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Damp Proofing Question
We are having a lightwell created in our front garden to create light in our basement. We have been offered 2 options RE drainage and I'm not sure which one makes the most sense...
1. Cast new 150mm concrete floor slab incorporating natural drainage pipe work encased in pea shingle with a plastic outlet gully.
2. Drain the water into the Cavity Membrane system of the basement (not fitted yet) and get rid of it that way.
RE option 1 - Would this pea shingle drain work like a french drain? Would it be at the foot of the house where it meets the light well floor?
And which option do you think is best and why?
Lightwells can be problem if they're not drained correctly. I would certainly not advise option 2 as this system is only designed for small amounts of water percolating through the brick and it may put undue stress on the sump pump. I would not wish to encourage more water to go in the basement.
Option 1 doesn't quite make sense; I would cast a concrete base on the lightwell with a fall away from the basement window into a trapped gully which then terminates into a soakaway. The concrete can be tiled or shingled or anything else you desire.
You could also consider a glass roof over the lightwell!
hope that helps
Answered 4th Oct 2013
Hi, The shingle aspect of option 1 is not visible, so not a french drain, it is only to protect the pipework from movement in the ground. This option is only possible if the existing sewer/storm drain pipework is low enough, If you use this option make very sure you include an anti-surge valve(one way valve) after the gully to ensure that any drain blockages don't flood your property,(possibly in sewage). As JLM suggests option 2 also has drawbacks if you use this option Locate the sump in the light-well with TWO pumps with warning systems in case one fails, they will need to be bigger volume pumps and a larger sump. Option one is the best system as there is less to go wrong as long as the existing drainage is low enough and you really MUST install an anti-surge valve...I have been back to 2 jobs to fit after their 3rd floods!
Answered 17th Jan 2015