# Attic rafter insulation. What should I do?



## joecaption (Nov 30, 2011)

#1 Please go back and add your location to your profile, imposable to make many suggestions without it.
Just go to Quick links to edit.

http://www.energystar.gov/index.cfm?c=home_sealing.hm_improvement_insulation_table

It's a common newbee misconseption tha t when you see all that "wasted" space that you can just add a room up there.

I think your going to find your joist are under sized for a real floor, there will need to be a permit for this type of work, there needs to be a real set of stairs built to get up there to make it legal


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## Beyhan Trock (Apr 25, 2013)

R49 in Ceiling? You should know that most jurisdictions have adopted the IECC 2012 code that requires ceilings to have insulation with an R value of 49. That's huge! Even if you use 12" rafters, you won't be able to get more than an R-38 using Owens Corning batt insulation, and would need an additional 3 1/2" (R11), plus the extra 1" air space above the rafters for ventilation. If you don't have 16+ inches, (and who does?), here's an alternative. Do an unvented ceiling with a vapor barrier placed above 3" of closed cell foam (R6 per inch) and then 8" of batt (R30) below that. The closed cell insulation also acts as an air barrier.


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## AGWhitehouse (Jul 1, 2011)

The above response is correct in that those ceiling joists may not support the live/dead loads of an occupiable space. Also, those 2x6 rafters don't have enough depth to properly insulate nor enough strength to accomodate exterior-applied ventilated nailbase panels. The only way you're going to get a room in that attic is to rip off your roof, lay in a new floor, and build a properly insulated/ventilated roof deck. That gets pricey, so if that's not an option, call in the cellulose crew and blow in an R-49 thickness and plan on a play room elsewhere...


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## Gary in WA (Mar 11, 2009)

You will need more than 3" of SPF to get the R-30 required (plus cavity insulation) to control condensation for a closed roof system for your location- Our Zone 7, see map; http://www.buildingscience.com/documents/published-articles/pa-crash-course-in-roof-venting

Be sure to check weight limits/span on existing ceiling joists with added cellulose (R-49= 1-1/2# per sq. ft.) loaded on already 8# per sq.ft. for plaster/lath, or if 1/2" drywall, 24"o.c.; https://docs.google.com/viewer?a=v&...xf51fE&sig=AHIEtbQixCH3AO0RugCGh3VLQNBaXp54rA

Gary


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