KHouse Modern – Foundation Progress

Bob Borson —  April 28, 2014 — 45 Comments

If you are an architect, and you like to get things built, getting the foundation going on a project is one of the most exciting times to be found. It’ been a while since I gave everyone an update on the KHouse Modern project, but it hasn’t been due to lack of anything going on – quite the opposite. A whole lot of something has been going on, but this house has a fairly significant and complicated structural system for a residential project and the work is deliberate and methodical.

So let’s take a look at what’s been going on since construction started – the foundation.

The short description is that the site had to be cleared (architectural speak for scraping the dirt and landscaping away as needed), the piers have been drilled (holes dug into the ground down to rock which will be filled with concrete and rebar) and formwork is getting set. Formwork is a structure, usually temporary, used to contain poured concrete and to mold it to the required dimensions and support that concrete until it is able to support itself. I should probably explain some of the other parts that make up a pier and beam foundation since it seems that so many people don’t really know what they are or how they work but this post will already be bordering on head-explodingly long so I’ll save that for another time.

Let’s get to the pictures shall we? This is the easiest way I know to illustrate and explain this process.

Drilling piers

At this point, the site has been cleared and the drilling rig is on site drilling holes. This project has mostly 16″ diameter piers and due to that size, a big drill bit is needed.

tying rebar cages for the pier

While the piers are being dug, the rebar cages are being built off to the side. This massive ring of … rings, is individually tied to 4 long pieces of steel rebar at a spacing of every 12″. This part is obvious for two reasons – the first is obvious (we’ll get to the second reason in a minute): steel is an important part of the piers that are being dug. The steel cages are built and placed into the holes and concrete is poured in to complete the structural assembly (you know, because concrete is strong in compression and steel is strong in tension but hey – nobody cares about that but structural engineers. *note* structural engineers will be dying to elaborate on this … don’t let them).

drilling 16 inch piers

The process of drilling this piers is pretty quick – in our case 60+ piers we completed in two days and that’s the second reason it’s important to have the rebar cages ready to go as you are drilling: the hole gets dug, the steel goes in, followed by the concrete ON THE SAME DAY! You don’t dig these holes and then leave them open so the contractor only drills piers that he is prepared to complete on the same day.

pier holes with rebar cages

Here’s a look at the rebar cages sitting in the holes. Fascinating?

foundation piers in place

Two days later, 60+ piers are in place and we are ready for the next big step in the foundation process: formwork.

starting the formwork

When the formwork goes up, an interesting thing starts to happen: the building takes shape … kinda. You start to get a feel for the house as you can physically move around the site and imagine the spaces (i.e. “I am standing in the bathroom”). In fact, it is quite common for me to walk through the site at this point with the owners and play the “this is where the [fill in the blank] would be” and it is a very exciting moment for everyone.

Site Meeting to discuss structural progress

Of course, getting the foundation as close to perfect as possible is the goal and having a job site meeting with the structural engineers, the contractors, and myself is a good idea … it’s not much fun because structural engineers are super boring but they do add value to this part of the process.

structural drawings on site

This is the foundation plan for this project – beautifully rendered by the contractor. The contractor has a lot of notes on this page and I learned that this is the reason why the contractor doesn’t want new sheets issued when revisions are made – they don’t want to transfer all this data onto the new sheet.

KHouse Modern BIM terrace view Jan 2014

I thought I should include one of the rendered images to remind you what this corner of the house looks like – it’s a little easier to visualize than this next picture …

grade beam formwork

This is the same corner of the house as the rendered image above – do you recognize it? It might take some visualization skills …

grade beam formwork

This house has a crawl space underneath it that’s over 48″ deep – this is where our mechanical equipment will be placed and distributed. Part of the programming requirements for this house was that the owner wanted to house to be elevated from street level – this means that the finished floor will actually be about 24″ higher than the top of the formwork you see in these images.

pier detail - drilling into solid rock

This site is basically sitting on bedrock – the deepest pier we have is 10′ deep and 36″ of that length is embedded into the bedrock. That is pretty salty my friends.

drilling 12" diameter piers

I mentioned that we had 16″ diameter piers on this job – which isn’t all that common actually, at least not for residential work in Dallas. Part of the reason we had that site meeting with the structural engineers is that the contractor wanted to change some of the 16″ piers to 12″ piers so that he could use a smaller drilling rig (the bobcat pictured above). He made this request so that he could avoid damaging the tree canopies in a few areas and he needed to get the structural engineer to sign off on the additional smaller 12″ piers (which he did – whew!).

