Zen1

The pipe will be going the full length of the greenhouse and around the side, so water would safely drain away to the far end with the correct fall, away from the base. Yes that's my grass but I have to leave it as it is and not actually drain it.

Hello, I have a wooden greenhouse/shed on a 4 inch concrete base with a rain water issue. In extremely wet periods (not normal rain) water is seeping in across the concrete base from the garden side of the greenhouse. The soil level on that side being about 2 ft or so higher than the concrete base. There's also a brick retaining wall and the water moves through that too. My drawing is obviously not to scale but if I were to lay a 4 inch perforated drainage pipe at the level shown, in conjunction with permeable fabric and gravel will that work or would the pipe have to actually be below the concrete slab to prevent water hitting it and gradually making its way across..?. I thought the issue at first was being caused by gutter over flow so installed the pond liner and gravel you can see in the photos...however that made no difference at all. Any help with this would be great ...thanks in advance.