Idea for attic ventilation

[Todd Burch]

Location: Brenham, Texas. 77833.

I'm working on a fixer upper. Just put new hardie siding (trim, eaves, rakes, frieze, unvented soffits) and painted it. Looks great.

I went with unvented soffits for this reason. The house was built in 1960 with simple open overhangs - just the rafter tails and 1X6 T&G decking above them. Between each pair of rafter tails, a 2X4 was fit. It would have been a ton of work to remove all of them, so I left them. (As a side note, I've never been too impressed with the effectiveness of soffit vents. Attics are still convections ovens around here.)

I'm supposed to be getting a new roof this next week, if the weather holds out. Roofer (a good one, and a friend) is asking me about ridge vents, and he's reprimanding me for not knocking out all the 2X4 blocking and putting in vented soffits. Too late now - I'm not tearing the soffits and blocking out. (Side note - the paint is still drying - I finished it today).

So I have an idea for good attic ventilation, and would like y'alls feedback. All I have right now is 3 gable vents (3 @ 16 X 24) and two turbines.

The house is pier and beam, with a crawl space under it. There are 6 foundation vents around it (~5" x ~18"), with just the north side of the house ventless (the garage is sunken to the main floor on the north side).

I'm thinking about boxing in a vertical pipe somewhere inside the house, that will connect the <cool> crawlspace to the attic. Visualize a flue pipe, or large plastic pipe, (or, heck, dust collector pipe!) with a screen on the bottom and top, creating a direct duct from the crawlspace to the attic.

What do you think? Think it would be effective? I'm thinking it would suck up a ping pong ball on a hot day. I would probably forego the ridge vents if this will work (save some $$) and the turbines and gable vents would suffice.

Todd

[Phil Thien]

Wouldn't that possibly introduce quite a bit of moisture into the attic?

[Todd Burch]

Don't know.

We had the floor open during this renovation, and on a hot day, standing over that hole, there was a definite breeze, and it did smell musty. Currently the grade of the lot causes water to drain towards the foundation at the back of the house. I'll be changing the grade over the next month or two.

Taking June as an example, morning relative humidity is 92%, which, has quite a bit of moisture in it. Afternoon RH, on average in June, is 56%.

[Brian W Smith]

All things considered in our part of the country,we'd be better served taking the air from attic and "pressurizing" the crawlspace.Due mainly to the damage the moisture does in crawl.Also here,soffit vents when engineered into a complete attic "system" is the only way to fly.

[Jim Matthews]

We used this system with a ridge vent.
The original soffit "button" vents had been painted over by
the previous owner.

http://www.airvent.com/pdf/literature/VentedDripEdgeSellsheet.pdf

[Jamie Buxton]

So you're sacrificing interior floor space to get cooling to the attic. Maybe that's not so good?
Say your cooling pipe has a 10"x10" cross section. Go back to thinking about knocking out 2x4 blocking around the periphery of the roof. Knocking out just two of them would give you more cross section than the 10x10 cooling pipe. I hate re-doing work, but it does seem like the better solution here.

[Todd Burch]

I guess I could hole saw a couple holes in each one from the inside. Sheetrock and insulation aren't up yet. I'll have to get a ladder this evening to take a look. Perhaps holes in the blocking combined with the vented drip edge might work well enough.

[Joe Tilson]

Todd,
If you drill hole in the blocking, think about gluing screen mesh over them to keep out bugs and rodents. I have done it several times and it works very well. Put the screen mesh on the inside of the attic space to keep from painting over it, if applicable. Hope it works out well for you, whatever you come up with.

[Jim Matthews]

You're in a very different climate than mine, so YMMW.

We needed to create a path from the drip edge vent
to the attic space. The previous owner had filled the rafters with fiberglass insulation.

Once a path was established, the roof held snow all Winter and the
bedrooms below were 1 - 5 degrees cooler on average.

I think of an attic space as a hat for a house.

I have found that decoupling the attic space from the interior of the house
has made things a little more comfortable - delaying the start of our brief air conditioning season.

If you want a chimney effect, separate the air source from your living space.
You have described an "Earth tube" system.

If your water table is low enough, it might reduce attic temps appreciably.
I would concentrate on reflective or shading strategies, first.

