Roofing and Roof Ventilation

A ridge vent (continuous roof vent cap) should work very well. You also need to make sure there are vents in the eaves to supply air. Then the air will flow into the eave vents, up along the inside of the roof space, and out the ridge vent. I had a ridge vent installed several years ago and it helped a lot with condensation problems I was having in my attic.

Thank-you very much for your input, do you think the idea of adding 2x3's in a cross format would benefit also, allowing cross ventilation. Is there any way to calculate how efficient both of these solutions will be. Trying to estimate the prolonged life I will get on the shingles.

You'd really need to talk with a roofing expert to answer those questions.

First let us make sure we understand what you are describing. You are using 3-tab shingles on an expansive virtually flat (1/6-in-1) rooftop. Underneath a vault-style, rock ceiling is attached to 6-by rafters. It is not stated whether two roof decks meet at a ridge, or if it's a building extension where the "flat" roof meets a wall or the eave of a higher pitched roof.

You also did not say what the failure mode of the shingles is. Are they deteriorating (as in losing granules), curling or lifting, or blowing off? (Typically, blow-off would be a virtual certainty with 3-tabs--even fairly new ones.)

Let's start at the top and work down. There can be little doubt that shingles, especially three-tabs, is a poor choice on such a low-pitched roof, and the problem is made worse by use of 3-tabs, which have poor durability--even poorer wind resistance--even under the best conditions. So your starting point is to begin using different roof material. A cheap alternative is a roll roofing designed specifically for such an application. (Check with roofer for the best and less than best types.)

I can see little advantage, if any, for going to all the trouble to install ridge vents in your situation...unless the cavities above the ceiling are totally devoid of insulation...and any other obstruction such as cross pieces to stabilize the rafters...in which case, if you go with ridge venting, you will be unable add any insulation other than flat panel insulation...which will probably requre removal of the roof deck. You would also need to install soffit vents at the eaves, or the ridge vents will be to no avail. (I am not sure if gable vents would be an answer since you have no attic; and for the same reason roof top vents (turbines, dormers, eyebrows) probably won't work either....but that's why your thinking of ridge vents anyway, I would guess.

A somewhat more expensive, but much more durable choice would be to install a membrane roof with granular cap sheet for appearances. There are torch downs and cold process varieties available. A mop down, multiply is also conceivable. With this, you will not be facing frequent replacement, only infrequent inspection and maintenance--say, every ten years or so, depending on climate conditions. Or, in place of a granular cap sheet you could mop on a reflective cold process coating to reflect heat away from the roof. This would have the advantage of allowing you to do the upkeep if you wished....say, brushing on snow roof or similar product when the roof starts to show excessive wear or leakage.

The best, and most expensive solution would be to install a single ply PVC roof membrane such as an IB roof. This is a system that is totally impervious to moisture penetration, even under standing/pooling water. It is installed with a fibrous blanket underneath to permit air circulation between roof membrane and the roof deck (and felt). It can optionally be installed with insulation underlayment. Standard installation is warranted, for the life of the building, against any tearing, water penetration, or winds up to gale force. AS an added option, the installation can be specified for wind resistance up to near hurricane force winds. Choosing the white option will yield almost total solar reflection, thus keeping the ceiling cavities and the room space well cooled. There are also installations which will allow for construction of a roof top deck on top of the IB roof. The IB roof also is installed with a maintenance free perimeter facia which also includes drains and down spouts designed (and guaranteed) to be self clearing/clogproof. Cheap? No. But considering it's the last repair of reroof you wil ever need, it would prove far less costly that replacing a roof every few years, or every 10-20 years as with even the premium kinds of standard roofs. This was the solution I opted for with a probably worse, near flat roof situation...and have complete satisfaction now for almost eight years. And I figure if I sell the house, the IB roof will command a price premium exceeding the installation cost...because the warranty is assignable.

Posted again with revisons as the web site is having processing problems.

First let us make sure we understand what you are describing. You are using 3-tab shingles on an expansive virtually flat (1.6-in-1) rooftop. Underneath a vault-style, rock ceiling is attached to 6-by rafters. It is not stated whether two roof decks meet at a ridge, or if it's a building extension where the "flat" roof meets a wall or the eave of a higher pitched roof.

You also did not say what the failure mode of the shingles is. Are they deteriorating (as in losing granules), curling or lifting, or blowing off? (Typically, blow-off would be a virtual certainty with 3-tabs--even fairly new ones.)

