You can use a brush or a roller, but it will be difficult. The best tools to apply paint to lap siding are spray guns and pad applicators. The pad applicator is ideal for lap siding because it can reach under the laps. Downward strokes with the pad applicator allow paint to penetrate lap-siding grooves. A spray gun is also useful when painting lap siding because it can easily cover all surfaces on lap siding, provided the gun is used properly. If you choose the spray gun method, three light coats of paint should be applied from different angles. First spray from below at a 45° angle, making sure the paint penetrates under the laps. The second coat should be directed downward at a 45° angle, and the third should be sprayed directly on the lap siding. Do not try to spray in direct sunlight; the paint may dry before it hits the wall.