Composite decking

[bar2345]

Hi all, I will build composite decking  at the beginning of June, 52m2, will be installed on the existing patio on slabs. Slowly preparing everything. Frame will be wooden, joists 6x2 treated tanalised c24, my question is:

Is there anything I can use to extend the life of joists? Will use decking tape on top, but what about the rest? Bitumen paint doesn't have good recommendations, maybe some wood preserver? pine tar oil? or maybe normal fence paint goood enough?

 

 

[Temp]

Welcome to the forum.

 

There are composite joists as well but quite expensive..

 

https://ecodek.co.uk/product/ecodek-super-stiff-composite-joists

 

https://build4less.co.uk/products/composite-decking-joists-plastic?variant=31679927976032

 

If it doesn't need to be 150mm tall there are cheaper lower profile composite battens for use where decking is going something like an existing concrete slab. Lower height also avoids needing planning permission.

 

 

 

[Conor]

Plenty of air circulation underneath and dpc under the joists where they rest on top of the support pads. Fyi 4x2 is normally more than enough for a deck, as you can put plenty of support pads in.

[Pocster]

I’m going to use ryno . Joists are aluminium .

[bar2345]

Unfortunately I already ordered and paid for timber joists

[Pocster]

Literally just paid for mine .

[Radian]

On 14/05/2022 at 21:57, bar2345 said:

Hi all, I will build composite decking  at the beginning of June, 52m2

Are you going to take out a Mortgage to pay for that? 🤣

 

I keep meaning to start a topic on the eye-watering cost of composite decking and how the financial side stacks up.

But yes, as Conor mentions, good air circulation is probably the most effective measure for preserving the 6x2s. But are you planning to rest them directly on the patio slabs or space them off with something?

[bar2345]

3 hours ago, Radian said:

Are you going to take out a Mortgage to pay for that? 🤣

 

I keep meaning to start a topic on the eye-watering cost of composite decking and how the financial side stacks up.

But yes, as Conor mentions, good air circulation is probably the most effective measure for preserving the 6x2s. But are you planning to rest them directly on the patio slabs or space them off with something?

Yeah it will be expensive 😀 

 

It will be directly on slabs, unless you know better solution?

[markocosic]

Keep it dry.

 

Airflow underneath it.

 

Don't rest it in "waterproof bowls" of supports. Do rest it on a piece of DPC where the supports are porous (e.g. concrete) and ensure that the DPC is 'n' shaped not 'u' shaped.

 

Cut ends to hang in "fresh air" - you support the beams some distance back from the cut edge so that the bit that might be touching water is side grain.

 

Consider something on top of it - especially the cut edge - such as a strip of roofing felt (easier than DPC as sticks in place) again in an 'n' shape  to shed water.

 

Other than being kept dry you shouldn't need to do anything with tanalised timber.

 

 

Here's ours (my wife has since been introduced to the concept of a straight edge) with some leftover acrylic facade paint (got frozen in winter so not much good but very sticky) holding the bitumen down until the deck boards are fitted. Water falling through the gaps in the deck drip-edges off bitumen onto either the floor or another piece of bitumen and then the floor. (noggins make an enormous difference to stiffness; install near the bottom so that they're clear of your deck boards)

 

 

 

If you have any posts that are just in compression the threaded feet are excellent for keeping them dry and levelling them.

 

 

 

Consider cleaning. How are you going to hose cat / fox piss and shit out from under the deck when they move in? Leaves that blow in under the deck? You might want some 1/2" mesh dug into the ground and fixed to the bottom of the deck edge to keep the wildlife and leaves out.

 

 

 

[markocosic]

Directly on slabs - no.

 

Adjustable feetsicles make life easy:

https://timberfixings.com/store/Eurotec-Adjustable-Decking-Pedestal-ECO-M-Adjusts-from-35mm-up-to-65mm-p50614257

 

Or slice up something that doesn't rot with chopsaw and stick a piece of DPC on top if you're being cheap.

 

Timber doesn't sit on paving slabs directly.

[Pocster]

1 hour ago, markocosic said:

How are you going to hose cat / fox piss and shit out from under the deck

Human also for when the party goes ‘ that ‘ way …

[bar2345]

1 hour ago, markocosic said:

Directly on slabs - no.

 

Adjustable feetsicles make life easy:

https://timberfixings.com/store/Eurotec-Adjustable-Decking-Pedestal-ECO-M-Adjusts-from-35mm-up-to-65mm-p50614257

 

Or slice up something that doesn't rot with chopsaw and stick a piece of DPC on top if you're being cheap.

 

Timber doesn't sit on paving slabs directly.

