Pier and Beam Foundations – KHouse Progress: As part of our company, we install a lot of pier and beam foundations for houses. Other possibilities include post-tensioned slab on grade and plain slab on grade. All of them are suitable under the correct circumstances, but if I had to select (which I generally do), we would go with the pier and beam structural foundation. The soil in my area of practise is loose because it contains a lot of clay, which expands and shrinks when water is added. It grows when rain or irrigation gives water to the soil. When the soil loses water due to hot and dry weather, it shrinks. All of the earth movement develops fractures in the home. A pier and beam foundation is something we prefer to employ since it eliminates the challenges associated with shifting soil.
Most individuals have heard of a pier and beam foundation at some point in their life, but even “experts” make mistakes from time to time. Because there was no earth beneath the grade beam where he checked, a home inspector advised me that the house I was going to purchase had structural issues.
The home inspector claims that the house was improperly constructed.
Bob: What? What did you look for?
Home Examiner: When I was in the crawl area, I saw several vacant spaces beneath the grade beam.
Bob: Okay, so what precisely was the problem?
Home Examiner: If your beam is not adequately supported, it will droop with time. Someone will need to go down into the crawl area and fill it with soil.
What? There should be no dirt under the grade beam. You are aware that soil does not support the beam; rather, the piers do.
I’ve been a house inspector for a long time, son.
Bob: That’s correct.
If it wasn’t previously evident, the grade beam in a pier and beam foundation is NOT supported by soil.
Because many people don’t seem to comprehend this concept, I decided to design some illustrations to assist clarify what I mean. I hope what I say helps you comprehend if you can’t read drawings.
A typical portion of a wall through a pier and beam foundation is seen here. The grey area is the home, and it doesn’t matter what it’s for in this discussion. The key point to understand is that a pier, which may be compared to a concrete column, is drilled into the earth until it can rest on rock. This is significant because rock does not expand or shrink in response to the amount of water in its surroundings.
The grade beam is a concrete component that runs from pier to pier, similar to the beam that runs from wall to wall in the ceiling over your head.
Under the grade beam, there are “void cartons” or “void forms” (it would have helped if I had labelled them in the sketch above, as it is, it is shown as a grey rectangle with two diagonal lines in it.) Even if you don’t believe it, empty shapes are composed of cardboard and filled with concrete. They are robust enough to support the weight of wet concrete, but the cardboard will rot away over time, long after the concrete has solidified, leaving a hole.
In the drawing above, the “soil retention boards” are the last item to notice. These are essentially plastic planks that prevent dirt from entering the area left by a decaying carton.
Here’s an example of a standard grade beam after rot has eaten away at the space. There is now room between the grade beam’s bottom and the soil below. This is excellent, this is significant, and you want this gap.
What is the purpose of a gap? You want it to be this way so that the soil surrounding it doesn’t press up on the grade beam as it absorbs water and develops. With this space, you won’t have to worry about cracks in your brickwork or doors that stick during specific seasons. Piers are constructed on bedrock, grade beams sit on piers, and your home will not shift if there is no earth beneath your grade beam.
I told you all of this so you could better comprehend the visuals. We recently poured the grade beams at the KHouse, and it was quite a spectacle for a home job. This foundation pour was completed with the assistance of 13 concrete trucks that arrived every 30 minutes. We’re around 80% do currently. The basement walls, driveways, walkways, and exterior steps are all that remain.
To reach all areas of the site without damaging the trees, the contractor had to employ a massively armed concrete pump truck. This machine takes concrete from the rear and pushes it via a network of pipes attached to the arm.
We had to be cautious not to harm any of the trees. It had a significant role in determining where to place the concrete. These pump trucks are seldom utilise on residential works, but they are often employ on commercial operations.
This is the pump arm extending. You can get a fair estimate of how far it can go. Pouring concrete is back-breaking labour. Except for the person who controls the pump arm, who has the finest job on a construction site ever, I frequently believe this is the worst job on a construction site, except from being a roofer in the summer.
