Subfloor for timber deck over concrete slab

[philjay]

Hello l am building a subfloor frame for a timber deck over a damp timber slab what should l use the insulate the timber frame from the damp concrete l am looking at using 70 x 35 treated pine for the frame

Thankyou in advance

[Jason]

Welcome to Workshop @philjay. It's great to have you join the community. We have loads of clever and creative members sharing helpful advice and inspiration on the site every day, so we're sure you are going to get lots of value from joining us. 

Let me tag some of our experienced members in @Adam_W, @ProjectPete and @Brad to see if they might like to kick off this discussion for you.

A photo might help members to see what you are working with. You might also want to edit your post for clarity to other members. I assume you mean a "damp concrete slab" rather than "damp timber slab".

Many thanks,

Jason

[Adam_W]

Hi @philjay and welcome!
Okay, just to clarify... so you have a damp slab outdoors that you want to build a deck over?
Do you know the reason why it is damp? Is it moisture rising through the slab or water flows over it when raining?
In all honesty no regular timber will survive well in contact with a consistently damp slab. You'd need to be using H4 treated pine as it's more tolerant of moisture but that will be more costly.
The concerns I would have are to do with where the moisture is coming from and how much air circulation you'll have under the new deck. If circulation is reduced by a very low deck then the moisture problems will only get worse. Even if you could elevate the timber adequately to stop direct contact with the damp slab it will still be in a very humid environment.
Could you give us some more details & maybe photos?

[Jason]

Hi again @philjay. Just wondering whether you were able to provide more detail and perhaps some photos as per Adam's message so our amazing members can assist you?

Thanks,

Jason