attic ventilation

Leah4 · #1 Sep 30, 2009, 02:41 PM

When you go into your attic during the day, should you see light or should it be completely dark? Also how much light should you see out of your roof vents? How many roof vents should you have for a 1575 square foot home?
Thanks
Leah

dhatura · Oct 5, 2009, 07:31 AM

what kind of roof vents are they? that could cause a huge difference of the amount of light seen. Some are fully enclosed so you may not see any light and some allow light to flood in. Where do you live? Climate can also have a huge impact on the type and ammount of ventilation you may need.

Leah4 · Oct 5, 2009, 05:00 PM

I have 4 roof louvers on the living space side and 2 over the garage. I also have baffles every 8 feet from the soffit vents. On the north side of my house, when we took off the soffits there was batt insulation rolled where the soffit meets the roof so the air that enters the soffit area has no where to go. We are adding more baffles and removing some of the batt insulation because no air can enter the attic. We live in Nebraska so there are very cold winters and hot summers. Could this be the problem of the walls freezing on the north side since the outside air is trapped between the soffits and the insulation?

dhatura · Oct 5, 2009, 05:17 PM

sounds like what you really need is roof exhaust fans set on a theromstat, so they stay shut in the winter and only turn on in the summer when it is hot.as far as soffit vents... do you have plugs, continuous strips or perforated aluminum or vinyl soffit? also, on the gable ends, stuff some insulation in the gable studs at the joists for the bottom 2'.

dhatura · Oct 5, 2009, 06:22 PM

yes, but the summer is the only time the air needs to be PULLED out with the humidity in the summer. there is still good circulation year round with the soffit vents and louvers. just so it has a little something extra for those hot muggy days, so moisture doesn't sit on the wood and cause another mold problem. The fans actually force the air to circulate pulling air from the soffit vents to the rooftop.

cyberheater · Oct 8, 2009, 04:15 AM

Attic fans are not always necessary, and insulation plus vapor barrier is important with the right ventilation.

Without a pic, I may be misunderstanding you.
You are correct when you want to have air/venting at the soffit, and you do not want to block that area with insulation. Idea is to keep the conditioned space warm air (or cool air from the airconditioner in the summer) from reaching the attic air and causing more moisture problems when different temps collide.

At the point where I think you are talking about - where the roof sheathing meets the ceiling joists - is where you are concerned with? It sounds like it.

Adding more baffles at this point cannot hurt and will help the air from outside from the soffit vents along the sheathing of your roof.
Removing the insulation blocking that air from the existing soffits is also important as you state. It sounds like you know the problem and are trying to correct it.

Ballanger's method of removing the insulation to a point at where it first meets the rafter has also been done. Usually, this is where the wall below (ext. framed wall) is located. I have seen this done when there are no baffles and you can see a space where the air comes in from the eaves or soffit.

I do and have installed baffles and like them because it not only provides an area for the air to flow, but at that location where the ceiling is so close to the rafters on the outside wall, it adds one more layer of protection from warm air (or cold from air cond in summer) from hitting that point.

Ballenger says that all insulation blocking at point (the rolled up insulation you found) should not be there at all. What you found, I believe, was attempt to block cold air.

Just add more baffles like you orginally thought and remove that insulation blocking the air to them.

If you consider an attic fan, there is more to consider. Sometimes attic fan can draw up more air then is good. There are many more things to consider with that and do not do this without looking at cfms, and how much that attic fan draws.

If you can do the job without one, your ahead of the game.

Leah4 · Oct 8, 2009, 11:50 AM

We have blown in insulation in our attic, do you need a vapor barrier between the drywall and the blown in insulation? What type of vapor barriers are used in the attic. In this first photo shows the baffles stuffed by insulation and this is every 8 feet. The second photo shows where our bathroom exhaust vents and they have insulation stuffed above the area without any baffles. On the inside walls of my bathroom is where I have areas that are 35 degrees in the winter and will freeze.