Attic Insulation at Eaves

[Jim Robinson]

When there are soffit vents, it is important not to block them with insulation. I have a client who is insulating his attic with blown in insulation of some type. It's not a foam type. I think it's fiberglass, but not sure. There are no soffit vents in his house. I know that's a different topic, but that's not the question. His question is if it is okay to insulate tight to eaves, since there isn't going to be any air flow up and over the insulation anyhow. There are gable vents at each end, three in total. My instinct is that there should be an air space or baffle, but I can't back it up with any logic. There will be a temperature difference between the roof decking and the attic ambient temperature, but that will also exist if there is an air space or a baffle. The main thing in my mind is that if there is any condensation at the eaves, the insulation will trap it and prevent it from evaporating due to air flow via the gable vents.

Any thoughts? I tried to look through Dr. Joe's stuff, but he didn't seem to address this situation.

[Billy Stephens]

When there are soffit vents, it is important not to block them with insulation. I have a client who is insulating his attic with blown in insulation of some type. It's not a foam type. I think it's fiberglass, but not sure. There are no soffit vents in his house. I know that's a different topic, but that's not the question. His question is if it is okay to insulate tight to eaves, since there isn't going to be any air flow up and over the insulation anyhow. There are gable vents at each end, three in total. My instinct is that there should be an air space or baffle, but I can't back it up with any logic. There will be a temperature difference between the roof decking and the attic ambient temperature, but that will also exist if there is an air space or a baffle. The main thing in my mind is that if there is any condensation at the eaves, the insulation will trap it and prevent it from evaporating due to air flow via the gable vents.

Any thoughts? I tried to look through Dr. Joe's stuff, but he didn't seem to address this situation.

I would recommend installing soffit vents.
*if none are present blown in is installed all the way to the edges of the attic area.

[Mike Lamb]

I would recommend installing soffit vents.
*if none are present blown in is installed all the way to the edges of the attic area.

.Why?

[Billy Stephens]

.Why?

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

Of the two camps concerning attic ventilation. I subscribe to balanced vented. Soffit, Ridge and gable as a personal choice. Do you prefer a closed in attic with no ventilation?

[Jim Robinson]

Let's accept that there are no soffit vents, and there are not going to be any. We can argue that topic in another thread. Would you be concerned about condensation occurring where the insulation is touching the underside of the roof decking where there are no soffit vents? Any field experiences? I've seen mold where they were relying on the soffit vents, which were blocked.

[Billy Stephens]

Would you be concerned about condensation occurring where the insulation is touching the underside of the roof decking where there are no soffit vents?

Nope.

Why would condensation be more likely there than on any other place on the decking?
*the blocked vents are the source of moisture.

[Raymond Wand]

Ventilation Calculator Based on U.S. VA/FHA Guidelines


GAF | Attic & Roof Ventilation Calculator (http://www.gaf.com/Roofing/Residential/Products/Roof_Vents/Ventilation_Calculator)

[Jerry Peck]

If there are no soffit vents now and no soffit vents are going to be added, then one can either insulate to the outside plane of the exterior wall (as a minimum) or insulate out over the soffits, albeit that is a waste of insulation.

I would not recommend soffit vents, ridge vents and gable vents as combination, however, I would recommend soffit vents and ridge vents, or soffit vents and gable vents.

[Billy Stephens]

I would not recommend soffit vents, ridge vents and gable vents as combination,

Don't see a lot of in line gable vents. Agree if the gable vents have meaningful cross ventalation.

[Jerry Peck]

Don't see a lot of in line gable vents. Agree if the gable vents have meaningful cross ventalation.

gable vents and ridge vents don't go together anyway. Gable vents only are so-so, ridge vents only are almost useless, soffits only work as long as additional soffits are install too meet the increased required, soffit vents and ONE gable vent work (multiple gable vents in the same attic area will negate the usefulness of the soffit vents), but not as well as soffit and ridge vents.

[Billy Stephens]

gable vents and ridge vents don't go together anyway.

I like em. :D

[Eric Barker]

Jim, To your specific question and ventilation aside - in my experience insulation in contact with the sheathing is not a problem.

[Mike Lamb]

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

Of the two camps concerning attic ventilation. I subscribe to balanced vented. Soffit, Ridge and gable as a personal choice. Do you prefer a closed in attic with no ventilation?

I cannot easily explain attic ventilation as a science regardless of what Airvent or code says. It can be confounding.

I have found that large gable end louvers (usually in pre-1960 older houses) at each side of the house with no other vents, with or without good insulation nearly always produces a dry attic. I am pro gable end venting.

I will never mess with an old attic ventilation system that isn't broke.

[Raymond Wand]

Why fix that which is not broken? If current conditions indicate there are no condensations stains, et cetera, it seems to me changing the ventilation by adding soffits is not going to improve much of anything.