Let's start at the top and work down. There can be little doubt that shingles are a poor choice--probably installed originally only to cut costs--on such a low-pitched roof, and the problem is made worse by use of 3-tabs, which have poor durability--even poorer wind resistance--even under the best conditions. So your starting point is to begin using different roof material. A cheap alternative is a roll roofing designed specifically for such an application. (Check with roofer for the best and less than best types.)

I can see little advantage, if any, for going to all the trouble to install ridge vents in your situation...unless the cavities above the ceiling are totally devoid of insulation...and any other obstruction such as cross pieces to stabilize the rafters...in which case, if you go with ridge venting, you will be unable add any insulation other than flat panel insulation...which will probably requre removal of the roof deck. You would also need to install soffit vents at the eaves, or the ridge vents will be to no avail. (I am not sure if gable vents would be an answer since you have no attic; and for the same reason roof top vents (turbines, dormers, eyebrows) probably won't work either....but that's why you're thinking of ridge vents anyway, I would guess.

A somewhat more expensive, but much more durable choice would be to install a membrane roof with granular cap sheet for appearances. There are torch downs and cold process varieties available. A mop down, multi-ply is also conceivable. With this, you will not be facing frequent replacement, only infrequent inspection and maintenance--say, every ten years or so, depending on climate conditions. Or, in place of a granular cap sheet you could mop on a reflective cold process coating to reflect heat away from the roof. This would have the advantage of allowing you to do the upkeep if you wished....say, brushing on snow roof or similar product when the roof starts to show excessive wear or leakage.

An even better--and more expensive expensive solution would be to install a single ply PVC roof membrane such as an IB roof. This is a system that is totally impervious to moisture penetration, even under standing/pooling water. It is installed with a fibrous blanket underneath to permit air circulation between roof membrane and the roof deck (and felt) and keep the wood dry. It can optionally be installed with insulation underlayment. Standard installation is warranted, for the life of the building, against any tearing, water penetration, or winds up to full gale force. As an added option, the installation can be specified for wind resistance up to hurricane force (100mph) winds. Choosing the white option will yield almost total solar reflection, thus keeping the ceiling cavities and the room space well cooled. There are also installations which will allow for construction of a roof top deck on top of the IB roof. The IB roof also is installed with a maintenance free perimeter facia which also includes drains and down spouts designed (and guaranteed) to be self clearing/clogproof. Another virtue is the relative quickess of installation--typically a day or less including tear off. Cheap? No. But not prohibitively expensive either. And, considering it's the last repair of reroof ever needed, it could prove far less costly that replacing a roof every few years, or every 10-20 years as with even the premium kinds of standard roofs. This was the solution I opted for with a probably worse, near flat roof situation...and have complete satisfaction now for almost eight years. And I figure if I sell the house, the IB roof will command a price premium exceeding its installation cost...the warranty is assignable.

CowAnon - i just got a quote for an IB roof and was rather surprised with the price. It sounds like you have had a good experience with it and hope you don't mind a few additional questions.

- do you live in the south (TX coast here) and have you noticed any difference in cooling or heating costs

- what pitch does your roof have, I have a 2/12 tar and gravel that is probably from the 70's.

- what sort of price per sqft did you end up paying (if you don't mind) - this quote came in at 2x for other applications.

thanks

Dear finnadat,

Don't mind at all answering your questions. Overall I have been very pleased with the IB roof...in fact intend to get more on another flatish portion of the house. My house is located in the Central (Sacramento River) Valley (between coastal range and Sierra Nevada. The climate is "Mediterranean" by which is meant, long, hot, dry summer seasons and cool, wet winters; whereas Texas is wet summer, dry winter. Highest temperatures here are somewhat hotter and of longer persistence than coastal Texas, but lower humidity. The pitch is about the same as yours--however, since yours is a tar and gravel roof it might well be that your roof experiences some ponding--something for which IB blanket roofing is (by design) perfectly well suited. The portion of my house to which IB was applied is noticeably cooler but, then, being shaded by trees from the hottest sun rays of the afternoon, it was fairly cool before--to the extent that very little AC cooling was needed. I can only say that the cooling costs are not higher and probably lower than before. My main consideration in opting for IB was its wind resistance, its low to zero maintenance requirement, yes, its heat reflectivity, and its lifetime-of-building warranty against failure or need of replacement. With your patience, I will need to get back to you on the cost-per-sf matter--so I can be sure the info is accurate. I do remember that I was given a very good deal on the installation. So, I'll be back with more cost info asap. I would think, however, that your region would be very well suited to IB roofing...especially if, like me, you don't want to be bothered with maintenance and future reroofs. Until later...

Regards,

Cowanon

PS: You we're surprised...at the high price? or lower than expected price?

