Roof ventilation information

[bowlofsalad]

Hello,

Instead of writing out a novel on my journeys of do it yourself remodeling, I guess I'll just share a bit of information I've found highly useful concerning roof ventilation and related. I was completely unaware of (as are every local experienced roofer I've contacted) this information despite months of research until I found these videos along with lots of other stuff. With this information you might gain some comprehension on how roof ventilation works and why. If you happen to have a roof over your head, knowing this information is likely to be insanely useful to many.

I don't know if this information applies to every type of roof there is, but it seems to apply to a large number of roofs I am familiar with.

www.youtube.com/watch?v=vShj1l0PnF0
www.youtube.com/watch?v=fB6CbJsb1FM
http://www.nachi.org/forum/f16/too-much-roof-attic-ventilation-51244/

 

[will_newton]

This is officially the most off topic post ever. I don't mean this in a bad way. I would feel the same about a roof ventilation post anywhere.

I want to give you some kind of award for it. :lol:

 

[Punx0r]

You guy put holes in you roofs? Bonkers

 

[kd8cgo]

I researched this exact thing when I bought my first house, as I noted that among the energy problems it had was a huge delta T between the unconditioned attic space and the exterior air temperature. It was the cheapest energy savings I think I've achieved, probably the best kWh/dollar ratio of all the mods so far. Good post!

 

[marty]

delta T? Thanks for teaching me a new word.
https://www.google.com/#q=delta+t+temperature
“Delta T” is the most common use of the word delta in the HVAC industry, meaning temperature difference. If the temperature before a cooling coil is 75F and the temperature after the cooling coil is 55F, subtract 55F from a 75F to find a delta t of 20F.

 

[kd8cgo]

Cool glad to help. Delta is just an english spelling of the greek letter (Δ) - for some reason we like to use greek/latin letters for techy stuff...

Here's something cool from Wikipedia I didn't know:

A river delta (originally, the Nile River delta) is so named because its shape approximates the upper-case letter delta (the shape is a triangle).

 

[LockH]

Cool (pun intended). When my father quit the Canadian navy (early, but not early enough to damage retirement income. It's the only way for Canadian military to protest "stupid" politicians and their "stupid" ideas like combining our armed forces) they'd been already buying a patch of land in the Bahamas (not big Exuma, little Exuma). So they had to build a new house and went "Bahamian-style" where the walls don't actually go all the way to the ceiling, just supported by the wood posts in the walls.
Windows not with glass but wooden louvers that open/shut. It's all about the air flow in a hot climate.

BTW. Watched those vids and oddly maybe no mention of roof turbine vents (big fan of wind (solar) power here).

 

[bowlofsalad]

BTW. Watched those vids and oddly maybe no mention of roof turbine vents (big fan of wind (solar) power here).

http://www.youtube.com/watch?v=iavtcaPNLoY

Personally, I think that attic turbine vents are a scam at best, something people try to sell to you trying to convince you you need something when you don't. At worst they (the powered ones) are a fire hazard. As the video I linked to describes, as well as others, air sealing is a largely ignored but wholly important idea, perhaps the most important element to consider when looking at a roofing system. I know air sealing is both expensive and difficult but a severely under rated idea. I am sure most who sell or install any type of turbine vent don't have the slightest understanding on how roof systems function. So just to make sure you or anyone understands, humidity and temperature exchange to and from the attic isn't solved by more ventilation, it's solved by insulation and air sealing. Air sealing is a wonderfully interesting subject. A lot of my initial interest and discovery into this subject stems from this forum concerning water getting trapped inside of electronic and motor housing. The summary is that short of potting something air sealing in most circumstances is basically impossible. This is why in an attic we use expanding polyurethane spray foam and a relatively small amount of ventilation. After a lot of reading and research I am realizing that unless you have excellently sealed rigid foam board as some form of sheathing, large amounts of spray foam is the way to go for sealing.

From there, all you need to worry about is having enough ventilation, watching the net free area video I linked to will educate you on most of what you need to know on that front.

Personally, I lean towards gable vents with really solid stainless steel meshing to cover it externally, or http://www.homedepot.com/p/Active-Ventilation-12-in-x-15-in-Aluminum-Flat-Roof-Exhaust-Static-Vent-in-Mill-Finish-KV-12/204203059 something like these. In my opinion, these types of vents are least likely to leak or get clogged. When I say leak, I mean from rain, when I say clogged, I mean from snow and ice. To me, soffit ventilation seems like primarily an aesthetic preference more than anything else.

The wind powered vents you mention can't light themselves on fire, but they don't actually help anything, the best case scenario is they are worthless and require oiling when they start making noise while spinning, at worst they help create scenarios like ice dams by accentuating air leaks from a homes interior.

A large part of why I am trying to share this sort of information where I can is because in the past few months I've spoken to several experts in the fields of insulation, roofing, ventilation, architecture, general contracting and so on, nobody local to me knew any of this information in the slightest, most of the responses to my questions have been flat out bullshit or sort of half baked comprehensions of whatever they imagined in 5 minutes of thought. To my surprise, only one guy I spoke with about these sorts of roofing and ventilation subjects had the decency to simply admit they didn't know rather than try to bullshit me. Can you imagine talking to the owner of a company that installs roof vents and they couldn't tell you what net free area is, or worse yet, try to toss out a lie as fact? I think this sort of information is insanely important in relationship to a house or most types of structures but I didn't even know what a soffit vent was until not very long ago in spite of living in buildings my entire life. It's like someone riding bicycles for many years but having no clue what a ball bearing is, or worse yet, being a bicycle mechanic and not knowing what a ball bearing is.