What color is the roof?

http://www.permies.com/t/18609/homestead/Passive-Cooling-Ideas-Hot-Humid

[Stephen Musial]

Winter would be the problem I see. You're going to draw moist air up into the attic and then it will condense against the cold roof. Not good. I'd go with the ridge vents, gable vents and put one of these (http://www.northerntool.com/shop/tools/product_200367065_200367065) in. Won't cost anything to operate and will keep everything ventilated all year long.

[Jim Koepke]

One of the reasons for soffit vents is to help in keeping the roof from getting warm and melting snow in the winter. Melted snow can turn into ice dams along the edges.

Roofs and attics are amazing science. Done properly they can last for decades. If done poorly, you will be doing it over fairly soon.

jtk

[Mark Bolton]

The problem with centralized makeup air for the ridge vent (gable vents for example) is they don't provide for smooth, uniform, laminar flow, of air under the entirety of the sheathing. Simply supplying an adequate quantity of makeup air isn't enough. The goal is a uniform laminar flow of air from the eave to the peak. And it's has nothing to do with cooling then attic regardless of climate.

[Jim Matthews]

OP lives near Houston, Texas.

[Jim Matthews]

Flesh that out, please. Should attic spaces be dynamic, or static features? Is the attic a maintenance system for roofing materials first, insulation for living space second?

I'm genuinely interested and the OPs question parallels many of my own.

[Stephen Musial]

The idea is to keep the roof the same temp as the outside air so it doesn't bake from the inside out or freeze from the outside in. The more stable you can keep your roof temp, the longer it will last. This also alleviates ice dams in cold climates. In a perfect world, the attic is the same temp as the outside and the insulation keeps the warm air from migrating up and the cold air migrating down in the winter (and the opposite in the summer).

How it's done via soffit vents, ridge vents, gable vents, power vents, etc. is up to you, the house, and your checkbook. Be aware though that some shingle companies won't warranty the shingles if there is no ridge vent installed.

[Jim Matthews]

Thank you.

That was clearly stated.
When I put on my roof, the ridge vent was only included in the quote that got the job.

The other three thought it was pointless.
It made all the difference in our house.

[Steven DeMars]

I live in Baton Rouge, LA area. . .

You really want to pull from the soffits up and out . . . No power vents required.

Soffit vents do work, but total area open on intake(soffit openings) HAS to exceed the total area of your exhaust vent capability.

I have (3) 14" wind spun turbines on my roof and they do a fantastic job. Home is 1600 sf. living.

They spin non-stop day & night . . . To do what the OP is suggesting would bring "cooler" air into the attic quickly. When you do this there is a very good chance you will hit the dew point during the night in the months before spring starts.This will cause all that hot "MOIST" air to condense and dump right on top of your insulation. Now you will have to deal with wet insulation, which will give you mold and an unbelievably wonderful environment for termites.

I did a lot of research on this a few years back. It became a "hot" topic in the engineering office I was working in at the time. We were all schooled by a ChemE as to what would happen. My plan was to bury 60' to 70' of duct work 18" to 24" and pull through it to cool my attic during the day. Same principal.

Steve

[Mike Lassiter]

I recently had to replace my roof and make some repairs and improvements to the 28x60 mobile home I live in. Bought it new in late 1996 and it had 4 of the black plastic vents near the ridge on the rear side of the roof. Soffit vents all around but the vents the hot air come out of was really a joke the way they were done. One had the opening in the decking cut out about 1/2 the size of the vent, another likewise, but also when the shingles were laid down the roofer ran one run over the bottom half of the small opening and left it that way. 15 seconds to cut the shingle so it wasn't blocking the opening. I patched the 4 areas and closed them off and installed 2 solar powered vents from Home Depot that required a 15" diameter opening in the roof decking.

Standing on the roof after adjusting the solar panel on the first vent in the sun I blocked the sun to the panel and the fan obviously stops running. I stood there about 30 seconds with my hand at the air outlet area then moved to let the sun shine on the panel and the fan started running again. In the brief time the solar panel was blocked so the sun couldn't hit it the air temp of the air the fan began blowing out was noticeable warm, not hot by very warm in that short time. Sun shinning on shingles heats them up. Sun shinning on the solar powered vent makes it run faster up to it's max speed in full sun. Clouds slow it down some, but I was very happy with seeing just how much difference the air temperature was with no fan running and running. I installed two of these divided on the roof. Shingles will have much longer life now due to reduced heat buildup they will see. Attic will be much cooler because the air is being pulled in at the bottom and exhausted at the top. No gable vents installed, just decorative plastic to look like one. I have considerable more open vent area for the air to exhaust from now that I have 2 full 15" openings in the roof over the 4 puny opening the manufacturer provided. Can't say it helps with cooling cost as I have R 38 I think in ceiling, but surely will some with reduced temperature difference between ceil inside and attic temp. Fans cost about $200 each I think, but cost nothing to operate and even if it's cloudy but still hot the opening allow more air to flow by convection current than could have through the vents installed.

