Do our twin homes need roof vents?


#1

Our twin homes were built in the mid 70s. We’ll be replacing our roofs (second time) in a few years, and I’ve always wondered why none of the buildings have roof vents or gable end vents. They have continuous soffit vents under the eaves, but no roof vents. We haven’t had any systemic moisture problems, but still, I wonder if I should be advocating for roof vents of some type. What do you think? Thanks, Tim


#2

Yes,your roof needs the air to circulate.soffit vents alone is not enough.you can figure out how many roof vents are needed by how many squares are there.there is a formula you can probably find by looking up roof ventalation.hop.e this helps


#3

1:300 is code (in some places) 1:150 is highly recommended

Meaning 1 square foot of soffit vents and one square foot of roof vents for every 150 square feet of attic floor space.


#4

Thank you for the replies. Would you indulge a couple of follow-up questions?

In your experience as contractors, have you encountered homes like ours, where there have never been any roof vents? And where there have been no moisture related problems?

Is it possible that our homes were designed without roof vents? They have had cedar shakes since they were built in the mid-70s. Is there some attribute of cedar that negates the need for vents? We will not be using cedar for our new roofs. Is it possible that lack of vents in steel or composite roofing would become problematic, where in cedar it was not?

In a nutshell, I’m trying to figure out how common it is to not have roof vents, and how heavily I should be advocating for them. Thanks much. Tim


#5

Should you decide on having roof ventilation, for a common void roof area I would suggest a Cupola as one large opening is better than several smaller, with the convergence of volume prior to release to atmosphere is far more efficient than having to establish varying flow paths to individual roof ventilators.
http://architecturalnotes.com.au/


#7

Yes cedar roofs breathe through the spaced sheathing unlike other roof systems. The best we can hope for with ventilation after resheathing and composition install is to ‘break even’. This is after installing necessary eave and ridge vents.


#8

Regarding cupola for main vent, that isn’t best application in our area. We live in a giant country with many different climates so researching ventilation will make your head spin. In our area, Pacific Northwest, balance is the key. Your soffit or eave vents should be balanced as closely as possible to upper vents. You want to achieve consistent draw and not leave any dead spots in the attic to produce stagnant air. A cupola vent would not do this. Continuous soffit vent and ridge vent is ideal if ridge lines are long enough. Hip roofs need rvos or other dormer style vents.


#9

Several photos of your roofs from different angles would help in providing you with better answers.