What materials for low-level deck over rainwater drain?

[rpankaj39]

Hello guys,

I am a newbie, planning to build a low-level deck on top of the rainwater pipes running(underground with one drain on the top). The size of the deck will be 2.8m * 6m approx. I don't want to dig and install the footing. I need some help with the foot and material.

Q1- Can I use Pedestal or tuff block for the footing? I am planning to prepare the floor using the builder's membrane and gravel.

Q2 – Can I use 90 x 45mm MGP10 H2F Termite Treated Blue Pine Timber Framing for Bearers and  Treated Pine Outdoor Timber Framing 90 x 45mm for joits? There are limited options in the MGP10 frame in my location.

Q3 – What size of screws shall I use?

Q4-  List of tools?

@MitchellMc  I read your blog. It helped me to understand the Flooring structure. Thank you for that.

Thanks

Pan

[MitchellMc]

Welcome to the Bunnings Workshop community Pan (@rpankaj39). It's a pleasure to have you join us, and many thanks for your question on deck construction.

Pedestal feet or Tuffblocks would be an option. Tuffblocks have a wider surface area and are specifically designed to sit on the soil. 

You'll need to use Treated Pine Outdoor Timber Framing 90 x 45mm for the entire structure as the blue treated pine is only suitable for indoor use.

Zenith 14G x 85mm Galvanised Type 17 Batten Bugle Head Timber Screws would be suitable for joining your joists and frame together.

At a minimum, you would need a drill driver, circular saw and a tape measure.

If you haven't already checked it out, make sure you read through @Adam_W's article on How to build a low-level deck.

Please let me know if you have more questions or need further assistance.

Mitchell

[rpankaj39]

Hi Mitchell @MitchellMc

Thank you so much. Could you please help me with the structural design as well?

I think 6 bearers at 1400MM(approx) distance sitting on 3 Tuffblocks each and 6 Joist on top at 500MM(approx). All using Treated Pine Outdoor Timber Framing 90 x 45mm.

Thanks

Pan

[MitchellMc]

Hi Pan (@rpankaj39),

I'm not quite following how six bearers spaced 1400mm apart would be used on your 2.8 x 6m deck. If you could draw a quick sketch illustrating your proposed layout, it would be helpful. Joists spaced 500mm apart sound correct.

Mitchell

[rpankaj39]

Hi Mitchell @MitchellMc 

Sorry, I think it would be 5 Bearer +6 joist. Please refer to the below diagram and Ignore the spacing in the diagram. It is a dirty drawing :). 

[MitchellMc]

@rpankaj39,

Having the 90 x 45mm timber span 1400mm between the bearers is starting to be a bit of a stretch and almost at its allowable span distance. I'd be more comfortable if you re-assessed and had the bearers spaced at 1200mm. This would be the same for the bearer, and it would be better to have four supports instead of three.

The issue with pushing limitations is that, at the least, you'll end up with a spongey deck that will flex underfoot as you walk on it, and at worst, a deck that could potentially collapse.

Mitchell

[rpankaj39]

Hi @MitchellMc 

Thank you!.

I will decrease the space between bearers and add additional support. I am excited, will share the before-after and progress images here. 

Thank 

Pan

[MitchellMc]

I can't wait, Pan (@rpankaj39)!

Reach out if you get stuck, and I look forward to seeing those images.

Mitchell

[rpankaj39]

Hi @MitchellMc 

I am confused about the face(45 or 90) for joist and bearers.

Would bearer be on 45 face top and joist 90? i.e height will be tuffblock+90(Bearer) + 45(joist) ? or it will be tuffblock+ 90(Bearer)+ 90(Joist).

It's a floating deck. So will it move over time(slightly)?

Thanks

Pankaj

[EricL]

Hello @rpankaj39

I believe the sequence would be Tuffblock + 45 (Bearer) + 45 (Joist), have a look at the photo below. Having the timber on its short or narrow end will provide maximum strength loading rather than having it on its wide side.

If you need further assistance, please let us know.

Eric