Hi @Racsop,
Thank you for your question about reducing moisture in your shed.
Foam fillers, like this Suntuf Black Corrugated Foam Infill or this Crommelin 1m Custom Orb Superseal are great for blocking the gaps between the roof sheets and the wall and will help to prevent airflow and water ingress through these gaps that can contribute to moisture.
Unfortunately, it can be tricky to seal up a shed and stop water from getting in as they aren't really designed for it. On houses, you'll use a moisture barrier like this Ametalin 2740mm x 30m VapourTech Brane VHP Vapour Permeable Wall Insulation on the outside of the framing to stop condensation from getting in, but this isn't possible in sheds without additional framing.
It sounds like you want to line your shed with plasterboard or fibre cement. Is that correct?
If so, you'll need to build a frame to attach your sheet material to. You can build a timber stud wall on the floor, attach the vapour barrier to the outside of the wall then stand it in place.
With this frame, you will create a cavity where insulation such as batts or foilboard can be installed to further insulate the wall and stop moisture from developing.
Check out How to insulate a metal roof? by @bowmatty for a great example of a similar project.
Ultimately, as sheds are not airtight and they are prone to condensation, some moisture is still likely, but these products will certainly help.
Let me tag @Dave-1, @Nailbag and @Jewelleryrescue for their thoughts.
Let me know if you have any further questions.
Jacob
Note: For our New Zealand readers, please note that the use of foil-covered insulation products is banned in New Zealand.
