If you go up into your attic, look for baffles between rafters. And allow moisture build up in winter.Ĭlick here to learn more about proper attic ventilation> CHECK YOUR ATTIC FOR RAFTER VENTS This can lead to heat buildup in the attic during the summer months. When intake vents are blocked, the amount of fresh air needed to properly ventilate your attic is impaired. Common baffle colors are pink, blue, and tan. Rafter baffles should be placed on your attic ceiling in between the rafters at the point where your attic ceiling meets your attic floor. Rafter baffles come in 4-foot lengths and 14-1/2 and 22-1/2 inch widths for different rafter spacings. Rafter vents ensure the soffit vents are clear and there is a channel for outside air to move into the attic at the soffits and out through roof vents. Rafter vents, often called roof baffles to protect intake vents in your attic from becoming clogged or covered by insulation or debris. I could try to trim them to 18.75" (which would still work, just more difficult to install) if it would make a difference.RAFTER VENTS – ARE YOU BAFFLED BY RAFTER BAFFLES? They are only 37.5" long, which is how I originally intended to use them. 2" deep baffles I can only find from one mfg. Big box ones come 48" long, so I could trim to 2' each and they would work
Rafter baffles free#
If the soffit takes in 6.65 si, is a rafter baffle with 15 si free area noticeably worse than a rafter baffle with 28 si free area?
air comes out of baffle and floats freely in attic, hopefully to ridge vent The big box "ProVent" for example, state they have 15 square inches of net free area each, and after the 1" flange each side, are 12" wide.ĭ. air gets channeled through the rafter baffles. air floats freely around the soffit over the Hardie panelsĬ. air goes through small holes in the Hardie soffit (first restriction) at a rate of 6.65 square inches per rafter bay (16" oc) - although probably a bit less if there are joists extensions holding up the soffit.ī. So is there any sort of calculation that can be made to possibly use the big box store vents, or is that so impossible that it drive the recommendation for the 2" ones available only online to get the most depth?Ī. The soffit is a flow restriction of only a fraction of an inch, but the baffles are several feet long. It doesn't cause big problems, because that fitting might only be an inch or two long. Plumbers use this principle all the time with fittings that drop down to half or less the internal diameter of the pipe they're dealing with. So a 1 foot section of 3/4" pipe followed by a 200 foot section of 1" pipe will end up having a lower flow than either section would experience without the other being present, and the 200 foot section is likely a larger portion of the flow restriction than the short 3/4" stub. In reality, the pressure drop ("energy wasted on friction squeezing through a space") is proportional to some exponent of the aperture (diameter^3? diameter^4? diameter^5? Something in there, depends on turbulence), multiplied by the length that flow is choked down to that aperture. If you have two sizes (eg a 1" diameter pipe and a 3/4" diameter pipe), then "it's only restricted by the smallest aperture flow passes through" sounds like a good intuitive model - one we adapt to other situations with the term 'bottleneck'.
Flow-rate through pipes and ducts is tricky.
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