Concrete base liner for garden cabin - flat sheet or up at sides?

[Mikster]

Hi all, hoping to get advice on this - I've built a timber garden cabin on a concrete base. Cabin is mid-size (4x4m with a side shed). I'll be putting down 100mm jablite insulation with chipboards over that then parquet laminate flooring over that (no bearers - floating floor).

Query is: should I put the initial plastic liner membrane flat on the concrete, or have it then come up at the sides and attach to the inner timbers of the cabin thereby fully sealing like a large "basin"?

Bear in mind I'm a very moderate DIY-er (so go easy on me ) and/or if there's any better methods of putting down something between concrete and the insulation please do let me know

Much appreciated. Cheers,
Mik.

 

[Deluks]

What happens where the floor meets the walls?
Can water run underneath from outside?

 

[Mikster]

What happens where the floor meets the walls?
Can water run underneath from outside?

hi @Deluks , the actual floor will have a 1-2mm gap from the internal wall for potential movement, hidden over with skirting.

Water could potentially run underneath from outside yes. Whole cabin is up on composite plactic foundation beams but there are some gaps.

 

[Mikster]

wondering if there's any more experience / suggestions on this..?

 

[Deluks]

Not entirely sure how this is built.

Your first post indicates a shed without a floor, straight onto a concrete base, but in your second post you mention plastic beams underneath, so I'm a little confused.

 

[Mikster]

So its one of those garden 'log' cabin kits (Tuin) with composite plastic foundation beams/bearers which are under the perimeter of the cabin 'shell', as in directly underneath where the walls meet the base so they're a protective barrier between the concrete base (and water etc) and the timber structure. So they're not where the floor is to be, just under the walls.

Think of it like a picture frame laid down on a table. The picture frame is the plastic foundation beams, then the cabin's log walls are built up from the frame.

Where the 'picture'/canvas would be is empty - concrete base, ready for floor to be put in.

So in this area is where the plastic sheet membrane will be laid down, between concrete base and insulation, then floor boards etc.

My query is: do I just lay down plastic membrane flat on the concrete with insulation on top of it, or do I have it come up and the sides and attach to structure forming a large 'basin'..?

 

[Deluks]

Got it. Yes, fold the membrane up in the corners, making a paddling pool.
Run them past the joint between wood and plastic by an inch or so, tape it into place.
You can cut off the excess, flush with the finished floor after you've done it.
Creative origami folding in the corners is preferable to just forcing it into place, as it's quite stiff and will just bunch up.