Eddie Van Halen Sues -- Contractor Left Me with a Moldy Shaft

Hope Eddie Van Halen swims as good as he plays guitar -- 'cause his L.A. home got drenched after a contractor screwed up his remodel, and ended up costing him more than a million bucks ... according to a new lawsuit.

The lawsuit -- which was filed today by Eddie's family trust -- says Troy Builders Group was hired back in 2008 to do a remodel and construction, but the project was rife with major problems ... most relating to waterproofing.

In the docs, Eddie says the shoddy work included poor drainage, leaky roof and chimney, poorly installed gutters and flashing -- all of which caused water to flow into the home.

But here's how you know the house belongs to a guitar god -- EVH claims he also suffered mold damage, not just on wood surfaces, but in his ELEVATOR SHAFT.

Moldy shaft ... never good.

According to the docs, Eddie's already out more than a million bucks to repair the damage. He's suing the builder for the cash plus interest.