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Finding Hidden Rot on a Pasadena House Before Paint Covers It

Rot does not announce itself. By the time decayed wood is obvious from across the yard, it has usually been working for a long while beneath a painted surface that still looked sound. The weeks before a repaint are the best time to find it, because this is the one moment when every piece of wood on the house will be looked at up close. A careful inspection with a few simple tools lets you find soft wood while it is still a small repair, and it keeps you from paying to paint over boards that will fail within a year.

Tools for the job

An awl or a small flat screwdriver. The basic probing tool. Sound wood resists the point. Rotted wood lets it sink in easily.
A flashlight. Even in daylight, a light held at a low angle shows bulges, cracks and texture changes in painted surfaces.
A moisture meter, if you have one. A pin-type meter gives a reading of moisture in the wood. Unusually high readings compared with nearby boards point to a problem area, even when the wood still feels firm.
Binoculars. For looking at fascia, rafter tails and gable trim before you get on a ladder.
A notebook or phone. Record each suspect spot with a photo and a short note about its location.

How to probe without doing damage

Press the point of the awl into the wood at an angle, with steady moderate pressure. On sound wood, the tip goes in only slightly and the wood around it stays firm. On decayed wood, the tip sinks in with little effort and the fibers crush or crumble around it. Pull a small splinter up with the tip: sound wood tends to lift a long, fibrous splinter, while rotted wood breaks off short and brittle.

Probe in less visible spots first, such as the underside of a sill or the back edge of a trim board, so you do not leave a row of holes on a face that is otherwise fine. Small probe holes in sound wood can be filled and primed before painting. On homes built before 1978, probing and scraping disturb old paint that may contain lead, so keep chips contained and clean up with a HEPA vacuum.

Signs you can see before you probe

Paint peeling repeatedly in the same spot. Paint that keeps failing at one location, even after touch-ups, often sits on wood that is staying wet.
Cracks across the grain. Sound wood tends to crack along the grain. Cracks running across it, or a checkerboard pattern of small cracks, can indicate decay beneath.
Soft, sunken or wavy surfaces. Paint that dips, ripples or looks slightly collapsed has often lost the wood behind it.
Dark staining. Discoloration at the ends of boards or around joints suggests moisture has been soaking in.
Swollen joints. Joints that have opened up or pieces that no longer sit flat can mean the wood has swelled from water and then begun to break down.
Fungal growth. Visible fungus, whether a fuzzy growth or a shelf-like fruiting body, is a definite sign of active decay.

The places to check first on Pasadena homes

Window sills and the lower sash

Sills are designed to shed water, but they are the most exposed horizontal wood on most houses. Probe the front edge, the ends where the sill meets the casing, and the underside. On wood windows, check the bottom rail of each sash and the joints where the rails meet the stiles, since water gets into these joints and softens them from inside.

Door casings and thresholds

The bottom few inches of an exterior door casing often sit close to a porch floor or step, where rain splashes and water collects. Check where the casing meets the threshold and the bottom edge of the door itself.

Rafter tails, purlins and beam ends

Craftsman bungalows are known for exposed rafter tails and decorative beam ends extending past the roofline. These show their end grain to the weather. Probe the ends and the tops. On mid-century homes with long overhangs and exposed beams, check each beam where it passes through the wall and at its outer end.

Fascia and the edges of the roof

Fascia boards sit behind gutters. When gutters overflow, leak at joints or are clogged with leaves from street trees, water runs behind them and soaks the fascia. Look for staining and softness, especially at gutter corners and downspout outlets.

Porch posts, columns and railings

Posts rot at their base, where end grain sits on a concrete or wood floor and water pools around it. Tapered Craftsman porch columns are often built up from several boards, and their bases can decay inside while the outside looks intact. Probe the bottom of each post and look for a gap or stain at the base. Check railing caps and the joints where balusters meet the rail.

Siding near the ground and near sprinklers

The bottom course of wood siding and the trim at the base of walls take splash-back from rain and spray from irrigation. Probe along the bottom edge, especially behind shrubs and near sprinkler heads.

Anywhere two materials meet

Wood trim against stucco, a chimney against wood siding, a deck ledger against the house: all of these joints can trap water behind them if the flashing or sealant has failed.

What to do with your findings

Mark each soft or suspect area with painter's tape and record it. Then trace each one back to its water source. A soft spot at the base of a post points to water pooling there. A soft fascia points to the gutter. The water source has to be fixed along with the wood, or the repair will fail.

Group the findings by severity. Surface softness a fraction of an inch deep on a non-structural piece is often a candidate for consolidation and filling. Rot that goes deep, covers a large area, or affects a structural member such as a post, beam or header needs replacement, and may need a contractor's assessment. If probing turns up clean galleries, small pellets or mud tubes, stop and have a pest inspection done, since that is termite activity rather than rot.

Keep the list with your paint records. Knowing where rot appeared before tells you where to look first next time, and those spots tend to repeat until the underlying water problem is solved for good.