As Eric pointed out its common to see insulation touching the underside of the decking.

[John Kogel]

I would look for light at the soffits with the flashlight turned off. There is sometimes a big crack or two in the eaves area. If so, I would leave a gap between the sheathing and the insulation.
But every climate and microclimate will have its own requirements, as Mike said. It could be complicated or simple.

[Eric Barker]

I would look for light at the soffits with the flashlight turned off.

I completely agree. If I don't see daylight then I have no reason to believe that there is proper airflow from the soffit vent.

[Jerry Peck]

I completely agree. If I don't see daylight then I have no reason to believe that there is proper airflow from the soffit vent.

Even seeing daylight does not provide reason to believe that there is proper air flow from the soffit vent.

All seeing daylight tells you is that at least some of the soffit venting is open, not how much is open or how much is there, thus I would not use the word "proper" to describe the amount or direction of air flow.

[Richard Burkard]

Even seeing daylight does not provide reason to believe that there is proper air flow from the soffit vent.

All seeing daylight tells you is that at least some of the soffit venting is open, not how much is open or how much is there, thus I would not use the word "proper" to describe the amount or direction of air flow.

The reason why soffit vents and ridge vents work together well is because when the outside air is still or blowing, air is drawn in the soffit vents, heats up and vents out the ridge vent. Gable only vents work properly only when the wind blowing. You could put a thermostate controlled attic fan in a gabe end to make it work more efficeintly. Insulating the soffits won't do a thing for you, but it won't hurt you either, other than your pocket book.

[Jerry Peck]

The reason why soffit vents and ridge vents work together well is because when the outside air is still or blowing, air is drawn in the soffit vents, heats up and vents out the ridge vent. Gable only vents work properly only when the wind blowing.

The reason soffit, gable, and ridge vents do not work well together (using all three types of ventilation) is that the gable vents short-circuit the effect of the soffit vents.

[Billy Stephens]

The reason soffit, gable, and ridge vents do not work well together (using all three types of ventilation) is that the gable vents short-circuit the effect of the soffit vents.

Not if the gable vents are exhausting the heated attic air.

*soffit vents up drafting out the gable and ridge vents.

[Jerry Peck]

Not if the gable vents are exhausting the heated attic air.

*soffit vents up drafting out the gable and ridge vents.


The gable vents will short circuit that by allowing air in and up to and out the ridge vents ... unless, of course, there were gable vent EXHAUST fans installed and operating all the time, then, sure, the air would be exhausting out through the gable end vents, the air would be coming in through the soffit vents AND the ridge vent, but, sure ... that would still work ... but no one was talking about having gable exhaust fan installed, much less operating all the time. :)

[Billy Stephens]

The gable vents will short circuit that by allowing air in and up to and out the ridge vents ... unless, of course, there were gable vent EXHAUST fans installed and operating all the time, then, sure, the air would be exhausting out through the gable end vents, the air would be coming in through the soffit vents AND the ridge vent, but, sure ... that would still work ... but no one was talking about having gable exhaust fan installed, much less operating all the time. :)

Jerry, Jerry,Jerry,

Hot air expands and rises. It doesn't care what the opening in the building envelope is called to exit the space. Cooler air will be drawn in from the bottom. If no soffit vents are present then this air could be drawn from and depressurize the conditioned space.

[Jerry Peck]

Jerry, Jerry,Jerry,

Hot air expands and rises. It doesn't care what the opening in the building envelope is called to exit the space. Cooler air will be drawn in from the bottom. If no soffit vents are present then this air could be drawn from and depressurize the conditioned space.

Billy, Billy, Billy,

Hot air expands and rises. It doesn't care what the opening in the building envelope is called to exit the space, so it exits the ridge vent ... but it does not care that it is called "the ridge vent", the hot air just exits there ... and in exiting there some of the replacement air is drawn in through the LOWER gable vents ... but it does not care that these are called "gable vents" instead of "soffit vents" ... all it cares is that the ridge vent is higher and the gable vent is lower and hot air rises --- just like you said.

The above is on a still day, however, on this day we have a slight breeze ... and it blows INTO the gable vents and in doing so some air makes it across the attic and out the other gable vent, some air makes it up and out the ridge vents, and, yes, some air may even make it down and out the soffit vents if the breeze is strong enough or gusty enough to pressurize the attic and cause the air in the attic to go out any opening it can find. And, yes, this air can also pressurize the conditioned space through all of the openings in the attic, but that is another discussion for another time and day.

Now, with no breeze and with ONLY soffit and ridge vents ... the hot air will rise from the soffit vents and exit the ridge vents ... but the house does not care what we humans happen to have chosen to call those vents ... that is the way it works.

On a breezy day and with ONLY soffit and ridge vents ... the breeze will blow some air in the soffit vents, and even blow some air across the attic and out other soffit vent and some air up and out the ridge vents, heck, for ridge vents without baffles sometimes the breeze will blow air IN through and down into the attic from the ridge vents - but that upsets the normalcy of the air flow equation.

