Low level decking Help

[Sam_Newbie]

Hi guys,

New to  DIY and this amazing website. I wish I found this earlier!

I just finished frames (all H3 treated pine) for my deck today (5.2m x 2.7m).

After reading a few posts on low level decks in this group, I am really worried for 2 reasons:

1. I have only 1 off 140x45 bearers, and not 2 off them screwed together as advised in some other posts here. My posts are placed 1300 apart. Posts are 100x100s 350 to 400 deep. Joist are all 90x45s.

2. What worries me more is that my bearer are sitting very close to the ground, it is touching the ground in some location. How can I waterproof it? 

Community manager's note: Check out How to build a low-level deck for expert advice.

 I have attached some pictures if that helps.

The height of the decking currently was druven by the nayural ground and level of the house. Now I understand i should have dug and removed some dirt. Too late for that now, I guess

Any suggestions will be really helpful.

P.S: do I need to put timber between joists and connect them to prevent warping?

[Sam_Newbie]

I have tried to slope the ground to the stormwater drain roughly at the centre to help with the water draining.

[Jason]

Hi @Sam_Newbie,

Thanks for your post. Let me tag the wonderful @Adam_W who has a lot of experience with decking projects. He might have some helpful advice for you. 

Welcome to the community. I trust you'll get loads of helpful information, advice and inspiration for all your projects around the house from our amazing members. It's great to have you join us.

Jason

[Adam_W]

Hi @Sam_Newbie and welcome!
Okay... lots to unpack here...
First off... the timber. H3 timber will rot if it is in contact with soil and having it too close to the soil, say, within less than 150mm, is a risk too as it will be regularly exposed to high moisture levels.
If your posts are only H3 then they definitely will not last.
Personally in such a situation I would have rested the bearers into galvanised stirrups concreted in rather than timber posts as you can be assured of their durability and they won't wick moisture.
I would be concerned about any of that timber that is on or too close to the ground. In seriously heavy rainfall it will flood under there and stay damp for a while. Over time too soil levels rise in low areas as fine material washes and blows in.
If you are to continue with that design you will need 'noggins' between those joist to stop twisting.
I'd also be adding a lot more nails to those hanger brackets. Most appear to only have a couple in each.
Waterproofing underneath? Difficult.
The underside of all timber could be waterproofed before installing it.
Pre-construction you could have excavated, added a drain, laid a pan of drainage gravel etc. but that would have been a major undertaking and the issue there is that over time it will clog up.
Steel may have been a better choice but even then this close to the soil I'd still be recommending additional painting with protective paint.
If I can be brutally honest, and I know you won't want to hear this, but unless you want to replace all of that timber with minimum H4 timber it's going to become a heartache project. It may be great for 12 or 18-months and then problems will start.
In all honesty this is the sort of situation where I would install or recommend paving or concrete (and then tiles) pitched towards the retaining wall with a nice drain on that edge, not a deck.
Now don't get too freaked out as we may have some of the others have some input that can work better for you.

[Sam_Newbie]

Thanks @Adam_W. Sorry, I shoukd have been clear the posts are all H4 treated pine. 

I will add additional nails and noggins as you have noted. Thanks for the advice on that.

Really hoping there is a way to get some level of waterproofing to the bearers as taking them out and putting back H4 is a lot of work and break my budget. All the joist have 50 to 70mm gap between them and ground. 

Due to all this issues now I am thinking to go with Treated pine decking rather than the costly Merbau option we wanted when we started the project. If the decking  fails in an year or two like you have noted atleast I save some m money on d3cking boards this way

[Adam_W]

Hey @Sam_Newbie ,
If you can get that sort of level of clearance across the entire area then it's okay, not ideal but okay.
You could attempt to paint them underneath but that would be difficult and messy. If you can remove a little more soil then lay filter fabric/drainage mat and a thin layer of drainage gravel that will keep the moisture further away.
Treated pine is quite good and can be stained a merbau shade. I'm more concerned about the timber failing below than the decking itself.

You can also add a dampcourse on the bearers/joists before decking is laid to help reduce water movement and build-up.

[Sam_Newbie]

Thanks Adam. I have got the deck tape from Bunnings today. Will pit them on the top of beams and joist before laying the boards. I am also planning to get some dirt scrapped of the ground to create some gap. This will be very hard given all joists are installed. Nevertheless, going to give it a go.

With nothings, do I just nail them or need a joist hanger for them too? Assume one per section will be enough? 

With the additional nails you have mentioned for the joist hangers, should input a nail in each if the holes?

If anyone else could kindly reccomend a way to get some level of additional waterproofing to the underside of the bearers kindly advice me. 

Thanks again @Adam_W 

[ProjectPete]

Great to see you giving it a crack @Sam_Newbie. 

@Adam_W is spot on about moisture, clearance, rotting, etc. It's not something you want to risk so should certainly take the extra time and effort now to address those issues.

I'd get in there and clear as much soil as possible to achieve a minimum 150mm clearance like @Adam_W said. It really should be 250mm or 200mm minimum though. Once you've cleared it, give the undersides and sides of the timber frame 2 coats of waterproofing agent such as this or a cheaper and still adequate option in this. It'll be a bit of a paint to paint the underside but just slap it on thick with a small roller and you'll be fine. It'll be well worth the effort.

You really should nail every hole in those hangers for structural integrity and to prevent noise (creaking).

Are those blocks between the centre bearers set in the ground?

[ProjectPete]

And remember to paint the top of your frame black so you don't see the timber frame between you decking. Ideally go down the sides of the timber at least 30mm too.

[Adam_W]

No worries at @Sam_Newbie,
Sound advice from @ProjectPete too.
Okay, yes, as Pete said get a nail in every hole.
You don't technically need hangers for the noggins as they are really just a rolling brace but there is no harm in using them if budget allows. If you don't add them make sure they are well nailed off to prevent any movement. You'd use 75mm+ long builders nails hammed in from the other side of the bearer/joist (that's why the noggins tend to be staggered, otherwise you can't get nails in).
The noggins should be a tight fit too to allow for shrinkage.