Why Your Foundation is THE Most Important Part of Your House

It may seem like a simple part of the overall construction process, but getting the foundation right is incredibly important. The biggest reason for this is that any mistakes you make in the foundation will only get worse as you go up. It’s known as compounding defects and it means that mistakes grow. Here’s an example: You notice that your slab foundation is 3/4” out of square when you start framing. It’s also 1/2” out of level across the total building. You figure, “well, I can handle that. I’ll just adjust it in the framing.” As you complete the framing, you get up to the roof and notice that the building is now 1” out of square and 3/4” out of level. Bummer, but you figure you can capture it in the roof framing. By the time you metal roof shows up, the square panels don’t fit on your out of square roof and you have “to make it work.” In the end, everyone and your grandmother can see that the roof is out of square and the simple mistake in your foundation has ruined the look of the house. I’ve actually seen this happen to someone. It was a “simple” mistake and it just got worse and worse as he went up in the construction process.

Here’s another reason that your foundation deserves the highest focus and attention to detail: your entire house sits on top of it! If you skimp here and something fails, it’s not an easy fix. Is it worth the extra few dollars to add a bit more rebar to the slab? Yes. Ensuring that the foundation is built to the very best standards possible is very much worth it. Here are some simple things to look out for when building your foundation and/or slab.

  1. Make sure that the rebar is the right size and is laid out in the right spacing for your soil/geological conditions. A typical residential house in the United States uses #4 rebar in the foundation walls and #3 in the slab on an 18”x18” grid pattern. The layout for the foundation rebar depends on the size of foundation wall and the local codes.
  2. Do not allow any rebar to “daylight” or even come close. No rebar should end or be placed within 4” of the edge of the concrete. Rebar closer than that can draw moisture from the outside and rust. That rust will creep down the rebar and, over time, render the entire rebar system useless.
  3. Pay extra attention to the layout of your foundation and slab. Make sure that the corners are square and level. The closer to perfect you are, the better, but in no case should you be more than 1/4” out of square or level for a roughly 2000 SF house. Use a laser level if you have one or the best standby of all time: a water level. It’s the cheapest level you’ll ever buy. It’s basically some clear plastic tubing, water, and a little red food coloring to help you see the level lines better. You can even use this set by yourself.
  4. Wait until the water has evaporated off of the top of the slab before you start finish troweling. If you press that water back into the surface of the concrete, it will weaken it. Allow it to cast off the water it doesn’t “want” and then get on it for the finish work.
  5. If you plan to acid stain your concrete, don’t over finish the surface. If you polish the surface too much, you will seal it beyond what the acid stain can react with. You can definitely get the surface smooth, don’t get me wrong, the key is not to power trowel the heck out of the slab.
  6. Use a stepped foundation when applicable to minimize concrete use. If you have a sloped site, step the foundation up or down the hillside to work with the topography. Be sure to measure the steps and keep them in line with the bale courses so you can step the bales too down the road if that works with your design. This won’t apply in all cases, but if it does, it’s great to get it right when stepping the foundation to keep your bale work easy.
  7. Spend some extra time around your foundation bolts when finishing the slab. Many people don’t put a lot of attention here because they figure “it will be buried in the wall so who cares if it looks good.” This is one way that mistakes compound. When you add your 4×4 toe ups to a series of foundation bolts sticking out of poorly finished concrete, you will quickly find that the 4×4’s won’t sit flat. The thick 4×4’s won’t bend like a 2×4 to fit flat either, so you will be left with a toe up that’s up in the air in some spots and flat in others. This not only allows for air gaps through which bugs can also travel, but also messes up the framing before you even start it. Finish those areas well and you will be happy you did.
  8. Use Wedge Bolts or other “after cure” anchors for the interior toe ups. By adding the interior anchor bolts after the concrete has been finished you can get a better finish on the concrete (not only for the bolts as described in #7, but also for your floor which will come very close to the anchor bolt locations). Using the drill in bolts also makes the layout and installation of the interior toe up a lot easier and more accurate.
  9. Be sure to vibrate your form boards to eliminate “honeycombing” of the concrete. This not only improves the strength of the wall, but increases the beauty. This can be as simple as pounding a hammer against the form boards while the concrete is still wet. Do this BEFORE you finish the surface as the vibration can make the surface of the concrete drop a bit.
  10. Use adequate bracing for your pours. There is nothing worse than having a form board blow out during a pour. It means more concrete will be used and your nice straight line will be shot. Use lots of diagonal braces to support the forms during the pour.