Now, if one wants to depressurize the living space below the ceiling ... install a powered EXHAUST fan for the attic, it will exhaust the attic air quite well, and also draw some of the air from inside the house into the attic depressurizing the living space within the house such that air from outside will be drawn into the living space ... all in an effort to balance the pressures outside, inside, and in the attic.

[Billy Stephens]

Billy, Billy, Billy,

Hot air expands and rises. It doesn't care what the opening in the building envelope is called to exit the space, so it exits the ridge vent ... but it does not care that it is called "the ridge vent", the hot air just exits there ... and in exiting there some of the replacement air is drawn in through the LOWER gable vents ... but it does not care that these are called "gable vents" instead of "soffit vents" ... all it cares is that the ridge vent is higher and the gable vent is lower and hot air rises --- just like you said.

The above is on a still day, however, on this day we have a slight breeze ... and it blows INTO the gable vents and in doing so some air makes it across the attic and out the other gable vent, some air makes it up and out the ridge vents, and, yes, some air may even make it down and out the soffit vents if the breeze is strong enough or gusty enough to pressurize the attic and cause the air in the attic to go out any opening it can find. And, yes, this air can also pressurize the conditioned space through all of the openings in the attic, but that is another discussion for another time and day.

Now, with no breeze and with ONLY soffit and ridge vents ... the hot air will rise from the soffit vents and exit the ridge vents ... but the house does not care what we humans happen to have chosen to call those vents ... that is the way it works.

On a breezy day and with ONLY soffit and ridge vents ... the breeze will blow some air in the soffit vents, and even blow some air across the attic and out other soffit vent and some air up and out the ridge vents, heck, for ridge vents without baffles sometimes the breeze will blow air IN through and down into the attic from the ridge vents - but that upsets the normalcy of the air flow equation.

Now, if one wants to depressurize the living space below the ceiling ... install a powered EXHAUST fan for the attic, it will exhaust the attic air quite well, and also draw some of the air from inside the house into the attic depressurizing the living space within the house such that air from outside will be drawn into the living space ... all in an effort to balance the pressures outside, inside, and in the attic.

Jerry,

Think volume not trickle. Large area of hot air flooding out of a space not an orderly trickle.
Small slits verses a large hole the volume of air will exit at the least resistance. As the pressure builds at the ridge vent the hot air will find other points of exit. That's out not in.:D

I will agree on the powered exhaust fan pulling the conditioned air up and out of the dwelling.

[Jerry Peck]

Think volume not trickle.

Billy,

Think breeze, not still air.

Most places have moving air (breeze, wind, storm) much more often and for far longer periods than they have still air.

Moving air will blow into gable vents - in one ear ... er ... gable vent ... and out the other. :)

[Billy Stephens]

Billy,

Think breeze, not still air.

Most places have moving air (breeze, wind, storm) much more often and for far longer periods than they have still air.

Moving air will blow into gable vents - in one ear ... er ... gable vent ... and out the other. :)

That's a good thing. Then the hot air is evacuated which is the Goal.

Having multiple avenues for the attic to vent is a good thing.

I still like soffit, gable and ridge vents.:D

[Jerry Peck]

I still like soffit, gable and ridge vents.:D

And I still like Buddy Holly, The Big Bopper, Richie Valens, and the Beatles. :biggrin:

[Billy Stephens]

And I still like The Big Bopper, ........ :biggrin:

Yeah I can see the resemblance. :p

The Big Bopper - Purple People Eater Meets the Witch Doctor - YouTube (http://www.youtube.com/watch?v=ae0u5PZCbn0)

The Big Bopper - Chantilly Lace - YouTube (http://www.youtube.com/watch?v=6_smW8lBL_0)

[Jerry Peck]

Yeah I can see the resemblance. :p

Hey, I still had some brown in my hair then. Cool.

Not sure why I had that look on my face, no one was in the house with me to bother me ... I think I recall that house, I was there 4-5 days as I recall ... hmmmm ... maybe that is why I had that look - 'oh no, not something else to write up' (as I recall the stairs were 12' 6" from floor to floor, and we all know that the maximum height is 12' ... bummer with a stair like that :dance: ).

And that was not a mirror I was looking into, that was a highly polished marble wall or something, but not a mirror.

[Ludwig Maxwell]

Here in Tampa Bay Florida, Roofs with all three vent systems have the longest shingle life, surprisingly 10 to 15 years. The less air movement, the sorter shingle life. I have not found any new or old home with soffit and ridge vents system moving sufficient air (flow) to reduce attic temp in what I call safe range of 15 degree above outside temp.

The homes with all three type vents (soffit, gable, and ridge vents) still have a hot spot in the center of the home.