condensation in attic

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Permalink Reply by David Meiland on February 10, 2013 at 9:20pm

>>attic floor has been sealed and all known penetrations from conditioned space to attic have been sealed

Is this what the owner stated, or something that you inspected? 

>> attic has five soffit vents in front and 5 in back

Standard recommendation would be to add ridge vents and possibly remove hat vents.

>> homeowner keeps a humidistat in attic as humidity sometimes runs above 80%

What does the humidistat control?

This sounds like a typical moisture investigation. Is the basement damp? What's the story with the ductwork? What are moisture levels in the house? Do they have a humidifier? Are the bath fans correctly ducted out? It can be hard to figure out the exact cause in one trip, and it may have multiple causes.

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Permalink Reply by Dwayne M Petko on February 11, 2013 at 4:34am

I inspected attic floor early in process and it was decent then.  Since this point homeowner covered attic stair, sealed around exhaust fan and sealed bypassess from front porch to attic.

I did not mean to say humidistat, he has a remote humdiity sensor monitoring levels.  

there is no ductwork in attic, moisture in house is around 50%.  moisture in basement is a little high (don't know reading)  ducts you saw in attic were for bathroom fans.  

there are baffles protecting the.  House is very normal except the turbines.  not sure if they are proper or not.

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Permalink Reply by Bud Poll on February 11, 2013 at 2:03am

Hi Dwayne,
In addition to Davids comments and questions:

The three aura vents on top of roof are listed as turbines with a NFA of 113 in² each. However, being turbines they can act as exhaust fans under windy conditions which could be pulling moist air out of the remaining leaks from the house.

We do not know the total soffit vent NFA of those 5 front and 5 rear vents. The balance between high and low on a traditional attic should favor more NFA to the soffits to keep the ▲p across the ceiling as low as possible. Is the 6.6 referring to the house or attic and exactly what is it?

Is this a traditional attic with front and rear soffits at the same height, rear is not in view from the photo?

Humidity readings need to include the temperature to tell us the moisture content. We should also have the readings from inside and outside the house.

Is that flex duct in the attic a supply vent for the heating system? It looks like it is not at its best and should be checked for leakage.

I don't see baffles to keep the insulation away from the soffit vents. May be there, just can't see them.

An infrared inspection could help to locate the heat/moisture source into the attic. Do you have IR?

Where is the dryer venting? If to the outside is it well clear of the soffits? Generally, moisture being pulled in through a soffit will create a more localized condensation issue. This house looks like the problem is uniform all over. Is it?

We assume the moisture is not coming from the outside, thus as David asked, how is the house doing, temp and RH and if high, where is the source.

I'll stop there.

Bud

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Permalink Reply by Kari Sauder on February 11, 2013 at 9:06am

I'm reading this discussion with interest and agree that it could be more than one water source or venting issue -- I'm just adding that in the picture of the house there is a good size water source in the backyard near the house (the pool) and if the prevailing summer wind for the site is blowing across the pool and into the back of the house, the attic soffit vents (and the open windows & doors, if any) on that side may be catching the extra humidity.  I guess this would be answered by a close examination of when the humidity is worst in the attic -- just pool open season or is rainy spring and fall bad as well.

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Permalink Reply by Dwayne M Petko on February 11, 2013 at 5:27pm

thank you for the suggestion, I had not considered the pool.  condensation (sometimes frost)is during the winter months as well.  I do not know if the pool is covered or drained during the winter months, but I can find out. 

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Permalink Reply by Kari Sauder on February 11, 2013 at 6:22pm

---while you're checking on the pool -- how about leaks (or excessive splashing)  into the surrounding ground making the basement damper.  The question would be, do they have to top off the pool often to keep the water level up.

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Permalink Reply by Kari Sauder on February 12, 2013 at 6:13am

while we're discussing gross water infiltration...I took another look at the house picture and have another question...how's the drainage off the roof?  The land looks pretty level and if the down spouts don't have extentions or if the gutters aren't functioning well...A rain event of say 1" on that size roof can yield hundreds of gallons of water at the foundation.  Couple that with soil that has a high clay content or a basement wall that is not sealed well and you get the picture...  swimming pool in the basement not the backyard.

The basement of every house we've reno'd has had an improvement in the dampness level by just making sure the gutters, downspouts, extentions and site grading was functioning properly.  I like to say, "build a roof in your yard".  Your grading (5% slope) away from your house is a must.

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Permalink Reply by Bruce Navin on February 11, 2013 at 1:03pm

As I understand it, the homeowner did the airsealing. Was a blower door test with IR completed after the sealing? And the points made regarding soffit baffles and a ridge vent are also good points. 

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Permalink Reply by Kari Sauder on February 11, 2013 at 2:31pm

I agree on the soffit baffles -- my 1990's ranch has blown FG installed in the attic and vented soffit -- they used faced FG from ceiling joist bays bent up to the rafter bays to chorral the blown FG and rafter mates on underside of the roof deck and ridge vent so there's great airflow and no moisture problem.

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Permalink Reply by Eric Kjelshus on February 11, 2013 at 7:04pm

What is the RH of the House?   What is the RH out side   I have seen a water leak up the RH 40%  -   I saw a roof leak next to condenstat line dump 4 gal a day into the home.    I have seen dryer vent into attic  and rot all the plywood in attic.    I have seen water/plumbing back up in craw space run all the way to attic and frost on nails.    Must find the water 

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Permalink Reply by Dwayne M Petko on February 12, 2013 at 1:36pm

I will ask for a record from homeowner.  I think he is keeping records of temp and humidity.  we have eliminated all sources of water into attic except moisture in basement (not excessive water) just basement dampness. 

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Permalink Reply by Bud Poll on February 12, 2013 at 7:19am

Hi Kari,
Since I see you pay attention to details, in my northern climate (Maine), not sure where you are, but we have to add a bit more to the slope adjacent to the house. Depending upon the soils, frost can lift the soil 6" or more about two feet from the foundation. Next to the foundation, the heat from the basement holds the frost down. What looks like a generous drainage slope in the summer can turn into a trap that drains everything from the roof down along the foundation wall, which remains unfrozen all winter. If you have ever seen some of the old homes up north, they will often have a berm up against the foundation that drops a foot or more about 3 or 4 feet out.

Bud

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