When the roof was replaced did they add a ridge vent? I have a customer who had major condensation damage because the new ridge vent pulled air through the gable end vents and not through the soffit vents. The area of the roof below the gable vents was coated with frost, the sheathing had mold and the insulation was wet.
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mellow
Resident Stove Connoisseur
Interesting to know, I had a ridge vent cut into mine when the new roof was put on last year. I will have to check into this and make sure the same thing is not happening to me, how did they fix it so air came from the soffits?
I do not agree with the comment about the gable end vents short-circuiting the ridge vents. Its a common misconception by people who do not understand air flow. Its also a big problem in areas with significant snow. Unless an attic is poorly ventilated and warmer than the outdoors, ridge vents can and do get covered with snow and that negates any air flow through them until the snow melts them off. I have observed my ridge vent covered with snow and effectively blocked for weeks some winter. Gable end vents on the other hand ventilate all the time. They do on rare occasions let snow into the attic which is pretty easy to solve but builders want to save bucks and a vented ridge is quicker and cheaper.
Warm air rises, cold air sinks. Vent a ridge does not create a suction in the attic, all it does is allow hot air a path to go outside to where its cooler. The trade off is that the paths to the outside are somewhat restricted by the material used. In my experience with a home that started out with gable end vents and was equipped with vent a ridge later, on the attic temps did not change. Note that many homes had gable end vents and soffit vents vastly undersized and the approximate square area of the soffits should equal the ridge or gable venting.
Ice damming is caused by the overhang being colder than the main portion of the roof over the attic space. Framing details also factor in, the standard approach to framing a roof rafter is to notch it to set down on the top plate of the wall. Its quick and its strong but if you draw up the detail you will see that heat from the conditioned space down below gets transferred through the top plates directly into the soffit space with far less insulation. This makes the area above the outer wall under the sheathing warmer and that causes the beginning of ice damming. Some folks try to stuff insulation in this area but then air flow through the soffits is blocked and any moisture from the house that gets up in the attic does not vent well. Eventually the attic gets warm and snow melts a bit higher up on the roof and ice damming starts but this time it leaks in higher up the roof. I see in some cases the builder went with one row of ice and water shield and there is an obvious drip line at the panel seams right where the ice and water shield stopped. Proper vents that convey cold soffit air up against the roof help but the best approach is to go with a more advance framing technique that opens up the area between the top wall plate and the roof. Dams are built at the end of the ceiling joist bay with sheathing and then the attic insulation is extended out over the plate with a gap between the insulation in the roof. The alternative is go with a "cold roof" where layers of foam are installed on top of the roof sheathing. any heat in the attic just never gets up to the roof deck to cause ice damming. The fairly effective compromise is Ice and Water shield under the shingles or metal roofing all the way up the roof. The product seals the roof so even if ice damming occurs it just does not leak into the roof sheathing. The tradeoff is it can still form large icicles and rip off gutters but at least water is not dripping down into the ceiling and out the light fixtures.
If someone in a snow zone does not have gable end vents and has to deal with blocked ridge vents, a vented cupula on the roof will make a big difference. Just make sure the vents are higher than the potential snow pack. Like a gable end vent, fine blowing snow can sometimes get in past the louvers and screens so a flat plastic lined tray larger than the opening should be installed below the opening so that any snow that does sneak its way in drops down into the tray and eventually melts or sublimates.
Warm air rises, cold air sinks. Vent a ridge does not create a suction in the attic, all it does is allow hot air a path to go outside to where its cooler. The trade off is that the paths to the outside are somewhat restricted by the material used. In my experience with a home that started out with gable end vents and was equipped with vent a ridge later, on the attic temps did not change. Note that many homes had gable end vents and soffit vents vastly undersized and the approximate square area of the soffits should equal the ridge or gable venting.
Ice damming is caused by the overhang being colder than the main portion of the roof over the attic space. Framing details also factor in, the standard approach to framing a roof rafter is to notch it to set down on the top plate of the wall. Its quick and its strong but if you draw up the detail you will see that heat from the conditioned space down below gets transferred through the top plates directly into the soffit space with far less insulation. This makes the area above the outer wall under the sheathing warmer and that causes the beginning of ice damming. Some folks try to stuff insulation in this area but then air flow through the soffits is blocked and any moisture from the house that gets up in the attic does not vent well. Eventually the attic gets warm and snow melts a bit higher up on the roof and ice damming starts but this time it leaks in higher up the roof. I see in some cases the builder went with one row of ice and water shield and there is an obvious drip line at the panel seams right where the ice and water shield stopped. Proper vents that convey cold soffit air up against the roof help but the best approach is to go with a more advance framing technique that opens up the area between the top wall plate and the roof. Dams are built at the end of the ceiling joist bay with sheathing and then the attic insulation is extended out over the plate with a gap between the insulation in the roof. The alternative is go with a "cold roof" where layers of foam are installed on top of the roof sheathing. any heat in the attic just never gets up to the roof deck to cause ice damming. The fairly effective compromise is Ice and Water shield under the shingles or metal roofing all the way up the roof. The product seals the roof so even if ice damming occurs it just does not leak into the roof sheathing. The tradeoff is it can still form large icicles and rip off gutters but at least water is not dripping down into the ceiling and out the light fixtures.
