Pyramid hip ventilation

Matt Hausmann
4/28/2014
Project: reroof Roof: 35'x35' Pyramid hip. Pitch: 2.5/12 Instinct says to stay away from hip vents. Considering either two large static vents, or making my own cupola. I have two questions. 1) where can I find static vents that work with metal and this slope? And are they installed/flashed like a pipe boot? And 2) if I go with cupola, how do I arrive at the Net free area number? It would be a screened louvered cupola. Thanks
Info @windowsonwashington.net
An informed customer is our best customer.
4/29/2014
What type of metal roof to start with? Exhaust is usually not as big a drawback as lack of intake but they do need to be somewhat balanced. NFA is based on attic footprint, type of insulation, vapor barriers, etc. Regardless, if you are worried about venting, be sure to air seal and insulate the attic. This will dramatic lessen the condensation potential and allow you to more safely run the ventilation to the 1:300 square foot level and reduce your overall need. Good vented soffits?
Matt Hausmann
4/30/2014
Roof will be tuff-rib/ Ag rib exposed fastener. I have calculated NFA at almost 300sq in for each. Soffitt venting is no problem and will meet this requirement. Joists currently have r-19 and support pine decking in attic. Considering blown in on top to reach r38. Trying to understand A) appropriate size of a cupola vent Or B) proper material and flashing detail for static vents near the peak. Thanks, Eric
Info @windowsonwashington.net
An informed customer is our best customer.
4/30/2014
Matt, What look do you want? Both will work. If you stay with the 1:150 rule (very safe), you will need approximately 550 sq/inches on the soffits and 550 sq/inches on the exhaust. If you go 1:300, cut those numbers in half. Upgrade you insulation levels but air seal all the top plates and penetrations first before the additional insulation. At that level, you can get away with one roof top mounted powered vent. I like the OC solar fan with the monitor. Should be more than enough to vent the 1,200 sq/ft footprint.
Matt Hausmann
4/30/2014
Eric, Thanks for your expertise. Considering the roof is seldom seen, I may opt for your suggestion of a solar vent. I assume installation is the same as a vent pipe boot: screw down with sealant underneath? You have raised another question: best way to blow in insulation and not restrict rafter airflow. The joist/rafter meeting point is very tight in this pitch of roof. Thanks again, the website has been a great resource.....Matt
Info @windowsonwashington.net
An informed customer is our best customer.
5/2/2014
Matt, No replacement for getting out to the eaves and maintaining unobstructed airflow via baffles/vent chutes. The solar fan with the monitor is a nice touch as well and lets you keep track of function. Fan install is the same. I would build up a small framed section and work/flash the metal around that and then mount the fan. Should the fan crap out down the road, much easier to leave the roof intact and service/replace with that style setup. If you are worried about blocking the soffits, you can run a sort of smart vent (DCI) or similar breathing allocation at the eave.

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