Insulating a 2/12 roof above the roof deck
My first house, purchased a couple of years ago, needs a new roof. We recently had a major storm in the area and all roofers seem to be so busy that it is difficult to have someone over to discuss my case. So far I spoke with 3 roofers, each with a different idea, so I am doing my own research to see my options.
I have done some research but none of discussed roof setups was identical to mine.
– Zone 5 (Chicago), cold winters and hot summers,
– Basic gable roof, two slopes only,
– 1 story ranch on slab,
– 2/12 roof pitch,
– Unvented roof,
– No attic
– No ceiling insulation,
– Existing (old) natural fiberboard insulation installed above the roof deck, most likely ¾” thick, maybe 1 ½”,
– Roof deck consist of 2×6 tongue and grove lumber exposed on the interior side/ cathedral ceiling
– Roof deck extends into 24” overhung , no ventilation in soffit,
– Built-up roof,
– Roof penetrations: furnace vent, bathroom vent, oven hood exhaust, plumbing stack,
– AC duct entirely in slab,
– 2 electrical boxes installed on the roof deck for kitchen light.
Since the old insulation got wet and it’s insulating properties are poor anyway I am considering installation of the new insulation. Remember, insulation entirely above the deck.
ICC requirements most likely will not be met because the amount of insulation on the roof would be around 10”, creating odd thick roof. I am comfortable with up to 5” extra on rooftop…
I am trying to find out if I need venting in my new roof. Throughout my search I found contradicting opinions in that subject.
I am aiming to achieve up to R-20 which will be significant improvement comparing to my current condition. Seems like Cornell ThermaCal1 (SIP) vented panels on roof deck would be my best option.
I am aware that installation of the shingles on a 2/12 roof is questionable, however I came across GAF and ARMA guidelines for installing the shingles on low-slope roof. Besides, half of the houses on my street with the same roofs are shingled. Membrane roofing is not out of the question, it’s just the shingles are my preference…
I would appreciate your 2 cents on my choices. Your comments/suggestions would help me to get my roof before the winter!
Many Thanks + Regards,
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