How do I build a small deck over rock?

jtg

Hi there

I’m very new to DIY and don’t have any trade experience, but I’d like to build a small deck over the area shown in the photo. The section I’ve outlined in red is mostly solid bedrock with a bit of soil and grass around the edges.

I’m trying to figure out:

• Is this a suitable base to build a deck or should I forget about it

• The best way to anchor or support deck framing on top of bedrock (since I can’t dig in posts easily).

• Whether I should use adjustable pedestal supports, masonry anchors, or just build a freestanding frame.

• Any tips for levelling the deck on uneven rock and preventing water pooling or rot (particularly in the middle where there is a natural gutter).

• What kind of timber/materials are easiest for a beginner to work with.

I’d really appreciate any advice and/or product recommendations.

JacobZ

Hi @jtg,

Welcome to the Bunnings Workshop community, it is wonderful to have you with us.

It wouldn't be the simplest decking project, but I still think it is achievable.

If it's bedrock, there isn't really a better base you can have because there's almost zero chance it is going to move. The main issue with natural stone is that it is not perfectly flat, and it is not perfectly level. 

One option, which I think is probably the best option, is to drill holes in the bedrock, insert reinforcing dowels, then create a form around the reinforcing and pour small concrete piers for pedestal feet to sit on or for post anchors to attach to. This would be a relatively simple way to both utilise the strength of the stone and create a flat base for the pedestal feet to sit on.

Another option is to drill, grind and chip away at the natural stone to create flat spots to place your adjustable pedestal feet on. As long as the pedestal feet sit flat and they can be adjusted enough to account for any slope in the stone, this could be an option. 

Water pooling shouldn't be too big of an issue as long as the frame sits up from the stone a suitable distance. The more height between the deck frame and the stone, the better, as this will allow airflow beneath the frame. If you can use a taller pedestal, like the Builders Edge 70 - 170mm Bigfoot Xl Pedestal Feet, this would be best. 

In terms of materials, H3 framing pine is relatively easy to work with for your frame. It is softwood, so it is not particularly prone to splitting and cracking. It's also easy to drill and drive screws into.

I'm sure there will be more questions along the way, but I am confident you can make it work and I would be happy to help as much as I can.

Let me know what you think.

Jacob