French Drain. Pea shingle or pebbles?

[fallschirmjager]

I've read pea shingle should be used in french drains, however I'd have thought pea shingle would still hold water against an exterior wall, especially over time when it becomes more compact and more dirt mingles in with it.

I was thinking of filling my french drain with large(ish) pebbles (40-90mm) as there would be much less contact overall against the exterior wall.

Am I missing something here? I'm no expert in this matter.

Regards.

[Feltwell]

Pea shingle is cheap and readily available in tonne bags, big pebbles tend to be expensive and in smaller bags as they're sold for decoration rather than utility, I suspect that's the main reason!

Pros and cons to both but I see no reason why either would not do the job.

[fallschirmjager]

Thanks Feltwell. The pebbles are only £250 per 850kg bag so will go with the pebbles. I think it will also look nicer than pea shingle.

[Feltwell]

I agree, it'll look nicer. Pea shingle is about £40 for a tonne bag, so a big difference.

The only point I can think of is if the side of the trench is not otherwise supported, pea shingle would do a better job of holding it back.

[RBailey]

I generally use washed 10-20 mm which (I think) is the size up from pea gravel.
The main reason is that pea gravel can be easily sucked up by my leaf vac. The next size up does not get sucked up as easily so I can blow / vacuum the gravel easier.
I also find pea gravel migrates easily and get stuck in shoes, tires etc..

I also have a couple of areas where there is 10-20 covered with washed cobble stones. This is because the chickens love digging out the gravel.
Chicken damage

but with cobbles


Hope this helps.
Cheers,
Richard B.

[fallschirmjager]

Thanks RB. I really like the look of the cobble stones.

[Surveyorman]

The reason pea shingle is recommended as good building practice is because smaller shingle allows for better percolation. If you use larger pebbles or other materials eg crushed up slates, these run the risk of creating pockets of water. If it’s a matter of aesthetics, the top layer can be scattered with the larger pebbles providing that beneath that the channel is filled with graded pea shingle.