Roof decking condensation.

Background: Foreclosed home. New England (Connecticut). House has been winterized. The outside temperature is about 25-30 degrees in mid January. Dewinterized for maybe a week. No heat noted on second floor of a 2-story home.

Problem: Heavy moisture (total wet/soaked) noted in the attic on the underside of the roof deck (half the way up). Water droplets on the insulation (attic floor insulated). Client said a “structural engineer” took a look (about 2 weeks after the inspection) and said this was common in a foreclosed home. It is condensation.

Is he right?

No, he is not right. There should never be condensation on the underside of the sheathing. Even if the second floor was heated, the heat would not transfer to the attic area becuase of the insulation. Sounds like a ventilation issue. What year was the home built? Got pics? Why would a structural engineer be looking at condensation in an attic? Was there somehting wrong with the trusses? Why not a roofing contractor? Just imagine that condensation damaging the sheathing and causing fungal growth. FYI, if the insulation is “wet”, it should be replaced.


Do you have any pictures?

Being common in a foreclosed home may be true; still doesn’t make it right.

So, what was the ventilation and insulation like ?

Thanks for your help!

Go here for pictures

To answer Rob:

I called for a structural engineer for the basement. Columns and beams were everwhere. This house in built in the 1700’s.

The client girlfriend’s said he was a structural engineer. He was possible a roofer as I suggested. Yet to be determined.

To answer Bob:
Ventilation included a ridge vent, sofit vent, and roof fan.
Insulation was noted on the attic floor (and yes some facing the wrong way)

I aggree with ccurrins. Something is not right here. The decking was wet. Not just damp.

In cold climates poor ventilation means condensation. Happens every time. Funny, a foreclosed home would probably have less codensation since no one is living in the home. No cooking, showering, breathing, fish tanks, etc. Maybe even no heat.

I agree it sounds like ventilation . Look at the basement I expect it is damp .
I think you are getting too much air into attic from the home .
Look for attic entrance Look for a hole from basement into attic like opening beside the chimney .
Look for open plumbing vent in attic How about Kitchen ,bath, exhausting into attic .
It could too much air leaving the attic causing stack effect pulling air from the home .

I just repaired a water leak on the roof of one of my rentals. The source was a few nail pops that allowed water intrusion. It is not cold down here but the moisture pattern on the sheathing was the same as in your pictures. Could be a combination of poor ventilation and a leaking roof. I would take good look at the roof over the wet areas.

Roy: I am going to re-arrange some of your post…

"I agree it sounds like ventilation (yeah too much for this house situation and attic!!). It could too much air leaving the attic causing stack effect pulling air from the home . (right on) I think you are getting too much (MOIST) air into attic from the home.

Look at the basement I expect it is damp.
Look for attic entrance Look for a hole from basement into attic like opening beside the chimney .
Look for open plumbing vent in attic How about Kitchen ,bath, exhausting into attic .


Here’s a short excerpt from the above document…

[FONT=Trajan-Regular]***What to do about *a wet attic

[/FONT][FONT=AGaramond-Regular]There are many signs that an attic is wet. Prolonged wetness will rot out
the roof sheathing. Often this is first noticed when re-shingling. If you
have ceiling leaks only in the spring, it may be that ice has been forming
on the sheathing all winter and it suddenly melts when a warm spell
arrives. You may see water stains or evidence of mold on the sheathing,
rafters, or trusses when you are inspecting the attic. You may find
the insulation has been packed down or stained by water or ice. The smell
of a moldy attic will enter the house under certain weather conditions,
usually in summer.

***The usual response is to increase ****attic ventilation. This is the wrong *approach. In some cases, adding ventilation will actually pull more moist house air up into the attic and make the problem worse. The best way to fix a wet attic is to stop air movement from the house. Once this is done, the existing ventilation is usually more than enough to keep the attic dry.

It is important to stop air leaks because a heated house is much like
*a chimney. Both a house and chimney are containers of warm air surrounded by cold air. Both tend to draw air in at the bottom and expel it at the top. All winter, a heated house is trying to push air through the top**floor ceiling into the attic. Block up those air leaks and keep the warmth *in the house to save both energy costs and damage to your attic.

My analogy to putting more venting (read: “holes”) in the roof is a boater with water in the bilge…

Solution: Drill a hole in the bottom of the boat to let the water out…doh!!!

I’ve worked on a number houses where owners had “wet” houses for a number of reasons and, of course, wet attics. (the last one was a week ago). You have got to control the water produced in and by the house (usually basement or crawlspace).

Where do you think the water condensed as moisture or frost on the roof sheathing came from? Except in some rare, mostly coastal situations, the condensed water was in the house and got up into the attic as invisble vapour with the leaking warm house air…(Hey! didn’t we pay to heat that air and now we’re letting it escape EASILY…how smart is that?)

Roy’s right on the money. Air movement will carry moisture. Condensation is caused by warm air meeting cold air. I would recommend air sealing and insulation before more ventilation.

Condensation is caused by warm, moist air contacting a cold surface…like when a person’s glasses fog up after they enter a house in the winter.

Warm air meeting cold air will only mix and come to an intermediate temperature but warm, moist air meeting cold air should form fog, clouds, rain etc.!!

If the house is winterized (no heat on same) then with proper roof ventilation there should not be an imbalance in temperature to the extent you have fiberglass insulation saturated… sounds like a ventilation problem to me.

There can still be air leakage from the basement to the attic caused by (1) wind conditions creating negative pressures in upper levels of the house and (2) stack effect in houses caused by air temperature differentials. If the house sat at 40F for a week or so with no heat on, a cold snap of 10-20F or lower sets up chimney or stack effect with the warmer (than outdoor air) interior air rising to the attic.

If no one is living in the house producing moisture, where is it coming from??

Adding heat, does not change the amount of moisture in the air (it only allows a greater amount of moisture capacity of the air). The dew point temperature does not change with the addition of sensible heat.

My analogy on this is; when you have an issue such as this, you need to address the source of the issue not the issue.

Adding ventilation in the attic (where it is stated that several sources of ventilation are currently installed) will work. However is it really necessary to put a 4 x 4’ agricultural ventilator fan in the gable? If you move enough air, fast enough you’ll prevent condensation on the roof. You will also be sucking all the air out of the house.

The water under the roof is coming from latent heat in the air. It’s your job to locate where this latent heat is coming from. It can be coming from either interior or exterior of the house. What were the previous weather conditions to this inspection? I get condensation in my barns and shop all the time when climatic conditions change (because there is no heat in these buildings). If I prevented ventilation in these buildings, I wouldn’t get condensation.

Latent heat in the air comes out of the air in the form of condensation when it comes in contact with an object below the dew point temperature of that air.

Building envelope leakage is most prevalent in homes of this era. A test should be conducted to evaluate the building envelope.

The house was just winterized one week previous. Somebody could’ve dumped the hot water heater in the basement and it is just now drying up. High temperature and high vapor pressure will move towards the attic if there is a passage opening.

The house is vacant, so you don’t have to worry about occupant activities adding to moisture (such as taking showers, cooking etc.).

Your job should be quite easy. Just find the source of latent heat and block the passage to the attic.

If the moisture is coming from the exterior, this is just a temporary thing and there is nothing you can do about it. Adding more ventilation will make it happen even more.

Adding additional ventilation is not the appropriate remediation for this issue.