House Floor Framing and Structure Support

Post 116 of 157

We are getting closer to the end of crawling through the Crawlspace Inspection. In Part Six, we’ll take a closer look at the floor framing and floor structure support …

1. Cracked foundation / possible structural problems
2. Leaking foundation
3. Drainage problems / flooding crawlspace
4. Plumbing components issues – leaking water supply lines, drain pipes, crawlspace water heater installation problems
5. Heating system issues
6. Electrical components issues
7. Floor framing and structure support issues
8. Structural pest infestation – those are Termites, Powder Post Beetle, Carpenter Ants
9. Mold problems
10. Crawlspace ventilation and insulation

7. Floor framing and structure support issues
Depending on your house age and design, there will be different types of floor framing support installed in your crawlspace. Some types of the support are much more vulnerable to various conditions than the others. The most typical is a beam, made out of wood or steel, usually located under the center section of the crawlspace width, and supported along its length with columns resting on … well, sometimes it is hard to say on what. Ideally, it should be resting on a concrete footing, but older houses might have literally anything – and sometimes nothing – there.

You might want to look at your floors above the crawlspace first, and if there is any significant sloping, your doors cannot be closed, or walls are showing significant fractures – try to locate the corresponding area in the crawlspace so you can pinpoint the possible problem.

To make it easier for you, just pick your column type from the list:

1. Concrete / Cinder Block columns – if they are properly centered under the beam with a proper footing, there’s rarely any problems. However, you should check the space between the top of the column and the beam. The column is usually slightly shorter to accommodate some type of a spacer / shim that allows for proper leveling of the main beam. But, creativity of the builder and sometimes other conditions cause that little piece of something to crumble, fall apart, or disintegrate, which might be causing your floor to go out of level and causing several other problems throughout your house.

2. Brick columns - bricks are strong in compressive strength, but weak in tensile strength, and they are also quite porous which makes them easily degraded by moisture and minerals that are drawn from the soil which weaken their structure. Also, if it’s an older house, they might have been jointed with sand-lime mortar mix that deteriorates more rapidly than most modern concrete mixes. Therefore, look for missing, delaminating bricks, usually along the base of the column. There might be some crushed ones at the top, and if the damage is severe, beam support compromised–servicing will be necessary.

3. Stone columns – depending on the stone type (usually limestone) and the way it was put together (sometimes without any mortar, or with sand-lime mortar mix that turned into sand over the years), they might require rebuilding. If they are still intact, check mortar between the stones – does it still hold, or can you scrape it easily? Also, the limestone itself disintegrates over time, especially in a moist environment. There are compounds you can use to reinforce the column on exterior, but if the deterioration process progressed deeper into the column, patching it won’t help much.

4. Wood columns – in older structures, redwood or other decay resistant species were used. Pressure treated lumber replaced them completely decades ago. Wood columns should be anchored / secured in place at the bottom end because moisture level changes, wood shrinkage, settlement, and load changes on the floor above; they might become loose and simply fall onto the ground. They shouldn’t be smaller than 4”x 4” (no 2”x 4” please). Check if properly secured, probe it for soft spots with a sharp pin – the critical area is along the base, especially when installed directly on the concrete footing or if in contact with soil. It also won’t hurt to test few other spots along the column – if your pin (3”- 4” inches long would be perfect) goes in easily, I’d recommend to have it replaced by a professional and determine what’s causing deterioration.

5. Metal columns – shouldn’t be less than 3” in diameter, just like wood columns must be anchored to the footing. The metal will not shrink, but load changes, settlement of the footing, and wooden beam shrinkage might cause it tip over. All surfaces should be treated with coatings to provide corrosion resistance. If the bottom section protrudes from the concrete footing, look for blistering and water leakage from those blisters – an underground water table might be high enough to force water inside the column and accelerate the corrosion process.

And now a few words about floor framing made out of wood;

the most critical areas are along the foundation, where the framing members (floor joists) rest on top of the foundation, and under any sources of moisture – bathrooms, kitchens, laundry rooms, furnace / water heater closets.

If your foundation top is below the soil, landscaping, or in the area that occasionally fills up with water, you’ll notice seepage stains along the top edge of the foundation. This means that any framing section sitting directly on top of the foundation was also exposed to moisture and might be decaying – use that pin tool of yours on all wooden surfaces you’re testing. And don’t throw it away just yet, you’ll need it for the rest of our journey. Look for soft areas, damaged / rotten sections, mold contaminated, or an infestation with Termites, Powder Post Beetle, Carpenter Ants – that’s in the next post.

Floor framing sections under the bathrooms are often in poor shape, and not always because of water leaks or moisture – but because whoever worked on the plumbing system didn’t care much about framing, and sliced it or drilled it whenever it was convenient.

A couple of simple rules for notching and drilling through the floor joists:

  • notching along the joist can be a maximum 1/6th of the joist depth (for a 6”joist, the notch would be 1” deep … actually less than that because 6” is not 6” any more)
  • notching at the end 1/4th of the joist depth max.
  • no notching in the middle 1/3rd of the joist
  • holes must be located a minimum of 2” from the top and bottom, and the max diameter should be 1/3rd of the joist depth (for a 6” joist, it would be less than 2”)

And you know what – not many people care …

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This article was written by Dariusz Rudnicki

I'm a retired Illinois home inspector, founder and editor of checkthishouse.com, a blog which attracts around 2 thousand readers daily and is dedicated to answering the many questions of home owners and home buyers. Connect with me on Google+ Find me on Google+ Local

1 comment:

Nathan Poole,Sr. at Reply


I have a question. My house was built in 1999. My floor is built of wood. My question is, would my floor be considered as part of the structure?

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