Thread: Proper attic ventilation in Florida

The typical method for ventilating the attic on an average home is soffit and ridge vent. I come across many homes that originally had soffit venting and wind turbines at the peak but continuous ridge venting was added later during a re-roof. I suspect the thinking was the more the better. I've read where this disrupts the natural flow up from the soffits due to old turbines and new ridge vent pulling in air from each other. My main question is, do most HI's comment on this or just let it go. I could use some opinions and if you do comment; an example would be appreciated. Pay no attention to W.H. gas flue near vents; it is now electric.

Mark,

Would you charge your location from just "Florida" to a place in Florida ... a city is best, but a county would help.

Allows us to provide better answers to questions when we know more of "where" you are. Florida is a big place and conditions change over the length of Florida - things change from south Florida places to central Florida places to north Florida places to Panhandle places.

Even if you inspect in multiple counties, providing the main or centralized city/county helps.

Thanks

Originally Posted by Jerry Peck

Mark,

Would you charge your location from just "Florida" to a place in Florida ... a city is best, but a county would help.

Allows us to provide better answers to questions when we know more of "where" you are. Florida is a big place and conditions change over the length of Florida - things change from south Florida places to central Florida places to north Florida places to Panhandle places.

Even if you inspect in multiple counties, providing the main or centralized city/county helps.

Thanks

I'm in central Florida just west of Ocala, I went to profile and it only asks for the state, not sure if I got it right but will work on it. I've been studying on this forum for some time and going out with a few inspectors in the area and really appreciate all the help. My background is an amateur home builder (I'm currently in sales) other than that, no background. I think I missed my calling as I've always had a thing for houses. Not sure if I'm going for full inspector yet. I've learned and know a lot but not everything. I've built three homes from scratch for our personal use subbing out only the concrete, HVAC and once setting trusses on a two story so you'd think I would be ready. Smart enough to know that inspecting is whole different animal. The home I'm working on now will be the first where I've done the foundation, got it all ready for concrete crew to do the pour. We ran across this home with the turbines and I asked the inspector about it. He started thinking and said he wasn't sure so thought I'd run it passed the experts.

I like ridge venting a lot. Turbines may draw some air from the ridge, but so what? You still have convection circulation. Air is still being drawn through the soffit vents. "Ventilation appears serviceable", and move on.

A funny thing happened at a fix n flip on Thursday. There wasn't a shred of attic ventilation. It wasn't a conditioned space. The flipper had put on a new composition roof in addition to some extensive roof repairs, including replacing all the insulation in the attic. His GC told me that attic ventilation isn't required. So, here I go again, having to look up the code reference to attic ventilation. HIs should not and cannot be code enforcers, IMO. It's not a job that any of us should want, but sometimes, when a licensed pro tells you that you're wrong, you have to prove yourself. I emailed the code reference to the flipper and his GC. The flipper sent me a thank you. No comment yet from the GC.

Mark,

Where the location asks for state, type your location there - I typed "Ormond Beach, Florida" there.

Wind turbines have never been an approved ventilation opening method.

The house likely had soffit vents only - soffit vents only has been a long accepted ventilation method.

The wind turbines were likely homeowner added at some point.

The ridge vent may have been added by the roofer or may have just been replaced by the roofer.

If added by the roofer the opening is likely not correct - the opening is likely too wide ... too narrow ... or they likely set the blade too deep and cut into the top chords.

The ridge vent itself may have been installed incorrectly.

The wind turbines should be removed. When high winds come, that turbine top is supposed to be removed and replaced with a cap which is secured to the turbine body.

Originally Posted by Jerry Peck

Mark,

Where the location asks for state, type your location there - I typed "Ormond Beach, Florida" there.

Wind turbines have never been an approved ventilation opening method.

The house likely had soffit vents only - soffit vents only has been a long accepted ventilation method.

The wind turbines were likely homeowner added at some point.

The ridge vent may have been added by the roofer or may have just been replaced by the roofer.

If added by the roofer the opening is likely not correct - the opening is likely too wide ... too narrow ... or they likely set the blade too deep and cut into the top chords.

The ridge vent itself may have been installed incorrectly.

The wind turbines should be removed. When high winds come, that turbine top is supposed to be removed and replaced with a cap which is secured to the turbine body.

