I am about to have a new roof installed on a cape cape that has no eaves, thus no eave vents. It has 3 shed dormers, and a side vent at the highest point of the gable wall on each side. The roofer claims to get the manufacturers warranty, a ridge vent must be installed, but that make no sense in a cape cod with no eaves. He suggest a smart vent, but that will be a fair bit extra, and that will force the air through my insulation, as the house (built in the 50’s) does not have those foam channels that sit between insulation bats and the sheathing. Thoughts?
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a ridge vent, as I think you know, will only work if it has an in side for the air at the soffit. I'm at a loss for options, I know vented drip edge won't get you enough and you don't have the channel vents to allow it anyway.
I would be tempted to expand what you're doing if your budget allows and pull out the fiberglass insulation and spray in foam. Foam doesn't need venting so that would deal with that problem. You can pull off the sheathing in a patchwork pattern to get the fiberglass out and have them spray the foam from that side too so you don't bother the plaster inside. We did this on a cathedral ceiling when we had foam sprayed a few years ago. Depending on where you are, you might need to replace some or most of the sheathing anyway since it is not vented. If your roof is not vented, the moisture going through the plaster does a number on the sheathing. Also, the vapor barrier and what not gets beat if it isn't vented. Check with your state or the feds and see if you get get tax write offs on insulation upgrades that might pay for it completely or at least cut the cost down considerably.
Energy cost are probably going to stay the same or go up, so its something that will pay off quickly and after that its all money in your pocket. And if you plan on being in the house long term, the first spot to spend is windows, doors, insulation, heating/cooling systems, etc. Get the stuff that will lower your costs upgraded.
Edited 7/1/2008 10:58 pm ET by DDay
Foam doesn't need venting ....
Which comic book did that come from...?
Dinosaur
How now, Mighty Sauron, that thou art not broughtlow by this? For thine evil pales before that whichfoolish men call Justice....
I believe he is talking about a hot roof.
I haven't looked at a bundle, but does it really say the warrantee is void without ridge vent or is that a story?
I believe he is talking about a hot roof.
If that's the case, he should say so. (I don't believe in hot roofs, either, but that's because where I live, they don't work. In no-snow climates, I understand some people have had success with hot roofs.)
But stating 'foam doesn't need ventilation' baldly like that is very misleading. Assuming your goal is a cold roof, foam insulation needs to have vent channels above it just like any other insulation...because no insulation stops heat from getting through it; all any insulation does is slow down the heat transfer. It does not stop it happening.
That said, it's obvious that if you want the roof deck to stay cold, you have got to ventilate it to evacuate the heat as it leaks through the insulation. If you don't, you're gonna wind up with snow melt on the underside of the snowpack, and ice dams at the eaves. Not to mention condensation, frost, and spring showers in the attic.
I haven't looked at a bundle, but does it really say the warrantee is void without ridge vent or is that a story?
I haven't looked at a bundle recently, either, but I wouldn't be surprised to find such wording in the fine print. I don't count on a shingle warrantee paying off anyway, though, as there are so many conditions in those things that even a very good, conscientious roofer can hardly meet them all. Basically, I think of shingle warrantees as marketing yak.
Dinosaur
How now, Mighty Sauron, that thou art not broughtlow by this? For thine evil pales before that whichfoolish men call Justice....
it was not misleading, you just didn't comprehend it very well. Also, you vent a roof with fiberglass, blown in, etc. to get ride of the moisture, no the "heat".And using foam for conditioned attics do work in cold climates.
it was not misleading, you just didn't comprehend it very well.
If you want to teach, pal, you'd better learn the first aphorism of pedagogy before you start pontificating: "There are no bad students, only bad teachers." In other words, if somebody doesn't comprehend what you've said, it's because you said it badly.
Also, you vent a roof with fiberglass, blown in, etc. to get ride of the moisture, no the "heat".
I had just finished reading the BS article to which you provided a link in your other post, and I was preparing to critique it as there are several very basic problems with the unnamed author's fundamental thesis.
But if you understand thermodynamics so poorly that you really believe 'getting rid of' heat isn't what roof venting is all about, I can see I'd be wasting my time (and yours) discussing things at that level. We'd have to start back around Grade 8 General Science.
Dinosaur
How now, Mighty Sauron, that thou art not broughtlow by this? For thine evil pales before that whichfoolish men call Justice....
"In other words, if somebody doesn't comprehend what you've said, it's because you said it badly."Or in your case, you just seem to lack the ability to comprehend. I guess your the lab rat that, despite continued training just keeps gets shocked.You don't understand the subject very well, so that either speaks to your intelligence or how far behind your area of Canada is from the rest of us.
