[Kenneth Patchen]

I have a question about blown-in cellulose insulation for an attic roof. Here in freezing snowy upstate NY, fifteen years ago, we had blown-in cellulose insulation added to the walls of our 103 year old house. Recently a free energy audit, which included IR imaging, showed some settling of the insulation which is to be expected but it also showed several empty areas that the original contractor missed, which was not expected. We now plan to have new insulation blown into the settled and missed areas as well as adding insulation for the attic roof. Here's the question: the contractor's plan for the attic calls for placing Tuff R-2 foam board against the rafters with cellulose then densely packed between the foam board and the roof decking, i.e., the cellulose would be packed directly against the roof decking. I know that placing fiberglass insulation directly against the roof decking is a no-no as fiberglass insulation requires separation with a spacer to allow for proper ventilation to prevent mold growth, ice damming etc. However, the contractor told us that when cellulose and foam board are installed properly no spacer is needed. He claims the dense pack cellulose with the foam board create a proper barrier so the moisture does not condensate at the bottom of the roof decking. He explained that there is a whole building science field now so they have a much greater understanding now how the different materials respond under different circumstances. 

Does having cellulose densely packed directly against the roof decking without a spacer for ventilation make sense?

My thanks in advance for your time.

Kp

[Big Red Machine]

While it is a small area on the lower edge of the roof, I would not do it because moisture can build up and rot wood, etc. With the spacer the air flow is supposed to prevent moisture buildup and let the eave vents breathe up and over to the ridge vent.  This is an easy project to do with a buddy down below feeding the blower machine btw.

[thunderbrick]

Don't do it.  Spend your effort sealing gaps between the living space and the attic.  Did the auditor do a smoke test to see where air is leaking between the two areas?  If not, he didn't do a thorough job.

Make sure there attic is properly vented from the eaves to the peak.  You want airflow up there to let moisture escape, and stopping the summer heat by insulating the rook deck could shorten the life of your shingles.

[Kenneth Patchen]

I should have added is that the goal is to turn the attic into a 'shared, man cave/audio space with my wife claiming a third of the space for her use.

[bladesmith]

You  can use soffit vent extensions that run in btwn the rafters and then blow in insulation.

V...

[Atlplasma]

I think your contractor is giving you good advice. If you want more informed opinions on his strategy, go to www.greenbuildingadvisor.com and post your question. Those guys are the building science experts your contractor was referring to.

[thunderbrick]

I should have added is that the goal is to turn the attic into a 'shared, man cave/audio space with my wife claiming a third of the space for her use.

Ahhh, that's different!  In which case you do need to staple those thin foam channels to the roof decking, then finish it off.  No question about it!

[JLM]

Yes, the attic must vent, from soffits to ridge/individual vents near the peaks to avoid heat build-up and condensation (leading to rot).  Best to insulate directly against living space and leave a minimum 2 inch space for ventilation.  Regardless tight packing of cellulose makes no sense as it's the (dead) air spaces between shreds of paper (cellulose) that provides the insulation value.  In fact there are physical limits (15 - 18 inches) of how thick you can pile blown/loose insulation before it compacts under it's own weight enough that no additional insulative value can be generated.  I'd consider a solar powered attic fan to keep attic temperatures down.

A portion of my roof is made of SIP (structural insulated panels, which is 9 inches of styrofoam glued to two sheets of plywood).  Super strong (spans 16 feet) and if a whole house were built that way, you'd have a plywood refrigerator (no studs to shortcut insulation or leak air - very low energy losses). In that case the roofing paper/shingles are applied directly to these panels.  In 10 years there is no difference between those shingles and the shingles on attic spaces.  So being in indirect contact with insulation is not a problem for shingles (better than typical 140F attics in the summer).  But the attic space itself must be vented!  Sounds like the guy is a wack. 

Yes, the energy firm should have done a blower door test, to determine where air is leaking in/out of your house.  Infrared testing is best done at night (less background infrared light) in the winter (maximum temperature difference inside and out).  Install door seals and caulk windows.  Insulate/seal at the rim joists (if you have access).  Caulk around exterior electrical plugs, outdoor spigots, and attic mounted electrical boxes (smoke detectors/can lights, ceiling lights).  I recommend pushing a couple of handful of fiberglass batting into the outside air intake if you have a high efficiency furnace or direct vent water heater.  And keep the clothes dryer door closed (avoid outside air back drafting into the house).  You can hold a lighter/match against all these on a windy day to see if there are significant leaks.

