Condesation Roof Leak?

Radonguy

Hi,
I built this house about 5 years ago and have had a small leak occur usually about twice each winter. Today I get the dreaded call, the temperature is 20°F and about 4 inches of new snow fell today. It started leaking in late afternoon. This is one of the common patterns. The other will occur in late winter on the 1st really warm day. The leak appears very high up under a valley beam, it's at least 20 feet up from the eve.

The pitch on this roof is 14/12 and I have reroofed the entire valley a couple of summers ago. There is a continuous ridge vent and plenty of soffit venting. Up the valley where the jack rafters meet the valley beam the plans called for a 1" x 2" notch to allow for air to travel up along the beam to the peak.(I have often wondered if this was enough)There is no attic space, the cathedral ceiling is put together with 2 x12's with 2" x 2" nailed on top to allow for venting above the insulation.
The homeowner insists on running his furnace humidifier to stop the interior woodwork to reduce shrinkage.(floors, walls and ceiling are all wood). Thus he has runs the humidifier cranked on high all winter. His observation is the windows never get condensation on them so the humidity is to low and his wood floor develops spaces between the boards, so he leaves it running. Last winter he ran the furnace fan all the time which kept the humidifier running too. This year he let the fan only cycle with the furnace. We have just had about 3 weeks of cold weather below 20°F most nights were in the single digits.

So my question what happens to all this humidity? Would it be reasonable to conclude that it mostly rises up to the top of the 22 foot high great room at the center of the house. The ceiling is all tongue and groove siding and I'm sure there are plenty of leaks around this and I'm sure there are a couple of thousand nail holes in the plastic for the air to leak into the attic. Will discontinuing to use the whole house humidifier make a difference? Help! I ready to tell him to sue me and get it over with!

Best regards,
Val

Ed the Roofer

If he does not take your written suggestion, he should be responsible.

Hot moist humid air rises. When it meets a surface it can collect on, it condenses. 324 nails per square of roofing alone, not counting all of the T & G ceiling fasteners. The vapor barrier is penetrated throughout already.

Check out the buildingscience website for vapor transmission studies and ventilation articles for off the wall scenarios.

Ed

Radonguy

Thanks Ed,

Can you give me the link to the web-site you mention. And is this a common problem with whole house humidifiers?

Ed the Roofer

This is just one small portion of this massively informative website.

http://www.buildingscienceconsulting...sources/roofs/

Click on the other links on the left column to browse through a whole bunch more information, but I thought this page would be good to start with.

Here is the link to the main home page too:

http://www.buildingscienceconsulting.com/

Ed

Ed the Roofer

Here is another lengthy report with interior RH being discussed.

http://www.osti.gov/energycitations/...e/10186298.PDF

Ed

reveivl

I would adjust this to: "When it meets a cool surface it can collect on, it condenses.


I guess this ends the discussion about hot moist air sitting stagnant at the eaves due to 'short-circuiting' of the venting?

Bit of a thread-jack but I didn't feel that previous discussion ever went where it needed to.

__________________
From where does knowledge come? If you need to know what is in a box, you could ask someone (not reliable), you could pray, (not useful), you can consult with the scripture (not helpful) or you could open the box (science)

Ed the Roofer

I do not believe I ever stated that hot moist air sat stagnant at the eaves, regardless of the "short-circuiting" aspect.

In the OP's scenario, their is continuous ridge exhaust ventilation plus continuous soffit intake ventilation.

His 2 x per winter seasonal condensation leak calls seemingly are due to the additional humidity levels introduced by the home owner in an effort to thwart interior wood shrinkage.


You misperceive the affects of short-circuiting the entire attic ventilation system, as it relates to any discussion of this particular circumstance.


Ed

Tom M

Im surprised anything leaks on a 14 on 12. How can it even hold 4 inches of snow? Clearly that tight corner of the valley didnt provide enough area to insulate. There is probably little insulation packed into the tight acute angles where the rafters meet. Some furring and styrofoam would have help maintain the needed R-vALUE.

Radonguy

Tom you raise one of my suspicions about the valley since it's formed with 2 14" lam beams. They were wrapped in plastic but there is no insulation above or below the beam itself. Where the valley rafter meets the main ridge beam there is a massive joist hanger to carry the two valleys. This may be where the frost occurs.

The other thing that I have wondered about was snow getting through the Shingle 2 ridge vents. Thus forming a small pile that waits for a warm up to melt.

Grumpy

And so it begins... Every year about this time, the number of questions regarding roof condensation and ice damns is staggering.

