Need help with low-level decking in alfresco area

[Faheem]

Hi,

I need some help with type and dimension of fixings and timber I need to lay decking in my alfresco area.

The width of the total area is 4670mm. 
The length is 5310mm
The total height is between 160-170mm (if I flush it with the existing brick edge at the bottom of the sliding doors)

I am planning to use 90x19mm merbau decking.

I need to know: 

1) The dimension of the bearers and the required gap between them. And how many? 

2) The dimension of the joists and the required gap between them (I read it should not be more than 450mm)  And how many? 

3) How to connect the bearers with the ground? The dimension of the fixing needed? I read Anka Screws are better than Dyna bolt and easy to work with for DIYers.

4) Hw to connect the joists with the bears. Name and dimensions of the fixing please?

5) I want to lift he bearers slightly above the ground to minimize erosion. Will 10mm window packing work ? or are there any alternatives? 

6) Do I need rubber paint coat on the slab before laying anything?

Thanks alot,
Faheem

[StevieB]

Welcome to the Bunnings Workshop community @Faheem. We look forward to following along with your deck project.

Let me tag @Adam_W, @tom_builds and @MitchellMc for their thoughts. @MitchellMc will be happy to help with any questions when he's back on the site on Friday.

If you haven't already, check out How to build a low-level deck by @Adam_W and Inspiring low-level deck builds by Workshop community members.

Stevie

[MitchellMc]

Hi @Faheem,

I'd encourage you to read through some of the many low-level deck projects our members have contributed. They all feature a similar approach detailing the answers to your questions.

Are you creating a single level deck? If so, you don't really have any bearers; you have joists and a frame. Commonly, in such small space requirements, our members build their structure with 90 x 45mm H3 Pine. 450mm is a good spacing for joists, and the amount required will be your width divided by 450mm. How you run your decking boards will determine how many you need. The decking boards are run perpendicular to the joists.

You'll have a 61mm gap under the timber once you remove the 19mm decking and the 90mm joists, so I'd recommend using Builders Edge Pedestal Foot Smallfoot 35 - 60mm to support the timber. These will allow you to adjust for any slope in your slab.

You can use Pryda Joist Hanger Stainless Steel Suits 45 x 90mm to connect the joists to the surrounding frame or simply screw the timbers together.

By creating a single level deck, you'll have 61mm below your timber and the concrete slab. This will give you a decent amount of room for airflow and to stop water buildup. You could still paint the bottom of the timber with some type of rubber paint, but I see no benefit in painting the concrete slab.

Please let me know if you have any questions.

Mitchell

[Faheem]

Hi @MitchellMc , 

Thanks for the detailed response. Much appreciated.

Just few quick questions. 

1) I really want to join the joists with the concrete slab and Builders Edge Pedestal Foot Smallfoot 35 - 60mm do not have any hole to connect the footing with the concrete with some kind of dyna bolt or anka screws? Do you recon, I am overthinking this part? I think I should connect the deck with the ground otherwise it can move over time? 

2) Do I need to connect the frame edging with the brick wall with dyna bolt or anka screws?

3) How much spacing I should have between Builders Edge Pedestal Foot Smallfoot 35 - 60mm each foot? and I read the specs and it only support max 220kg each. This mean three people (or two bulky folks like me) standing very close to each other can overload a footing? My weight is now 94kg! Hope the decking project will help to shed some weight

Thank you so much for you help. I will read the article you shared above. 

Thanks, 

Faheem

[MitchellMc · Accepted solution]

@Faheem,

Unless you're expecting an earthquake or tornado, the deck shouldn't move. The issue is if you don't use the feet, it's going to be hard to fix 90 x 45mm timber 61mm up in the air. You'd need to switch to something like 140 x 45mm, and that will only leave 10mm for airflow and drainage underneath.

You don't need to connect the frame to the brick wall. You'd only do this if you were unable to support the timber. It's more common to see a ledger board when you are concreting in posts and can't do so right next to the wall, so you use it as the support instead.

The surrounding footings bear that weight as well as it is distributed out through the frame. You'll never put 250kg all on one footing. Our members quite often use one footing per meter. I wouldn't advise you to go over that, or you'll end up with a bouncy/spongey deck.

Mitchell

[Faheem]

Thanks @MitchellMc , 

So I have seen some videos and they used some kind of galvanized brackets with 10-12M holes to attach the frame with the concrete slab and tied that with the anka screws or dyna bolts. And for spacing (for the air to flow below the deck), they used some kind of wood footing or 10-20mm window packers? You recon that's not the right approach?  Thanks

[MitchellMc]

I'd have to see the brackets you are referencing @Faheem. Can you find a picture of them? 

I'm just not familiar with 90mm timber that high in the air supported on brackets, I'm sure it can be done though.

Mitchell

[Faheem]

Something like this. I couldn't find these brackets on Bunnings online.

[MitchellMc]

That's a standard bracket which you'd use on a ground height deck, @Faheem. We have plenty of those. But you have a height of 170mm to fill with only a 90mm joist, so it will be up in the air. Unless, of course, I've misunderstood and you wish to have a step down onto the deck. In that case, those brackets are perfectly fine to use.

Mitchell

[Faheem]

Thank you @MitchellMc , I was initially planning to use 70*45mm bearer and 70*45mm joists. This will be give me 140mm height and with 19mm merbau. I will have 159mm total height. I have total height to work between 160mm-170mm (there is a minor slope on one side of the slab) so I was thinking I will use window packers to lift the deck for 5-10mm?

But is this against the best practice of having sufficient space from the ground to allow the deck to breath?