What Causes Dry Rot And Wood Decay

The first and most important thing to do once decay is discovered, is to figure out where it started.

If it is not wood destroying insects, it is water. So we have to figure out where the water is coming from and fix the leak or water penetration. If it is insect damage, call professional exterminators first!

For water damage, in order to check for the origin of the problem, start by checking for the obvious – roof and plumbing leaks, and missing or punctured flashing.

If the problem is not obvious, look for stains and follow any dripping tracks outside and inside of walls.

Another very common problem, is the size of your eves. Are your eaves wide enough to prevent water from cascading down sidewalls?

In addition gutters are a big culprit. Are gutters poorly maintained or missing?

Grading create other water leaks inside that create dry rot and other major problems. Do finish grades slope towards or away from the foundation? Are foundation cracks not waterproofed, if not, is it admitting water?

Other reason why carpentry is needed to repair structural or non-structural lumber, is when water pools on or is too close to it. Is untreated wood in direct contact with concrete, masonry, or soil? Check to see if crawl spaces have soil covers, and if venting and/or insulation is present, adequate, and properly placed.

Damage at the top?

The same goes for attics and spaces in between roof and the ceiling of your home.

The name is misleading, and that matters

Dry rot is not dry. It is fungal decay, and fungus needs moisture to live. The name describes how the wood looks at the end, not how it got there.

Which means the useful question is never how do I treat the rot. It is where is the water coming from.

Treat the decay and leave the source, and it comes back in the same place. Remove the source and the decay stops, whether or not you treat anything.

Where to look, in order

1. Roof and plumbing leaks, and missing or punctured flashing. Look for stains and drip tracks rather than for active dripping

2. Eaves that are too narrow to keep water off the wall below them

3. Gutters that are missing, full, or discharging against the building

4. Finish grade that slopes toward the foundation rather than away from it

5. Foundation cracks admitting water

6. Untreated wood in direct contact with concrete, masonry or soil, which is a detail that quietly causes decades of problems

7. Crawl spaces and attics without adequate soil cover, ventilation or insulation

Peeling and blistering paint frequently signals inadequate interior ventilation or a missing vapor retarder. Water stains on framing inside a wall usually mean condensation rather than a leak.

Where it shows up on a Southern California house

• Deck and balcony ledgers, which is the highest-consequence location of all

• Window and door sills, particularly on the weather side

• The bottom of exterior trim and siding, where it meets the slab or the soil

• Fascia and rafter tails, behind the gutter

• Posts set into or onto concrete without separation

• Under bathrooms and around showers, where the leak is slow and interior

The first one is the one that takes buildings down, and it is now the subject of state law for apartment and condominium buildings: balcony inspections under SB 721 and SB 326.

Decay is a structural question, not a cosmetic one

Decayed wood loses strength before it loses appearance, and there is no reliable way to judge how much strength is left in a member that has started to decay.

Which is why anything load-carrying is shored at detection rather than monitored, and why cutting back to sound wood means cutting past what looks affected. Early decay extends well beyond the visibly rotted area.

The repair side of this, including when a member can be sistered and when it has to be replaced, is covered in dry rot repair.

What it is not

Two things get confused with fungal decay, and the difference changes the treatment.

• Wood destroying insects, which leave galleries and frass rather than the cubical cracking of decay. Different problem, different specialist

• Surface weathering, which is grey, shallow and cosmetic, and does not reduce strength

Start with a free 15-minute call

Tell us where you found it, whether the wood is soft when you press it, whether anything above or behind it could be leaking, and whether it is carrying load. In fifteen minutes we can usually tell you whether this is a finish repair or a structural one.

Call (323) 651-0635 to book the free 15-minute consultation.

The Ultimate Pro, Inc. CA License 831700, Class B General Building. Serving Los Angeles, Riverside, Orange and San Bernardino counties since 1996.