Okay, you’ve seen the concrete get poured on top of those pretty red water heating pipes in this post. Now let’s step back a few steps to what went under the concrete.
After the roof was put on, the basement floor was the first significant task that Leanne and I took on ourselves after things fell apart with our contractor, so it was a big deal for us.
In a nutshell, the plan has always been to dig deep enough to give us some reasonable ceiling height in the basement. We also wanted to add a lot of insulation under the house which meant digging even further.
Digging is not cheap so an easier option, since we were pouring a new foundation, would have been to raise the house as high as we needed. In your case, that may well be the best option and there are several houses in the neighbourhood which have had this done. Often they go further and add a whole new floor on the bottom.
In our case, it was important to us personally not to change the exterior look of the house so drastically. This priority is reflected in our Heritage Revitalization Agreement which protects the character-defining elements as described in our Statement of Significance.
Not to say that raising the house a few feet wasn’t an option. Once you have an HRA, you can apply for a Heritage Alteration Permit which gives permission to alter the house in as sensitive way. So we could have asked the City of Maple Ridge for permission to raise the house, but we didn’t want to.
We soon learned, however, that we couldn’t dig as deep as we wanted and add 12 inches of styrofoam under the house. Why? Well, the perimeter drain–that perforated pipe that circles the footings of your house–has to drain downhill into the closest storm drain. (I’ll elaborate on that in another post as soon as I can think of a way to make the topic interesting!).
So we dug as deep as the storm sewer would allow us to dig.
The other constraint was ceiling height. The BC Building code won’t let you have a ceiling height of less than 2.1 meters (about 6’10”) in a living space. What we had before was technically a crawlspace.
To achieve the required ceiling height, we had to raise the house a little bit. I’m not sure exactly how high we raised it in the end, but it was supposed to be about 8 inches. It’s hard to tell because the elevation of the ground has changed.
Anyway, after you have poured your footings and foundation walls and determined the final elevation of your basement floor, you need to consider what goes underneath. The plan was 4 inches of concrete (the slab) and 3 inches of styrofoam insulation (that was all we could fit).
Under those 7 inches is crushed rock. (I used to call this stuff gravel, but I have learned that gravel is a more general term.) Three-quarter-inch crushed rock is good stuff to have under your house in our temperate rain forest climate. It drains well. We know that as the global climate changes, we can expect more extreme storms and, around here, that means more rain.
Does it look like a lot of crushed rock to you? We checked the level we needed to fill to by using a piece of wood measured from the joists above. I was surprised by how much room we had and how much “crush” we needed. Every time we added more I wondered if we could have planned better and added another inch or three of insulation instead.
Now I know we could have.
After we filled to the correct level, it was important to compact the rock so that the concrete slab wouldn’t settle. We rented a compactor for a day.
It’s a lot like using a self-propelling lawn mower. Our neighbour let us borrow his laser level which shot a red line around the room. I could see from the line on the side of the compactor roughly whether a spot was high or low.
Next step: Terrafoam!