We generally try to avoid flaming around here. Even the Tavern stays pretty civil......
I was not putting you down, just trying to be helpful. I question the idea of a hot roof also, I guess we will see.
I have not depended on shingle manufactorers, since the time 25 years ago they refused to accept responsibility for a roof that failed to seal. I ended up paying my men to lift each shingle and seal each and every one. Since that time I buy shingles based on price alone.
I didn't think you were trying to put me down, bro. Furthest thing from my mind. Your suggestion that the guy who believes that nonsense about foam not needing to be vented was thinking 'hot roof' was a good one. I just thought it was important--especially for the O.P.--to point that out, since it wasn't made clear.
My problem with the 'hot roof' concept is two-fold, and can be summed up by pointing out the fallacies in the following statements from that 'Building Science' website article:
These two statements postulate unvented 'hot' roofs based on (1) sloppy application of thermodynamic laws, and (2) a philosophy of building houses based upon convenience and laziness rather than upon good design and workmanship.
1. In the first case, it is simply not true that the choice of venting or not is not determined by physics (specifically, thermodynamics). The physics of the roof's thermodynamic behaviour in relation to the rest of the building and to the environment in which it is sited will always dictate whether the structure will perform acceptably. A building code may say whatever its writers wish it to say; however they cannot change physics, and a code which permits a 'hot roof' in an environment where physics does not is a bad code.
Thermodynamics is too complex a subject to cover here in its entirety, but for our purposes only the following two facts need to be remembered:
I'm going to talk only about winter conditions in these examples. Roof venting is important in summer too, but for different reasons. Just remember, the heat tranfer rules don't change; the heat will still move from the hotter to the colder.
Building insulation, no matter how good it is and no matter what it is made of, does not stop conductive heat transfer. It merely slows it down.
In any heated building, some of that heat will 'escape' through the attic/roof insulation and warm up the roof deck if it is allowed to do so. The sole purpose of venting a roof is to evacuate that leaked heat to the outside air before it can transfer to the roof deck itself and warm it up. If a sufficient supply of cold, moving air is provided between the insulation and the roof deck, those leaking heat calories will be 'absorbed' by that air mass and moved out of the structure. If there is not sufficient cold air moving through that vent cavity--or if there is no vent cavity at all--the heat will transfer to the nearest colder object: the roof.
Putting more R-value between the heat source and the roof--or trapping warm air inside the building envelope--doesn't change this. Over time, all the heat inside the building will move through the insulation to the colder, outer air, until the inside of the house and the outside environment are at equal thermal potential. The amount of time this takes to occur is determined by the area of contact and the thermal conductivity of the interface.
This is important: Conduction heat transfer is measured as a function of time; the formula is:
HEAT FLOW OVER TIME = CONDUCTIVITY x (AREA/LENGTH) x ∆TEMPERATURE.
In other words, the higher the 'R' value (the inverse of 'conductivity' in the forumla), the slower the heat transfer rate. But to get that rate down to zero, the 'R' value would have to be infinity.
The only thing science knows which has an infinite R value is a perfect vaccuum. And they don't sell any of that at Home Despot (although there are times when you'd swear there was an unlimited supply of it between the ears of the floor staffer 'helping' you...).
Dinosaur
How now, Mighty Sauron, that thou art not broughtlow by this? For thine evil pales before that whichfoolish men call Justice....
Edited 7/5/2008 1:05 am ET by Dinosaur
2. In the second statement, the (unnamed) author of this article asks 'Why change a good thing?', and then goes on to attempt to justify exactly that by condoning bad design and sloppy building practise. It's too hard, he complains, to ventilate 'complex' roof structures containing 'multiple dormers, valleys, hips, skylights combined with cathedral construction with interior soffits, trey ceilings and multiple service penetrations'. So since it's so hard, well, just don't bother. We're scientists; we've got letters after our names that say it's okay; you can take that to the bank....
To my mind, that is a perfect, microcosmic reflection of the sickness from which human society has been suffering since 'do it right or don't do it' went out of favour (about the same time television came into favour). If it's too hard to do it right--or too expensive--well, then, don't re-design it so it can be built properly, just kludge up an easier, cheaper, lazy way to do it wrong instead.
What's really sick is that so-called 'building scientists' would put the stamp of authenticity on this nonsense and label it 'science'. I don't know who wrote that article--and I don't think I want to know, either--but science it is not. It is intellectual laziness; it is egocentric, non-functional design masquerading as architecture; it is fast-and-dirty workmanship based on flat-price bidding. It is all of those bad things and more...but it is not science.
