Low-level decking construction

Welcome to the Bunnings Workshop community @Amin88. It's fabulous to have you join us, and many thanks for your decking question.

With 60mm to work with, you'd be looking at using 90 x 45 H3 Pine on its 90mm face. So, it will be 19mm for decking, 45mm for joist and a 16mm gap underneath for airflow and drainage. Since you'll be working with a sloped slab, the use of Builders Edge Pedestal Feet would be ideal. They are easily adjustable to suit your slope.

If you haven't already read through @Adam_W's article on How to build a low-level deck, then I'd suggest that's a great place to start your project.

What direction do you plan to lay your decking? Parallel to the house wall or perpendicular to it?

Please let me know if you have questions.

Mitchell

https://www.workshop.bunnings.com.au/discussion/comment/13551#Comment_13551

Thanks @MitchellMc for your prompt reply. I never heard of laying 90 x 45 by the face of 90 mm. Having said, it’s a viable option for me. What would be spacing of supporting the 90 x 45 you reckon? Also, I’m planning to lay the decking parallel to the house. The length of the area is 9 m. Thanks in Advance!

https://www.workshop.bunnings.com.au/discussion/comment/69282#Comment_69282

Generally, it's best not to lay timber on its face as it doesn't have as much structural rigidity @Amin88. However, there really isn't enough room to build the structure conventionally close to the house in your case. I'd suggest that the joists should be supported at least every 700mm, and they would be spaced 450-600mm apart.

Once you move further away from the wall and the height allows, you could switch the orientation of the joists to be sitting on their 45mm side. In fact, when you get to the outside of the concrete slab nearing the 270mm mark, you'll need to switch to post supports as even the largest pedestal foot will run out of height adjustment.

Mitchell

https://www.workshop.bunnings.com.au/discussion/comment/97646#Comment_97646

Thanks @MitchellMc . That makes sense! What’s the best way to support the joist to concrete near house end where the joist is only 16 mm spaced from concrete floor? Also, how to switch the orientation of the joist, use different piece of timber? Thanks

https://www.workshop.bunnings.com.au/discussion/comment/115501#Comment_115501

You can pack out under the joist with shims and then Dynabolt through the face of the timber directly into the concrete.

To switch the timber's orientation, you'll simply turn the 90 x 45mm joist from its 90mm side onto the 45mm side. By that stage, you'll likely have enough room to use the pedestal feet instead of the shims.

Mitchell

https://www.workshop.bunnings.com.au/discussion/comment/125637#Comment_125637

Thanks @MitchellMc . That gives me a starting point to get my work. My question is can I use the 12 mm bolts and nut instead of dynabolt? Because, with dynabolt, it’s hard to manage the height, particularly at a sloping surface? Also, is it a bad idea to choose 35 x 90 treated pine with their 90 side is faced up? That will give me additional 10 mm space.

StevieB

https://www.workshop.bunnings.com.au/discussion/comment/132440#Comment_132440

Great to see that you're well on your way to getting started on your deck @Amin88

@MitchellMc will be happy to help with your question when he's back on the site on Friday.

Stevie

https://www.workshop.bunnings.com.au/discussion/comment/132440#Comment_132440

Hi @Amin88,

I apologise for the delay in my reply.

Could you please provide a little more detail on how you would like to use the 12mm bolt and nut in this application? When using Dynabolts, you would manage the timber's height with shims. Pack out under the timber with shims until you reach the required height and then Dynabolt through the face of the timber directly into the concrete.

Having an additional 10mm under the timber would be beneficial, but you need to weigh that up against the thinner timber issues. It is already not a recommended building method to turn joists on their face side if any other option is available. If you then go from a 45mm to a 35mm, you risk having a springy deck, and you'll also need to have the joist supports closer together.

Mitchell

https://www.workshop.bunnings.com.au/discussion/comment/136589#Comment_136589

Thanks @MitchellMc . I will consider the 45 mm timber in this case for structural stability. With bolts, I thought of using the bolts exactly same as dynabolt. Driving the bolt through the timber and into concrete floor (like how they connect the ledger using the bolts in the attached photo) after fixing the height using shims.The bolts will be countersunk into timber. I prefer bolt instead of dynabolt because it can be removed later. Please share your opinion.

