For homes not built on a slab, humidity can become trapped under the floor in the crawl space. As this moisture attempts to evaporate upward, it can cause damage to the subflooring materials. To keep family members from stepping through your floor, you'll want to replace the subflooring and install your final flooring of choice. However, before you do that, you'll need to remove old rotten subflooring. Let's at look at how this can be done. 

Combating Moisture

Unless the home is a historical landmark, the floor usually did rot by itself. Moisture is the most likely culprit. Before you replace the subflooring, you'll want to determine the moisture's origin or your work will be in vain. Inspect the crawl space areas around water lines, windows, or the attic for signs of water damage. If none of those give you any clues, its likely that moisture from the ground around the house is to blame. There's a good chance that older homes have no water-resistant barriers between the ground the home, so you may consider installing one. Also, a lack of rain gutters can cause water to pool around the outside of the home that makes its way into the crawl space. So, not only is it a good idea to install ample guttering with downspouts but also to install a crawl space fan to let vapor escape the under belly of the house. 

Inspecting Floor Joists

Subflooring is most susceptible to rotting due to its thinner, cheaper material—usually plywood or a form of particleboard. Floor joists, however, are likely more durable and less in need of maintenance. However, it is essential to inspect joists before the work begins. If they are badly rotten, you likely have much more work ahead of you than merely replacing rotten subflooring. 

To Patch or Replace?

If only sections of the floor appear rotten and the moisture problem is handled, you may be able to get away with simply patching decayed spaces where it is necessary. While this may seem like a pretty easy fix, make sure that doing so will allow floors to continue to match up with each other throughout the house. Patch jobs can make floors unlevel, leading to a variety of annoying problems within the home. If it is not possible to patch the floor without leaving areas unlevel, it may be necessary to remove the subflooring in space altogether to ensure it is level—even some flooring that is not rotten. 

Get to Cutting

Once you've removed any top-side hardwood flooring, tile, or carpet from the subflooring, holes in the floor will likely give you an idea of the thickness of the subfloor material. Carefully measure the thickness of the subflooring and use this same measurement to set the depth of your circular saw. Setting the circular saw to the thickness of the subfloor will ensure you don't damage your floor joists while cutting. For less rotten parts of the subfloor, you will need to make cuts with the circular saw. More rotten sections of the subfloor can be knocked out with a well-placed sledgehammer stroke. To clean up jagged edges, you can use a reciprocating saw. Remember to remove all remaining subfloor nails with a pry bar and pick them up from the crawlspace. A magnetic nail-finder is a nifty tool to have for this job. Dispose of all the removed rotten subflooring in the proper receptible. Remember always to don necessary protective gear when performing these jobs. 

If all of that sounds like a time-consuming, messy, complicated, and potentially dangerous job, that's because it is. If you'd prefer to leave it to the demolition professionals, feel free to consult the demolition experts from Expert Dumpster.

Source: http://dtwreckit.com/blog/posts/view/253/how-to-remove-rotten-subflooring