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v12357 09-14-2008 02:35 PM

Insulation question.....
 
I have an unfinished 2nd level to a cape style home. Ceilings are cathedral style and rise to a point. All insulation (R19)was installed to the peak with the foam airflow installed from eaves to the ridge vent. No problems. Originally having collar ties at about the 9' height. I didn't like the look of the collars so contacted an engineer and was able to put collar ties about a 3rd of the way down creating a flat ceiling and removing the 9' collar ties. No problem again, but my question is since the insulation was installed to the peak originally do I need to put insullation on the now flat part of the ceiling or will it be fine as it is? It's about a 4' distance down from the peak to the new ceiling location. Any help would be greatly appreciated.
Ralph

Big Bob 09-14-2008 04:12 PM

Ralph, wise of you to have consulted the Engr.

If you still have easy access I would remove insul at top area and reuse above the new ceiling plane. (pull lose from the top add more proper vent at your new wall ceiling intersection.) Score facing on insul where it over laps. (maybe add a little more unfaced on top) I would add a gable end vent.

Why? Elementary heat transfer theory. Conduction, Convection, & Radiation.

I'm from the keep the shingles as cool as you can school for longest possible life. Also ( Vapor barrier and insul should be as close as possible to your conditioned space.)

v12357 09-14-2008 04:50 PM

Big Bob
 
Thanks for the explanation...it makes total sense. I still have some access but I am curious...1) if I didn't add any insulation the the new flat roof would that cause any problems? and 2)if I did add insulation to the flat roof and left the insulation on the pitched roof section above would that cause any problems? Thanks for your input.
Ralph

Big Bob 09-14-2008 05:19 PM

Quote:

Originally Posted by v12357 (Post 158119)
Thanks for the explanation...it makes total sense. I still have some access but I am curious...1) if I didn't add any insulation the the new flat roof would that cause any problems? and 2)if I did add insulation to the flat roof and left the insulation on the pitched roof section above would that cause any problems? Thanks for your input.
Ralph

to your ?'s
1. you would be subject to faster heat gain and loss in this area.

2. your shingles will cook when they do not have to. If you insulate both areas, be sure you add a gable end vent. The K factor of insulation is measured at a various RH levels.. the higher the RH the higher the K factor... the higher the K factor: means the lower the R value benefit you receive.

I hope the above is not too muddy.

Do you have any ridge or off ridge vent through the roof?

v12357 09-14-2008 05:35 PM

I do have a full lenght ridge vent but no end vents.

Wildie 09-14-2008 08:04 PM

I had a similar situation at my place.
It had R12 to the peak, so when I finished to the collar ties I insulated with R20. (ties were 2X6) before installing the drywall.
Then, I pulled the roof insulation down and laid it transverse on top of the R20.
This gave me a total R value of R32.
Made a big change in my heating and cooling bill!


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