Okay, that oughta be enough to put the fat in the fire. Over to you, Andy Engel....
Dinosaur
How now, Mighty Sauron, that thou art not broughtlow by this? For thine evil pales before that whichfoolish men call Justice....
I was not disagreeing with you. I have a hard time with the concept of a hot roof also.
OK, Dinosaur, just for grins here...
I have a typical cape. No overhang, so no eaves vents. Has the code mandated ridge vent. There are small, low gable end vents (no doubt nowhere near enough sq.ft. to match the ridge vent).
Knee-walls and floor in space behind knee-walls are well sealed & insulated .
Rafter space in the angled portion of the living space ceiling filled w/FG insulation.
Flat ceiling joists filled & overlaid w/FG.I'm in Buffalo. We get snow. The gutters fill with ice pretty early in the winter.Just for experiment, I pushed a section of plastic "air chute" up through one of the rafter bays, thinking I might improve cold air flow from the low "attic" space up to the real attic space & ridge vent. The immediate result was that the snow on the roof over that bay melted away much faster than on the rest of the roof....and I imagine contributed more to the ice damming.So, as I see it, I tried the current accepted practice, and it made things worse.
Just for experiment, I pushed a section of plastic "air chute" up through one of the rafter bays, thinking I might improve cold air flow from the low "attic" space up to the real attic space & ridge vent. The immediate result was that the snow on the roof over that bay melted away much faster than on the rest of the roof....
It sounds like the "low 'attic' space" you're talking about was a source of warm air instead of cold. I assume this low attic space was that area behind the knee walls.
You said that space was well sealed and insulated, but remember, that insulation won't stop calories from inside the heat envelope transferring through to the cold area behind the knee wall; it will only slow down the transfer. From the result you got, it sounds like the heat-transfer rate through your kneewalls & floors was high enough to melt the snowpack as soon as you gave the warm air from the kneewall space direct access to the underside of the roof deck.
To make venting in the sloped ceiling area work properly, it looks like you'd have to have inlet vents in the gable walls leading directly into the kneewall spaces. Or so I imagine, from your description. Correct me if I've misread you somehow....
Dinosaur
How now, Mighty Sauron, that thou art not broughtlow by this? For thine evil pales before that whichfoolish men call Justice....
"But stating 'foam doesn't need ventilation' baldly like that is very misleading. Assuming your goal is a cold roof, foam insulation needs to have vent channels above it just like any other insulation...because no insulation stops heat from getting through it; all any insulation does is slow down the heat transfer. It does not stop it happening."
And an interesting post to follow. But, it's not correct. Foam does not need to be vented.
Jeff
Under what conditions, and for what purposes does foam not need to be vented?
Dinosaur
How now, Mighty Sauron, that thou art not broughtlow by this? For thine evil pales before that whichfoolish men call Justice....
Under what conditions, and for what purposes does foam not need to be vented?
When it is not going to out-gas, for one.
Since this has sort of degenerated into hair-spliting, the foam needs no venting. The roof deck might. Code might require venting (even when contraindicated by local conditions), All sorts of conditions apply.
Like in the article you cite. It reads badly, and I fear that an editor skilled at verbiage but not the topic rendered it so. After going back through it again, it is my belief that the author meant to say, since labratory conditions are not achievable in the field in every condition, then, chosing a solution which can ba achieved, and achieved well, in the field can be selected, even when that is not at the ideal condition.
And no editor would let that sentence survive. Parsed into individual sentences, they run the risk of being cut for column length, let leaving the "bits" out changes the intent.
BUt, perhaps, I'm cynical about practice in th efield having watched the work on the house next door. They opened a former window and put in a french door, and replaced the kitchen window they brok prying the siding loose. They have removed a good half ot the siding in this work on this itty-bitty gable end. They have stuffed FG into the space between the frames and the framing. Mind you they have not felted nor insulated any of the open work--even though they are fully priming the new claps being installed. Leak-stopping the frames andnot the wall ought to cut down on drafts . . . Occupational hazard of my occupation not being around (sorry Bubba)
the foam needs no venting. The roof deck might
LOL.
Thanks for lightening this up, Cap.
(BTW, it wasn't me who cited that silly article; it was whassisname, the arts guy with the flamethrower who was science-deprived as a schoolboy. I was just doing a critique of his source for the benefit of the OP, who, after all, came to BT looking for information, not myths.)