Didn't know about the caps, never seen one before, good info. Still though; I've read that an older home with just gable vents was retro-fitted with soffit and ridge venting and the gable vents were not closed off. The new ridge vent pulled in air from the gables which diminished the flow up from the soffit vents leaving the lower section of the attic not vented as well as it would be. The same article noted what you see in the photo and it stated that the ridge and turbine vents will pull in air from one another causing the same effect. Maybe I'm over thinking or getting too technical on this. Just wondering what others might say in their reports when they run across multiple venting types other than standard soffit and ridge. BTW; wind turbines are very common here (older homes) and are generally used in conjunction with soffit vents w/o ridge venting.

Originally Posted by mark petty

BTW; wind turbines are very common here (older homes) and are generally used in conjunction with soffit vents w/o ridge venting.

Wind turbines are quite common in many places ... until a high wind event come through, Florida has it share of tornadoes and more than its share of hurricanes - either will tear those turbines off the roof, leaving a big hole in the roof through which bad things can happen (nothing good can happen with a 12" or 14" hole through the roof).

With soffit vents only, the required minimum net free vent area is twice that of soffit and ridge or off ridge vents, I would not even add wind turbines into the venting area calculation.

Thanks for updating your location, it helps.

This is the 2006 Georgia code (the 2006 IRC, I did not find any Georgia amendments affecting this section): (bold is mine)
- R602.8 Fireblocking required. - - Fireblocking shall be provided to cut off all concealed draft openings (both vertical and horizontal) and to form an effective fire barrier between stories, and between a top story and the roof space. Fireblocking shall be provided in wood-frame construction in the following locations.
- - - 1. In concealed spaces of stud walls and partitions, including furred spaces and parallel rows of studs or staggered studs; as follows:
- - - - 1.1. Vertically at the ceiling and floor levels.
- - - - 1.2. Horizontally at intervals not exceeding 10 feet (3048 mm).
- - - 2. At all interconnections between concealed vertical and horizontal spaces such as occur at soffits, drop ceilings and cove ceilings.
- - - 3. In concealed spaces between stair stringers at the top and bottom of the run. Enclosed spaces under stairs shall comply with Section R311.2.2.
- - - 4. At openings around vents, pipes, ducts, cables and wires at ceiling and floor level, with an approved material to resist the free passage of flame and products of combustion.
- - - 5. For the fireblocking of chimneys and fireplaces, see Section R1003.19.
- - - 6. Fireblocking of cornices of a two-family dwelling is required at the line of dwelling unit separation.

- R1003.19 Chimney fireblocking.
- - All spaces between chimneys and floors and ceilings through which chimneys pass shall be fireblocked with noncombustible material securely fastened in place. The fireblocking of spaces between chimneys and wood joists, beams or headers shall be self-supporting or be placed on strips of metal or metal lath laid across the spaces between combustible material and the chimney.


R1003.19 reconfirms what is stated in R602.8, 1. & 2.

Jerry,
I'm curious as to why you posted Georgia code.

"Wind turbines are quite common in many places"

The Michigan HVAC instructor many years ago called them politely "chicken coop" ventilators. Here in the Midwest there is either too little breeze to make them worthless or on the other extreme 40 mph gusts making them not needed. Never the perfect breeze and often they would be seized up for one reason or another.

Originally Posted by Rick Cantrell

Jerry,
I'm curious as to why you posted Georgia code.

Rick,

Because I was thinking of another post from a question on another thread from Georgia ... OOPS! ... Me Bad.

If you noticed, the content of the code was for the question regarding fireblocking from person in Georgia ... Double OOPS! as I somehow managed to posted it in the wrong thread too.

I keep saying that I've made mistakes before and that I will make them again ... and this was definitely a mistake - posting the answer in the wrong thread.

Originally Posted by mark petty

The typical method for ventilating the attic on an average home is soffit and ridge vent. I come across many homes that originally had soffit venting and wind turbines at the peak but continuous ridge venting was added later during a re-roof. I suspect the thinking was the more the better. I've read where this disrupts the natural flow up from the soffits due to old turbines and new ridge vent pulling in air from each other. My main question is, do most HI's comment on this or just let it go. I could use some opinions and if you do comment; an example would be appreciated. Pay no attention to W.H. gas flue near vents; it is now electric.

