“Steel or cribs?” is often the first questions I hear when discussing a new dock or boathouse.
Is an engineered steel pile frame the most reliable foundation in a lake, or is the traditional timber-and-rock crib best?
A “crib” foundation is an open rectangle of heavy timber, connected at the corners with spikes or long steel rods, something like the “log cabin” set I had as a kid. The first layer is set on the lakebed, then in alternating layers the crib is built up to the surface, filled with rock for mass and stability.
A steel pile foundation starts with steel – “H”-section or circular – pinned, piled vertically or augured into the lakebed (depending on the nature of that lakebed) until solid bearing is encountered. The piles are then all cut to the same height above the waterline, connected by steel beams across their tops and cross-braced vertically and horizontally – to form a rigid frame.
Joists are then placed atop either foundation system, topped with cedar or other decking.
A key benefit of cribs is that they muffle wave action; a slip between cribs can be calm on the windiest days. But cribs are limited to perhaps 8’ to10’ of water depth, new cribs will always settle, and timbers at the waterline will inevitably rot, requiring replacement.
Steel docks can be engineered for deep or sloped lakebeds, they have far less impact on existing fish habitat and water circulation, and are a solid foundation the moment they are built. But waves are unimpeded and steel will eventually corrode at the waterline.
So are you building a simple swim dock or planning a 2-storey boathouse atop? Is your lakebed deep – or steep, is your site exposed to large waves or boat traffic?
The answer to “steel or cribs?” is – it depends!