Here's the IB cost information you asked about. The job was bid and paid for 800sf x 3.28/sf = $2625

The amount included edge fascia and three eave drains; two formed-IB permanently sealed roof jack boots; two sewer vent caps and sealed boots; tie into sloped roof.

I provided three metal downspouts (to permit roofer to continue work without having to leave) plus obtained my own permits prior to work commencement.

Overall I would expect prices from $3.28 to $3.88 to be within a range of reasonable rates--your price might be less due to the generally low labor costs in Texas. Most jobs should require no more than two persons: an installer/contractor/proprietor and one helper. In our case, work progress proceeded at approximately 1/2 or less the rate of standard types of roofing.

As with any construction--especially roofing--examine bid very carefully and be alert for trickery. You're well advised to perfom your own measurements rather than rely solely on roofer measures as this is an area where measurement error or bid padding can occur.

My election to go with IB was predicated on the assumption that over 30 years the combined costs of ongoing maintenance and reroofs of cheaper, conventional roofs (built-up or single ply (with capsheets)), or roll roofing would amount to not less that $3,600, possibly much more, plus bid costs and frustrations, and with questionable permanent assurance against leakage/damage...plus the other methods would have poorer insulation qualities and less resistance to moisture/consensation entrapment underneath.

Please feel free to send private message (click on screen name--not the mantid) for further advise based on my experience with the product, prior to and after installation.

Dear CowAnon,

I was browsing web looking for info on flat roofs. I live in Sacramento and noted that you report you live in Sac Valley and had a roof installed within last three years.

Your roof product appears similar to mine (Snow Roof system).

I was hoping you could provide name and number of company you hired.

Thanks.

#19 Guest,

Not sure what is meant by Snow Roof Systems: another type/brand of single ply? or Snow Roof (brand) in a can that was spread on over your roof? Anyway...

See about IB roofing This mfr's page gives links to product info, factory certified installers, projects done, and such....

Our IB roof installation was done by Flat Roof Specialists, proprietor Art Melick in Auburn--just up the road on I80 from Sac: his IB installer

ps. let me know how it goes. Getting reroofs around sacramento can be such grief.

Yes, In the past, 3-tab shingles have been used, on an expansive virtually flat roof approx 2/12. Yes underneath a vault style, rock ceiling is attached to the 2x6 roof joists. Yes the two roof decks meet at a ridge, it is not a building extension meeting a wall or a higher pitched roof. The failure of the shingles is curling. Surprising enough, blow off does not seem to be evident. Thank-you for your thoughts about the roll roofing, I am now cosidering it. The cavities are not totally devoid of insulation, based on my inspection from the eaves end it appears that there is approx 4 in of rock wool insulation. There does not appear to be cross pieces. Also, I will be removing the roof deck, as some one prior to me has installed plywood directly on top of the original roof deck, black paper and shingles. To clarify the last point, currently there is original roof deck, black paper, shingles, new plywood roof deck, black paper, and shingles. Again from my inspection from the eaves end, it appears that some of original roof deck has deterioated so badly that it is sagging into the cavities, therefore I will be removing, both sets of shingles and roof deck and re-installing one deck. I will be re-doing the eaves and installing perforated soffit as well as attic rafter vents. You are correct, gable vents will do nothing, as there is no attic to speak of. And yes that is why I am considering Ridge roof vent plus 2 Maximum Catherdal style roof vents. Trusting this answers all of your questions. I await any further feedback that you might have. Thank you for taking the time to reply to my question and partaking in this discussion.

You're welcome; and your plan sounds good. With the curling it definitely sounds like a problem...and I would guess both heat and moisture intrusion. Just a few more pointers before I go.

If you're going to remove the rockwool, you are probably going to want to replace with a few inches of foam sheet, laid snugly (and even taped along the edges to the 2x6's) in the rafter bays above the ceiling...so you will still have the comfort benefits and energy savings from increased R value...and remember: with ventilated rafter bays, you will no longer have any dead air for insulation above the ceiling. Due to wood's high R value, the rafters themselves will provide more than enough insulation between the foam sheets. The vent air streaming upward from the undereaves can just flow through the space over the insulation.

I would recommend using 30#, and not 15#, felt paper. It is not significantly more expensive and, after all, it is the paper that is most indispensible, and really does most of the work, on an asphalt/glass roof. The shingles/rolls/plies serve mainly just to hold the paper down in place, and for appearance. If you use standard asphalt roll roofing, be sure to get rolls with selvage strips, not the plain rolls like they sell, for example, at the Depot. With the selvage, you will be able to overlap and cement down over the nails--no nails will be exposed which you will have to seal, or which will rust or work loose, permitting water penetration, as time goes by. With luck--and I'm confident your going to be better off than with the shingles--you will be able to simply add a new layer of roll roof on top of the old when the time comes for the next reroof--hopefully only after at least 10 years or more. Good luck with it.

