Can I drill holes to drain pooling water on decking

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Hello,
Decking of our new home has water pooling in the middle. See the attached image.

We moved in last year and the deck was in a very poor condition after this winter, it definitely got ignored by us over the winter amid the chaos of moving, but quite sure that previous owners also had not been looking after it very well. Its like 4-5 years old, so there was not much/any damage, it was just coated with dirt and slippery with algae/mildew in lots of places.

A month back I cleaned thoroughly and oiled and it looks much improved, no more slippery and I could see the wood. It has been re-oiled. But I have noticed that water pools in the middle on many of the boards. May be it was not installed correctly or it has bowed in the middle following the contour of the garden? In summers the pooled water dries quite fast but in winters its there for a long time.

Can I drill a few holes, 1-2 in each groove where water collects? I will treat the hole with the decking oil I used on the surface, can do 4-5 coats. Think that should prevent the rot to start from the holes. But I am concerned that it might affect the strength of the board? Attaching a picture of the problem.
PXL_20220618_164546267.jpg
 
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a few 8mm holes will help try to spread them out so they don't create a weak spot in the plank. The other option is to unscrew pack some ply under one end to give a lift.
 
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have a look underneath. one or more of the supports has probably sagged or rotted (or was omitted in the original build)
 
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If you can’t see underneath, try squeezing a phone in somewhere to take a photo? Please don’t drop the phone between the boards though!

Or a decent endoscope might help; the cheapo eBay/Amazon jobs typically don’t focus more than a few inches away so might not be much help.

Otherwise…

Drilling holes as you describe sounds OK to me. Might be ugly though? Esp. if the holes are staggered / not in a straight line? In any case be careful not to drill where there’s a joist underneath :)

That said, seeing that photo, a rotten/broken frame was my first thought too. I may be tainted by my own experience though - there are surely other possible causes as you suggest.

Still I’d prefer to check the frame for peace of mind… any rot will likely get worse and might cause danger. If there’s no damage, packing with shims sounds worth a try, as already suggested.

Fwiw, some notes on removing deck boards for re-use, based on my recent experience…

My deck screws were of a type that break easily if over torqued – true whether they’re going into a new deck or coming out of an old one!

The screw heads also had gunk build-up from years of oiling so the Phillips head bit in my drill would just spin when I tried to unscrew… fixed by hammering the screwdriver bit into the screw head before attempting to unscrew.

I left the bit in its holder and just hammered the top of the holder (that’s the holder that goes in the drill/driver). Having a spare holder and bit helps. Still there were lots of broken/stuck screws left to deal with before the boards all came up.
 
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I thought all decking did this and that's why it's always slippery no matter how well you look after it ;) It seems reasonable if you don't go overboard. Holes the thickness of the grooves in the decking...

Is decking supposed to be laid with a slight incline if done properly so it drains?
 
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So from my understanding so far and from reading numerous other posts and forums... Firstly yes decking should be installed at an angle to drain water along one end. If my decking was installed properly or not, I dont know because it was done 5 years ago by previous owners. There is clearly a bow in the middle probably one of the joists/supports sinking a bit. Secondly the better way of installing decking is smooth side up. This is much more comfy to sit/walk/kneel on and also much easier to clean and maintain. Grooves not only trap moisture but dirt and gunk!! Its not straight forward to broom them clean - you need to use a hose! Grooves might look aesthetically pleasing but I am convinced that they are not functional...

Now back to my situation, I have decided to not drill holes. Tested on a piece of wood and I would need ~8 mm holes to drain water. But that could weaken the planks. Smaller holes would trap dirt/debris and promote rotting. Shimming up the underneath support is not possible without unscrewing all of the decking its almost 5 m x 5 m. If I do end up doing it, I would just reverse the planks. At the moment I will try keeping them clean and oil every 6 months. Next summer I will turn them over!

Have our second child on the way, expected to be born in a months time, so there is too much excitement, lots of work in the home still remaining and not much time! :) :)
 
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If decking was supposed to be the other way up, they wouldn't spend all that time making grooves in it and it would be much cheaper. :)

Relaying it does sound a nightmare (you might just push the dips along if you shim) so good maintenance is your best bet.
 
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If decking was supposed to be the other way up, they wouldn't spend all that time making grooves in it and it would be much cheaper. :)

Relaying it does sound a nightmare (you might just push the dips along if you shim) so good maintenance is your best bet.
Some decking has two different machined faces so he might be lucky. That said any decking I've ever seen after it's been taken up will have dark srips on the underside where it's been in contact with the joists and won't lend itself to being flipped anyway. All assuming the screws come out OK of course. I'd just continue with maintaining it.
 
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If you can’t see underneath, try squeezing a phone in somewhere to take a photo? Please don’t drop the phone between the boards though!

Last year friend dropped their phone on a friend's decking. Although almost exactly the same width as the gaps in the decking, it managed to fall through the gap. At very short notice, I was summoned to lift a board to retrieve the phone. Needless to say, The screws were rusted. I mullered a brand new 8mm Heller cobalt bit drilling the screwheads out.
 
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Well which is the right way of installing decking is debatable but you can find a lot of information from reputable sources who recommend smooth side up. Like this one https://www.wood-finishes-direct.com/blog/what-way-is-the-right-way-up-for-decking-boards/. I trust the advice from this source. Personally, have a friend who followed this advice roughly 5-6 years back when getting their new deck fitted and as per them they find it very easy to keep their decking clean.

Now back to my situation - I am not doing anything this year, just clean and re-oil early next spring. Next summer will try to unscrew a couple of boards and see if I can reverse the planks. If not then shimming would be the next option.
 
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That article also recommends removing any standing water after it rains which seems a good idea, whenever practical to do so.
 
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I can't really see shimming working, the levels changes will be so subtle it will likely just push the problem elsewhere.
 
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That article also recommends removing any standing water after it rains which seems a good idea, whenever practical to do so.
YEs but it will be many times easier when smooth side is up. With grooves you will need to sweep all the way to end of each plank! or use a mop to sock it up and squeeze it out! Water is one problem, other is dirt and gunk.
 

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