What foundation for low-level deck build?

bilbomanu

Hi

I m getting on the project to build a deck of 5m by 5m, low to the ground ( about 25 cm from the ground). Its very sheltered as the four sides will be flush with 3 retaining walls plus the house wall. I was brainstorming about what foundation would be best and cost effective.

Given the high of the deck i was thinking of a flotting deck on soil ( sand, gravel, paver and pedestal feet).

First of all considering the size of the deck is it a good idea or Would it be better to use piles foundation. 

On a second hand cost wise is it cheaper to put use pile foundation or prepare a leveled soil with sand,gravel and use paver and pedestal feet.

( the soil is clay)

Many tanks for your insight

Manu

MitchellMc

Welcome to the Bunnings Workshop community @bilbomanu. It's terrific to have you join us, and many thanks for your question about building a deck.

Building a floating deck can definitely be a cost-effective and practical solution, especially given its low height and sheltered location. However, the clay soil on your site is a key factor to consider. Clay tends to shift with changes in moisture, which could affect the deck's stability over time. To combat this, you’d need to excavate the area, remove some of the clay, and replace it with a compacted gravel base. This helps with drainage and provides a stable foundation for the pavers and pedestal feet.

In terms of cost, floating decks can be more affordable because you don’t need to pour concrete or install deep foundations. The materials for preparing the base, like gravel, sand, and pavers, are relatively inexpensive, and you won't need the same level of excavation as for piles. However, piles or a deeper foundation may offer more long-term stability on clay soil. If your area experiences heavy rainfall or the clay is highly reactive, piles might provide better support and peace of mind, although they come at a higher upfront cost due to the labour and materials involved.

Here's a helpful guide: How to build a low-level deck.

Please let me know if you have any questions.

Mitchell