Here’s a look at the controller for the pump arm. That’s what the man said to me, and he should know. Everyone else is moving about wet concrete, but he is standing in the shade, playing with the joysticks.
Some of the people pouring concrete into the plywood shapes resembled this. As I was taking this photo, the guy in the plaid shirt in front of me stated, “You really don’t want to stand there.” I know, but I had to snap the photo. After about 5 seconds, an air bubble popped through the line, the concrete spluttered, and then BOOM! I was completely coat with concrete from head to toe (I didn’t photograph this). The only nice thing, while all the concrete workers laugh, was that the contractor was standing right next to me and was also struck.
When we speak about the contractor, that’s him in the white polo shirt sitting on top of the concrete mixing truck. That is what we call doing your job.
This is a view of the grade beams from the top. Wet concrete is represent by the dark grey stripe in the centre. The crawl area will be little about 4 feet deep in total, as seen from the top of the grade beam. We are installing our air-handling units underneath the floor in this project, and here is where they will be.
Because no discussion about pouring concrete would be complete without mentioning a vibrator, I feel obligate to include it. The vibrator is place into the concrete as the concrete is pour into the formwork to ensure that the aggregate is equally distribute and that there are no air pockets. It’s a simple job, but you have to be excellent at it… The concrete will not be out uniformly if there is not enough vibration. If there is too much, the concrete will be overmix and the aggregate will settle to the bottom rather than being evenly distribute.
The last point I wanted to mention was the concrete testing. This does not happen in many residential projects, but this is not just any residential project. An independent testing company arrived to inspect the concrete from two random concrete trucks, performing slump tests and collecting compression core samples. They check the temperature of the concrete to ensure that it hasn’t been in the truck for too long after leaving the batching plant and is still safe to use.
Here is a collection of images depicting a slump test in action. The metal cone is fill three times, with the metal rod tamping down the material 20 times each time. The cone is then progressively remove and place next to the freshly dug-up mound of concrete. The metal rod is place across the top, and the distance from the rod to the top of the “sloping” concrete is measure. The amount that this load of concrete slumps may be use to determine its strength. I believe the structural engineer requested 3,500 psi concrete, so we expected a 4″ slump, which we received. The concrete would have been throw away if it had too much slump.
After just a few days, the plywood shapes are remove and the final concrete product is visible. When I consider how difficult it was to get to this point, I am often astonish at how simple everything seems, yet appearances may be misleading. Everything else will go incorrect if you make a mistake here. All embed plates, drop heights, brick ledges, invert brick ledges, joist pockets, and other details must be coordinate and resolve. The objective is that it seems simple.
Here’s an in-depth examination of corrugated plastic soil retaining boards. Surprised?
The three items discuss in today’s article are see in this image: the concrete grade beam, the soil retention boards (the black panels above), and the cardboard void form (look to the left of the guy above – you can still see the void forms before they get cover up by the soil retainer boards).
And here’s a close-up of how a finished corner appears. Notice how the planks that hold the dirt are notch-cut? This little concrete component is part of the pier on which the grade beams rest (if you want to see more about the piers on this project, read this).
Finally, here is the attached garage on the right and the main home on the left, separated by a walkway. In the ditches visible on each side of the walkway, there will be perimeter drainage pipes. But that’s a topic for another day.
I attempted to strike a balance between making things simple to comprehend and providing enough information to make them helpful. We brought a large number of staff members out to witness how things work on the day when concrete was pour at the KHouse. On the work site, we even met the owner. We go beside him while the concrete was being pour, explaining what was going on. This kind of material might seem dry and monotonous, but as I’ve mentioned before, you have to comprehend something in order to appreciate it. This is not a cheap project or foundation. Therefore all signals point to the notion that the more time. We spend informing the owner about what is going on at the site. The more enthusiastic he will be about the eventual result.
When our customer tells others about his home. I’m confident he’ll say more than “this is white oak flooring” or “this is a pier and beam foundation. “This is white oak flooring, and this pattern is call “cathedraling.” His grade beams require 13 tonnes of concrete to be pour.” That, in my view, is really great.