[Atlplasma]

I will disagree with JLM's statement that an attic has to vent. It doesn't. You can extend the insulation layer to encompass the attic and turn it into treated (heated and cooled) space. You can insulate on the inside as your contractor suggested, or, if you need a new roof, you can use exterior rigid insulation to create the R value you need. You can also use a combination of inside and outside insulation to achieve your goals.

I agree that a blower door test is a good idea. Sealing as many air leaks as possible will help to prevent issues with heat lose and problematic Rh. Again, talk to the guys at Green Building Adviser. There are plenty of ways to insulate and improve the efficiency of your home.

[Kenneth Patchen]

Thanks to all. I'll email Green Building Advisor.

Cheers,
KP

[thunderbrick]

I will disagree with JLM's statement that an attic has to vent. It doesn't.

I disagree.  It can be insulated AND vented with those foam channels.  Together they will reduce the temperatures that the insulation must cope with, and that will make it more comfortable.

[JLM]

I will disagree with JLM's statement that an attic has to vent. It doesn't. You can extend the insulation layer to encompass the attic and turn it into treated (heated and cooled) space. You can insulate on the inside as your contractor suggested, or, if you need a new roof, you can use exterior rigid insulation to create the R value you need. You can also use a combination of inside and outside insulation to achieve your goals.

I agree that a blower door test is a good idea. Sealing as many air leaks as possible will help to prevent issues with heat lose and problematic Rh. Again, talk to the guys at Green Building Adviser. There are plenty of ways to insulate and improve the efficiency of your home.

I've been around construction for 30+ years, live in the great white north, and hate not having drawings to "talk" with.  Any leftover attic space (such as created by knee walls) must be vented (could be done with the ubiquitous "forget me not" 10" x 10" roof vents.  The proposed attic living space (walls, angled/flat ceiling) should be directly insulated against as well as existing ceilings that won't have the new attic living space above it.  My SIP panels have drywall on one side (the ceiling of the great room) and shingles on the other side (no attic space). 

Attic space = vent, no attic space = venting optional, living space = insulate directly against it.

[Atlplasma]

I've been around construction for 30+ years, live in the great white north, and hate not having drawings to "talk" with.  Any leftover attic space (such as created by knee walls) must be vented (could be done with the ubiquitous "forget me not" 10" x 10" roof vents.  The proposed attic living space (walls, angled/flat ceiling) should be directly insulated against as well as existing ceilings that won't have the new attic living space above it.  My SIP panels have drywall on one side (the ceiling of the great room) and shingles on the other side (no attic space). 

Attic space = vent, no attic space = venting optional, living space = insulate directly against it.

JLM. I'm not spoiling for a fight. It's just that I recently completed an Earthcraft/Energy Star Platinum level house. During the course of that build, I learned a bit about current thinking on building science. Attics is one of the more contentious issues. Here is an article that provides a good overview of code requirements and best practices, which aren't always the same thing.

http://www.greenbuildingadvisor.com/blogs/dept/musings/all-about-attic-venting

[JLM]

Thanks for the link Atiplasma.  I've been interested in this stuff since the 70's and in fact took a one day class in super insulated houses last December.  We've learned a great deal in the last 40 years, but have also made some mistakes. 

It's been 10 years since we built our EPA 5 star home and just tried to get an energy audit from Dr. Energy.  The young man really didn't want to crawl into the attic on a summer afternoon, so didn't.  As part of the EPA certification we'd had a blower door test done, so he passed on that too.  I showed him the EPA certification results and the one place in the basement (small utility space) that doesn't have a finished ceiling so he could see the construction.  He never bothered going upstairs.  I'd invited them in before dropping money on a PV solar system to get a second opinion.  All he could suggest is beefing up the sealing/insulation at the joist level (which it already has), sealing the drywall in the attic, and beefing up the attic insulation from R51 to R60.  But overall he thought my idea to add solar would provide the biggest bang for the buck.  What a dud. Oh well, conformation is a wonderful thing.

Much of what I'd recommended above is also recommended in the link: 2 inch vent gap at underside of roof; insulate against living space; attic venting is effective on steeply pitched roofs (like the OP has); seal at penetrations including electrical boxes & recessed lights; venting does reduce the attic temperature.  And note I said "solar powered" attic fans (no cost to operate and with a thermostat should run only in the summer). 

As a former building official I'd like to point out that the purpose of codes are not to reflect ideals, but to set a minimum standard.  Folks that build to just meet code should be given a grade of "D" (barely passing).  It's easy to blame the code officials, but who's stopping you from going above and beyond code?  Now I know there's good and bad inspectors, like in any profession, but the code exist to protect from unscrupulous builders.

