Posts for raised decking: timber or plastic?

[crispy_wafer]

steel frame?  then clad it, if you want a timber look!

Edited June 8 by crispy_wafer

[Lift span]

I'm going round in circles with this!

 

I've contacted two manufacturers of plastic posts. One says you can't use their posts in raised decks over 1m and the other says you can with diagonal bracing. I just don't see any evidence of anybody using it which puts me right off.

 

 

The other issue that had come up is the balustrade. A manufacturer advised it may be better to fix into steel at that height. So, I've started looking at steel frames as you say Crispy.  This is all turning into a massive time waster!  I can see why the pros just concrete timber in the ground and let the home owner worry about it in a few years!

 

On 08/06/2024 at 06:20, crispy_wafer said:

steel frame?  then clad it, if you want a timber look!

 

[Lift span]

On 05/06/2024 at 18:11, JohnMo said:

A snippet of our drawings for our deck structure, we moved the hill about instead of a big support structure.  Fairy simple steel, galvanised and wood between.

 

 

 

 

How did you attach your balustrade?  Seems that there are lots of ways to do it and some are a bit dodgy for raised decks.

 

I'm after this style of rail below but not sure if it's acceptable just to screw down into the frame at the bottom of those posts.

 

 

 

 

The second half of this video shows some common issues:

 

 

 

[JohnMo]

9 minutes ago, Lift span said:

How did you attach your balustrade?

You really need a proper design, depending on actual drop and wind load and infill type, will change things dramatically.

 

27 minutes ago, Lift span said:

I'm going round in circles with this

Because you are trying to do a job a structural engineer needs to complete.

[Temp]

I wouldnt put wood into the ground unless it's oak. Pressure treated softwood is barely OK but never use a strimmer near it. It cuts the pressure treated layer. I found out the hard way.

 

Our house has some external oak posts, typically holding up roof overhangs. We dug pad foundations filled to just below ground level, then brick piers (1.5 * 1.5 bricks, 4 courses high with the top course being 45 degree plinth bricks). The hole in the middle was filled with concrete with a Stainless Steel pin sticking out the top. Then a square of lead was put on top, dressed about 1" down the slope. Then the post drilled with a hole to take the pin.   

 

 

You could also buy or cast your own concrete block pier to get the wood out of the ground...

 

https://www.ebay.co.uk/itm/275700203774?chn=ps&_ul=GB&var=577119817626&_trkparms=ispr%3D1&amdata=enc%3A1l_9kbZx_TFyjSM9PSQnmNw71&norover=1&mkevt=1&mkrid=710-134428-41853-0&mkcid=2&mkscid=101&itemid=577119817626_275700203774&targetid=1647205089000&device=c&mktype=pla&googleloc=1006886&poi=1006818&campaignid=21194089662&mkgroupid=162053931300&rlsatarget=pla-1647205089000&abcId=9406426&merchantid=6995734&gad_source=1&gclid=CjwKCAjwyJqzBhBaEiwAWDRJVIW55VLnv0qmo2qIlY1t4Av1Unz35lGaM2bEf3tGRdE1ezBMKB1ZZRoCV-EQAvD_BwE

 

 

 

 

 

 

[Lift span]

12 minutes ago, JohnMo said:

You really need a proper design, depending on actual drop and wind load and infill type, will change things dramatically.

 

Because you are trying to do a job a structural engineer needs to complete.

 

 

You may well be right! I'm a chartered engineer myself so I'm generally happy with the numbers and I've had mixed success with structural engineers in the past. With a timber build I'm happy all the information is out there eg. The TDCA Code of Practice  - Raised timber decks is pretty comprehensive. Yes, no timber is the ground thanks!

 

It's just the alternatives I'm looking at. No doubt I'll just end up with 150mm timber posts (probably oak) on steel brackets in concrete with a standard timber frame above with lots of cross bracing.

 

I will ask my local SE though to see what they say.

 

Different view points are always appreciated though!