Need advice on removing humidity from attic
First time poster, had a question about reducing humidity levels in my attic.
About 3 years ago, I had my attic and basement rim joists air sealed, and cellulose insulation blown into my attic to R49. Fast forward to now, and recently I noticed a 1-2 sq/ft area of my roof caving in. Went into the attic to inspect, and it doesn’t appear that the affected area is leaking (no water spots, insulation underneath area feels dry). Called roofer for estimate to repair, and the guy explained that excessive moisture in the attic could cause the sheathing to bow.
Went into the attic some days later to inspect the damaged sheathing for water leakage after a snow storm, and noticed light frost on the sheathing and nails. So, I put a weather meter in the attic to measure temperature and humidity levels. For the most part, temps/humidity match outside weather conditions +/- a couple degrees and humidity percentage. Inspected the bathroom fan (vented out of roof) and reinforced the insulated ductwork with foil tape around the connection point to the roof exhaust box.
My attic has gable, ridge, and power fan venting, but NO soffit venting.
There doesn’t appear to be widespread mold that I can observe; just a few dime size spots of white mold here and there.
Which finally brings me to my question: how can I reduce the humidity levels in my attic to acceptable levels? And, since the attic is supposedly air sealed, how much of an influence will the outside temp/humidity have on the attic space?
Right now, adding soffit vents isn’t an option. So, what can I do? Currently, I have a box fan running up there just to keep air flow moving.
Having an energy audit tomorrow, in the hopes that the blower door test may be able to identify spots in the attic floor that may have been missed during air sealing.
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Replies
Make sure you don’t have areas of stagnant air. You really want soffit vents with a ridge vent. I’d check to see if any of your vents are short circuiting other vents. Ideally you want cross flow through the entire attic which is likely to be difficult with the vents you currently have.
Bill
Bill,
Right now, soffit vents aren't really an option due to cost. I have vented, aluminum soffits installed on the house; problem is they appear as if they were installed over the original soffit of the house (ranch style, located in PA, built early 60s). If I understand the process correctly, it would require removing the gutters, fascia, metal soffit, cutting holes in original soffit, and then removing insulation around the soffit area and installing rafter baffles.
So, what I'm trying to do is find a (more) effective way to get air flowing through the attic with the existing systems I have in place.
Hi Grave461.
If you have ridge vents and a power vent and no soffit vents, and if you have a leaky ceiling, the air exhausted from those vents is likely pulling conditioned air from the house into the attic. The ceiling should have been air sealed before the insulation was installed, but may still need to be done to remedy this problem. Here are two articles that may be helpful: How to Insulate an Attic Floor and Air Sealing an Attic.
Also, there are some options for intake vents that may be less work. See this article for ideas: Venting a Tricky Old Roof
That was a pretty interesting read, thanks for sharing it.
The insulation company did air seal the attic floor prior to blowing in the cellulose. My initial thought is perhaps a few places were missed.
I'm going to await the results of the energy audit to see what they say.
As far as the under shingle vents, I was offered a similar solution by a contractor, which involved installing 4-5 slant back roof vents, approximately 2ft from the bottom edge of the roof; in effect acting in a similar fashion as a soffit vent, but instead pulling air in from under the eave, it's pulling air in from above the roof.
Get yourself one of those solar powered attic vents. Some of them have thermostats some don't. It may help with winter time air flow and summer time exhaust.