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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.

enter image description here

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.

enter image description here

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    "This will give us the full flat backyard," In other words....a pond when it rains. Drainage should be the number one priority. – Steve Wellens Mar 12 at 5:41
  • @SteveWellens - if we left the incline, I guess the pond will be surrounding the house rather than (potentially) being absorbed by the grass. So it seems like it wouldn't make it worse, right? How would we know if the drainage was sufficient? – LeopardSkinPillBoxHat Mar 12 at 5:52
  • You will know that the drainage is sufficient if you do not get a pond when it rains. And with a slope of 101.6m that is a lot of slope - unless you confused metres with millimetres. – Solar Mike Mar 12 at 6:26
  • @solarmike the slope is only 1m. The 101.6m value was the elevation not the slope. – LeopardSkinPillBoxHat Mar 12 at 6:47
  • When I built my shop and later my house, when I had to deal with sloped land, I just put up taller stem walls and backfilled to them (with proper waterproofing and drainage), saved the cost of additional excavation, building a retaining wall, etc. Since then parts were "Earth sheltered", it stayed very cool in the hot summers but held heat in the winter. – George Anderson Mar 12 at 14:55
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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.

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  • Thanks for the advice. With the drainage suggestions, is there anything I need to notify the builder about up front, or can I do all of this stuff once the build is complete? Their build finishes at the slab and they aren't doing anything beyond that. – LeopardSkinPillBoxHat Mar 12 at 7:50
  • So the builder will level the site, install the retaining wall / deal with fence, put a footing down to frost depth and have a concrete wall >6" taller than finished grade, install a perimeter drain around the outside of the foundation that slopes to the city storm, install the sewer line to the slab, install the water line to the slab and pour/finish the slab? You should be able to tie into the perimeter drain easily and since it should be at the bottom of the footer and your backyard isn't huge you'll have plenty of available slope. – Fresh Codemonger Mar 12 at 8:03
  • The builder is only levelling the site for the slab, but everything around the slab is left as-is. They aren't building any retaining walls; that's up to me afterwards as part of landscaping and excavation of the yard. I just want to know if there's anything that I need to proactively ask the builder to do during the building of the house/slab itself to avoid any problems for me (and the landscaper/excavator) afterwards. – LeopardSkinPillBoxHat Mar 12 at 9:41
  • Talk now to whoever you would likely be engaging to do the backyard excavation. Perhaps the backyard excavation and retaining wall should be done first. – Jim Stewart Mar 12 at 11:40
  • Since your drawing doesn't appear to be to scale, it could be that getting digging equipment into the back yard after the house is up could be quite difficult. That means that any post-build excavation might have to be done by hand and that can only increase costs as the labor costs skyrocket. – FreeMan Mar 12 at 12:45
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I have to post this as an answer, because SE doesn't support pictures in comments. So here goes. I deleted a previous comment bc it no longer applies. On the first pic you can see the tall stem wall from the outside, it's about 5' tall, tarred and then delta dimple mat applied, drain rock next to the stem wall to a foundation drain, backfilling as the drain rock was brought in. Been here 15 years now and have never had a drop of water come into the shop thru that wall. Like I said before, keeps it cool in the summer being partly Earth sheltered and somewhat warmer in the winter. I like my shop at about 58-60 degrees and mother Earth does a pretty good job of that. I may not be comprehending your issue correctly so this could all be worthless, at anyrate, here are the pics:

Pic of tall stem wall

Interior pic of tall stem wall.

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