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No Roof Venting


Mike Lamb
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This modified bitumen roof has no venting of any kind. There are cathedral ceilings throughout the whole interior except for two bathrooms and a hallway. My major concern is trapped moisture in the rafter cavity and heavy icing. The house is 60 years old. It occurs to me they might have installed mod bit because of ice damming.

There is no way for me to know how well the ceiling is insulated and sealed. My guess is the roof is 3 to 5 years old with no signs of moisture issues inside. There is no insullation on top of the roof sheathing. I'm not so sure on how to report this. Building Science suggests that venting doesn't do a lot with moisture issues but a JLC article says continuous ridge and soffit venting is the way to go. How would you report?

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Jim,

I may have mis spoke/typed, I was referring to some turtle caps. Not a continuous ridge vent. I see that pitch as similar to a manufactured home, which has turtle caps installed.

Actually, I was referring back to Mike's original reference to "continuous ridge & soffit vents."

You're right about the similarities to a MH. But I'd be very wary of advising someone to cut holes in a perfectly good roof to fix a moisture problem that might not exist. I've seen lots of shallow-pitched, unvented roofs that never had a problem with moisture, including the roof over my own kitchen.

If I were in a particularly risk-averse mood, I might recommend some discreet surgery to allow me to view the inside of the cavity to determine whether or not the existing arrangement was allowing moisture to accumulate.

Roof venting just isn't a well understood science and doesn't yield predictable enough results. If what's there works, I say let it be.

- Jim Katen, Oregon

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I don't understand the choice of modified bitumen on a roof surface with that much slope but in any case the underside of the roof deck should be ventilated. I would include a comment in the report that this vital ventilation is absent. I would add to this comment what the reasons for it are and what the consequences might be if it's missing. Finally, I would look for signs of moisture intrusion for additional findings. If I were to make a recommendation on it, it would be 'further evaluation by a qualified roofing contractor. I wouldn't want the liability of suggesting a course of action on this unusual type of roof construction. Leave that liability to the roofer.

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Hi,

I agree with Jim; we see low-slope roofs covered with modbit all the time here and plenty of them aren't vented and we're known for our somewhat less-than-dry climate. I call 'em B52 ramblers because the pitch is about equal to the wing droop you'll see on a B52.

I've squeezed my butt into a lot of those 12 inch deep 50 year old roof cavities and inch-wormed my way along the entire length of those things and only found moisture issues in a few circumstances. Don't know why.

Like Jim said, performance isn't predictable. A peek above the drywall in a couple of places might be in order but unless you can identify an issue you might be making a mountain out of a molehill.

ONE TEAM - ONE FIGHT!!!

Mike

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but in any case the underside of the roof deck should be ventilated.

Says who? How many flat roofs have you seen ventilated? what if they sprayed the underside with foam insulation, would it need ventilation then?

I would include a comment in the report that this vital ventilation is absent.

Who says it's vital?

I would add to this comment what the reasons for it are and what the consequences might be if it's missing.

Marc, if somethings missing, and you really think it should be there, then advise the client to remediate the missing whatever. There's no need to explain it. If anyone asks, explain it then.

Finally, I would look for signs of moisture intrusion for additional findings. If I were to make a recommendation on it, it would be 'further evaluation by a qualified roofing contractor.

Like the roofer that screwed it up to begin with? Marc, you should be fully capable of rendering advice for moisture in attics. If any investigating is needed, you're the best man to do it.

I wouldn't want the liability of suggesting a course of action on this unusual type of roof construction. Leave that liability to the roofer.

Don't try and cover your butt. Do what Jim Katen preaches, think in terms of covering your clients butt, and then yours will be covered.

Chris, Oregon

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OK,

Ventilation is not necessary beneath an insulation level (foam on underside or top side of roof deck.

Say that there is some air space between the ceiling and roof sheathing. Say there is a fiberglass batt insulation installed between the sheathing and ceiling level. Assuming you can't see into this cavity, or barely can see in, are you guy's advocating ignoring this in this scenario?

I thought that ventilation not only helped with moisture removal (when designed properly in my climate), but helped with energy conservation as well?? PS: I'm ready to read any studies you can throw at me...[:-slaphap

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OK,

Ventilation is not necessary beneath an insulation level (foam on underside or top side of roof deck.

Say that there is some air space between the ceiling and roof sheathing. Say there is a fiberglass batt insulation installed between the sheathing and ceiling level. Assuming you can't see into this cavity, or barely can see in, are you guy's advocating ignoring this in this scenario?

I'm just suggesting that it might not be wise to recommend putting holes in a roof that's probably never had them and that probably doesn't need them. I'm not sure about how they worked in Mike Lamb's area, but around here, those houses would have originally had tar & gravel covers and no vents through the roof surface. I've inspected a bunch of them, and I can't remember any that had condensation issues.