I had some what similar problems years back and have come up with an invention that will cater for all your and other roofing, insulation and protection needs. So much for the good news.

The bad news is that negociating with companies to allow this system to establish it self is very time/money consuming and risky. Patent protection is in its final stages and if some one wants to take it on, you are welcome to assist me. If not, all you people with roofing, insulation and protection problems will have to wait until I have wondered through the mine field of new product placement, Patents and the "Legal Eagles". R&D (including 3D cad presentation) has been financed by my self and will be in the future. This will take longer but I can be assured that a "one man show" will leave only one man to blame if it fails. Not the product, but the commercial aspects and their complexity. I am dealing with a large US company and if they would get off their back sides and comply with standard legal requirements the product could become available within a year or so. As you will appreciate, I cannot disclose any details of this system as it would create a "prior art" situation. What I can tell you, is that it will cost about 1/3 of conventional methodes and could be installed by a competent handy man on any kind of surface including corrugated iron. Just bare with me. Sorry I can't help you any more at this moment in time. Good luck.

KY

I also have a very low pitch roof on my house that is about 40 years old. The rafters are 2x8s on one half and 2x12's on the other (don't ask me) and they form a cathedral ceiling on the inside. I've had a rubber membrane covering for almost 17 years. My main concern is the insulation. I know from remodeling that it is in very bad shape and in the summer I get some condensation and I can tell that some sheeting below the membrane needs replacing. I have soffit vents but no ridge vent. The ridge would be a moot point anyway because there are many places where full size bracing was installed perpendicular to the rafters to form cavities and impede any air flow. There's also a bathroom where the roof has been dropped to form a flat ceiling inside. Needless to say I have many different situations to deal with and when the roof needs replacing I want to take care of the insulation. Anything I will do will have to be from above. What I was thinking was to remove all the sheating and replace the insulation, drill holes in the rafter blockage to let the air flow, and install a ridge vent. Does this make sense? Questions would be fiberglass vs. cellulose, a radiant layer (foil-type layer) between the rafters and sheating to help with heat in the summer, and would those styrofoam air channels be of any help? The other big question would be just filling everything with insulation and not worry about air flow. I've read a few articles where this has been mentioned for cathedral ceilings. Any help would be appreciated. BTW the house in the midwest (for temperature considerations). Thanks.

You ought to check out www.corwinsmartventilationsystem.com they have two products that address the issues of roof ventilation. A plastic clip is used with 1" foam to form a 1" gap between the sheeting and the rafter cavity. the foam is run from the soffit to the ridge vent. This directs outside air to the ridge vent while keeping the roof cooler. They also have a molded plastic vent that is used for venting blocked roof cavites. The rafter is notched for the vent and can only be installed from the top side without the sheeting.

Hope this helps.

The rafter(?!) is notched? So that air flows across to an adjacent, unobstructed rafter bay?

Or the bridging (the so-called, blocking between rafters) is notched? So that air continues upward through the same rafter bay?

Or the sheathing sheet or board is "notched" (has an opening cut out adjacent to its nail-down to the bridging)? So that air flows directly skyward out the "vent" accessory--and also directly downward and in through the vent accessory, in order to ventilate the rafter bay above the bridging?

The first case--actually notching actual rafters--seems like a precarious course...in possibly overweakening the rafter; and in possibly compromising sheathing &or roofing material attachment by removing "nailing" surface. Wonder how this would pass code?

Before anything is notched the span chart on the website should be referenced. the span chart was established by an engineering firm. Another engineering firm completed the ASTM testing for fastener removal.

The vent is structural and is be notched into the blocking and rafters. (If the blocking is some sort of fire blocking, then the vent should not be used) The purpose is to enable ventilation of all roof cavities. If the ventilation path is blocked by the framing of a skylite, then the air flow needs to be vented into the adjacent cavity to allow ventilation out the ridge vent. The vent will allow this.

