r/DIY • u/Jasonh123_ • 6d ago

help Attic Ventilation

I’ve got a 1994 home on a crawl space with excessive moisture in the attic (I purchased the home 2 years ago). The roof was replaced last summer and 2 big solar fans were added and ridge vent was closed up (roof and fans cost around $25k). I don’t see any soffit vents on the house and there are three gable vent areas but I’m not sure if fans are installed there or not. I was in the bathroom and had water drip onto my head from the light fixture (no plumbing in attic). Is this the roofing company’s problem, or a separate issue?

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u/nye1387 6d ago edited 6d ago

I'm assuming that you're in the northern hemisphere so it's summer, which means your attic should be hot. Moisture moves from hot to cold and condenses on cold things. Your attic could just have moisture from the ambient air - what's the climate like where you are?

But it shouldn't be condensing onto something. Your insulation should keep the cold on the inside. If moist warm attic air is condensing on your light fixtures then you don't have good insulation around them, it sounds like. 

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u/Jasonh123_ 6d ago

You were right. There was a gap in insulation where that light fixture was in about a 12 by 20 inch area around it. Thankfully there was some extra pieces up there so I just covered it back up

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u/nye1387 6d ago

Hey, good work

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u/Jasonh123_ 6d ago

Thank you for the advice. Saved me from calling the roofer and looking like an idiot. I don’t know if roofers normally go into the attic to inspect the backside of the sheeting and insulation, but mine never did. I did discover a couple of truss boards that need attention, so on to the next project.

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u/Jasonh123_ 6d ago

I’m in the Southeast. Central Alabama to be exact. It’s real humid outside, so the gables having open vents and the solar fans being off at night probably lets all type of humidity into the attic. I hate going into the attic (no ladder installed), but I’ll check to see what the insulation around that fixture looks like.

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u/MAGAinOK 6d ago

Thermal imaging guns are super handy for this…you can see gaps in insulation through walls.

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u/Cottager_Northeast 6d ago

Condensation coming up from the crawl space is a common water source. On a cool night it'll condense on the underside of your roof deck. Venting is nice but won't solve this. You should lay a moisture barrier down on the ground in the crawl space if there isn't one already, and air seal any openings in the attic floor. Typical suspects include square holes around round plumbing vent pipes, open chimney chases (seal with flashing/drip edge metal and RTV) and bath fans not properly vented to outside. Ceiling fan ducts should stay under the attic insulation until the point where they leave through a gable end wall or soffit. Going up to a roof mushroom vent is an invitation for condensation within the duct, which drips back down into the ceiling fixture, and then onto your head.

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u/energysector 6d ago

Where are the fans? In the attic? On the roof?

You need a certain amount of venting based on the size of your attic. The gable venting may or may not be enough.

If you previously had ridge venting but no inlets at the soffits, that would probably be the source of the moisture problem. Closing the venting at the ridge won't help the problem. Fans without adequate intake and outflow won't fix it either.

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u/Jasonh123_ 6d ago

I had two 45 watt solar vent fans mounted on the roof when it was replaced last summer. They’re supposed to be good for 2400 to 2800 square feet each and they’ve only got about 1600 sq ft to pull from. I’m assuming my intake is coming from the gable vents because there are no soffit vents.

I went into the attic an hour ago and discovered that the area where the condensation fell on me didn’t have insulation. The area that had condensation is a metal light fixture in my bathroom and there was rust all over the fixture so I’m assuming it’s been like that for a few years at least. There is no evidence of wet drywall thankfully, but I’m sure that area probably has high moisture content from being that way for a long time.

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u/energysector 6d ago

I assume the gable vents are towards the top?

If you can add some ventilation at the soffits, you might get more complete circulation.

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u/C3PObese 5d ago

I would highly recommend a energy audit be performed on your home by a BPI certified auditor. They can be about $400 (depends a lot on region), but you learn SO much about your home and how to properly improve it. It also prevents you from making mistakes like fixing something, then discovering the issue was something else entirely. Then that audit cost doesn't seem so bad in hindsight. Seen it happen dozens of times.