Come to think of it, I have seen some of these houses with tiny little gable-end vents (if you can call that a gable). But I doubt that they did much to remove moisture. The "vents" usually consisted of a few 1-1/2" holes drilled through the siding.

I thought that ventilation not only helped with moisture removal (when designed properly in my climate), but helped with energy conservation as well?? PS: I'm ready to read any studies you can throw at me...[:-slaphap

Perhaps. There's conflicting information on that point. The current science seems to show that the ventilation reduces the temperature of the attic in summer, but the ventilation also tends to draw air from the house into the attic. That, in turn, draws more outdoor air inside. The outdoor air contains a high level of moisture and increases the overall cooling load by a greater amount than the attic ventilation reduces it. This results in a net increase in cooling costs.

As far as I know, the best reference material on the subject to date is by William Rose. Chris turned me on to his excellent book, "Water in Buildings." Check it out.

My personal belief is that attic ventilation is a chaotic system that's difficult, or maybe even impossible, to accurately predict. More than any other system in a house, attic ventilation is one where I tend to place great trust the sleeping dog paradigm.

- Jim Katen, Oregon

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I wouldn't be too excited about the condition unless there were a bunch of can lights perforating the ceiling. I'd also be very sure that any mechanical vent actually exhausted to the exterior.

In any case, I'd urge the buyer to gain physical access to the space or ask the seller to allow moisture testing (for an additional fee) 1/8" probe holes are easily filled.

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Original quote by Chris Bernhardt:

Like the roofer that screwed it up to begin with? Marc, you should be fully capable of rendering advice for moisture in attics. If any investigating is needed, you're the best man to do it.

I'm not the best man to do everything, Chris. Don't want to be. Just want to be the best home inspector.

When I'm wearing my home inspection cap, I don't wear a roofer's cap, framer's cap or builder's cap though I've worn them before and many others too. I wear just the home inspector's cap on that job because those are the only liabilities that I'm willing to assume at that moment. I do use every bit of knowledge that I have to come up with a report that paints a picture of the condition of the dwelling that is as precise as possible for my client. That, for me, is a challenge because there is so much that I cannot see when the house is completely built.

Of course, everyone's entitled to do business as they wish and I still learn from a lot of people who participate in this forum.

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With a great enough delta T, this would be an excellent place for a thermal scan.

As far as adding ventilation goes, I'm with Jim. I've said this many times before, ventilation needs to be designed by someone other than the roofer or the siding guy, all too often these guys bang nails 'cause they aren't smart enough to run the cash register at a burger joint.

Tom

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I'm not the best man to do everything, Chris. Don't want to be. Just want to be the best home inspector.

When I'm wearing my home inspection cap, I don't wear a roofer's cap, framer's cap or builder's cap though I've worn them before and many others too. I wear just the home inspector's cap on that job because those are the only liabilities that I'm willing to assume at that moment. I do use every bit of knowledge that I have to come up with a report that paints a picture of the condition of the dwelling that is as precise as possible for my client. That, for me, is a challenge because there is so much that I cannot see when the house is completely built.

I understand. Many of us get started in this biz worrying about controling liability; you can't control liability. Thinking in terms of your liability is like walking a tightrope looking down and saying to yourself "I hope I don't fall!"; it's a recipe for disaster. Instead change the perspective to covering the clients ass; only then and only then will yours be covered.

It's a myth that whatever contractor you want to punt the client over to is going to be smarter than you, understand the problem better than you and cover the clients ass better than you. If you were to really follow what happens when you punt, you'll find that most often either nothing is done or the wrong thing is done.

I'm very interested in black attics and have been studying them for a while and I can tell you there aren't any roofers around here that have a clue.

The best source on the subject of moisture in buildings is William B. Rose. Get his expensive book - Water in Buildings. Google his name and download other more recent articles written.

Chris, Oregon

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I'm not the best man to do everything, Chris. Don't want to be. Just want to be the best home inspector.

When I'm wearing my home inspection cap, I don't wear a roofer's cap, framer's cap or builder's cap though I've worn them before and many others too. I wear just the home inspector's cap on that job because those are the only liabilities that I'm willing to assume at that moment. I do use every bit of knowledge that I have to come up with a report that paints a picture of the condition of the dwelling that is as precise as possible for my client. That, for me, is a challenge because there is so much that I cannot see when the house is completely built.

It's a myth that whatever contractor you want to punt the client over to is going to be smarter than you, understand the problem better than you and cover the clients ass better than you. If you were to really follow what happens when you punt, you'll find that most often either nothing is done or the wrong thing is done.

Chris, Oregon

Roger that. Well said.

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Yes. Well said. Be the expert, because there aren't many out there to refer folks to, especially roofers.

Here's what else I know for sure about flat roof venting.

3 1/2 years ago, I inspected a condo building for a buyer, a big hitter litigator for a large law firm. The flat roof lacked vents. I said there should be vents. The architect, 2 engineers, the builder, the insulation contractor, and the roofing contractor all said I was an idiot. Flat roofs don't need venting.

