreated wood for the elements to get into. On the wooden bits of my boat I scrub down once per year with a weak solution of oxalic acid. I do the same to the decking at home and thats all the time it gets. Its lasted 6 years so far.
I suspect the various potions sold in the big diy sheds are all a variety of snake oil.

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#12
The pressure washer obliterates the treated surface of the timber, leaving an abraded layer of untreated wood for the elements to get into. On the wooden bits of my boat I scrub down once per year with a weak solution of oxalic acid. I do the same to the decking at home and thats all the time it gets. Its lasted 6 years so far.
I suspect the various potions sold in the big diy sheds are all a variety of snake oil.

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Okey doke, cheers.


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#13
Ideally, the deck surface should not be above the DPC layer (Same applies to patios). Reason being is that when it rains, the splashes will bridge the DPC with a risk of rising damp developing. If you must have it at the height you describe, make sure there is a small gap between the deck and the house wall and build a slight fall in level away from the house to prevent water collecting and bridging the DPC. Avoid damp at all costs as it could become costly to fix.
 
#18
That's my next garden project when the paving is done.... raised decking on stilts as my back garden has a slight slope. To be honest not looking forward to doing it but the other half wants it! :(
 
#20
We do 100s of m2 Decking every year, with everything in life, theres decking, then theres Decking.

I would never use a Softwood for any of our decks, you might just get away with a good Siberian Larch, but thats it.

Most popular timber here is "Bangkirai", with a density of 0,9 it is hard, ******* hard and properly installed will last centuries. Its expensive, at the mo €6-8 per LM, but well worth it. Once this has been oiled, it will retain its colour, even on a south-west location.

Proper installation is vital, and is in simple as follows:

Level the area. Use the same grade and type of timber for the base construction as the decking. never lay timbers on earth, use small paving slabs, dependant on timber dimensions, every 1m with the length of the base timbers, and spaced every 60cm in the other direction. Using rubber pads of differing thickness, or Bitumen felt, adjust the base timbers to a 1-2% elevation away from the house. It is best to run the decking boards with the grooves 90 deg from the house to assist drainage, but obviously some people run it the other way. Pre-drill all boards, regardless what Screw makers claim, if they dont rip whilst screwing, they will in time. If you are building the deck in a high humidity period, i.e. Autumn or Spring (or incidently this present ******* "Summer"!) a 3mm expansion gap between the boards will suffice, the timber has in itself a high humidity content and will shrink. If on the other hand, it has been very dry for a long period, i.e. summer, increase the gap to 5-8mm, because the timber will expand in Autumn/Spring. For end-grain gaps, 3mm is enough, although this tends to clog with dust and shit, can get and stay wet and will eventually start to rot the timber, therefore it is better to have a 1cm gap which you can clean now and again. Sand off all sharp edges and fit plinth boards all round, making sure that they too have no contact with the earth or plants. Use stainless steel screws, they wont bleed into the timber, and wont rust, rust actually also attacks timber.

The best surface treatment is with oils, they are flexible, dont flake and protect the timber against the elements all year round. It will also stop the build-up of moss and therefore will not become slippery.

And never ever pressure wash anything made from wood, it will take off the first layer of fibres thus opening the timber for insect and mould, and is prone to excessive flaking.

Any timbers properly installed will, or should last a lifetime.

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