We have plans for a new house build – see my attached crude mockup where the front of the house is on the left and the backyard is the green shaded area.
The land has up to 1.8m incline from front to back (these are the elevation values):
- 99.8m SW corner (top-left)
- 100.2m SE corner (bottom-left)
- 101.3m NW corner (top-right)
- 101.6m NE corner (bottom-right)
The slab has an elevation of 100.6m.
This means there is a 1 metre uphill incline from the back door to the NE corner of the yard (over a distance of 4.9 metres), with a slightly smaller incline of 700mm from the back door to the NW corner.
The builder's original proposal was to build a 1 metre deep footpath around the property, and then a retaining wall with 2 steps up into the backyard. We didn't like this as it would mean the flat portion of the yard would be approximately 4 metres from the retaining wall to the fence.
What we are proposing is to excavate the land around the back/side of the property to lower it to slab height, and then build a retaining wall at the fence line. This will give us the full flat backyard, without any awkward steps or retaining walls in the middle.
Based on these measurements and figures, does our option sound feasible? Our main concerns are:
- Cost of excavation
- Whether retaining wall will be effective enough (neighbours houses will be 1 metre higher than ours)
- Whether we will become vulnerable to flooding in heavy rain (note we're not in a flood prone area)
I guess we just want some reassurance that what we're proposing is a fairly "normal" thing to do, and we won't run into any major complications after the build.
Best Answer
I assume this is going to be a slab on grade house.
I assume the plan is for rain drains which feed into a perimeter drain which goes out to the city storm drain.
A 1m tall retaining wall is nothing. A nice flat backyard is good.
Unless your lot is down slope from many other lots and there is a natural tendency for water to run into your yard and your neighbors don't have good drainage I like your general plan. Even if there was a drainage issue, as long as your house is protected with perimeter drains, you could cheaply add more drainage and hook into your perimeter drain. Leave a 1' wide area over your perimeter drain in the backyard to serve as drain rock and easy drainage should the backyard get more water than is desired.
Cost to excavate 1m should be pretty minimal ( assumes that isn't 1m of bedrock and there aren't truck sized bolders in that 1m ).
The biggest expense is likely to be the larger retaining wall and the extra coordination with the neighbors depending on how you site the wall and how you site the fence with relation to the wall.