[ctviggen]

I used to do a ton of research on this.  Attics don't have to be vented.  At all. Now, in my house, I'm leaving mine vented, but it's because I don't trust the people who do the sealing with spray foam.  It's not because I think the attic needs to be vented. 

[Atlplasma]

Thanks for the link Atiplasma.  I've been interested in this stuff since the 70's and in fact took a one day class in super insulated houses last December.  We've learned a great deal in the last 40 years, but have also made some mistakes. 

It's been 10 years since we built our EPA 5 star home and just tried to get an energy audit from Dr. Energy.  The young man really didn't want to crawl into the attic on a summer afternoon, so didn't.  As part of the EPA certification we'd had a blower door test done, so he passed on that too.  I showed him the EPA certification results and the one place in the basement (small utility space) that doesn't have a finished ceiling so he could see the construction.  He never bothered going upstairs.  I'd invited them in before dropping money on a PV solar system to get a second opinion.  All he could suggest is beefing up the sealing/insulation at the joist level (which it already has), sealing the drywall in the attic, and beefing up the attic insulation from R51 to R60.  But overall he thought my idea to add solar would provide the biggest bang for the buck.  What a dud. Oh well, conformation is a wonderful thing.

Much of what I'd recommended above is also recommended in the link: 2 inch vent gap at underside of roof; insulate against living space; attic venting is effective on steeply pitched roofs (like the OP has); seal at penetrations including electrical boxes & recessed lights; venting does reduce the attic temperature.  And note I said "solar powered" attic fans (no cost to operate and with a thermostat should run only in the summer). 

As a former building official I'd like to point out that the purpose of codes are not to reflect ideals, but to set a minimum standard.  Folks that build to just meet code should be given a grade of "D" (barely passing).  It's easy to blame the code officials, but who's stopping you from going above and beyond code?  Now I know there's good and bad inspectors, like in any profession, but the code exist to protect from unscrupulous builders.

When we were building, I found the lack of knowledge (and lack of interest in being knowledgeable) among the various trades to be quite astounding. My builder -- a neighbor -- turned out to be a huge disappointment. When he poured the foundation in the wrong location, I knew my wife and I were in trouble. By being super vigilant, we avoided total disaster (but the house did end up $100K over budget). My last blower door test indicated 1.1 air changes per hour. But that will improve once I seal a gap between the front porch and the exterior drain plain, which resulted from my builder/neighbor not following direction. It is pretty much the last major re-do on my list (and a very complicated project).

I agree that the OP can use the approach you suggested, but those old houses often have fairly shallow rafters. He may not be able to get the R value he really needs for his climate. If his roof needs replacing, I would consider exterior insulation. There are some good deals out there on recycled rigid foam. As you pointed out, it is similar to creating a SIP for the roof.

On your SIPs, do you know how they sealed the gaps between panels? I have read some horror stories about moisture damage caused by air infiltration between panels. I hope your panels weren't installed over them. 

[JLM]

Being the owner of a new house build ranks right up there with shopping for a car or undergoing surgery, NO FUN.

My know-it-all contractor made numerous mistakes and would admit to none of them.  Half way through he was calling me names while asking for my advice.  My wife had to take over.  And by the end he was yelling at me (with his subs working in the house) and telling me that "the customer is always right" adage was a pile of sh*t.

Witnessed the SIP panels being installed (lived 50 miles from the build, so keeping a close eye was impossible).  They were caulked in between.

Depth of rafters should have nothing to do with how much blown insulation can be used.  (I believe the article was trying to describe the pitch of the roof which would increase effectiveness of attic venting.)  Again, bemoan not having drawings to "talk" with.

[2bigears]

   kinda makes perfect sense to vent a cold space.  R-100 in the ceiling should be min code in my books. 

[JLM]

  kinda makes perfect sense to vent a cold space.  R-100 in the ceiling should be min code in my books. 

Yep, but at some point extra insulation is pointless.  For heating, consider the heat generated by appliances, occupants, and the water heater.  (R60 homes can reportedly be heated in northern climates by a hair dryer!)  For cooling a small split-design system is enough in those same R60 homes.  Air leakage (infiltration) versus insulation becomes the key factor.  Plus R100 would exclude purely blown/loose insulation as it's own weight compresses the dead air space within the pile (that provides the insulative property).

[2bigears]

when it's -40 degrees here for 2 weeks straight in the dead of winterland,  I say 100 is better than 60 by aboutttttttt oh say r40. Too much insulation ,  really. Do people complain their car gets too good a gas Milage. A heat exchanger and well sealed vapor barrier ,, your off to the races.  .