Do ridge vents really add value for low slope?
mikeolder
| Posted in General Questions on
I cant seem to find the smoke test video that showed no chimney effect in the tested roof section, but Im wondering if ridge-vent is really necessary for my 3:12 peaked roof which spans 16′. It has no hangover at the eave so the plan is to add outriggers to the tops of each truss, fill the truss space with insulation and use the new 2×4 rafter space as ventilation. I figured winds are the main driver for ventilation and good open continuous soffit ventilation would be enough. After all, ridge vent doesn’t breath at all when its covered in snow here in Iowa, at the time you need it the most.
Thoughts?
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Replies
If you haven't already, I recommend reading Martin's article: https://www.greenbuildingadvisor.com/article/insulating-low-slope-residential-roofs. Your 3:12 slope is a bit higher than the 2:12 normally considered the upper threshold of "low slope" but it still has good information.
If you can get 1/150 of the floor area in the soffit vents, then ridge vents aren't required by the IRC. If you have ventilation balanced at the ridge and soffits, you can reduce venting to 1/300 of the floor area.
Snow is air-permeable in the densities it usually falls on roofs.
Thanks Mr Maines.
That stack chimney effect article and video are here.. https://www.greenbuildingadvisor.com/article/wingnut-testing-soffit-ridge-roof-venting
smoke test.. https://www.youtube.com/watch?v=SyIw2GTiKvQ
A ridge vent covered in air-permeable snow will be restricted, and the wind will bypass it and take the path of least resistance imo. Good ridgevent isn't cheap is why I questioned if it added value.