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I wanted to add insulation to an old ranch house. However, the insulation contractor wants to add static vents (2 turtles and 2 pipes). He says I don't have enough ventilation in my attic. The roof already has a ridge vent. It also has a gable vents but no soffit . The attic seems fine to me. The attic temperature is always within +/- 10 of the outside temperature. The house is in MA; so we have extreme weather. Even in the coldest winter, there has never been ice damns. There is no known mold issue. The shingles have aged well. Now, the roof is almost 25 years; I think it's time to start thinking about a new roof. Should I think about changing the roof or keep it as is? I'm a big believer in "If it's not broken." Was the insulation guy misinformed?

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    Perhaps the existing vents were sufficient when you had no insulation - if you add insulation then the vents may need improving. Did you consider that the insulation guy took that into account? – Solar Mike Jan 7 at 13:26
  • I'd go with the soffit vents and avoid any new holes in the roof. Ridge and gable to be truly affective need soffit vents. Just be sure that they are not obstructed with new or old insulation. – Micah Montoya Jan 7 at 14:33
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I would not anything more to the roof. You probably have enough flow through the ridge and gable vents.

If you're really concerned, soffit vents should be next. But a lot of them I've seen do not have enough free space area, or net free area to be effective.

  • What is free space in reference to soffit vents? Do you mean people block them with junk in the attic? Thanks for taking time to answer my question. – Thanh Tran Jan 7 at 15:10
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    Free space area, or net free area is the effective, or useful open area of the holes in a soffit vent. Because the hole or slots tend to be small, the effective area for air flow is less than the measured aea of the opening. – SteveSh Jan 7 at 15:17
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Adding openings below ridge vents short-circuits venting function. There are several physical principles at play (convection and scavenging, put simply), and you degrade them by adding openings between the soffit and the ridge. Even gable vents are often ill-advised with soffit and ridge vents. They can hamper air movement at the outer edges of the attic.

Unless you have a hip roof with very little ridge, leave it alone. There are plenty of calculation tables to be found indicating the amount of venting you need for a given attic space. They assume adequate soffit venting, but they're a good guide.

  • The roof is a dormer (that is the term I think). It has gables at the two ends and on the protruding section. It has a ridge vent down the middle but no soffit vents. The roof protrudes; I believe soffit vents can be added. – Thanh Tran Jan 7 at 15:18
  • A dormer is a small roof in the plane of a larger roof. It's not a roof type itself. Your contractor is probably correct that you could use more venting (for the outer edges of the attic), but the plan you describe is not great. Soffit vents are the ticket. – isherwood Jan 7 at 15:23
  • Yes, you are correct. The dormer hangs over the front door vestibule. It has a gable. The larger roof has the ridge vent with gable vents on the ends. – Thanh Tran Jan 7 at 15:37
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The code requires a certain amount of attic ventilation.

Attic Ventilation shall be “cross ventilation “ and shall be 1/150th the area that is to be vented. (See ICC R806 Vents.)

However, there is one exception: The attic ventilation can be reduced to 1/300th the area to be vented provided one of the following items are met:

1) a Class I or II vapor retarder is installed on the “warm-in-winter” side of the ceiling, or

2) not less than 40% and not more than 50% of the ventilation is located in the upper portion of the attic. The upper portion is defined as: “Upper ventilation shall not be lower than 3’ below the ridge or highest point of the roof. “ (See ICC R806.1.2.)

Also, the Code says you shall maintain a 1” clearance between attic insulation and framing.

So, you can see there is clearly a benefit to having ridge vents, gable vents, etc. , but in a proportion that allows COMPLETE CROSS-VENTILATION to the attic.

Soffit vents with ridge vents obviously meet that requirement best, but gable vents and “turtle vents” (as you call them) are also effective.

So, if you have a 2,000 square foot house, you’ll need 13.33 square feet of vents if about half is NOT located in the upper portion of your attic,

Or

You’ll need 6.66 square feet of vents if between 40% and 50% of the vents are in the upper portion of your attic.

You can easily calculate the amount of ventilation on your roof, if you use about 2” wide per foot for ridge vents (about 0.15 square feet per linear foot) and about 1/3 square foot for each roof vent. (The free area of vents are reduced due to insect screen, which is required in every vent. However, this rule of thumb will give you a good idea of how much ventilation you have.)

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