Replies

1. 
   Mike_Smith | Oct 18, 2000 09:30pm | #1

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   how do they make this stuff up.....what vents the other two bays ?

   what is the reasoning ?

   this is daffy... at least the NO-VENT bunch has a reasonable explanation for their method...

   this is someone repeating something they were told without thinking it thru........

1. 
   Crusty_ | Oct 19, 2000 05:07am | #2

   *One of the main reasons given for venting is to keep the roof deck (especially the shingles) cool. The air flow through the rafter bay is essentially laminar, that is, it is not turbulent (like forced air flow) so the air will only cool the rafter bay through which it's flowing. In fact you don't want turbulent flow (IMO) which is one of the main reasons most folks say not to use a gable vent if you have a soffit/ridge vent combination -- the flow through the gables will disturb the laminar flow from the soffit to the ridge.(This is the looooooooong version of the answer Mike gave.)

1. 
   Mad_Dog | Oct 19, 2000 11:21pm | #3

   *Alan,Do you happen to be an artist? I am a great admirer of the works of Alan and Robert Bateman...MD

1. 
   Gene_Leger_ | Oct 20, 2000 05:13pm | #4

   *Alan. Ridge vents must be driven: provided with air from the soffit vents. Ideally, the soffit vent net free venting area (NFVA)should match the ridge vent NFVA. However, an absolute balance is not necessary. It is preferable to have 10 to 15% more soffit NFVA. As the soffit NFVA is reduced, a point is reached where the ridge vent reverses: the windward side becomes an intake vent and the leeward side becomes an eahaust vent.When the ratio of ridge vent NFVA(9 square inches)to the soffit NFVA(6 square unches)is 9:6 there is little possibility of ridge reversal. Caution. If the soffit vent openings are circular (0.125 inches in diameter)there is a possibilityof reversal as the circular openings become blocked with dirt.Ridge reversal is is highly probable when the ridge to soffit NFVA ratio is 9:4 or 9:3. Therefore, install a double louvered continuous soffit vent located next to the fascia board.The ideal distance from the exterior wall is 8 inches. But in any event keep the soffit vent next to the fascia board. As you get closer to the outside wall you get into an area of high wind pressure and snow or rain penetration is a real possibility.GeneL.

2. 
   Alan_Bateman | Oct 20, 2000 05:13pm | #5

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   The crew working on my addition says you only need a rafter vent in ever third bay or so ( cathedral ceiling ) This sounds a little strange to me. Any help would be great.

   Alan