ᐅ Ground construction for a stilt house by the water intended for residential use

We want to renovate our stilt house located on the water and are looking for the most practical solution for the floor construction.

The starting point is a 40mm (1.6 inch) thick ship deck made of larch boards with about 5mm (0.2 inch) wide gaps, through which you can currently see the water below. The distance to the water surface is about 1.20m (3 ft 11 in).

Criteria: The new floor construction above the existing ship deck may be a maximum of 40mm (1.6 inch) thick.
Sealing against rising moisture from the water and choosing the right materials are essential!

Our desired concept or idea for the build-up is as follows:
1) Bitumen membrane as protection against rising moisture above the existing ship deck
2) Substructure of OSB boards, 19mm (0.75 inch) thick, tongue-and-groove, glued
3) Impact sound insulation with 3mm (0.1 inch) cork roll mats
4) Finished parquet flooring, 16mm (0.6 inch) oak planks in a 3-layer construction as the final floor

Can this floor construction work without the OSB board starting to crumble due to possible rising moisture or the parquet floor breaking down?
… or would it be better to lay a solid spruce ship deck floating on, for example, Styrodur?

Who has experience with building on the water? I look forward to your thoughts!
Many thanks!

I think your questions would be better addressed by the next harbor master 😉

Chris117 schrieb:

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Who has experience building near water – I look forward to your thoughts on this!
Many thanks!

Unfortunately, I can only offer limited qualified advice, even though I have (older) experience with structures in and near water as well as with OSB in relation to moisture, because these experiences are hard to directly apply to your specific project.

Also, pictures would be appreciated by all of us and would help clarify your requirements (is this a small cabin of 4m² (43 sq ft) or a full-sized vacation home?).

First, regarding OSB: it does not tolerate water well. It swells badly and eventually rots (unfortunately, I have had firsthand experience with OSB in floor construction). Your bituminous layer will not last forever under these conditions either. More durable would be plywood with a waterproof overlay, but only if you carefully seal every cut edge.

I built in water as a child in the stream on our property (various types of dams) and later studied it theoretically during vocational training and university (civil and road engineering + hydraulic engineering). Your laminated wood materials are definitely not suitable for this. Unless you encase your cabin in something like a stainless steel tub. Back then (30 years ago when I learned this), only appropriate water-resistant hardwoods (tropical hardwood) were used in hydraulic constructions (canals and ditches). These typically lasted around 30 years.

Such highly specialized questions are probably not well answered here in the forum. And if the financial risk doesn’t intimidate you, just try something and be prepared to redo it if it doesn’t hold up.

Massive WPC decking boards are also used in pier construction,
with the intermediate battens also made of WPC.
With a closed deck using rubber seals, you also get a ship deck appearance.

So, bitumen membrane – WPC mounting battens – WPC decking closed deck.

Thanks in advance! Basically, the whole construction project is intended to have more of a holiday home character and less of a beach hut feel.

What comes to mind spontaneously looking at the picture: Is this legally approved for building? You don’t want to have to dismantle everything in the end 😕