Maybe I will install posts on this and a piece of dpm

https://www.ebay.co.uk/itm/255258135847?hash=item3b6e920d27:g:uYoAAOSwP9VhpOfd&amdata=enc%3AAQAHAAAA8KQ9lyn%2F7aRf0wjEG6ROLR6EyGpziqbedhz9h3jM7lk95KsOQOsWHB4PBY6cIPNVZxZ5wpjg4CVLmN94xN3E3YOqZ5pbvpRtvJHn0r9Rbg%2FpN3a51tLfTRDaVZdf4l6gxUPyWYBL3RP9EDPYfQcPqcTEXTAC%2FvIb0ICcW7dd1q8yBVHelrfRmi8Ao55OOcwChxCKr%2FZLoFnKXkJOVrZYTCDG%2FtW%2BIXm0vR3Fn%2BTK7Xlea9oKCz4GiOOIzyR1%2B1AAUK2rq8bq%2BxMjiRv40MKWhGu8tXUgHUVxnalaQ9oSWwkCs0kZN41IoSjcuEr6c%2BiJPQ%3D%3D|tkp%3ABFBM5JXR35lg

What did you use to join joists? Screws or joist hangers?

My decking is a bit more complicated, 1/4 will be installed on concrete posts as seen on photo

 

 

Edited May 16, 2022 by bar2345

[AdamSee]

I built a deck for my parents summer house using recycled plastic wood bought from this place. https://www.earth-anchors.com/product-category/lumber/

 

The deck is in a really wet part of the garden and was worried that using timber for the structure and supports would mean that in a few years I would be doing it again. The top was still finished off using bod standard wood decking from wicks so that it could be painted to match. 

 

Peace of mind is worth its weight in.......recycled plastic, because its really bloody heavy if I remember correctly. 

 

 

 

[markocosic]

The screw piles are the equivalent of your concrete posts.

 

Bearers sit on top of these. They're only joined above the screw piles where there's no bending moment. They're sistered (more than one in parallel) with joints staggered (alternative scree piles) and were glued/screwed to stop them peeling away from each other sideways. The screws/glue don't carry any load though. The wood mostly sits there by gravity. Screes from the piles into the bottom of the bearers hold them down.

 

Then there are the joists. These sit on top of plastic shims near their ends to elevate them 5 mm above the beaters.A gain they are only joined where sit on the bearers so there's no load on the join. There's a 10 mm gap between them to let the end grain dry; with a short piece (600 mm) glued and screwed to the side. Again this doesn't carry load. Gravity sits them there. The joiners stop them moving relative to each other. A couple of tie downs hold the joists to the bearers in the corners for wind uplift; otherwise the joists and the deck could slide around on the bearers.

 

No meaningful loads are carried in shear. It's all stacked on top of each other for load carrying purposes. Only the tie down straps carry shear. The noggins are screwed because I had screws. If I had a nail gun I'd nail them.

 

 

In your case I would cut the tops of those posts level, and sit your bearers on top of those on spacers. Hold the bearers down using straps that are bolted through the existing holes on the concrete posts. I wouldn't try to attach the bearers to the sides using bolts in shear. They'll squash the wood then move. Sit the bearers on top of the slabs with spacers.

 

You know how well the slabs are levelled and how stable they are. I'd use the adjustable £2 spacers myself. £1 fixed spacers false economy. Sitting on the wall is probably better than sitting on the slabs of you can.

 

Do you plan to attach to the house itself? If so remember to leave a gap between the ledger board and the wall for drainage.

 

If you're short on height then you could use just hangers off the bearers rather than gravity. Just cover the tops of it all such that water can't run down into the joints.

[Temp]

On 15/05/2022 at 09:45, bar2345 said:

Unfortunately I already ordered and paid for timber joists

 

If you need to cut them to length try leaving the cut ends in a bucket of preserver/creosote overnight.

[bar2345]

27 minutes ago, Temp said:

 

If you need to cut them to length try leaving the cut ends in a bucket of preserver/creosote overnight.

luckily I will not have many cuts

[bar2345]

45 minutes ago, markocosic said:

The screw piles are the equivalent of your concrete posts.

 

Bearers sit on top of these. They're only joined above the screw piles where there's no bending moment. They're sistered (more than one in parallel) with joints staggered (alternative scree piles) and were glued/screwed to stop them peeling away from each other sideways. The screws/glue don't carry any load though. The wood mostly sits there by gravity. Screes from the piles into the bottom of the bearers hold them down.

 

Then there are the joists. These sit on top of plastic shims near their ends to elevate them 5 mm above the beaters.A gain they are only joined where sit on the bearers so there's no load on the join. There's a 10 mm gap between them to let the end grain dry; with a short piece (600 mm) glued and screwed to the side. Again this doesn't carry load. Gravity sits them there. The joiners stop them moving relative to each other. A couple of tie downs hold the joists to the bearers in the corners for wind uplift; otherwise the joists and the deck could slide around on the bearers.

