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I am building a wooden terrace based on frame made of pressure treated lumber (ground contact grade) placed on concrete blocks ("on-grade" footings). Something like this:

Wooden frame on concrete block footings

What I know is that I should prevent direct contact of wood and concrete (even if lumber is pressure treated) to stop moisture absorption.

What is the best solution for low budget project (also to not overdo it)? There is a roof over most of the terrace so I hope there won't be much moisture involved but I guess I want to insulate everything same way.

The options I am considering as separation layer and already having materials to are:

1. Bituminous paint layer only:

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2. Roofing pap:

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  1. Plastic strip: - not always possible as being thick and level of some of the footings do not leave space to raise the point up.

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4. Any combination of above?

It looks like any option should do as lumber is ground-contact grade pressure treated and do not even touch the ground but want to add extra caution anyways (seems there is never enough protection against moisture). Please let me know if I am overdoing it or there are other methods or aspects (like chemical interaction, standing water) I should be aware of?

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    1 and/or 2 look good.
    – Ecnerwal
    Mar 31, 2021 at 11:27
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    It's probably clean enough from the photos, but in case it is not: "Reglar" is the Danish word for (light) wooden beams - as opposed to bjælke(r), which are heavy construction / load bearing beams. (from proz.com/kudoz/danish-to-english/engineering-general/…)
    – Doug Deden
    Mar 31, 2021 at 17:57
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    Thx @DougDeden - I corrected the title. I didn't realise I did put danish work there - I am indeed from Denmark ;-)
    – Lukasz
    Apr 1, 2021 at 18:39

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I don't think the intent should be to separate wood and concrete. I think that applies to encased wood such as in footings where concrete retains moisture for some time. Wood and concrete are used together all the time. In your case its just wood on a flat surface but it doesn't really do much as it is a flat surface so water will sit there.

The plastic shims would be the best bet i suppose to raise up a bit but it seems you can't use them everywhere and it is a bit overkill. You can possibly use strips of closed cell rigid?

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