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So I have a townhouse with a small 20'x 30' backyard with a 20' x 7' garden in the rear that I'm converting into artificial grass (the green area in my diagram). I'm keeping 2 large tree-like shrubs in the corners and putting artificial grass all around it, and using a 20 mm playmat foam turf pad underneath. The bulk of the backyard is paver stones (in gray) with a surface drain in the center and a remaining garden strip on the right-hand side that I'm putting bushes in. The house is to the bottom of the diagram with a balcony and stairs to the garden, and the yard abuts other back yards made of pavement or dirt on every side.

My question is this: I see in the instructions for artificial grass to grade away from the house for drainage. Since I have such a small patch of turf that's separated from the house do I still need to grade for drainage? To mound up in the middle or to slope away from the house is a challenge as outlined below.

I tried flattening out all the dirt after removing the plants and it seems like there is a slight grade back to front towards the house (down in the diagram). Additionally, the area where the brush trees are slightly raised on top of that. If I were to do the easiest grade I would fill in a bit towards the middle top so that it's even with the raised dirt around the trees and slide the whole thing slightly towards the paver stones and house. However, that seems to go against the instructions to go away from the house.

Leveling the dirt around the tree bases and reversing the grade seems like a lot of work and might expose some roots.

So can I get away with either:

  1. not grading the dirt and leaving the dirt higher around the tree base
  2. grading the dirt to slope down towards the paver stones (and the house - down in the diagram) so that it can keep the dirt around the tree at its higher state?

or do I have to dig down around the trees and re-level the back garden area to slope away from the house to the top of the diagram?

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  • Remember, the current grass/dirt area will allow water to filter through it, while your new artificial grass will not. All the water that lands on the grass area now will end up going to the drain in your pavers if the yard is sloped toward the house. What works well for the paver area today may not work so well with extra water coming in from the rest of the backyard, even though it's small. Consider leaving a "hill" around each tree, then sloping down between them to form a valley that still runs away from the house. Also, be prepared for an angry neighbor [con't] – FreeMan Aug 2 at 16:57
  • ...when they discover that their yard is flooding because of extra runoff coming from your yard. – FreeMan Aug 2 at 16:57
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    wouldn't the artificial grass still allow water to filter through it as well? – MonkeyBonkey Aug 2 at 17:27
  • It may, depending on how it's made, but it may not. Since the instructions specifically call out grading away from structures, I'd say that the mfgr doesn't think enough water will filter through to be safe, and they don't want to deal with the potential complaints. – FreeMan Aug 2 at 17:30
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1/8" per foot or 1cm per m (minimum) slope away from the house is always needed, and will save a lot of problems with water infiltrating the house.

However, since this does not directly abut the house, if the paver area next to the house is properly sloped away from the house and the drain works, sloping the grass area away from the house is less important, unless there's so much water the drain is overwhelmed. I typically try to have 12 feet or 4 meters around the house consistently sloped away - after which things can change, if water management is adequate.

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