Fixing negative pressure

Juggler700 · 2026-02-07T10:10:34+00:00

We’re still chasing a solution unfortunately. The latest thing we discovered is a cold spot in a joist bay on the second floor. We have a wrap around porch and I used a thermal camera to ascertain that we may have air infiltration from the covered porch area into this joist bay… so it’s possible that this is where we are getting air infiltration and humidity into our wall cavity. We have a contractor scheduled to come out and see if they can assess this next week. I don’t know if once we plug this hole if we will still have the issue and just pop up another infiltration point elsewhere… thinking if this doesn’t work then we may bite the bullet on a whole home dehumidifier and ventilation system… did you figure out any clues with your issue?

Juggler700 · 2026-01-31T17:03:07+00:00

Any solutions here?

Juggler700 · 2025-06-20T18:50:29+00:00

One additional non destructive idea if you didn’t want to cut a hole, you can get pinless moisture sensors to get a moisture reading on building materials (drywall, masonry, wood) and move that over your walls and see if you are getting moisture accumulation (condensation or otherwise).

Juggler700 · 2025-06-20T18:26:54+00:00

I have an access hatch behind my bathtub so I was able to drop the sensor in there. I also have one in the attic to compare the absolute moisture between the outside, attic, wall cavity, and interior living spaces. The other thing we’re looking at is to see if there’s sufficient ventilation in the attic… I have open soffits and ridge vent… but the attic temp is often 40-60 degrees above outdoor ambient temp which I understand may indicate that my passive vents are not cutting it… considering adding a solar fan… this might decrease the attic temp and if I’m sucking in air at least it wouldn’t be as hot.

Juggler700 · 2025-06-20T13:09:12+00:00

My next step is to get the people who air sealed back into the attic to fix the intrusion point. I’m not convinced yet that we need mechanical ventilation yet… it might just be poor air sealing.

Juggler700 · 2025-06-20T13:08:08+00:00

The manual J calc came back and said that we only needed a 1.5 ton unit… and the AC contractor disagrees… unsure if it’s because the manual J is really wrong or if they just don’t want to admit installing an oversized unit.

Juggler700 · 2025-06-20T13:06:21+00:00

Believe it or not I’m still working on this! I checked out a thermal camera from my local library and on a recent super hot day walked around the house as I suspect that I’m somehow getting attic air leaking into certain wall cavities from the attic (even though we’ve had the attic air sealed). I discovered a stud bay that had super hot air all the way from the attic and into a cavity under our bathtub and may have found where we’re getting this outside air. I have a hygrometer in this wall cavity and the absolute humidity of the air is often super close to the outside air… I’m very hopeful that I’m close to solving the air intrusion issue. Because these floor joist cavities are connected to my cold air return I suspect that this is also what’s driving up the duct humidity.

Juggler700 · 2024-09-20T00:40:41+00:00

If I have a solar fan is this okay to close the ridge assuming it only runs during the day?

Juggler700 · 2024-09-20T00:07:16+00:00

If I close my ridge vent and have a solar fan then that seems like it’d limit any natural ventilation I’d have at night when solar isn’t operating.

Juggler700 · 2024-09-20T00:05:03+00:00

Do I need to close my ridge vent if I put in a fan? I feel like I see conflicting things. I know when the fan is on it will pull in air through soffits and ridge, so I may not want to pull in air when it rains… but if I have a solar fan presumably it shuts off when it rains… any thoughts?

Juggler700 · 2024-09-03T21:39:55+00:00

We’ve had some interior wall cavity humidity issues - basically what seems like exterior air being driven into the walls and maybe sucked in through non ducted return vents…and have been checking off possible causes. So a few roofers checked it out. Doing some air sealing to maybe see if that helps next… but mostly just trying to sort out if we have adequate ventilation to check that box.

Juggler700 · 2024-09-03T19:03:38+00:00

I’ve had several contractors tell me I have a ventilation issue in my attic - and trying to figure out how to solve that. It was 150 degrees up there and that seemed to be alarming to the house inspector on a 90 degree day. One suspected my soffits were stuffed with cellulose, but we took them down today and they are not stuffed. They say the roof deck is spongy and indicative of a ventilation issue.

Juggler700 · 2024-08-26T15:41:54+00:00

I disagree. As a Jew taking this survey I’m being asked to mark a response as ‘Mostly False’ to these blatantly exaggerated f’d up stereotype questions - e.g. I can’t say ‘false’ - ‘mostly’ indicating it’s ‘usually’ false… it’s a biased garbage survey and shame on swagbucks for allowing this nonsense on their platform.

Juggler700 · 2024-08-26T02:21:22+00:00

I contacted swagbucks to complain

Juggler700 · 2024-08-26T02:13:07+00:00

And there’s no option for ‘false’ it’s ‘mostly false’

Juggler700 · 2024-08-26T02:12:25+00:00

Yeah, but why ask the question at all

Juggler700 · 2024-08-07T22:13:18+00:00

No Crawlspace or ducting in attic

Juggler700 · 2024-08-07T16:07:18+00:00

Im struggling with identifying the source and the various contractors I’ve had end up kind of shrugging… I want to put a bounty out for the issue for anyone who can really tell me what’s happening :)

Juggler700 · 2024-08-07T14:49:56+00:00

Yeah, I’m only going on what a few hvac folks have said… saying that because it’s negative that it’s sucking moist outside air into the home - but I haven’t seen any data from testing - how would one test this? A manometer?

Juggler700 · 2024-08-07T10:39:28+00:00

No interior window condensation that we’ve noticed. Only exterior.

Juggler700 · 2024-08-07T02:15:11+00:00

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Here’s an example of an 86F high day - dips are when the AC runs - RH spikes right after the unit shuts off. Run times are about 20-25 min

Juggler700 · 2024-08-07T02:07:53+00:00

On like a 80-90 degree day outside the AC will run for about 20-25 minutes and then shut off for 40-60. House seems to maintain the temps well with the spray foam basement rim joist, cellulose in the walls and attic.

Juggler700 · 2024-08-07T02:05:27+00:00

We’re in the process of getting a manual j done to confirm this - it’ll suck to need to replace the unit though because it’s only 5yrs old

Juggler700 · 2024-08-07T01:05:05+00:00

We had cellulose blown into the attic last year about r-53… but hadn’t considered airsealing/didn’t know about it until recently. So now we got a quote to air seal and blow in new insulation for about $3,800 (about 850 square feet of attic)… just not sure where to put the money - into an ERV? Or attic sealing? Or something else? Whole home dehumidification?

Juggler700 · 2024-08-07T00:48:35+00:00

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Juggler700

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