Unless you're driving over it, black corrogated pipe will be fine. You can use a combo here if you must cross a driving path, putting solid piping under the place with the biggest load, and lighter stuff elsewhere. The black stuff is also better if you must do a curve.

But, ya know, French drains (at least the ones I'm familiar with and have installed) don't actually have pipe, just coarse rubble. They are basically rubble-filled trenches. Trenches with pipes are called tile lines (in the old days the pipes were terracotta).

However, if you are tying your down spouts in, then I'd definitely use pipe on the whole length as that amount of water over short periods might overwhelm a rubble pathway.

Another thing, is that I wouldn't delay getting those trenches backfilled. I'm not sure what your climate is, but you wouldn't want spring run-off to enlarge the ditches and threaten the stability of the earth close to your foundation.

And I wasn't sure if your question about the drainage related to two buildings (barn and house) or if you were jocularly referring to your house as a barn?

Have you thought of installing a good-quality vapor barrier directly on the soil under the buildings to interupt the upward migration of soil moisture to protect the wood components?

Molly~

Thanks for the answer, black pipe it is. Much cheaper and as you state, easier to navigate a non straight trench. I do have a tractor but won't driver over this too much as it is too close to the house.

Yes, my house is part barn. The barn was the orginal structure, which was added onto.

As for crawlspace, I intend to put insulation board between the joists (that can be removed if I need to repair rot etc) and a plastic vapor barrier on the ground, but I 1st want to address the water flowing under the structure, then possibly a sump, then the plastic.

Also, as you state, I intend to finish the trench in the next few days. Its getting colder so I am OK for now, but I don't want the trench to heave in.

Sounds like a good plan! Your situation may improve somewhat over time as you make the local drainage more efficient and get the surface water runoff directed away. This may allow the soil to dry out more than you expect. Good luck.

Molly~

My thoughts too.