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novaguy 12-09-2012 01:39 PM

vented vinyl soffit?
I'm trying to calculate how how much venting I need to balance my ridge vent.

These are the vinyl soffit panels I'm using (as well as the solid type): ications

My entire soffit is open to the roof deck. The only covering will be these vinyl soffit coverings. However, there is no NVFA rating on these vented soffit panels. Does anyone have a clue as to what it may be?

Similar homes in my neighborhood have every third soffit panel vented, others have every other, and other homes have every soffit panel vented.

Any help?

jagans 12-09-2012 02:16 PM

To: Nova Guy
Go all vented. Your soffit venting gets blocked up with atmospheric dirt, pollen etc. etc. in short order, and all your calcs go bogus

novaguy 12-09-2012 02:19 PM

From what I've read so far, it looks like the vented soffits with 1/8" holes spaced 1/2" on center give about 6 nvfa per square foot of soffit.

Gary in WA 12-09-2012 02:20 PM

The triple 4" are 4.65 NFVA per foot deep. Most ridge vents are 18 NFVA (good ones- to meet minimum 1/150) or 9NFVA per simple gable house side. You need a 2' deep soffit. Problem with your choice (design flaw) is dust/dirt moving through the very small holes deposit there from moisture in the air and restrict the NFVA to very little. Also, the best location for optimum air pressure intake is right next to the fascia board, not near the house; pp. 615-617;


novaguy 12-09-2012 02:39 PM

Wow, I'm more screwed up than I thought. I only have a 12" soffit on my garage. Looks like I need to get the 16x4 under-eave soffit vents. Each one (according to the home depot website) is 26 NVFA? That seems too high.

So, if I use the ridge vent with 18 NVFA, and I have continuous soffit venting along both eaves with 26 NVFA, I should be good, yes? Absolute no chance of ridge reversal there!

EDIT: I think I'll just order the SV202 vent as recommended in the book (great book, btw!) and that will give me a more balanced airflow between the 18NVFA ridge vent, and the 9NVFA SV202 on both eaves. Thanks again for the awesome help, GBR. I owe you a case of beer.

Gary in WA 12-09-2012 03:21 PM

Lol, H.D. info can confuse one, like watching TOH for DIY advice; 9 NFVA per foot is perfect. I owned/drove a '67 Nova wagon for about 12 years, had it painted before I sold it for 1/2 again more than I paid initially, nice car, solid.


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