It's been my understanding that 1x2" (as bought at home depot) is only 1/2" and not 1" or even 3/4" as other nominal 1" boards are. Manufacturers typically require 3/4" or more of free air flow beneath the roof deck. This may be a problem.

You say "plenty of soffit ventilation". Is the soffit vent continuous or spaced every few feet? If spaced every few feet that might be a problem, the intake might not be plenty.

Something else that caused me concern was how high he seems to be running his humidifier. This could definetly put undue stress on a roof's ventilation system. In addition, it's been my experience that sometimes these condensation "leaks", and I hate calling them leaks, go away when the humidifier is reduced to normal meters.

Why does this guy's floors experience such expansion and contraction? I have hard wood floors, no humidifier, and never a problem with gaps between the boards. That's the first time I heard of such a thing.

Radonguy

2" x 2" are placed on the 2" x 12" with styrofoam chutes on the underside of the roof deck. Sorry that was a misprint.

Tom M

This makes the most sense since warm air rises and condenses on cool surfaces. The cool surface is the one least insulated and creates the greatest tempature differential. There will always be moisture in any house where people shower and cook. Running the humidifier to reduce shrinkage seems like the exact opposite to me. Your sucking out the moisture in the lumber, floor joist shrink and the hardwood floor doesnt causeing creaking. This is going to happen the first 5 years for sure no need to speed it up.

I dont like ridge vent on roofs pitched over a 10. Personally I believe its a wind liability sooner or later, but I dont think the snowflake maintains its shape as it passes through a baffle. Water could be getting in and taking its time to roll down to the corner. Very possible. I wouldnt buy too much into this whole short circuiting thing. I have never had a problem myself. I also recently attended a mold, moisture and airflow seminar. The teacher had a PHD. He says they are finding new evidence that crawl spaces perform better without ventilation. Since ventilation can introduce moisture. He also said vapor retarders on wall insulation in mixed climates was is being proven to be a bad idea and might change the code soon.

Radonguy

So where would you start to identify where exactly the problem is?

thom

To add just a bit. I had a similar problem in one of my jobs years ago. I initially thought it was a roof leak. Fortunately I was able to get into the attic, I was hoping to look for a leak. What I found was the entire underside of the roof deck coated in 1/8" of shiney clear ice.

Every bit of moisture the guy puts into the house goes somewhere. Does he think that much water is being absorbed by the floor? It will flow through every gap into the attic. Even if the attic is vented, that moist air hitting a deck that is well below freezing will condense and freeze.

Look for any obvious leaks. Vent fans that are not ducted properly to the outside, including furnace and water heater vents.

Ed the Roofer

I absolutely agree with that.

It seems as if the HO is contributing to this condensation occurence.

Ed

oldfrt

This I have to disagree with!
I was in an unvented crawl space,working in a 2'high cavity, replacing insulation and sistering floor joists because of damage caused by moisture.
Thousands of carpenter ants,rotten posts ,and joists were like paper in some areas.
The house was only 9 years old.

As far as the matter at hand,
How is that valley done? Weaved?Open valley?

I got called back on a leaking valley(Half weave) once,where we found water was following the top of the shingle in the open side of the valley and running horizontally till it got under a shingle past the valley underlayment.The top of the shingle on the open side had not been cut back.
This usually happens on shallower pitched roofs,but I thought I'd throw it into the mix.

Radonguy

One side of the valley lays across and the other side is cut straight on top of the other, not sure what you call it. I dubbed the top corner of the shingles and caulked as well. The roof has never leaked during a summer downpour.

oldfrt

Some call this a California Weave around here.
If it doesn't leak in the summer,it's probably not the cause.

Real weird how it only appears on a couple occasions.

Probably have to control the use of the humidifier when this leak appears,and see if that makes a difference.
How long does the leak last?Does it stop when there is no longer snow on the roof?

Does the leak happen if there isn't any snow on the roof at all?
See what I'm saying,If it can't possibly be the snow melt getting in,you gotta concentrate on that himidifier.

Radonguy

It usually drips for a few hours and dries out by the morning.

There have been many snows without an occurrence, but the snow we had on Tuesday was 3-5 inches and no wind. The temperature never made it above 20°. I think it evenly coated the roof and the vents and trapped the heat under the roof enough to melt a little frozen condensation.

Another for sure bet will be the 1st 35° day in Feb. or March. I'm in Wisconsin by the way.

thom

I had that iced underside of the roof deck back when I worked in Chicago. That climate will do it.