[Mark Bolton]

There have been several studies showing that no form of roof venting can reduce attic or deck temps by any relevent amount. 10 degrees at best. Of course once the sun goes down they can help dissipate accumulated heat quicker.

In cold climates keeping the roof deck at ambient (venting leaking interior air) is the goal and in all areas venting interior moisture.

The asphalt roofing industry has tried to blame hot attics for warranty claims but the un-vented deck industries (SIPS is one) have long since undone that one.

[Kevin Bourque]

I agree with much of what has been said here. Moisture and heat are bad for an attic.

I would also like to add that gable vents are problematic too. They tend to leak, and also let in wind blown rain and snow. The powered vents are even worse. In new construction around here ( SE Pa. )they are rarely, if ever, used. Good soffit ventilation coupled with a ridge vent does a pretty decent job at exhausting moisture and keeping the roof less hot.

Also, using light colored shingles is probably the best way to keep the roof cool(er ).

[Mike Lassiter]

There have been several studies showing that no form of roof venting can reduce attic or deck temps by any relevent amount. 10 degrees at best. Of course once the sun goes down they can help dissipate accumulated heat quicker.

In cold climates keeping the roof deck at ambient (venting leaking interior air) is the goal and in all areas venting interior moisture.

The asphalt roofing industry has tried to blame hot attics for warranty claims but the un-vented deck industries (SIPS is one) have long since undone that one.

based on your saying "There have been several studies showing that no form of roof venting can reduce attic or deck temps by any relevent amount" it seems we all have no valid reason to vent the attic.

I disagree and will leave it at that.

I know how much the air temperature increased in the time I blocked the solar panel on my vent and it doesn't take a genius to know moving more air thru a given space will reduce the heat because the air that is moving thru it is carrying some of the heat gain out of the area. As pointed out by someone else, the air needs to enter at the bottom and exit at the top. Blowing air across the top may help the upper area, but does little for the lower area that the air is not moving in.

Your comment about SIPS is comparing apples and oranges. The SIPS panel is insulated and reducing the heat from building up in "the un-vented deck".

[Mel Fulks]

We had a similar thread some time back in which I said there is considerable debate among the experts. Still is. I have a cape cod type house which was pretty hot upstairs due to heat coming from under the roof behind the knee wall. Tried the venting ,fans , etc with no improvement to living space. The roof is the darkest color available short of black and is almost exactly south facing. Once I gave up on all fixes except insulation problem was fixed. I don't care how hot or cold it gets on the other side of the insulation ,the upstairs is now comfortable.

[Mark Bolton]

based on your saying "There have been several studies showing that no form of roof venting can reduce attic or deck temps by any relevent amount" it seems we all have no valid reason to vent the attic.

I disagree and will leave it at that.

I know how much the air temperature increased in the time I blocked the solar panel on my vent and it doesn't take a genius to know moving more air thru a given space will reduce the heat because the air that is moving thru it is carrying some of the heat gain out of the area. As pointed out by someone else, the air needs to enter at the bottom and exit at the top. Blowing air across the top may help the upper area, but does little for the lower area that the air is not moving in.

Your comment about SIPS is comparing apples and oranges. The SIPS panel is insulated and reducing the heat from building up in "the un-vented deck".

No one, including the studies, say that temps cant be reduced. The issue is are they reducded in any amount relavent to shingle life or that of conditioning the interior space while the sun is out. The answer is no. There is no reasonable venting that can offset the gain when the sun is shinning by more than 10 degrees. Many of these studies were done because shingle manufacturers were trying to void warranties over unveted decks and the results proved and showed clearly and scientifically that venting can not in any substantial way reduce the attic or roof deck temperature when sun is shinning. You can question the science or get yourself a thermometer and a laser thermometer and stand on your roof and take readings with your vents running and not.

The venting is for a reason, I install it regularly, but it has nothing to do with cooling the roof when the sun is shinning or for the life of the shingles. Ice dams, moisture, yes.

[Paul McGaha]

I do think it's a good idea to get the hot air out of your attic. It makes the upstairs level of your home markedly more comfortable.

