Most homes - regardless of age, size or style - have some sort of exterior trim. The frieze is the horizontal trim board along the top of an exterior wall just below the soffit. The fascia forms the face of an eave and provides a surface for attaching rain gutters. Rake boards angle up from the eaves to the ridge to trim a gable wall. Flat exterior casings frame windows and doors, while vertical corner boards often frame siding or shingles at inside and outside corners. Exterior trim is nearly always low-grade No. 2 pine or fir that's been painted. Pine and fir are prone to insect and weather damage, and the resinous knots on both tend to bleed through several coats of primer and paint. They also expand and contract as they absorb and shed moisture, causing split wood and cracked paint. In the end, you have to patch, scrape and repaint the trim every couple of years. Knot-free grades of cedar, redwood or sugar pine hold paint much better and are more dimensionally stable. But they still expand and contract. And that's bad news for paint.