To respond to your main question Mark - I always have recommended only having one type of upper vent, such as the ridge vent in your photo. If another type of vent is also present (can, gable, turbine), they should be blocked off so in the end there is only a ridge vent and soffit vents. Yes, you have read correctly that multiple types of upper vents will disrupt the tendency for air to be pulled into the soffit vents and exhausted out of the upper vents. If the present roofing has a decent amount of remaining life I usually suggest covering the other vent openings from inside the attic with plastic, to stop air flow through them.

Originally Posted by B vanderhoof

Yes, you have read correctly that multiple types of upper vents will disrupt the tendency for air to be pulled into the soffit vents and exhausted out of the upper vents.

What evidence do you have for this claim?

Originally Posted by Lon Henderson

What evidence do you have for this claim?

Hi Lon, My reasoning is formed from reading various reports and studies on the topic over the years and searching for concepts that appear true and logical. Regional climate differences and differences in how a home is constructed make this not a one size fits all issue - so perhaps the thinking in Florida would be a bit different than mine. In the end - all the information I see says that an attic works best ,overall, if air enters at the soffits and washes all the way up and out a ridge vent. If I also have a turbine vent near the ridge, spinning in the breeze and making a suction, a large amount of it's air will be pulled thru the ridge vent - that will compete with or lessen the draw from the soffit up the plane of the roof.

Originally Posted by B vanderhoof

Hi Lon, My reasoning is formed from reading various reports and studies on the topic over the years and searching for concepts that appear true and logical. Regional climate differences and differences in how a home is constructed make this not a one size fits all issue - so perhaps the thinking in Florida would be a bit different than mine. In the end - all the information I see says that an attic works best ,overall, if air enters at the soffits and washes all the way up and out a ridge vent. If I also have a turbine vent near the ridge, spinning in the breeze and making a suction, a large amount of it's air will be pulled thru the ridge vent - that will compete with or lessen the draw from the soffit up the plane of the roof.

I am not able to envision how hot air running up the underside of the roof sheathing is blocked by a low pressure created by a turbine or fan. I would have to see a smoke demonstration before I could be convinced. The unscientific studies I have made, measured by sweat in the eyes, suggest the more holes in the roof the better.

Originally Posted by Vern Heiler

The unscientific studies I have made, measured by sweat in the eyes, suggest the more holes in the roof the better.

Except gable vents in gable ends.

With gable vents, one allows air to be pushed in by positive pressure of the wind and the other one allows air to be drawn out by negative pressure on the other end of the gable roof - that air 'blowing through' the attic can disrupt the natural ventilation cycle created by low soffit vents and high ridge or off ridge vents.

The code only addresses soffit vents and ridge vents / off ridge vents as as: (bold and underlining are mine)
- 2012 IRC
- - R806.2 Minimum vent area.
- - - The minimum net free ventilating area shall be 1/150 of the area of the vented space.
- - - - Exception: The minimum net free ventilation area shall be 1/300 of the vented space provided one or more of the following conditions are met:
- - - - - 1. In Climate Zones 6, 7 and 8, a Class I or II vapor retarder is installed on the warm-in-winter side of the ceiling.
- - - - - 2. At least 40 percent and not more than 50 percent of the required ventilating area is provided by ventilators located in the upper portion of the attic or rafter space. Upper ventilators shall be located no more than 3 feet (914 mm) below the ridge or highest point of the space, measured vertically, with the balance of the required ventilation provided by eave or cornice vents. Where the location of wall or roof framing members conflicts with the installation of upper ventilators, installation more than 3 feet (914 mm) below the ridge or highest point of the space shall be permitted.

Gable roof vent system must meet the 1/150.

Soffit vent and ridge vent / off ridge vent systems only need to meet 1/300 IF 40% to 50% (no less than 40%, no more than 50%) of the REQUIRED vent area is at or within 3 feet of the ridge (or highest point), which means that 50% to 60% (no less than 50%, no more than 60% of the REQUIRED vent area is down at the soffits. Keep in mind, the 40% to 50% is of the REQUIRED vent area - you could have continuous soffit venting with as much ventilation as you wanted as long as the REQUIRED vent area at or within 3 feet of the ridge meets the 40% to 50% requirement.