I was an electrical contractor from 1992 to 2002. For the 1st 3 years of our company we did residential service work and providing roof fans was one of our biggest sellers in the warm months of the year. A typical installation would be a home with soffet vents and ridge vents and no motorized fans.

In the summers the outside temperature here in the Washington DC metropolitan area would be usually in the 90*'s and some days in the 100*'s. The temperature in the attics would reach about 130* to 140*.

A roof fan will drive the attic temperature down considerably, I'd say to around 120*. This makes the upstairs level of your home much more comfortable during the daytime. Say about 7 PM, when the sun is down and the hot part of the day is over, it takes a roof fan about 1 hour or less to cool the attic off to the point the fan reaches the set point on its thermostat (110*) and cycles off. At this point the upstairs level of your house is very comfortable, like it's not even hot outside, although it still is.

I'd guess we did maybe 500 roof fan installs. We used to furnish and install a very good roof fan (Nutone RF59N) for $220. Everybody liked them. I wouldn't be without one if I lived in a warm climate.

I'd highly recommend installing roof fans.

Gable fans do a similar job but I like roof fans better because I like the location of the fan better (backside of the house, centered left to right, up as high as possible but not so high you can see the top of the fan from the front of the house). Back in those days anyways roof fans used to have larger motors and move more air than a gable fan.

Gable fans do have the advantage of being easier to install though. And certainly better than not having any fans.

Good luck with it.

PHM

[Mark Bolton]

I do think it's a good idea to get the hot air out of your attic. It makes the upstairs level of your home markedly more comfortable.

After the sun goes down powered or even turbine ventilation will do a lot for bringing the roof structure and attic space closer to ambient more quickly and most definitely helps eliminate heat from the attic/ceiling structure from continuing to radiate into the living space in the evening. But again, this venting does virtually nothing when the sun is shinning. The solar gain is far greater than can be dissipated in daylight hours. Taking a roof deck or attic space from 140 to 130 or even 120 will provide little comfort to the occupants though it will reduce the load on a cooling system slightly.

The real issue is if possible, had the same dollars that were spend on the powered venting, installation, and electricity to run (for a non solar vent), been invested in additional insulation the space would be far more comfortable than any powered venting would achieve because it wouldnt get hot in the first place. Of course many structures simply dont allow for additional insulation so venting can surely help to cool the structure more quickly after the sun goes down.

[Harry Hagan]

I’ve skimmed the other comments and agree that venting your attic via the crawl space would be a big mistake—too much moisture being introduced in both areas unless you live in a low humidity climate.

Adding ridge vents made a 20° difference on the upper level of our house when we did away with the existing box vents and opened up the existing wooden soffits before covering them with vented vinyl soffits.

One sure way to vent that attic during summer months would be to add a whole-house fan; but high humidity makes them impractical in most areas.

[Todd Burch]

Mark, I would like your opinion on my idea for insulating the roof via rigid foam. Please see this thread and comment:

http://www.sawmillcreek.org/showthread.php?217271-Insulation-Question

Thanks.

[Mark Bolton]

Mark, I would like your opinion on my idea for insulating the roof via rigid foam. Please see this thread and comment:

http://www.sawmillcreek.org/showthread.php?217271-Insulation-Question

Thanks.


Todd,
I read that at the time and agree with the comets that said even though you had the ISO, a much better idea (if your in this for the long term) would be to have foam sprayed internally and encapsulate the structure. As with any of these options, they have to be looked and and approached as a system as opposed to the individual components.

Personally I can't see how the expense of installing rigid foam and the deficiencies that will inevitably be part of the install (gaps, seams, accessory costs) could compare even to the pricey cost of spray foam. But you hAve to factor everything fairly.

If your not planning on staying in this residence for a ver long time, or are not in a market where you have the potential to recoup you investment, you are best to measure your approach.

[Mel Fulks]

In the situation I had I used ordinary fg batts in the knee wall roof rafters with the plastic toward interior. Some said it
would soak up water ,but it has stayed dry and is used for storage and checked at least yearly.

[Jason Roehl]

http://www.amazon.com/Maurice-Franklin-Louver-3-Polypropylene-Louver/dp/B00AFESHDS/ref=sr_1_13?ie=UTF8&qid=1402442005&sr=8-13&keywords=3%22+soffit+vents
Hole saw, some work, a few bucks.