Dinosaur
How now, Mighty Sauron, that thou art not broughtlow by this? For thine evil pales before that whichfoolish men call Justice....
An insult from some backwards Canadian? Wow, that hurts, lol. If I were to be offended, I guess I would just look at your picture and understand lifes been very difficult for you with such physical "issues".You don't need to be a hack builder, educate yourself so you don't look so foolish on your little soap box. I know you look like an homeless drunk or dirty caveman but even you can be slightly smarter than one.http://www.jlconline.com/cgi-bin/jlconline.storefront/4872a81f0222439e27170a32100a0605/UserTemplate/82?s=4872a81f0222439e27170a32100a0605&c=99bed6c24948e67882b7559f41b7f06d&p=1
The sole purpose of venting a roof is to evacuate that leaked heat to the outside air before it can transfer to the roof deck itself and warm it up.
This is not exactly true. The warm air that is being evacuated contains moisture. If it is not vented out, it will condense on the cold roof and rust out the shingle nails thus voiding the warranty and drip into the insulation (I won't go into truss uplift). This will not happen if there is a foam barrier in the roof rafters. This is why some say it is not necessary to vent a foamed roof (I do not agree).
You get out of life what you put into it......minus taxes.
Marv
Edited 7/7/2008 5:35 pm by Marv
The warm air that is being evacuated contains moisture. If it is not vented out, it will condense on the cold roof and rust out the shingle nails thus voiding the warranty and drip into the insulation (I won't go into truss uplift).
In the hot, humid Southeast, that moisture also causes rot--a lot of rot. As a young man, I was a roofer. I noticed that some roofs had long nails--those that were used for installing the sheathing--sticking straight up out of the roof. Something had backed the nails out. After many such roofs, I noticed a coorelation: every roof that had nails poking up through the shingles lacked gable vents. Ridge vents were rare in those days (1970s) where I lived. I think that the southern yellow pine sheathing got saturated with water, swelled and pushed the nails up. Also the rafters swelled and pinched the nails out.
Last year, I fixed this roof shown here. The lady lives behind me, about 100-ft. away. My roof, which has gable vents has no damage. Hers was rotted out from within. When she first called me, I went up inside the attic and the entire underside of the deck on the north side of the roof was wet.
By the way, how do you guys embed photos in the message?
Amazing. and so simple to vent.
Edit: Was it above the bathroom?
You get out of life what you put into it......minus taxes.
Marv
Edited 7/7/2008 8:32 pm by Marv
That roof is a perfect example of a little bit of science being a bad thing. The eaves on the roof are 2-ft. wide. Originally they had a lot of vents about 8-in. 12-in. with window screen on them. This system was not perfect but it provided enough air exchange to keep the underside of the roof dry. It worked tolerably well for over 30 years.
When the lady had Sears install the roof in the mid-nineties, they also installed "maintenance-free" vinyl on the underside of the eaves. They weren't worried about ventilation because they heard that ventilation is not necessary. That's what the building scientists are saying, right?
For this lady, who is in her 80s and living on a fixed income, no vents nearly ruined her. If I hadn't come along, she may have lost her house. I agreed to let her pay me in monthly payments over fifteen months. I also gave her a fairly low price for a job I really didn't want to do at the age of 57. She paid me off completely a couple of months ago. I was, literally, an answer to her prayers, She told me that she prayed to the Lord to send her someone who she could work with and He did. So, in a way, it was one of the most rewarding jobs I ever did.
I'm not saying unvented roofs can't work. They can. But they have to be detailed carefully.
Edit: Was it above the bathroom?
The worst section was above the bathroom. But the entire north side was so rotten it was dangerous to walk on. My foot went through a couple of times. I had to move slowly and feel for the rafters.
The sole purpose of venting a roof is to evacuate that leaked heat to the outside air before it can transfer to the roof deck itself and warm it up.
This is not exactly true. The warm air that is being evacuated contains moisture. If it is not vented out, it will condense on the cold roof
You are quite correct, and I'm pleased that you brought it up. I omitted going into that aspect in the interest of keeping the explanation simpler, and I shouldn't have.
It's true certain types of sprayed foam act as a vapour barrier, and in theory, if no water vapour can pass the foam, there should be none to condense out on the next cold surface.
But not all sprayed foam is vapour impermeable, and even if one is using foam which is, it strikes me as a pretty expensive way to trap warm, wet air inside your house. Especially since you have to get it out of there somehow anyway....
