Hello,
I wanted to see if it was possible to have TOO much exhausting ventilation inside an attic? Inspecting a standard home built in 2003 and sized at 1,739 Sqft. located in NW Arkansas. There are 8 turbine vents present for the attic space which is more than I’ve ever seen on a home of this size. (Soffit Vents for Intake Air). Please see photos attached. (Normally on a house this size I only see 3-4 max)
There was a concern with high humidity levels inside the home where excessive moisture was building up on the windows and dripping off. (Lots of Water Build-Up Inside the Home on Window Glass) causing damage to the window sill and mildew developed. Not sure if this is related to the attic ventilating too much?
Thank you for any input.
What were the temperatures (inside vs. outside) when you were there?
Those look like pretty cheap / builders grade windows.
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What did it look like around the scuttle hole? Same question around can lights if there were any.
It looks reactionary to some kind of previous problem.
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You have an unbalanced attic ventilation system that creates excessive negative pressure in the attic. Attic ventilation should be balanced; output at ridge or turbines equals intake at soffit vents. The negative attic pressure is pulling makeup air from somewhere - probably the house proper. This results in excessive AC and heating costs.
Moisture on windows: Does the AC “short cycle”? It should run enough to reduce the home humidity along with cooling the home. Oversized AC results in short cycling which does not reduce home humidity. That might be the source of your window condensation. I believe the desired cycle is 15/20 minutes. I don’t deal with AC much, mostly heat and 15/20 minutes is the desired heat cycle.
These are my inconclusive observations and insight.
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What’s your weather like right now in this area? A quick Google search turned up about 40 F. in Arkansas today. You have excessive humidity in that home for sure. I don’t usually see condensation on widows like that until we get near 0 F.
Does the home have an air exchanger, and was it working? Whole home humidifier? How many people living there? They need to get the home (not the attic) ventilated better, or reduce the amount of moisture being produced.
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Thank you for the input. I might just state what I oberseved and recommend further evaluation by a HVAC guy. A/C was not running/tested since it’s winter time. Outside temp was 35 degrees and the heat was set around 68 degrees inside the home. Not sure what the average cycle is inside the home since during the inspection that is not something observed or noted. However, your answer was helpful. Thank you!
Ryan,
Thank you for the reply. Todays temp was 35 degrees and the inside thermostat was sent to HEAT 68 degrees. air exchangers are not common around here and I don’t ever see them in our area on any houses. Also the same for a whole home humidifier. Very rare to see around here. But thank you for the words of advice and trying to help. It was a family of 6 as far as I could tell. Bathroom fans observed inside attic were exhausting to the soffits. Only windows with moisture build up were the primary bathroom and bedroom. (Mildew in corners makes me think it’s been happening for awhile and not just today.) I might just state what was observed and recommend further evaluation by HVAC guy. Thanks for your help!
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When inspecting the attic ventilation it is important to also look at the air intake, not just the exit.
Was the soffit vent continuous or not?
According to leading building scientists, 2/3 or more of the nFVA (net free vent area) should be in the soffit and 1/3 or less at the ridge. This is so that the negative pressure that Michael Sentry mentioned does not occur and suck air out of the home.
We can’t answer if the turbine vents are excessive unless we know the soffit situation.
At a minimum, you should have 1ft² of roof ventilation for every 150 ft² of attic space. Turbine vents come in different sizes. If each of those in your picture are about 1 ft² then you probably have more than enough nFVA at the ridge. It might be too much if the soffit vents are not twice as much nFVA.
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Way Too Much exhaust ventilation. The home’s pressure will be unbalanced. It is likely the cause of the exhaust venting.
Typically, for every 300 square feet of attic space, ‘that is equipped with a vapour barrier,’ you install one vent, or double it for vapour barrier less attics.
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It looks like the blown insulation is covering the soffit vents. If that is the case, then the turbine fans are just sucking air out and almost creating a vacuum in the attic. Also, placing all of those vents next to each other is begging for a roof leak. Generally, the vents, and a gooseneck vent would have been fine, are on each section of the roof. Over the garage, for example.
When we reroofed our home, we added an additional 4 vents, 6 total…and I had the laborous task of removing the batts insulation which was covering all of the soffit vents…now our attic doesn’t get above 85 degrees in the summer…
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that makes sense
Now what if those were static roof vents instead of turbines? would they be “pulling” anything? wouldn’t they only allow as much exhaust as was let into the attic, without affecting the living space?
Being winter the AC isn’t running (and short cycling or doing anything else) and outdoor humidity is likely not very high. If this is just in the primary bed and bath the most likely explanation would seem to be showering without the bathroom fan on and that hot steamy humidity hitting cheap windows in the two connected rooms.
The draft seals on the windows are likely worn out. Many people seem to be averse to bathroom fans for some reason, or if it’s a big master suite the fan may not effectively pull out the humid air.
I’ve seen this same phenomenon in old high rise condos that lack powered bathroom vent fans. Ceiling paint is often flaking or alligatored as well.
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I don’t see too much ventilation as an issue, or capable of being the issue. Stagnant moisture causes the issues, not moist but moving or dry but stagnant air. Think crawlspaces, which have the same venting requirements. You have some with no skirt and others with the 150:1 (sometimes less) openings. The no skirt is better from a moisture control standpoint because it eliminates potential for buildup.
Most codes consider drywall a code approved air barrier. So the only affect would be soaking into the ceiling drywall, but the readily moving and highly ventilated air ensures the inside attic behaves like outside the attic (I.e. No moisture escalation and any present is allowed to dissipate; no buildup).
To me it looks like cold weather condensation. The interior is the hotter and more humid and the window is the condensation surface. Heaters do not dehumidify spaces, so evaporation has to go somewhere. If excessive maybe call it out, or if single pane windows or envelope breach contributed.
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My guess is the thermostat is set back to a very low temp at night allowing the windows to get cold as well as the moisture exhaled by the occupants at night, when warmed by the heat condensates on the cold surface.
The extra attic ventilation maybe a knee jerk response to that. My .02
Window treatments and heat vents under the windows cam be a factor.
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Was there a humidifier installed and turning on with the furnace? If there was, did you notice the setting it was on?
IMO you can get a stack effect from a low atmospheric pressure outside which of course would include the attic, but I wouldn’t think it would be enough to cause all that condensation on the windows.
Something else to consider is how much cooking they are doing, how often they are running the DW, doing laundry, how many are taking showers/baths, etc… Many things can contribute to a high moisture content in the home, and the more people living in the home usually will mean more moisture.
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