What kind of gravel?

For under foundations and making French drains, what sort of gravel is recommended? Seems to me there has got to be a "best practice" out there that pretty much everyone doing this sort of thing knows, but I don't yet;)

The bigger the gravel, the better the drainage, the harder the labor. The most important characteristic: clean and free of fines. What we call #87 (3/8-1/2") is probably the minimum. 3/4" is better and is probably the most common for french drain application. Be sure you wrap it/ protect it with something like geo-textile fabric.

The pre-cast concrete panels we use call for #87 under their walls. Its more easily leveled (labor). Seems like rubble trench foundations call for much bigger sizes, what we call railroad ballast and rip-rap.

Thank you Brian.

Hello Peter,

The post I started on Raised Earth Foundations has a fair amount of information regarding this topic in certain ways.

I can cover a lot of the different methods should you have specifics, yet Brian's response really covers the basics in the modern approach to this very old foundational style. I can share some additional "tidbits" like the fact that Frank Lloyd Wright was probably a pivotal architect to bring this system into the mainstream of current architecture in the last century. I can also share that all of the oldest structures in the world, stone, timber and/or earth almost all sit on some form of this style of foundation. I have cross sectional elevation plan drawings of this style from several different cultures, with some of the apex practitioners being the Chinese, Korean and Japanese builders.

I can share more if you ask specifics.

Regards,

j