How to build low-level deck over concrete patio?

sunflowerz

Hello,

I would like to install a deck over the concrete patio however the bottom of the weep holes are 70-100mm from the top of the concrete slab. I am unsure if it would be feasible to install a deck with this clearance.

I am hoping to do a picture frame border with merbau or spotted gum 135 x 19mm timber for the deck - I was planning on using hardwood for the frame but i'm not sure if this will fit. I have looked at metal framing but its too expensive for this project. And I don't want to do composite decking.

The area is undercover.

Thanks!!

JacobZ

Hi @sunflowerz,

This would be considered a very low-level deck, and unfortunately, decks built this close to the ground inherently have issues with airflow and moisture. With very little space underneath the decking, moisture can become trapped and cause problems with both the decking boards and the supporting structure.

For example, the Specrite Merbau Decking Installation Guide recommends a minimum ground clearance of 400mm to provide adequate ventilation. At the height you're proposing, the installation would not meet this recommendation and issues resulting from inadequate clearance and ventilation would not be warrantable.

Spotted Gum decking is likely to have similar requirements around ventilation and clearance, although you would need to check the installation requirements of the specific product with its supplier or manufacturer before proceeding.

You could still physically use these products, but it is important to understand you would not be protected by their warranty in the event their are issues arising from the suboptimal ground clearance.

I understand your reluctance when it comes to composite decking, however due to the low clearance, it is one of the better options. For example, some of the Ekodeck range, can be installed considerably closer to the ground. You would still need to check the minimum clearance, drainage and ventilation requirements for the specific Ekodeck product you intend to use; however, it is likely a better choice in this situation.

The framing is another consideration. At such a low height, standard above-ground treated-pine deck framing wouldn't be the best option. You could potentially look at H4-treated framing such as 90 x 45mm H4 TerraFrame structural treated pine, which is designed for much higher levels of moisture exposure.

In relation to the weep holes, as long as the deck is built independently of the wall with sufficient clearance so it isn't directly contacting it, they shouldn't prevent you from building the deck. The main concern would be blocking the weep holes or building the deck in a way that bridges the damp-proof course. Provided the deck remains separate from the wall and neither the weep holes nor the damp-proof course is affected, there shouldn't be an issue from that perspective.

With decks like this, the height is often set by the height of the doorstep. If this is higher than your weepholes, which they usually would be, as long as the weepholes are not blocked, you should have more space available for your framing, which is always going to be worthwhile for airflow and drying up any moisture that gets underneath your deck.

If you can let us know exactly how much height you have from the concrete to the underside of the doorstep, we can certainly have a closer look at what might be achievable.

Jacob