Shed Siding - Leaking and Wicking

by Rise Briggs
(Roseburg, OR USA)

View of outside of shed

View of outside of shed

I have a problem with wicking behind my T-111 siding on my garden shed.

We built it with the siding down to a Z-flashing resting on a 2x6 PT board running the length of the outside. We applied generous silicone caulking to all parts, including the "grooves" in the siding, but the water is coming up under somehow and making water spots on the inside wall.

We haven't put any interior walls in yet, as we need to get this fixed first. Any suggestions shy of removing the siding would be greatly appreciated.

Thank you.

John says:
Hi Rise,

Thank you for your question.

I would need to do some investigative ‘opening up’ to see exactly what the problem is. I would immediately be looking at two things:

Firstly what is the distance between the bottom of the siding and the horizontal leg of the Z flashing? This distance should be a minimum of 1/8 and as much as ¼ of an inch to give the water space to drain away.

Secondly is the bottom of the siding ‘sealed’ with paint/primer prior to installation? Having a cut edge of timber enables the ‘wicking’ that you refer to. Having the edge sealed prior to installation blocks the ends of the fibres that comprise the wood and so helps to prevent wicking.

Finally, do you really need to caulk the outside of that junction? Caulk looks a great idea but it can trap water in the joint and lead to problems that would otherwise be dealt with by the water evaporating.

I hope that this helps. I suspect that you may need to remove the siding and reconsider this junction.

Kind regards

John (

Click here to post comments

Return to Shed siding questions.

Custom Search

Keep in touch with our monthly newsletter

Shed Building Monthly




Don't worry -- your e-mail address is totally secure.
I promise to use it only to send you Shed Building Monthly.