We could go from here into a completely different argument, the one about how 'sick house syndrome' is being created by the new tighter houses. Houses so tight they need mechanical ventilation (air exchangers) just so they can outgass the water-vapour produced in the normal process of living in them (breathing, cooking, bathing, etc.). Houses so tight they rot from the inside out instead of the other way 'round. Houses so tight, gyprock companies are introducing paperless gyprock to eliminate a food source for moulds we never saw in houses 30 years ago....
Dinosaur
How now, Mighty Sauron, that thou art not broughtlow by this? For thine evil pales before that whichfoolish men call Justice....
I take it you are not very familiar with foam insulation, with a comment like that. This article talks about it some but there is plenty out there on JLC and others that cover the topic.http://www.buildingscience.com/documents/digests/bsd-102-understanding-attic-ventilation/view?searchterm=foam%20insulation
New insulation would be nice, but would be costly. Old board sheathing is pretty forgiving in terms of ventilation or lack thereof. It sort of vents through the cracks, I think. If it ain't broke, don't fix it, unless you have other reasons for upgrading your insulation.
There may or may not be some truth in what the roofer says. Call the shingle manufacturer to find out.
In general principal, the shingle manufacturer's warranty is going to cover manufacturering defects, period. They don't cover consequential damages. Usually, the warranty is limited to replacing the product. The warranty isn't worth losing sleep over. If you have a roof leak, the company is going to blame the installer. At best, they'll send a factory rep out who is highly trained at finding installation errors. Unless you have Jesus himself shingle your roof, there will be installation errors, from the shingle companies view anyway. Ain't worth the paper it's written on IMO.
There have been some warranty claims in the past, but I think it usually involves some type of class action.
Thanks all:I read the Certainteed warranty and it is rather vague. It asks for "adequate venting" as detailed in the install instructions. I find it hard to accept that Certainteed thinks I should rip off perfectly good sheathing, install channel vents and smart vents to get their warranty. I suspect Marson is correct in that they will find something else wrong with the install anyway.If I were going to go to all that trouble, I'd install foam everywhere, but I am not looking to spend that kind of money. I think I'll ask for no ridge vent and not worry about the manufacturer's warranty.
They do have ventilated drip edge. Sounds like it may not work in your instance though because the rafter bays are probably blocked anyway. OTOH, if the rafter bays were not blocked the vented drip edge might work well if used in conjunction with the ridge vent. Do you know what size the rafters are and how thick the insulation is? IE - I imagine there are knee walls on the 2nd floor with attic storage areas behind them? If so what do you see when you go in there?
I'd discuss the exact terms of the warranty with the roofer and see what he says. Really, the ridge vent wouldn't hurt anything. Might be a waste of money though if you have no intake vents at the eaves.
I think in your situation, you should do everything you can to guard the roof from ice-dam damage than insulation or warranty. There is not only the stick-on membrane, you can also have an electrician install ice melting cable on the roof as well as in the gutter.
My roof story is out of about 40 bundles, about 1 bundle of shingles began to either blister or begin to show signs of blister. I bought these from Homedepot. I contacted the roofing company directly and I was given a certificate for replacement. When I actually tried to use the certificate, the problems began. Usually the problem was about who has the record, who has the authority and even where the record went to. They make it as time consuming as possible. I was lucky in that one employee of the HD took it on herself to track the replacement process. It took more than a month of trying, but eventually I was given the replacement roofing.
I think if you find deteriorating roofing within a year of installation, you are more than likely to get some promise of replacement but they'll make it very hard to follow through. Even without the vented roof, your roofing will last long enough, and even in best vented roofs you can't realistically get the full promised protection. I read in this forum somewhere that if roofing says 25 years, you may get 15 to 20 years. If you wait out full 25 years, you may actually get worse damage, should the roofing fail at that point. If roofing becomes brittle, it should be replaced. Hope this helps.
"...even in best vented roofs you can't realistically get the full promised protection. I read in this forum somewhere that if roofing says 25 years, you may get 15 to 20 years. If you wait out full 25 years, you may actually get worse damage, should the roofing fail at that point."
That does not square with my experience. This fall I'm going to replace a roof I installed in 1980 on my parents' house on the coast of Maryland. It's a basic, black three tab shingle roof. IIRC, the shingles had a 15-year warrantee. It has never leaked and there is no damage to the roof structure as viewed from the attic. It is ventilated with roof-mounted vents. There is no ridge vent.
I moved into my present house in Durham, North Carolina in 1990. The basic, three-tab shingle roof was not new when I moved in. It is doing fine. It has gable vents and no ridge vents.