[Todd Burch]

Thanks for your comments everyone.

Spray foam might be best, but I don't need the best. I'm not so certain I would want spray foam regardless. I have the rigid foam, and have no other foreseeable use for it.

I'm trying to put this in perspective.

The house has survived with window A/C units, space heaters and no soffit ventilation, pathetic ceiling insulation and no wall insulation for 54 years. Granted, I haven't been living in it, but I would venture to say that 1/2 the houses in this town don't have a lick of wall insulation.

I gave an analogy to my wife this afternoon, comparing the inside of the roof deck to a pan that has been on the stove top. If you picked the pan up by the bottom, it would burn your hand bad. However, if you put on a cooking mitt, you can hold the pan just find. You have insulated yourself from the heat of the bottom of the pan.

Why wouldn't 2" of foam not have the same effect from the radiated heat of the shingles? Surely it has to have value, and I'm thinking significant value.

Why is rigid foam the go-to choice for commercial building roofs, and it's not appropriate for residential?

My buddy has spray foam in his new house, built by a high-end custom builder. It seemed awesome when the house was being built. When I walked into the house after it was insulated, it was like walking into an underground cave it was so cool - and the HVAC was not even on and it was the middle of summer. However, it also has a big drawback in his scenario. It's not his primary residence, so he doesn't run the A/C it all the time. If he does not keep the air on, or turn it on an hour before he arrives (via his phone), his house is hot. It takes forever (read, about an hour) to cool off. If doors are left open while you are there, again, it takes a long time to get the temp back to comfortable. How convenient is that? How is that the best system? Was his A/C undersized? No, it was sized for use with spray foam.

I don't have final numbers yet, but here is what I would anticipate:

Qty=60 sheets of 7/16" OSB @ above the polyiso would run just over $500
Qty=12 of 2X6X12' (ripped to two pieces of 2" widths) would provide a border around the roof (~200') and at the ridges (~80') @ $8 each = ~$100.
Qty=4 rolls of 3' X 150' tar paper for the extra layer @ $16 each = ~$70.
Qty=2,500 4.5" screws to go through the 7/16" OSB, through 2" foam and into the original deck. (They don't make 3.5", or else I could use those). (I took the 8d nailing schedule of 41 nails per sheet and used screws instead. But seriously, who installs OSB that uses a nail every 6" of the perimeter and 12" OC for the interior of the sheet? No one I have ever seen.). 2500 3.5" Headlok screws on Amazon would cost $800. Wow.
Labor - will find out tomorrow.

[Jim Matthews]

Your friends superinsulated house sounds like a refrigerator.

You still have to pump heat OUT, and that takes time.
Passive cooling systems will smooth out the variations,
but without a substantial heat sink, you will reach
the ambient air temperature.

Near Houston, that's pretty high on average.

I think you're on the right track to isolate the living spaces
and ventilate the roof for longest shingle life.

Is there anyone in your area that specializes in passive approaches?

A quick Google browse turned up these guys:
http://www.drenergysaverstx.com/insulation/attic-insulation/superattic.html

Remember that this is not just an investment to reduce cooling costs, it's also an investment
in your comfort while you live in your home.

[Mark Bolton]

One thing you may want to inquire about is some issues with regards to ISO collapsing slight over time. It may result in screw heads popping through your shingles if the ISO and the sheathing shrunk (even very slightly). Again I have no idea but just a concern where your not going to have framing on even wide centers.

Another issue will be what will you do at the perimeter to cover the additional thickness? Wide drip edge? Aluminum fascia?

Your friends house is what I'm speaking of. When you encapsulate and get higher and higher efficiencies the entire structure becomes a system. Like a commercial building. You can't just walk away without leaving some systems to run periodically whether it's an hvac system, air to air heat exchanger, whatever. There are pros and cons but again, at least to me, you have to weight then out honestly with regards to what your intent is for the home rather than hooking on to the bad things in support of your original plan. Its very easy to lock down on the things that support our original ideas rather than looking at everything by the numbers.

But everyone does what they want..

[Pat Barry]

I think the typical approach for the insulation board on top of an existing roof is to provide nailers 16" on center, lined up over your existing rafters. Then simply affix the sheathing to the nailers. What I don't recall, but I'm sure could be easily found is the ventilation, if any, for this type of application. My cabin has a similar roof - they did it so the inside of the cabin wouldn't have the ceiling (pine boards, log rafters) obscured by the internal insulation approach. They didn't do any ventilation that I can see and I suspect they should have.