pier top with sonotube cap

This is looking down at the top of one of the 12″ piers. You’ll notice that there is a brown ring around the pier – it’s only about 12″ deep and it’s in place to make sure that the concrete at the top of the pier doesn’t spill out (what we call “mushrooming”). We want a nice clean and nicely formed cap on our piers.

pier rebar cages detail

Here is a close-up look at the rebar cage for one of the 12″ piers …

grade beam formwork towards basement

This picture is looking back over the site – I am standing in a precarious spot taking this picture … 6″ to my left and I am falling into the basement.

side view of soil

If I had fallen into the basement, this is what I’d be looking at – the cross-section through the soil and rock of the project site. We hit rock after drilling for 4′ … like I said, this will be a salty foundation.

KHouse Modern BIM Alley view Jan 2014

Time for another finished project image reminder – this is looking up at the rear of the house from the alleyway. To the right you can see the basement level garage. As the site falls away from the street, the garage is halfway carved into the site which is easy to see …

digging out the basement

… in this picture. I think this is a pretty interesting photo, it also shows that our drawings were correct in terms of the topography (go Revit! … <sigh> I can’t believe I just said that)

basement desk

In this picture, I’m looking down in the basement level (plus, I always take pictures of job site desks for my growing collection). If Dallas had a rainy season, we would be in it. Since this basement is sitting completely within the bedrock, it basically doesn’t drain water. Right in the middle of the photo you can see a red with blue hose pump to remove the water. The concrete foreman in this photo is also doing something that I don’t see too often on our projects – he is building 2×4 wood stands to tie off his string level lines.

building stands to tie off level string

It might be hard to see the string lines in this image but they’re there. At the rear of the driveway, as it connects with the alley, you can see some of the 2×4 structures that have to be built in order to create the spot where the level string lines will get tied off. These string lines basically act as visual guides for the guys building the formwork as they move around the site. They use laser levels and survey equipment to locate everything and then run these strings as a reference.

hot pink formwork level string

It’s not rocket science but I will tell you that I am glad that color has been introduced into the strings – makes them a lot easier to see. There are literally dozens of lines crisscrossing all over the site and it’s easy to walk into one (or 10) as you are moving around the site. If you’re worried that they’ll break free when you walk into them, think again. They are tied around nails that are driven into 2×4’s and formboards that are extremely secured to the ground. It’s far more likely that you will garrote yourself than break one. It’s kind of embarrassing if you walk into them as well because those strings are hard to see – to someone looking at you from across the site, you simply looked like you are having a fit as you drop or stop awkwardly in mid-stride. Stupid architect …

concrete formwork loose ties

The things you see sticking out from the plywood above are called “form ties” and the ones we are using on this project are for light-duty (2,00 to 3,500 pounds) and is known as a “snap tie”.

concrete formwork tie rod detail with notes

Looking down on the snap tie, it easy to see how it gets its name – there is a weakened point in the rod so that when the concrete has been poured and is ready to have the formwork removed, the tie is simply “snapped” off at a weakened point. The washers you see in these photos press up against the inside face of the plywood formboard – this is what maintains a consistent distance between the two pieces of plywood. Since we will have a 12″ wide concrete beam, the snap ties are ordered with the washers spaced 12″ apart – just behind the washer on the image above and to the right, you can see a small ring on the tie rod that keeps the washer from sliding down and becoming closer than 12″ away from the opposite side.

setting concrete formwork brackets

This is the other side of the formwork boards from the snap-tie photo above. These are the guys that are putting up the brackets and 2x framing that will hold the plywood together under the weight of the concrete when it is first poured and while it is curing.

concrete formwork bracket detail

Here’s a close up look at one of the formwork brackets – you can see that the bracket swivels around the head of the snap-tie. This allows the snap-ties to be pulled tight while allowing some construction tolerance and flexibility on site. When I was on site for my field report (and I was taking these photos), I asked the concrete contractor a question:

Bob: Hey – is there was a special name for these “things” (holding up one of the brackets.)
Concrete Foreman: Yes.
Bob: Uh … great. Could you tell me what it is?
Concrete Foreman: That’s called a “bracket”.
Bob: A “bracket” … really? That’s it huh? There’s no special name for them?
Concrete Foreman: Well, we (gesturing to his crew) call them “cerditos” – that’s Spanish for piggy.
Bob: Okay … those are brackets.