Also, that is referring to "minimum net free ventilating area" which means you need to deduct for the screening, any louvers, any other blockage or restriction of the actual open area ... but that is a calculation which home inspectors are not expected to make - just use your judgement in guestimating the vent areas - many times your guestimate will be that the vent areas are too little ... and you will likely be correct that the vent area does not meet the requirements.

Originally Posted by Jerry Peck

Except gable vents in gable ends.

With gable vents, one allows air to be pushed in by positive pressure of the wind and the other one allows air to be drawn out by negative pressure on the other end of the gable roof ......

So what? Its all outside air ventilating the attic space. The more goesinta and goesouta the better!

Originally Posted by Vern Heiler

So what? Its all outside air ventilating the attic space. The more goesinta and goesouta the better!

Let's see ... wind blows in one gable end, through the attic, and out the other gable end ... wait ... the hot air down in the lower part of the attic is still there - that is why you don't want gable ends with soffit vents.

Originally Posted by Jerry Peck

Let's see ... wind blows in one gable end, through the attic, and out the other gable end ... wait ... the hot air down in the lower part of the attic is still there - that is why you don't want gable ends with soffit vents.

So the hot,lighter air, won't continue to rise or mix with the cooler heavier air that is blowing through the attic creating turbulence? Really

Originally Posted by Vern Heiler

So the hot,lighter air, won't continue to rise or mix with the cooler heavier air that is blowing through the attic creating turbulence? Really

Nope - won't mix and remove the hot air at the bottom AS INTENDED ... would you paint your house with only partially stirred and mixed paint ... or would you want the paint mixed AS INTENDED?

Originally Posted by Jerry Peck

Nope - won't mix and remove the hot air at the bottom AS INTENDED ... would you paint your house with only partially stirred and mixed paint ... or would you want the paint mixed AS INTENDED?

With the wind blowing through the attic, over rafters, floor joists, etc. and the natural rise of hot and fall of cool air, the paint (air) is more well mixed than with air channeled up rafter bays only.

Originally Posted by Vern Heiler

With the wind blowing through the attic, over rafters, floor joists, etc. and the natural rise of hot and fall of cool air, the paint (air) is more well mixed than with air channeled up rafter bays only.

The most efficient way for soffit vents and ridge vents / off ridge vents to work is to not disrupt the natural flow of hot air up (hot air rises, the gable vent air flow will disrupt that flow and blow some of the lower air back down.

I can see that you like swirls and varying colors on your house ... so be it.

Originally Posted by Jerry Peck

The most efficient way for soffit vents and ridge vents / off ridge vents to work is to not disrupt the natural flow of hot air up (hot air rises, the gable vent air flow will disrupt that flow and blow some of the lower air back down.

I can see that you like swirls and varying colors on your house ... so be it.

Efficient! I'm not concerned with saving the energy used to move air in this case. The maximum CFM's that can escape the attic is dependent on the size of the openings it must pass through and can be seen being backed up at the ridge vent by measuring the temp at the soffit compared to the temp at the ridge vent. On a calm day the extra vents mean less resistance and more volume that can escape. On a windy day, if some of the hot air is mixed with cooler air and blown or sucked out of the attic before it can reach the ridge, all the better.

Originally Posted by Vern Heiler

The maximum CFM's that can escape the attic is dependent on the size of the openings it must pass through ...

That is only one part of the equation ... the sizes and number of the openings does not cause air to move from place to place, that only allows the air to move from one place to another place.

Originally Posted by Jerry Peck

That is only one part of the equation ... the sizes and number of the openings does not cause air to move from place to place, that only allows the air to move from one place to another place.

.......like from inside the attic to outside the attic

I'm not surprised that no one has presented an actual study demonstrating how best to ventilate attics (no doubt different for different attic styles and areas of the country). I've tried to find some studies. But all I find are claims and recommendations without evidence to support those claims and recommendations. I agree that common sense has some merit in this area, but it would be nice to actually see some fact based recommendations. The code requirement for 1/300 is a back of the napkin calculation based on experience and observations.