Condensation in Roof cavity

Started by TV • 10 replies • 1297 views

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TV (Washington)
Posts: 122

Posted:

does anyone have experience with condensation in a roof cavity; 12" tall

we have replaced roofs, but there is a 12" tall roof cavity under the roof that condensation from units collects in.

this condensation is very bad, and the "rafter" bays under the roof have "baffles", and the rafter bay runs are not continuous.

how can we fix this condensation issue with out replacing the newly installed roofs?

BobD4 (up north)
Posts: 1,002

Posted:

Your battle with inadequate venting or obstructed venting within the mildly pitched roof, will be critical as you know. If bathrooms/kitchens other moisture sources have been vented into that space, watch out. You may need professional advice and to add effective additional mechanical venting to the internal roof cavity.

MelissaP1 (Alabama)
Posts: 13,836

Posted:

I agree with Bob. I would also go to Ask This Old House website for some videos and advice. Does this issue happen year round? Is it at winter? Has it been ongoing? Why did the roofer not discover the issue while re-roofing? I know when got mine re-roofed they did an inspection to tell me what boards were "soft" or needed replaced.

Next time make sure have someone not just go to the top but the attic. See if there was issues there as well. Everything does flow down. This may NOT be a roof problem so be prepared. It could be improper venting which will require a Plumber. That would be the next person to call unless it could be associated with air flow. That issue then need A/C expert.

Isolate the cause is the most important. You all may be best to hire a general House Inspector than individual experts. They could provide the right expert to go to.

Former HOA President

TimB4 (Tennessee)
Posts: 21,059

Posted:

TV,

Are all the units vented properly (that is to say, vented to the outside)?

When I purchased my home, being code at the time, the bathroom vents only went to the ridge vent. They never exited the attic. Until I reran those vents to the outside (I took mine through the eves), I had condensation and even ice forming on the rafters.

TV (Washington)
Posts: 122

Posted:

the units/buildings were built in 976, and at they time they were built to be vented to outside via vents thru the roof cavity

the condensation is huge issue, even after new roof, added vents, replacement of common area laundry vent fans and fan timers

the roof cavity collects moisture from somewhere; units vent to outside and/or common area laundry vents

i am looking for some guidance on a fix.. perhaps someone has dealt with this issue before?

we had consultants design roof, and "improve" air flow from rood cavity, but original condensation issue still exists from basic design in 1976

TimB4 (Tennessee)
Posts: 21,059

Posted:

Are the vents insulated?

If not, you may be getting condensation from the radiated heat (especially from a dryer vent).

TimB4 (Tennessee)
Posts: 21,059

Posted:

You may need to seek help within a DIY forum (as suggested by others).
Perhaps this can be of assistance as well:

Causes and Cures of Attic Condensation and Roof Ice Damming Problems A housing fact sheet from Cornell University.

Basically, you need to identify where the warm air is coming from.
This will require some time in the attic on a cold day.

It can come from radiating heating, improper venting, improperly sealed penetrations into the attic (from the ceiling or the roof).

Once identified, the steps are simple:
1) stop the leak (insulation, rerouting vents, caulk).
2) Ensure there is enough ventilation (are the eave vents blocked by insulation (mine were)), perhaps adding an attic fan.

That's the sum of my understanding of the issue and how I addressed a similar issue within my home.

JohnC46 (South Carolina)
Posts: 14,265

Posted:

Quote:

Posted By TimB4 on 02/05/2017 7:10 AM
You may need to seek help within a DIY forum (as suggested by others).
Perhaps this can be of assistance as well:

Causes and Cures of Attic Condensation and Roof Ice Damming Problems A housing fact sheet from Cornell University.

Basically, you need to identify where the warm air is coming from.
This will require some time in the attic on a cold day.

It can come from radiating heating, improper venting, improperly sealed penetrations into the attic (from the ceiling or the roof).

Once identified, the steps are simple:
1) stop the leak (insulation, rerouting vents, caulk).
2) Ensure there is enough ventilation (are the eave vents blocked by insulation (mine were)), perhaps adding an attic fan.

That's the sum of my understanding of the issue and how I addressed a similar issue within my home.

Sound advice.

TV (Washington)
Posts: 122

Posted:

this is NOT a home attic

it is a 12" roof cavity below a flat roof

NOT a space of size to fit into.. has baffles also

this is a real challenge

TimB4 (Tennessee)
Posts: 21,059

Posted:

The process is the same.
The problem is your available height to crawl into the area.

Unfortunately, you may need to tear up that section of the roof or, look for someone (or some roofing company) that can fit into that area.

JeffT2 (Iowa)
Posts: 880

Posted:

Here are some links I have found useful on this topic. These guys love figuring out this stuff. It's called building science. In addition to articles, you can post questions. You may need to get some closed-cell foam up there to seal off indoor air from getting into that space. Let us know how everything works out.

http://www.greenbuildingadvisor.com/blogs/dept/musings/all-about-attic-venting

http://www.greenbuildingadvisor.com/blogs/dept/musings/how-build-insulated-cathedral-ceiling

You can also check out the articles on www.buildingscience.com

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