How to build low level deck over concrete and grass?

rwa1994

Hi all,

I am planning to build my own deck out the back of my new house. I have some plans and some questions with the plans. 

My questions are:

1. What spacing do I need for my bearers, joists and stumps?

2. I only have 130mm clearance between concrete slab and doorway entrance. I am going to create a single layered structure that I saw on someone else’s post but am I able to use metal stirrups like this one and just dynabolt it to the ground and put the wood straight on the concrete?

3. Am I able to use 90x45 H4 treated pine for my structure? I can't use 140mm as it won't fit clearance.

 

Thank you!

 

 

JacobZ

Hi @rwa1994,

Thank you for your questions about constructing a low-level deck at your home.

Your joists will need to be spaced at most 450mm apart to sufficiently support the decking boards. You can use 15 joists like you have in your design, but reducing to 14 is possible within this allowable spacing.

Using the brackets to bolt the deck to the concrete is fine, but it's not advisable for timber to be in direct contact with concrete. Concrete is porous and susceptible to the phenomenon of rising damp. If timber is in direct contact with concrete, water will rise through the concrete, into the timber causing rot, mould and greatly reducing its lifespan. You can line the bottom of the joists with CAgroup 90mm x 30m x 500um Plascourse or paint them with Gripset Betta Waterproofing Membrane Bitumen Rubber to reduce this, but ideally the deck would not be in direct contact with the concrete.

I've created a render that would allow the deck to be raised from the concrete to create an air gap while still being in line with the Hyne Joist Span Tables. This would require you to use 4 brackets per joist and a 45 x 90mm Pryda Joist Hanger at each end of the joist. Assuming you use a 16mm decking board and 90x45 timbers, this will allow a 24mm air gap beneath the frame of the deck. While still extremely low, the timber will not be in direct contact with the concrete, so there is some ability for the timber to dry out.

There are no issues using 90x45mm timber as long as it is H3 treated, and everything is adequately supported.

Allow me to tag some of our helpful members to see if they've got any further advice to offer, @Dave-1, @Nailbag, @Jewelleryrescue.

You might also like to check out How to build a low-level deck for some further guidance and 25 inspiring low-level deck builds for some inspiration.

Let me know if you have any further questions or would like further clarification of my above points.

Jacob