This is officially the most off topic post ever. I don't mean this in a bad way. I would feel the same about a roof ventilation post anywhere.

So you post in a thread you call off topic that was posted in the 'off topic' section of a forum with an off topic post about how off topic this thread is? I am giving you this as an award for the most yo dawg post I've seen in the past 11.34 picoseconds.

I want to give you some kind of award for it. :lol:

I accept skyscrapers made out of gold or kingship of cities with populations of no less than 4 million.

 

[amberwolf]

Regarding the wind-powered spinny vents , at least on my house here in ultra-sunny Phoenix, AZ, they have a significant effect on the overall house temperature in the summer. We don't have much in the way of actual wind to spin them most of the time, but their presence to give a place for heated air to flow up and out (while the other lower vents let cooler air in) still makes a difference.

I expect t's not such a big deal now, after the post-fire rebuild, as there's a lot more insulation both in the walls and above the cieling, but before that it made anywhere from a handful of degrees to more than a couple of dozen degrees on main house temperature, for the times when they were non-operational.

Once was when my mom was still around, and had me go up there and cover them up because she was sure they were making the house hotter by letting hot air blow in (yeah, I know), and once years later when they broke from high winds in a storm, one having to be covered up to keep potential rain out of it's remains and the other simply not working cuz it's top bearing was broken apart, until they could be repaired/replaced.

The biggest temperature increase was from the first, completely covering them so no heat could go out the top of the roof via internal air flow. The other time when only one was covered and the other could still be a vent if not a fan, there was much less of a difference (relative to the actual temperatures involved).

I don't have the actual numbers anymore, cuz I wasn't posting here on ES then and none of my notebooks and such from then exist anymore, even if I wrote them down (which I probably did, but I don't remember), so I only have my fallible memory to go from, for the several days length of unintended experiment each time it happened.




I looked at some of the other info you linked to in the OP, though, and peeked around at the various vents on the house.

There's only one under-roof-edge vent left, and I can't see into it well; it sort of looks like it is no longer able to feed into the attic; I think it is covered from the inside by the added insulation. It's near the northeast corner of the house.

There is possibly another path in above the breaker box, though, because they never installed any boards over the area where they had to take out the old support/anchor for the AC line from the pole and install a new one (which looks identical so I dunno why they had to replace it), so the rafter ends out past the wall are exposed, and I can see at least a little bit inside where the insulation is. Dunno if any air can actually get in there.

The two "gable vents" (really not on actual gables but are rooftop vents too, one on west end and one on east end) might be blocked, too, can't see into them from the ground.

I can't get up into the crawlspace up there these days; it's way too hot in the daytime when I could see the vents by light from outside if they're not blocked. Have to wait a few months...


So unless the "gable vents" are open, then those other rooftop windpowered vents are probably not even doing anything right now, really--so it might be possible to have an even cooler house if there *was* more airflow up there. :?

 

[dnmun]

we had attic fan in louisiana and it would blow the hot air out of the attic when the air it sucked out of the inside displaced the hot air in the attic. we had big wide awnings to keep the direct sun out of the room and we had a big screen porch in back that had a big ceiling fan and we were able to cope.

in fact when we moved into a modern house with A/C it was stuffy and hot because my dad was too cheap to run the A/C 24/7 like everyone does now.

 

[LockH]

BTW. Watched those vids and oddly maybe no mention of roof turbine vents (big fan of wind (solar) power here).

http://www.youtube.com/watch?v=iavtcaPNLoY

Personally, I think that attic turbine vents are a scam at best, something people try to sell to you trying to convince you you need something when you don't. At worst they (the powered ones) are a fire hazard.

Ooops. My bad. (The reason why I write anything online in the hope that folks will expound/elaborate/shred what I have said.)

And yeah. Wasn't thinking actually electrically powered (energy cost, etc.).

And currently sitting in 30+C temps in front of a column-shaped rotating electric rotary fan.

Not sure that ice buildup much of a worry in a tropical environment though. :wink: And do have a tin of oil handy re my vehicle(s). (Probably ain't much that doesn't come with SOME sort of maintenance "built in".

But (oh oh... yah, I know or can guess) was thinking using wind (free solar) energy for SOME sort of moving air like a ceiling fan? Like the dutch use for windmills?

(Above actually "Dutch" but in England, in their "Broads".)

Amusing to read here:
https://en.wikipedia.org/wiki/The_Broads#History

"The Cathedral took 320,000 tonnes of peat a year. Then the sea levels began to rise, and the pits began to flood. Despite the construction of windpumps and dykes, the flooding continued..."

Rising sea levels a topic even today.

 

[will_newton]

Hey bowlofsalad, I didn't mean off topic in a literal sense, just most non sequitur in the general selection of topics one might expound on. I actually care a great deal about roof ventilation!

Your comments about more insulation as solution to humidity problems are spot on. I have a rental house that had a constant moisture issue in the hallway near the attic access. It was so bad you would have thought it was raining in the house. The hot,humid attic air would heat the door, which heated the air on the interior side. It was a three foot square micro-climate. This air mixed with the conditioned interior air creating condensation. The problem was solved by insulating the access door itself.

Also, I can personally vouch for the danger of those damned gable vent fans. While I was at work my wife called the Fire Dept because she was smelling something unusual in the house. They showed up with a FLIR camera and scanned the attic. The vent fan was insanely hot and was causing the dust collected on it to start smoldering. I think we were lucky she was home that day.

I also have fond childhood memories of the gigantic whole house vent fan at my grandmother's house. She would turn it on and all the grandkids would pretend it was a tornado. We would get in trouble for throwing things at the ceiling to see if it would suck up to the grate and hopefully through it to be chewed into shreds. Good times.

Here's that skyscraper you won.