Thanks

https://www.workshop.bunnings.com.au/discussion/comment/139461#Comment_139461

Hi @Amin88,

That's a sensible way of attaching the ledger if there is any chance you might want to remove it. I'd suggest glueing threaded rod into the concrete with Ramset 750ml ChemSet 101 Masonry Anchoring Adhesive Cartridge. You can then use a nut to attach the timber.

Mitchell

https://www.workshop.bunnings.com.au/discussion/comment/141388#Comment_141388

Hi @MitchellMc thanks for your prompt response. Do you have an schematic / image to show your described way of attaching to concrete? Is it a standard practice or I am better off choosing the dynabolt?

https://www.workshop.bunnings.com.au/discussion/comment/142838#Comment_142838

I apologise. I misread your post and presumed you wanted to fix a ledger into the side of a concrete slab as per your image.

If you want to fix your joist down to the concrete slab, you could use Ankascrews as normal bolts won't screw into concrete. These Ankascrews could be removed at a later date if needed.

I hope that clarifies.

Mitchell

https://www.workshop.bunnings.com.au/discussion/comment/143853#Comment_143853

Thanks @MitchellMc. sorry to bother you. what diameter screw would you recommend and what spacing in the joist

https://www.workshop.bunnings.com.au/discussion/comment/144635#Comment_144635

If you are counter-sinking them, something like a Ramset 10 x 100mm Galvanised AnkaScrew Masonry Anchor would be suitable. You could space the screws 500-700mm apart.

Keep the questions coming, I'm here to help.

Mitchell

https://www.workshop.bunnings.com.au/discussion/comment/145212#Comment_145212

Thanks for the continuing support @MitchellMc . Before driving the Ankascrew, what diameter drill bit should I use for predrilling the hole in concrete? Should 10 mm drill bit suffice or should I choose slightly less Dia hole (I.e., 9-9.5 mm)?

https://www.workshop.bunnings.com.au/discussion/comment/145667#Comment_145667

https://www.workshop.bunnings.com.au/discussion/comment/13551#Comment_13551

The hole drilled should be the same size as the Ankascrew. For a 10mm Ankascrew, you'd use a 10mm drill bit. The thread will then cut and bite into the concrete. If you use a drill bit smaller than the screw shank, you'll run the risk of cracking the concrete.

Mitchell

th-DIYER

Hey @MitchellMc this is connected to another post I put up earlier and then saw this cool project that @Amin88 is working on.
My small 1000x800 step/platform at the bottom of a staircase is also being built on a concrete slab that is sloped. Instead of using angle brackets and trying to get the frame level with shims could I use these adjustable pedestal feet? My only concern with it being a little platform I would want to secure the feet to the concrete when I have the right height. Is this possible?

Thanks in advance.

pete_brig

https://www.workshop.bunnings.com.au/discussion/comment/139461#Comment_139461

Hi @Amin88 / @MitchellMc

I'm not a builder but Heres my thoughts, for what they're worth.

If the deck area aligns with an outdoor area of the house, consider keeping the deck height level with the house to create a large flat area--lower clearance at the outer edge of th roof--1950mm-- is still adequate for th majority of ppl and may look low but a larger flat area is more functional.

Otherwise the step down is a good option, and can be used as a feature even if the deck is beside an outdoor area of th house (think of sunken lounges inside a house). Your suggested stepdown of 100mm is good to avoid it becoming a trip hazard. (I think 125-150mm is typical step height in stairs?)

Seeing as you're building over th existing floor, you could consider removing some of it (excavating) beside the house to give more room for your decking timbers. More work. Otherwise keep th spacing between the joists small as @MitchellMc suggested to avoid bounce in th floor.

Cheers, Peter

StevieB

https://www.workshop.bunnings.com.au/discussion/comment/69374#Comment_69374

Great to hear that you've been inspired by @Amin88's project, @th-DIYER.

@MitchellMc will be more than happy to help with your question when he's back on the site tomorrow. Thanks for your patience in the meantime.

Stevie