So there you have it – as comprehensive an update as I am willing to assemble. You are now caught up to date on our progress and my condolences for making this such a long post. I did debate on whether or not I should cut it up into to posts – but then you’d have two long and possibly boring posts rather than one long one. Next time I promise I won’t go so long between updates and we’ll focus in on something a bit more bite-sized.

Cheers,

Bob AIA signature

even better

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  • Muhammad

    I am in Pakistan,Thank you for sharing this now i can go in detail as my new project started,Your blog helpful to handle the project.

    • http://www.lifeofanarchitect.com Bob Borson

      Terrific!

  • Choc

    This is a great post. Would love to see more site progress jobs.

  • Maria A Valdes

    Thank you so much for sharing! As an ARE candidate over half-way done with testing, I can’t express how helpful it is to see real-life, real-time applications of construction elements outside of text books. There’s only so many Ching illustrations I can take. Love your blog and keep up the great work!

    • http://www.lifeofanarchitect.com Bob Borson

      Thanks Maria, seeing it in real life makes a big difference. There is no substitute for the real thing.

      Thanks for the kind words, I appreciate them.

  • Jānis

    Thank you so much for an amazing blog! I know, I know – you get this a lot, but it is truly refreshing to see architects who actually think about all the small details of our trade – be it the way the office is run, to the software we use, to actual ‘details’ of the buildings we design and the construction process. Great job!

    • http://www.lifeofanarchitect.com Bob Borson

      Thanks Jānis – there are so many great firms out there practicing the craft of architecture that it is easy to find inspiration. I try and find people who I can emulate and then try and live up to my own expectations. So far it’s working pretty well for me.

  • Dzintars Berzinskis

    i would like to see more things like this >.<
    i'm currently in China, just starting as an architect, and although they build everything really fast here, i actually don't get to see that much of technical side of the projects, or the site, at least not for now.

    • http://www.lifeofanarchitect.com Bob Borson

      I’ll do my best to show you what’s going on as these projects develop!

      • Dzintars Berzinskis

        thank you!! :)

    • Jānis

      Lai veicas, Dzintar!

      • Dzintars Berzinskis

        Pasaule liekas maziņa, kad sanāk dzirdēt/lasīt dzimto valodu neparedzētā vietā :)

  • Mark Mc Swain

    One of the odder things I have heard on returning back to DFW is that there is a cohort of people who use “pier & beam” to refer to a slab foundation set upon drilled piers (I get the impression that these are shallow piers down only to Autin Chalk, and not a designed, engineered structural item).
    Go figure.
    Personally, I find the use of wood framing far more sustainable than the excess tons of concrete used by tract builders seem to be enamored of.

  • M. Evans

    Very cool house and informative article. Like a previous commenter, I assumed the formed walls are over the piers. Are the formed walls the structural elements referred to in your reply as the “grade beam”? We of the non-architect, non-structural engineer, non-anything remotely connected to your industry (well, I do live in a house, that’s the connection I suppose) inquiring minds want to know. Thanks for the information and entertainment.

    • http://www.lifeofanarchitect.com Bob Borson

      The structural system for this house (at least the majority of it) is drilled piers, concrete beams that sit on top of those piers, and the walls are framed on top of those beams. There are also void cartons underneath the concrete grade beams so that when all the dirt goes back from where it is stored, there isn’t dirt directly underneath the grade beams. Since the piers sit on rock, they are not subject to seasonal movement based on the ground swelling with the addition or subtraction of moisture from the dirt. This is why a pier and beam house doesn’t get cracks or why doors don’t stick … the house isn’t moving.

  • Robert

    Nice to see this project being built! What do you mean by “salty” (an inquiring geologist wants to know. The rock looks like Austin Chalk…)

    • http://www.lifeofanarchitect.com Bob Borson

      well, what I mean by “salty” just refers to an old school method of doing something that still works really well.

  • ucon2

    i think the length of this post is just fine. i would even say feel free to go into more detail if u like. the info u provided was helpful and a great insight of what goes on at the site. i can’t wait for the next one.

  • archigirl

    great project! but i’d be having a field day griping about the rusty rebar and lack of rebar caps… but i’m mean to contractors that way *evil grin*

    • http://www.lifeofanarchitect.com Bob Borson

      Yes – I understand. It’s interesting the differences between residential and commercial construction (not that you were suggesting one or the other). The level of quality control and how it relates to owner cost shifts a bit between the two with most of it directly tied to the exposure of risk and liability.

