Q: Last weekend, I noticed some discoloration on my home's wood siding. How can I tell whether the siding needs replacement or just repair?
A: Mold and mildew are frequently to blame for discoloration. Often, this is just a surface problem. You can probably clean the siding using soap and water or a bleach solution. Painted siding may need repainting.
Decayed siding, however, should be replaced. If you don't, the nails holding it to the house may eventually come loose.
To test for decay do a "pick test." If you can easily push a nail into the wood where it looks discolored, it probably has rotted. Test a section above and below the questionable area to see how much of the siding is damaged. Don't assume that all the siding will need to be replaced, though. Pieces under eaves, for example, may have been protected from damaging moisture.