8 Responses to Why Your Foundation is THE Most Important Part of Your House

  1. Kim Davison Tue, December 27, 2011 at 10:25 am #

    Hey, Andrew!
    Hope all is well with you and your family. I had such a great time at the workshop in Tennessee last summer. I decided to pass on the land I was considering last fall. It just didn’t have enough level land to suit my plans. But, I do keep looking! Here’s a question: Do you send out your blog posts as you write them, or do I have to remember to go to your website and look for them?

    All the best to you in 2012!


  2. Andrew Morrison Tue, December 27, 2011 at 3:50 pm #

    Hi Kim. I do send out newsletters from time to time with some links to blog entries, but I don’t link to every entry I write. I suggest you check back when you can. You can always scroll through the entries from time to time. Hope you are well!

  3. Leslie C Tue, December 27, 2011 at 7:11 pm #

    Kim – Andrew does have an RSS feed available for his blog page; you can pop that into your homepage’s reader or newsfeed(or use onle of the handy “add to” buttons also on the blog sidebar if one matches your homepage) and then you’ll have a box on your homepage that will let you know at a glance when there is an update. I hope that helps; not sure how techie you are or if you have a techie friend or relative to help… :-)

  4. Lisa Haessler Tue, March 17, 2015 at 4:56 pm #

    Hi Andrew! My partner and I are planning to build a strawbale home this summer and we are considering adding a ponywall to the foundation to raise the bales a little higher off the ground as we live in Northwestern Ontario and we get a lot of snow (concerned about bottom course of bales being under snow for part of the year on whatever side of the house the window gusts against). However, building a pony wall thick enough to hold the strawbales means adding a lot more concrete to our build. Could we use rocks to in-fill the concrete forms of the pony walls, then pour the concrete in (we’d do this in lifts and tamp down the concrete to ensure no air pockets)? Does that sound reasonable or very risky?

  5. Andrew Morrison
    Andrew Morrison Tue, April 7, 2015 at 7:58 pm #

    That can be done if the building department approves it. There are risks involved, but it should be possible. I think a better way to go might be to add a lot of used concrete chunks to the forms and then pour a thin concrete slurry around all of it. use a vibrating machine to be sure that everything settles in and fills properly.

  6. Sarah Tue, November 17, 2015 at 9:19 pm #

    Hi All. I realize this article was a number of months ago, but it seems you know quite a bit about foundation work, so I was hoping you might have advice for us. We don’t know where to turn for second opinions.

    Here’s the doozy.

    After two years of preparation work, we finally got our house build moving forward. 1200 sq ft foot print. Everything seemed to be going well. Our builder subcontracted the foundation work. They poured the footings, built the forms, and about 9 days after footings were poured, the walls got poured. Major frustration aside, we found out today that the concrete workers were about 2 feet short on a wall. They measured wrong and now need to add concrete to an already-poured-wall that is about 20 feet wide. We are pissed to say the least. Our builder is taking the structural engineer up there to assess how to handle this. The weather is changing and freezing temperatures are due in about 8 days. Do you have any experience in this type of mistake, and if so is it possible to have a solid foundation wall that is “patched”? ie. wet concrete poured onto drier concrete. Please help with any advice….

  7. Sarah Tue, November 17, 2015 at 9:20 pm #

    Whoops. I meant Hi Andrew! Sorry bout that. Hope you can offer some advice…

  8. Andrew Morrison
    Andrew Morrison Wed, November 18, 2015 at 4:55 am #

    Hi Sarah. Sorry for the frustration. Things like that are very disappointing, especially when the excitement of building is interrupted. They should be able to add the necessary correction to the wall without too much trouble. I would expect the engineer to require that the new concrete be “tied into” the poured concrete via metal rods of some type. It’s not uncommon to join concrete in this way, although not as ideal as a correct pour would have been. Once “joined” mechanically, there should not be a structural issue at all moving forward. Good luck and let’s hope it’s all good news moving forward…

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