Yes, I see now. Labor would be a consideration in that the notches would need to be precisely cut for a perfect, tight fit--not an easy thing to do, especially insitu. So it seems the vents are intended primarily for new construction in progress. It might be quite a challenge for a DYIer doing retrofit. It appears also that the vents would be barely suited for 6-by rafters...probably intended for 8-by's and up...as in commercial/institutional construction mainly. On a more modest scale, it might occur to a retrofitter than merely boring holes in the rafter (along with possibly some perforated reinforcement plates, or insertion of pipe "grommets") could accomplish cross venilation around the obstruction (rafter bridging or skylights and such) in similar fashion, but far cheaper and less labor intensive. Apart from span considerations, precise placement of the vent inserts would also be problematic in respect of roof sheathing nailing placement--because it does not appear that the cross-vent inserts are intended to be nailed into. Again, new, pre-engineered construction seems to be the thing in mind of the vent purveyors. Site pictures of the vents being installed only in new construction seems to further support this conjecture.

The air channel clips shown on the site also are an interesting concept--but the features and benefits claimed are somewhat suspect. The notion of using foam boards/sheets to isolate and insulate the roof sheathing (and roof materials) from an attic space, while channeling air flow from soffit to ridge, as well as from soffit into attic space is (at least a) clever (gimmick?). One question that arises would entail the fact that styrofoam is subject to shrinkage, which could cause leakage and thermal shorts after a period of time. The claim that using the clips and foam channels will also insulate the "living" space is dubious, possibly intentionally misleading...especially as it seems to suggest the possibility of dispensing with insulating the ceiling joist bays. Since the clips are suited only to attic space installation--not to open or closed rafter, vaulted ceiling--it is hard to see how much advantage, if any, could be achieved over simply having adequate, possibly even passively powered, attic ventilation. For the probably significant investment needed to insulate the rafter bays with styrofoam it's hard to see how the law of diminishing $return would not be quickly encountered. And conveniently, the purveyors did not mention the maintenance needs long term: whether the styrofoam would need periodic replacement over the life to the building. So, without considerable mfr and distributor support, both these products would--to this writer at least--entail a considerable, perhaps unacceptable degree of risk to a DYIer--both as to cost-benefit, and otherwise.

Yes the Corwin Rafter Vent is primarily for new construction. With regards to a retrofit, the sheeting would have to be removed for installation of the vent. This would probably only happen if is cost effective. (Preventing water damage, wood rot and ventilation issues) The vents are suited for any size rafter as long as it meets the span requirement for the application. A retrofitter could merely bore holes in the rafter, but the retrofitter should also be aware that the rafter would be weakened. I am not a structural guru, so I can't comment if perforated plates or pipe grommets will maintain the span requirement. I do know that the vent properly installed will attain the span ratings noted on the website and will allow more ventilation then the other methods. The vent is designed to be manually nailed, pneumatically nailed, stapled and screwed to. The ASTM testing was requested by Vulex sp? skylites and was completed at a second party engineering firm that they requested.

I have spoken several times with Tom Corwin (inventor of the Corwin Smart Clip, Corwin Rafter Vent and former building contractor for 40 years) regarding the use of the products. It is no gimmick. My parents have retrofitted their second floor attic space with the Corwin Smart Clip System (4/12 pitch) and have found that it is noticeably more comfortable in the summer. Also, my parents had an addition put on their home five years ago. The valleys where the new and old roofs come together form ice inches thick. The water has backed up and leaked into the home. This year they are removing the sheeting and installing the two products.

I have seen the data of the results of having the clips & foam installed. A sub-climate of sorts is created in the attic. According to the data the 1" air gap between the sheeting and the foam reached 123 degrees. The rest of the attic topped out at 102 degrees. (outside temp was 92) Even with R38 insulation in the ceiling, heat is still soaked into the living space below. With the temperature differential 21 degrees less, there will be less heat soaked into the living space thus reducing cooling costs. A closed rafter cavity would probably not see much advantage to the clip system except for the R-value of the foam. (And if that were the case, then just the foam may be used.) An open rafter cavity would work much like the attic system described above. The key to the whole system is to have an entrance (soffit) and an exit (ridge vent or like) for the air.

A test house was set up on Cayman Island comparing a house with the Smart Clip System and one without. Temperature probes were placed in the 1" air gap, attic and outside. The power consumption of the home was also monitored. The home with the Smart Clip System used 40% less energy. (I think this partially because they only require R19 in the ceiling causing significantly more heat to be soaked into the house)

I am not familiar with polystyrene foam shrinking. I will have to check out my parents' attic the next time I am visiting. You have got me thinking and I also posted a question to Dow regarding the shrinkage. I am also curious about why the foam would have to be replaced during the life of the building.

If I remember correctly, there are some presentations available for download on the website. They contain a little better quality pictures and some more information.

That's an interesting sytem. Parts of it might work for certain areas of my roof. Thanks.