Share
Hello experts,
I am looking to do decking project (3.8m *5.7m ) to transform my back yard. The deck runs across concrete and the soil and the major portion lies on concrete. Attached is the plan of it.
Height difference between the concrete slab and the bricks under exist door is 60mm. How to achieve framing (driinage , strength etc ) in this low clearance situation ?
Hello @nvelaga
Thank you for sharing your questions about your deck installation project. I suggest having a quick look at these guides - How to build a low-level deck by @Adam_W and How to build a deck by @MitchellMc. I'm afraid 60mm is not enough space to build a low-level deck, because your deck is touching the concrete base directly moisture will be trapped underneath and will cause damage to the timber framing and shorten the life of your deck.
I suggest removing the concrete slab so that you'll have enough space for a proper low-level deck. The ground can then be levelled and sloped to provide a fallaway for the water. Weedmat and gravel can be placed underneath to facilitate drainage under your deck.
I also suggest looking at the Bunnings deck building guide:
- How to plan out your deck
- How to set out a deck
- How to install stumps
- How to install bearers
- How to install joists
- How to lay decking
- How to add a step to your deck.
If you have any other questions we can help with, please let us know.
Eric
Hi @nvelaga,
Joist-size timbers such as 90 x 45mm are only available in H3-treatment for above and not on-ground use. Theoretically, you could use 90 x 45mm joists placed on their face and then add your 19mm thick decking on top. This will give you a height of 64mm. However, what you are creating is an exceptionally low-level deck with no clearance, which results in a high-humidity environment and poor drainage and leads to the early onset of decay. If you are prepared to deal with the consequences, which could be a deck that lasts less than 10 years, then you could choose to implement this design.
Typically, our members would leave at least 10mm clearance under their joists so water has the ability to drain away.
Consideration should be given as to whether creating a deck over the concrete with your limited working height is a viable project. Perhaps you could tile the concrete area and then have those surrounded by the deck.
Please let me know if you have any questions.
Mitchell
Titan 5 x 72 x 100mm 4 Piece Yellow Packing Shims can be used to establish that 5mm gap @nvelaga. The joists will then be placed on top of them and Dynabolts through the face of the joists used to secure them to the concrete.
Mitchell
Hello @nvelaga
If the joist were facing the 5.7m length for example and you placed the joists at a distance 450mm from each other, you would need approximately 13 lengths. Running the joist over the soil will require an adjustable foot pedestal, but it all depends on how much space you have between the joist and the soil. The support for the joist will need to be very close to each other, this is to prevent the joist from sagging. Neither of those two products you mentioned will work as the joist is facing the towards the flat side.
Eric
