Ridge Vent / Soffit Vent Question

[toshradio]

Greetings:

I bought a 30 year old house with absolutely NO ventilation in the attic, which is about 1000 square feet.

This summer, I spent a few days with a hole saw drilling into the soffits. Every 4 feet, I drilled three holes (two and a quarter inch diameter) and covered it with a vent. This had to go not only through the vinyl, but also through a wooden soffit that was underneath the vinyl.

Then, in the attic, I inserted and stapled styrofoam baffle vents into the eaves where I had drilled the holes allowing for the air to come through. All tested OK as cool air came through.

Questions - for the size of the attic, was this enough, too much, or too little ventilation? My brother in law is a contractor, and he is coming in shortly to do the ridge vent, presumably along the entire length of the house.

AND, I was only able to vent about 75% of the soffits to date, as some of them were too high for me to use a ladder safely (prone to vertigo!) Should the entire perimeter of the attic be vented? At present, all of the shadier side of the house is vented, with about half of the sunnier side.

Thanks,

Dave

[kevin]

In general, the more the venting, the better. In the ideal case, the attic will never be above freezing unless the outside temp is too. In other words, the attic should be same temp as outside in the best case.

The only caveat is that sometimes it is better to strategically add vents to get good cross-ventilation, rather than just haphazardly. The recommended way is a continuous ridge vent (across the whole roof), and continuous soffit vents (a single opening along the entire soffit). What you have done is most of the way there...

[Ken]

You need a certain ratio of attic square footage to vent area square footage. Use this to help you figure it out:

When figuring vented area, make sure you include the reduction in vented area caused by the vent cover.

Ken

[loupark]

Not knowing where you are, be careful of ridge vents, heavy rains tend to bounce or push water into them, snow WILL blow into them. I can't tell you how many houses i've had to show a home owner a pile of snow in the attic.

[trader4]

I'd say it's very likely you don't have enough soffit venting. A 2 1/4 inch one every 4 feet isn't very much. IMO, it probably would have been a lot more effective to run a saw down the underside of the soffit and install a continuous vent.

[toshradio]

In my case, the batts block any circulation from the eaves/soffits as they are squeezed tight in there. The baffles help to create the airflow in my attic.

Dave

[nicksanspam]

IIRC, it was 3 holes every 4', ie 0.083 ft^2, or half that as open area and twice for both soffits. If each 600 ft^2 of attic needs a 1 ft^2 vent, with a vapor barrier in the ceiling and equal high and low areas, those 3 soffit holes can vent 49.7 ft^2 of roof, ie a 4'x12' section. We might want 6 holes per 4' of 24'-wide roof, or a 2"x14.5" screened soffit slot.

As an alternative, a WXL' attic might have WL/600 ft^2 of screened vents at the top and bottom of each endwall. A 30'x40' attic might have 4 1'x2' gable vents placed high and low, which might be covered in wintertime to conserve heat. IMO, continuous ridge or soffit vents are not required to eliminate "hot spots," since air can flow freely inside an attic.

Nick

[Ken]

Yes, that is the whole reason for the baffles, to hold back any insulation that might block airflow from the eaves into the attic area. If it was a finished attic or a cathedral ceiling, then you would run the baffles all the way from the eaves to the ridge to provide a continuous path on top of the insulation that is presumably put into the rafter spaces.

Ken

[C & M]

Does anyone know if the styrofoam baffles are at all useful? It would seem to me that they ae only required if you need to hold back the insulation batts.