French Drain around semi-basement

[Bemak]

I've posted a good bit lately about a refurb I'm hoping to embark on later this year / early next year. Part of the works will involve the installation of a french drain along some external walls to help with surface water drainage and to prevent the walls from soaking it up. One area where a french drain is being installed is along the southern elevation where the ground level is well above the internal floor level (approx 600mm). See attached pic. The area was concreted about 15 years ago to help prevent dampness internally and it has worked surprisingly well. The walls are quite dry internally. I'm tempted to leave all well alone but I'm sure it can be improved. 

 

 

 

I'm proposing to externally insulate the house so was wondering when it comes to this area I assume that I should tank the walls below ground first, then apply an insulation with high compressive strength before finishing off with the french drain etc? Something like the diagram below? Should I reinstate the concrete path outside the window and include a surface drain, or would I be as well to gravel it all - although if I do gravel it, I assume I'd be allowing more water to reach the drain?

 

 

 

[jayc89]

We have a similar problem, replacing the original clay tiles with a Limecrete floor seems to be reducing the moisture down there, it's been laid for a month now and the humidity seems to be gradually reducing (I guess that could just be the outside temp reducing too!)

Following this thread with interest.

[Tosh]

I don't see the point having a surface drain along with a french drain, at least not where it is on your drawing. I think the decision for a surface drain will be somewhat driven by your final paving surface. You could have permeable paving allowing the water into the french drain or non permeable leading to a surface drain. If your french drain is going to deal with storm water (in addition to ground water) have a think where it's all going to go i.e. storm drain or soakaway.

 

If your walls are dry then sounds like you don't have a ground water problem and the concrete is dealing with surface water already. If you're going to open all this up then you're in effect encouraging water against the wall hence your solution needs to be robust.

[Conor]

Just leave a 100-150mm gap between the wall and the path and fill with gravel, that's the detail we have around the perimeter of our basement house. Allows after to drain down to the drain below, and prevents Rain splashing up the walls or standing water to soak up.

 

Only detail you're missing is a cavity drain board against the EWI to protect it against damage from stones. It's not expensive or difficult to fit, just a dimpled palstic roll with fleece on one side. Also stops water pooling against the wall.