[Rick Fisher]

I have been in the supply business for 30 years. Sell millions of dollars in shingles each year and have been to a hundred claims in my life. Your roof would have no warranty in my area.

Air goes in the soffits, and out the ridge or roof vents. That is the deal. If you have sealed up soffits, and the shingles crack, degranulate, or buckle ( organic ) .. your out of luck.

Lots of weekend warriors like to argue and draw fancy pictures but your buddy the roofer is 100% ..

I should add.. 60% of the roof failures I have been too are due to exactly what you have .. the rest where .... sealing shingles on resawn boards, wind blow off, shingles nailed high and blowing off, or actual factory problems. The #1 source of claims however is ventilation .. exactly what you describe.

[Paul McGaha]

After the sun goes down powered or even turbine ventilation will do a lot for bringing the roof structure and attic space closer to ambient more quickly and most definitely helps eliminate heat from the attic/ceiling structure from continuing to radiate into the living space in the evening. But again, this venting does virtually nothing when the sun is shinning. The solar gain is far greater than can be dissipated in daylight hours. Taking a roof deck or attic space from 140 to 130 or even 120 will provide little comfort to the occupants though it will reduce the load on a cooling system slightly.

The real issue is if possible, had the same dollars that were spend on the powered venting, installation, and electricity to run (for a non solar vent), been invested in additional insulation the space would be far more comfortable than any powered venting would achieve because it wouldnt get hot in the first place. Of course many structures simply dont allow for additional insulation so venting can surely help to cool the structure more quickly after the sun goes down.

All due respect Mark I don't agree with your statement that reducing the attic temperature from 140* to 120* (with a roof fan) won't have an effect on the comfort level of the upstairs level of the home during the daytime. It most certainly will. And enough of an effect to easily justify the installation of a roof fan. Ivé seen numerous installations where it was the difference maker between the upstairs level being comfortable or not.

Roof fans aren't the only thing required to help keep your house cool. The attic has to be well insulated, Outside windows and doors need to be sealed properly, the air conditioning system needs to be in good working order, It's good to have a roof fan in the attic and ceiling fans in the bedrooms.

Get all those things done though and I've found that you can have a pretty comfortable upper level of your home with temps outside pushing 100*.

PHM

[Brian Elfert]

My buddy has spray foam in his new house, built by a high-end custom builder. It seemed awesome when the house was being built. When I walked into the house after it was insulated, it was like walking into an underground cave it was so cool - and the HVAC was not even on and it was the middle of summer. However, it also has a big drawback in his scenario. It's not his primary residence, so he doesn't run the A/C it all the time. If he does not keep the air on, or turn it on an hour before he arrives (via his phone), his house is hot. It takes forever (read, about an hour) to cool off. If doors are left open while you are there, again, it takes a long time to get the temp back to comfortable. How convenient is that? How is that the best system? Was his A/C undersized? No, it was sized for use with spray foam.


An hour to cool off a hot house doesn't seem unusual to me. I would put my heat at 55 degrees in the winter when I was gone for a few days. It would take the furnace 45 minutes or more to get the house back up to temp.

One problem with highly insulated houses is they don't cool off or heat up very quickly naturally with windows closed. If the temps drop to say 65 degrees overnight the temp in the house might still be 72 to 75 degrees. It can feel hot in the house because it is cooler outside and the A/C wouldn't be running.

[Todd Burch]

I decided to nix the 2" rigid foam - I don't have time to manage the changes. Took a framing hammer to the 1X4 blocking - came out pretty quick. PVC air vents were on clearance @ the BORG for $1.50 each. What you see is literally all I can install on the front of the house. However, the whole back of the house will get them. I think around 25 of them.

[Mark Bolton]

I have been in the supply business for 30 years. Sell millions of dollars in shingles each year and have been to a hundred claims in my life. Your roof would have no warranty in my area.

Air goes in the soffits, and out the ridge or roof vents. That is the deal. If you have sealed up soffits, and the shingles crack, degranulate, or buckle ( organic ) .. your out of luck.

Lots of weekend warriors like to argue and draw fancy pictures but your buddy the roofer is 100% ..

I should add.. 60% of the roof failures I have been too are due to exactly what you have .. the rest where .... sealing shingles on resawn boards, wind blow off, shingles nailed high and blowing off, or actual factory problems. The #1 source of claims however is ventilation .. exactly what you describe.