If someone in a snow zone does not have gable end vents and has to deal with blocked ridge vents, a vented cupula on the roof will make a big difference. Just make sure the vents are higher than the potential snow pack. Like a gable end vent, fine blowing snow can sometimes get in past the louvers and screens so a flat plastic lined tray larger than the opening should be installed below the opening so that any snow that does sneak its way in drops down into the tray and eventually melts or sublimates.
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After removing all the insulation and treating the mold on the bottom of the osb sheathing she had 6" foam screwed to the bottom of the rafters from top plate to ridge, continuous soffit vent and closed of the gable end vents. Essentially turning the attic into conditoned space.
Hi everyone,
Been a little while since I updated you all. I've tried various things but nothing really worked. I went up there and looked through some of the...questionable...insulation. I believe I found the main culprit. Half of the insulation (majority under the problem areas) don't have vapor barriers. Just drywall, insulation then open attic. I've replaced some but need to buy more and will have to slowly replace over time. I did notice that during Thanksgiving when there is a lot of cooking (think steam) going on the attic got really wet. I think this has to be the main problem. In the mean time while I am replacing, I will add a fan that exhausts out the gable on the problem side that reads humidity levels.
Wish it was a cheaper fix but there is some relief in (hopefully) finding the problem. Thanks to everyone who has shared!
Been a little while since I updated you all. I've tried various things but nothing really worked. I went up there and looked through some of the...questionable...insulation. I believe I found the main culprit. Half of the insulation (majority under the problem areas) don't have vapor barriers. Just drywall, insulation then open attic. I've replaced some but need to buy more and will have to slowly replace over time. I did notice that during Thanksgiving when there is a lot of cooking (think steam) going on the attic got really wet. I think this has to be the main problem. In the mean time while I am replacing, I will add a fan that exhausts out the gable on the problem side that reads humidity levels.
Wish it was a cheaper fix but there is some relief in (hopefully) finding the problem. Thanks to everyone who has shared!
Is the drywall in good shape and painted? That should be a vapor barrier.
Before I blew insulation into my ceiling I’d get those damp spots. I found they were cold spots. In my case it was condensation.
A few years ago I got a spot where the finish plaster decided to separate from the gypsum board. That was a roof leak.
Before I blew insulation into my ceiling I’d get those damp spots. I found they were cold spots. In my case it was condensation.
A few years ago I got a spot where the finish plaster decided to separate from the gypsum board. That was a roof leak.
EbS-P
Minister of Fire
I’m not sure you need a vapor barrier. Never seen one installed.
Two things, drywall isn't perfect and there are small cracks here and there in the ceiling. Not wide cracks but they are there. And by vapor barrier I mean the insulation didn't have that paper moisture block on it. Just the insulation, and some of it was R9 instead of R30!
EbS-P
Minister of Fire
Vapor barrier ie Kraft paper insulation is not air sealing. If you are getting condensation it is most likely due to air movement. Kraft paper won’t fix that.
You need to air seal with foam and caulk.
Lowes used to provide the machine for free if you bought the bags of cellulose. Messy job.
Ashful
Minister of Fire
I've always read that insulation is one of the few jobs as cheap to hire out, as to DIY. Not sure if that's still true, but it did appear to be the case for at least some types of insulation on larger projects in the late 1990's and early 2010's, the two times I really looked into it.
It probably still is. The insulation companies buy it in such bulk that their costs are low. They also do a lot of it so they are fast and have the right equipment.
There’s a huge difference between the insulation blowers you can rent at Home Depot and the ones professionals use.
There’s a huge difference between the insulation blowers you can rent at Home Depot and the ones professionals use.
I helped someone do a house once with "free" blower, it was piece of crap, we had to rewire it as the strain reliefs on the cables were and had been loose. We ended up sending someone to rent a pro one.
The pro one had a lot of pressure. The owner had a closet with an outlet cut out that had never been used. When he went around he found a closet full of shoes and clothes nicely insulated with cellulose
Lol, I can see that happening! We have a small blower, only blows a ton an hour, and can control feed rate and blowing speed.
I ran the big blowers for a bit when I was getting my business started and their hoppers are about 4 feet wide. We'd dump a 20 foot box truck full of cellulose in a couple hours. They were blowing the attics of apartment buildings. I'm sooo happy I dont have to feed that beast anymore!
Cool Machines CM 1500 CM1500-1 Insulation Machine
www.netzerotools.com
I ran the big blowers for a bit when I was getting my business started and their hoppers are about 4 feet wide. We'd dump a 20 foot box truck full of cellulose in a couple hours. They were blowing the attics of apartment buildings. I'm sooo happy I dont have to feed that beast anymore!
To close out the mystery for those who are interested:
The wall /roof where the issue is ultimately stemmed from some airflow near the gable. Not quite sure how or why, but when the fireplace was running, there was a massive amount of warm humid air getting into the attic through separation between the indoor plywood and the exterior wall. Not sure why there was this gap directly under the gable, but now that I have sealed it and put and exhaust fan for good measure on that side I haven't seen the issue since.
The wall /roof where the issue is ultimately stemmed from some airflow near the gable. Not quite sure how or why, but when the fireplace was running, there was a massive amount of warm humid air getting into the attic through separation between the indoor plywood and the exterior wall. Not sure why there was this gap directly under the gable, but now that I have sealed it and put and exhaust fan for good measure on that side I haven't seen the issue since.
Thanks for the update. Hope the fix has the issue permanently solved. The real test will be when the temps are in the teens.
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