Roofing co. insists on attic fan & cut-in soffit vents
jmcnamara
| Posted in GBA Pro Help on
This is my second post here on my attic insulation project. We decided to reroof as well and it’s getting interesting but not in a fun way. Just to give you some more information: the house was built in 1917; there is a ridge vent and gable vents but no soffit vents. Also, the attic doesn’t have knee walls.
The roofing project manager & his foreman came yesterday. The foreman walked the roof even though it was raining. Then he & I climbed into the attic, and he showed me points of water leaking in, gaps/daylight that indicated possible poor or non-existent flashing, and other details.
They said they would cut soffit vents along the southern eave, the northern (front) being too narrow. (The other contractor thought CertainTeed Intake vents would be sufficient and my insulation contractor agreed with that strategy.)
But this contractor also wants to replace the broken attic fan. In fact, they insisted that the attic should have an attic fan. Now I’m confused. My reading on attic ventilation and building science tells me that powered attic fans (not whole house fans) are a waste of money and energy. My plan was to have it removed.
I’ve got to get this sorted out & would greatly appreciate any thoughts.
I’ve got to get this sorted out & would greatly appreciate any thoughts.
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Replies
Unless you have some condensation related moisture issues, adding in more ventilation won't do anything. Adding in the soffit vents won't hurt, I wouldn't spend money on it if your existing gable vents are already correctly sized (ie gable + ridge vent area 1/300 of ceiling area)
The attic fan definitely needs to go, there are enough studies out there to show that these only make things worse.
John,
Your instincts are right. If the only damage you saw is caused by roof leaks, and there is none which might be due to the existing ventilation supplied by the ridge and gable vents being inadequate, there is no reason to cut in soffit vents - and certainly no reason to run an attic fan.
Make sure the ridge vent is clear, and use a proper ridge vent and not one of those "shingle over a piece of foam" things. Close off the gable vents after adding soffit vents so that the gable vents don't "short circuit" things. It's good to have slightly more soffit vents by unit open area than ridge vents, so that you slightly pressurise your attic (this helps reduce stack effect issues inside the house).
Once you've done all of that, there is zero need for a powered attic vent fan, or even for one of the wind-driven style fans. Natural convection airflow from the soffit to the ridge vent will take care of all your attic ventilation needs, and it uses no energy and has no moving parts that can break. Remove the existing fan.
Note that no amount of attic ventilation will fix water leaks though. A leaking roof is an entirely different problem,
Bill
Thanks for the help guys.
Interestingly, originally, the insulators had planned to install 2 slant back vents to get the balance they wanted. When I changed the plan to add the reroof, they were enthusiastic and supported the changed venting strategy even though it meant altering their schedule. (This was the CertainTeed system proposed by the previous roofer). But bottom line: they assert that there needs to be added intake or they won’t guarantee their work. There needs to be a discussion but I’m kind of committed (signatures, deposit, etc) to seeing this through with these guys.
Bill - I want to research your suggestion to block the gables because they wanted to keep
them. I’ve just read about the ‘short-circuit’ impact somewhere recently (GBH or FHB) and want to be sure.
Going back to the prior roofer, the CertainTeed system they propose will be a better ridge vent than the substandard kind you warn against.