Slow Rain Versus Hard Rain

Hard rain brings big leaks. Duh? Sometimes. One of Jon Wright's Laws of Roofs is "water takes the path of least resistance. When there are a lot of water molecules trying to go in on direction some of them find it easier to go sideways, or worse, no where. When something is submerged the water thinks it is in a pond. It doesn't matter much if the water is moving. It will still go up or sideways too.
Think about a bath tub. Even if it is draining it can overfill. So can a wide chimney. If it is over two feet wide a cricket is a good consideration.
Then comes the drizzle. Lots of it without sun and heat to evaporate the stuff. The first thing to come to mind is a chimney with an eroded mortar cap. The water starts entering the chimney and becomes suspended in the mortar. Soo it is one drop in and one drop out into the flue or out a cracked or eroded spot that leads to your ceiling.
MOM!
No, dad.
No dad? Mom.

Sometimes a leak will allow only a little water in per second and it doesn't matter if it is a hard or soft rain. The kicker here is the long rainy days let drop after drop after drop enter and the cumulative effect is a stain.

Before you Kilz that stain try this. Bleach and water. Put down plastic and towels because bleach has divorce written all over it. If you paint the stain it will bleed back through but Kilz is pigmented shellac. But it leaves a bright white spot and you usually have to paint the entire ceiling. If you bleach it out, carefully, with a atomizing bottle or a sponge, in a 50-50 mixture, the stain will usually come out. You may need to repeat a few times. Let it dry before you ruin the sheetrock with a total soaking. If the stain is real dark you might not want to try this. If the stain is only a circle then this will work.

I've seen leaks during hurricanes that would never leak again. Once in the early 1980's a monster hit Dallas and my answering service hated me. Real strong anger. 175 calls for leaks and they took them all. All in a day. Very few would ever leak again. I really hated the free estimate stuff but we created some good will over the next few days.

After two days of steady rain I'd go inspect my attic well and have a pot or two handy.

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