Dry rot is caused by microscopic fungi that grow in a moist environment. The fungi digest the fibers that give wood its strength, then move on to a fresh area, leaving damaged and rotted wood behind. If infected wood is not repaired or replaced quickly, the fungus will spread. Dry rot can be found in exterior materials like wood siding or a deck, or in a kitchen or bathroom subfloor or wall framing if there's even a slight ongoing leak.
Wood with dry rot might be white and spongy if still wet, or brown and crumbly if dried out. In advanced cases, large flat mushroom-like fruiting bodies may grow through plaster or paint. Earlier signs of dry rot include cracked, blistered or peeling paint, or wood that appears darker than the surrounding area or green with algae.
Typical costs:
If the area damaged by dry rot does not have to bear weight, it's possible to restore it by trimming away any damaged wood and filling it in with a putty-like two-part epoxy compound that hardens in place and can be sanded smooth. These epoxy compounds sell for about $35-$70 a quart, or $100-$200 a gallon. Major brand names include LiquidWood[1] and Boatlife GIT-Rot[2] . An inexpensive one-component alternative is Minmax High Performance Wood Hardener, which costs $8-$12 for a half-quart.
The cost to hire someone to make these repairs will vary considerably depending on the area damaged and the extent of the problem. For example, repairing a small area of dry rot at the foot of a single porch post might run $100-$250 (labor and materials), depending on whether the work is done by a handyman or a pest repair professional. A Minnesota contractor estimates that one out of eight homes will have dry rot under the existing siding, and that repairs needed before new siding can be installed might cost $50-$2,000 or more, but average $200-$500.
If the damaged area is structural or the dry rot infestation is advanced, the rotted wood must be removed and replaced. The cost will depend on the extent of the damage and exactly what needs to be replaced. Hiring someone to remove and replace a few deck planks or railings might run $500-$1,000; completely rebuilding a 20x20-foot deck using rot-resistant composite materials can cost $5,200-$8,000 -- see How Much Does a Deck Cost. Replacing one or more porch posts might be $200-$600; building a new porch could cost $10,000-$45,000 or more; see How Much Does a Porch Cost. Replacing a section of rotted floor joists can cost $5,000-$10,000; see How Much Does Repairing Floor Joists Cost.
Standard homeowner's insurance generally won't cover the cost of dry rot. If the rot is caused by a disaster such as flooding, it might be covered by flood insurance.
Dry rot fungi need an oxygen supply, temperatures between 40 and 100 degrees Fahrenheit, moisture and a source of wood. Generally, these fungi need a wood moisture content of at least 20%. The first step is to stop moisture reaching the wood -- if possible, eliminate any source by fixing plumbing leaks or drainage problems, or sealing cracks. The infested area must be thoroughly dried before any repairs are made.
A simple dry rot repair can be a fairly straightforward (if tedious) do-it-yourself project. Factsfacts.com provides instructions[3] for filling in with liquid epoxy compounds.HammerZone.com illustrates the repair of a porch post[4] .
Additional costs:
Dry rot is often confused with termite or carpenter ant damage. If the house hasn't been inspected in a while or there are reasons to suspect dry rot, it can be good idea to have a home inspection by a licensed pest control company. An inspection and written report can cost $65-$100 or more, depending on the size of the home. See How Much Does a Termite Inspection Cost.
Depending on the area affected, dry rot repairs can be done by painting contractors, siding installers, pest control companies, disaster recovery services or general contractors. Search for members of the Painting and Decorating Contractors of America[5] or the National Pest Management Association.
Get several estimates, making sure what is included in each quote; understand whether all prep and clean-up work is included. Be sure the contractor is properly bonded, insured and licensed.
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