Not to drag this out, but the entire construction industry including the NRCA, IBC, IRC, as well as all the major asphalt manufacturers (GAF, Owens, Certainteed, IKO, and more than likely every other) addressed the issue of unvented roof decks some 15 years ago. Asphalt manufacturers and reps had long blamed shingle failures (of which few were likely the fault of the manufacturer in the first place) on heat. It was an easy scape goat and an easy way to get out of a claim. However when unveted roof structures due to ever more complex roof designs, log homes, cathedrals, and the onset of encapuslation became more prevalent they were faced with either #1 turning away all this potential business, or #2 finally coming clean that heat has absolutely zero to do with shingle failure.

The driving factor behind this was from builders, architects, and designers, who were faced with either no longer using asphalt on the vast majority of their work (read VERY large/complex multi million dollar homes) or expecting the asphalt manufactures to see the light. If you look at many of large homes today with very complex roof layouts full of dormers, valleys, hips, and so on, there is simply no soffit to vent in the fist place. There is no "ventable" edge and little ventable ridge. Then you consider log homes, SIPS structures, and the like, and your talking a major chunk of the asphalt shingle industries customer base going bye bye if they stuck to this concept. Not to mention the manufactured industry which is horrendously poor about venting roof structures in the first place.

Needless to say, 15 years ago, the shingle industry "conveneintly" said that running their product over unvented decks was suddenly OK. Their warranties allowing this speak only to things like adhering to the building code and installing insulation as per the manufacturers recommendations. All the majors warranties allow things like minimum roof sheathing thicknesses of 3/8" ply. This speaks specifically to the manufactured home industry. Their details with regards to unvented decks speak to one thing and one thing alone and thats maintaining a stable sheathing surface and nothing with regards to heat or heat dissipation. All they are aiming for is a dry underside of the deck to prevent the deck from degrading or curling/cupping and tearing the shingle layer.

The simple fact of the matter is you can lay out some shingles on your asphalt driveway, the hottest surface out there, with no effect.

None of this is to say that roof venting is not essential and absolutely wise. Its just to say that there is no form of reasonably implemented passive, or active, ventilation which can cool a roof deck in the sun by any useful amount. It has never been what roof ventilation is actually there for. Cooling your roof more quickly after the sun is gone, sure, but at noon, there is zero gain.

All this aside, I can honestly say that in 20+ in the trade I have never once been around, or even first hand, seen a shingle claim that was a manufacturing problem. On the other side of that I could easily imagine manufactures paying out on claims that really arent their fault far more often than they have a problem.

Nearly every single shingle failure I have ever seen or been a part of fixing could either be attributed to siting/location, or installation.

[Mark Bolton]

All due respect Mark I don't agree with your statement that reducing the attic temperature from 140* to 120* (with a roof fan) won't have an effect on the comfort level of the upstairs level of the home during the daytime. It most certainly will. And enough of an effect to easily justify the installation of a roof fan. Ivé seen numerous installations where it was the difference maker between the upstairs level being comfortable or not.

Roof fans aren't the only thing required to help keep your house cool. The attic has to be well insulated, Outside windows and doors need to be sealed properly, the air conditioning system needs to be in good working order, It's good to have a roof fan in the attic and ceiling fans in the bedrooms.

Get all those things done though and I've found that you can have a pretty comfortable upper level of your home with temps outside pushing 100*.

PHM


Well, it is what it is. The physics of the situation are just there. Having a ceiling surface that is radiating 115 degress of heat out of the attic/roof structure and into the living space as opposed to 135 degrees is still going to result in one outcome, occupants getting away from that heat source. Like I keep saying, there are most definitely some structures that are not feasible to insulate and venting may provide some modest relief but I will guarantee you that if you were to accurately measure actual temps in full sun, the fans would be doing little to nothing. The sun is a very powerful thing.. ;-)

[Brian Elfert]

All this aside, I can honestly say that in 20+ in the trade I have never once been around, or even first hand, seen a shingle claim that was a manufacturing problem. On the other side of that I could easily imagine manufactures paying out on claims that really arent their fault far more often than they have a problem.


What about organic asphalt shingles? They were used extensively here in Minnesota. I don't know if you call those a manufacturing issue, or a material issue. Roofer knew I had organic shingles just by talking to him on the phone and describing the problems. Some insurance will either cancel insurance for homes with organic shingles, or cancel the insurance on the roof until the organic shingles.