I indicated that there were a half dozen mfg's. all making vent systems for flat roofs, the NRCA shows various vent considerations, and if it wasn't necessary, why were these folks making vents and the NRCA showing their use...(?)....

The customer eventually sided with all the experts, and decided I was a crank. In fact, he allowed as to how he was sorry he engaged my services. I was crestfallen.

This Spring, I got a call from the guy, asking if I remembered him and my roof vent recommendations. I said yes. He said that's good, because the entirety of plywood roof sheathing was mulch due to condensed moisture rotting it from the inside out. He sent pictures, and basically, the plywood is mulch and the cellulose insulation is paper mache.

He, and the rest of the association, are suing the developer for about $2 million. I'm now the go to guy for the entire law firm because I stuck to my guns about unvented flat roof assemblies.

Unvented assemblies, such as this roof structure, can condense amazing amounts of water. When you have a 5degF ambient outside and a 68degF unvented roof structure, you can get water. Not necessarily, and not always, but you sure as heck can.

There's any number of vents that would work on that roof; yes, they would require some additional dinking around to get them right.

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I've got a concern with cutting in inspection access holes and then sealing the holes. If I recommended that approach, I would recommend providing permanent access holes so that the area could be monitored. Maybe there won't be any signs of moisture issues during the inspection because a single person lives in the home, controls moisture levels, etc. What happens when the house gets rented out, and renters don't control moisture levels? What wasn't an issue could suddenly become an issue.

I have, and will continue to recommend ventilation be added above any ceiling insulation level to cover my butt, if for no other reason. I do enjoy seeing others takes on the subject. Maybe the answer lies in how the house/ structure is to be used?

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I've got a concern with cutting in inspection access holes and then sealing the holes. If I recommended that approach, I would recommend providing permanent access holes so that the area could be monitored. Maybe there won't be any signs of moisture issues during the inspection because a single person lives in the home, controls moisture levels, etc. What happens when the house gets rented out, and renters don't control moisture levels? What wasn't an issue could suddenly become an issue.

I have, and will continue to recommend ventilation be added above any ceiling insulation level to cover my butt, if for no other reason. I do enjoy seeing others takes on the subject. Maybe the answer lies in how the house/ structure is to be used?

Wisely said. I took some heat a few years ago because a guy sold a house I'd looked at three years previously, and the buyer's inspector found moisture problems in the attic. Nothing awful, but there definitely was some yuck.

Turns out the seller--my former client--was a missionary or something similar and had as many as fifteen people, primarily teenagers, living in the +/- 4,000 sq. ft. house at any given time. I think that's what caused the problems, but of course it's tough to be certain. I do know the attic was pristine when I checked it out, and the only thing that changed was the amount of bodies scurrying around beneath the roof and taking 1.5 showers per day.

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Consider

http://www.buildingscience.com/document ... ull_view=1

Wood Pitched Roof Construction

Building Science Digest 115: last updated 2009/08/10

By John Straube.

Bolds are mine.

Figure 4 describes the most common assembly geometry that results in a cathedral ceiling. In this case a ventilation space is kept above the insulation to provide a path for ventilation airflow between the ridge and soffit. This system often experiences performance problems in cold weather since the rate of ventilation is often quite small (due to the friction with the sides of the small space, the length of the run, the high probability of misplaced batt insulation blocking flow, and the many areas on roofs that do allow direct connections between the ridge and soffit). If air can leak outward during cold weather (i.e, an air barrier is not provided, or it has been breached by a light fixture, interior partition wall, etc) the ventilation gap provides an easy means of exiting the roof system. In this scenario, the ventilation of the roof encourages the outward flow of indoor air and encourages significant amount of condensation that cannot easily be subsequently dried.

As usual, he's got the physics right.

My only problem with that is it doesn't nail down actual performance scenarios. I see identical townhomes all the time; one has problems, the other right next door doesn't. There's other variables beyond what Joe takes into consideration. (Like 15 teenagers.)

And, stuff can dry out. Maybe not "easily", but it can dry out. I've seen wet attic conditions dry out. I've seen condensation problems with flat roofing be corrected with ventilation.

If this was a brand new joint with OSB and engineered lumber, then it's a problem. If it's a 60's place with 1x6 roof sheathing, it usually isn't.

I think this particular house should have some deep probe testing in the middle of winter to see what's what. It's only a couple little holes in the drywall, and it's easy.

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. . . My only problem with that is it doesn't nail down actual performance scenarios. I see identical townhomes all the time; one has problems, the other right next door doesn't. There's other variables beyond what Joe takes into consideration. (Like 15 teenagers.)

Yes, and that kind of stuff just isn't predictable. The variables are too complex. That's why I called it chaotic in an earlier post.

In the future, we have to move away from venting our roofs.

- Jim Katen, Oregon

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