 

No meaningful loads are carried in shear. It's all stacked on top of each other for load carrying purposes. Only the tie down straps carry shear. The noggins are screwed because I had screws. If I had a nail gun I'd nail them.

 

 

In your case I would cut the tops of those posts level, and sit your bearers on top of those on spacers. Hold the bearers down using straps that are bolted through the existing holes on the concrete posts. I wouldn't try to attach the bearers to the sides using bolts in shear. They'll squash the wood then move. Sit the bearers on top of the slabs with spacers.

 

You know how well the slabs are levelled and how stable they are. I'd use the adjustable £2 spacers myself. £1 fixed spacers false economy. Sitting on the wall is probably better than sitting on the slabs of you can.

 

Do you plan to attach to the house itself? If so remember to leave a gap between the ledger board and the wall for drainage.

 

If you're short on height then you could use just hangers off the bearers rather than gravity. Just cover the tops of it all such that water can't run down into the joints.

 

No I will only attach it to slabs and concrete posts

 

[bar2345]

What lenght of structural screws will be good to attach joists to ledgers? 100mm or 150mm? or 125mm?

[Dave Jones]

19 hours ago, bar2345 said:

What lenght of structural screws will be good to attach joists to ledgers? 100mm or 150mm? or 125mm?

use galv nails they are stronger. 90mm

[JohnMo]

21 hours ago, bar2345 said:

What lenght of structural screws will be good to attach joists to ledgers? 100mm or 150mm? or 125mm?

You be using hangers according to most design guides I have read.

 

 

design_a_deck_planning.pdf

[Bob77]

On 14/05/2022 at 21:57, bar2345 said:

Hi all, I will build composite decking  at the beginning of June, 52m2, will be installed on the existing patio on slabs. Slowly preparing everything. Frame will be wooden, joists 6x2 treated tanalised c24, my question is:

Is there anything I can use to extend the life of joists? Will use decking tape on top, but what about the rest? Bitumen paint doesn't have good recommendations, maybe some wood preserver? pine tar oil? or maybe normal fence paint goood enough?

 

 

What type of composite decking are you going for? I am planning to use some once the extension is finished, but it will be more like 20 sq metre so not quite as eyewatering. I've got a couple of dozen samples sitting outside in the garden at the moment, and have tested them with a few likely substances (oil, red wine, ketchup!) for staining. Not going to be ready for it until September/October so I've got a while to think about it.

 

Preliminary results are that cheap composite comes in two types: fake and plastic looking, or more realistic but with a porous surface that stains easily (and I suspect would fade more easily). Mid range stuff seems pretty bombproof, looks decent and has a nice waterproof coating (but may be a little more slippery?), whereas the high-end stuff from Millboard seems like a totally different animal - thicker planks but lightweight with an almost pumice-like texture to the core, and with a much more authentic wood grain finish. However at well over £100 a square metre so it ought to be. I'm erring towards the NewTechWood Ultrashield which comes in at about £84 a sq metre – pricey but it feels like decent quality stuff and the colours are nice.

Edited May 30, 2022 by Bob77

[bar2345]

On 30/05/2022 at 22:26, Bob77 said:

What type of composite decking are you going for? I am planning to use some once the extension is finished, but it will be more like 20 sq metre so not quite as eyewatering. I've got a couple of dozen samples sitting outside in the garden at the moment, and have tested them with a few likely substances (oil, red wine, ketchup!) for staining. Not going to be ready for it until September/October so I've got a while to think about it.

 

Preliminary results are that cheap composite comes in two types: fake and plastic looking, or more realistic but with a porous surface that stains easily (and I suspect would fade more easily). Mid range stuff seems pretty bombproof, looks decent and has a nice waterproof coating (but may be a little more slippery?), whereas the high-end stuff from Millboard seems like a totally different animal - thicker planks but lightweight with an almost pumice-like texture to the core, and with a much more authentic wood grain finish. However at well over £100 a square metre so it ought to be. I'm erring towards the NewTechWood Ultrashield which comes in at about £84 a sq metre – pricey but it feels like decent quality stuff and the colours are nice.

I  will use this stuff

 

https://dura-tec.co.uk/product/dura-tec-composite-decking-charcoal-3600mm-x-140mm-x-23mm/

[bar2345]

Project done!!!

Took 2 weeks, a lot more effort than I expected but was worth it.

[Radian]

Looking good! How do you rate the Dura-tec composite deck boards? They seem a fair bit cheaper than others I've looked at.

[bar2345]

25 minutes ago, Radian said:

Looking good! How do you rate the Dura-tec composite deck boards? They seem a fair bit cheaper than others I've looked at.

This is my first decking ever done so hard to say, I didn't have any issues with it. Probably need a few years to make a judgement. One thing that I notice is when you walk on it without shoes you will have your feet black, don't know if that is normal for composite decking