  • AlmostJane

    Not boring and not too long. I’ve been following-up posts like today’s by diving into my recently-acquired Francis Ching book. Between the two of you guys, I’m taking a course!

    • http://www.lifeofanarchitect.com Bob Borson

      Hard to go wrong with a Francis Ching book. Me on the other hand … you’re taking some risks!

      • AlmostJane

        I’ll take m’chances [grin]. PS – have you ever considered teaching? Seriously. This college educator has been reading her way through your archives since Christmas & believes there’s real classroom potential here. So many people teaching in colleges now are just treading water, my term for people who know their subject matter but can’t make it interesting or clear to others to save their lives. America needs people with both a passion for their fields AND teaching ability. Maybe you’ll consider it when/if you [A] get tired of what you’re doing, [B] win the lottery or [C] finish paying for Kate’s undergrad degree [the kid is on her own for grad school]. :>)

  • jel

    Bob,
    Love these construction site posts. Not boring at all!

    • http://www.lifeofanarchitect.com Bob Borson

      Glad you like it – there are so many things that I didn’t cover that I’m surprised I haven’t been called out for not providing but this post was already so long, I have a hard time imagining that anyone other than me actually read the whole thing. Glad to know I’m not alone!

  • Van Bennett

    Nice house! Reminds me of Mies Van de Rhoes’ clean lines. I remember working for an architect when I was his CAD monkey. The house I had been inputing into AutoCAD for a whole summer was finally being built. It was so cool to see it go up and knowing I had a hand in the construction documents. It must be very gratifying for the architect once the buildings foundation is finally poured. Thanks for sharing.

    • http://www.lifeofanarchitect.com Bob Borson

      Thanks Van –
      It is gratifying to see the house be built, and it is a lot of fun to walk the project during this time with the owner. For several, this is the time when the clients are finally able to start visualizing their project after looking at drawings for so long. It’s much more real for them as they are able to physically walk through the project and imagine what is going where.

  • HalifaxShippingNews

    Am I correct in assuming the Formed wall sits on the piers? Is there a reason for doing it this way, rather then a Slab on Grade, or a full 8′ foundation wall with footing?

    • http://www.lifeofanarchitect.com Bob Borson

      Yes – the grade beams sit on the piers. One of the reasons we are using a pier and beam foundation system over a slab on grade (other than they are vastly superior) is that we are using the crawl space we are creating for mechanical distribution and for locating some of the mechanical equipment.

      In the lower basement level garage, we do have some full length wall footings.

  • Alejandro Lara

    Fascinating!!!

  • Damian

    The rendering looks nice, but I would like to see it in the context.

    • http://www.lifeofanarchitect.com Bob Borson

      We are building it in context …
      I don’t particularly care for what I call “railroad” 3d images (photo realistic) and as a result, we do not spend the time creating trees and surrounding buildings on our residential projects. These renderings are a result of documenting the project in Revit, no additional time (or fee) is spent elaborating on the 3d images.

  • Lora

    How does the tie-rod snap if it’s embedded in concrete by then?

    • http://www.lifeofanarchitect.com Bob Borson

      It’s weakened just inside the wall of the concrete so that as the tie-rod gets wiggled up and down (or more likely “twisted”) it will break. You then have to come back and patch the hole left behind with mortar or a concrete slurry.

  • Kerry Hogue

    thanks for the update Bob. one thing I have learned is that there are a lot od thingies and dodads on a construction site.

    • http://www.lifeofanarchitect.com Bob Borson

      I like to learn those names so I can sound like I know what I’m doing. It also allows those guys a moment to “teach the architect” something – which I know they all appreciate.

  • David Conley

    I think I recognize the structural engineers – they look familiar for some reason…

    • http://www.lifeofanarchitect.com Bob Borson

      engineers – they are all alike, pretty sure they take a class in that while in college. I told someone else that I prefer my engineers boring – if they seems like adrenaline junkies or like “thrills”, I’m not sure that they should be engineers in the first place.

      • David Conley

        I would make a great engineer, then – cuz I’m boring as…well, you know…

  • nathan

    oh, and also, killer house Bob, I’m really excited to see it take shape!

    • http://www.lifeofanarchitect.com Bob Borson

      thanks

  • nathan

    We had footings go in last week for a project that has been on the boards for over a year…very exciting indeed!

    • http://www.lifeofanarchitect.com Bob Borson

      Yes – there is that moment when the project really starts to feel real and there’s nothing more real than pouring concrete. (I made that up)

      • Kerry Hogue

        okay be that way. then the ring of rings are actually stirrups.