There is no typical percentage for something like this. In fact, mold remediation could INCREASE the value of your home if done correctly!
For example, if you had a home with a mold problem that is worth 300,000 and the mold was removed by a REPUTABLE, ESTABLISHED & PROFESSIONAL company that offers a long term warranty on their work, then the home should now be worth MORE than it was with the mold problem.
Another major aspect of this is whether the source of the mold was also repaired? If the home has a leaky foundation, did you have a REPUTABLE, ESTABLISHED & PROFESSIONAL company repair the leaky foundation so that the mold will not come back? Remember, you can spend all the money in the world removing mold and have the best warranty, but it does you little good if you still have the moisture problem that caused the mold in the first place.
I hope this helps! Let me know if I can be of any more assistance.
Chapman Hall Realtors Premier
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