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Renewable Energy for the Home

Foam Insulation in Attic Rafters

15 years ago

I've been thinking about having foam insulation blown into the spaces between the rafters in my attic.

The attic floor is insulated with cellulose, and the attic is open to the outside with a couple of whirly-gigs and two gable vents.

Would insulating the rafters give me any benefit at all?

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Comments (14)

solargary
15 years ago
Hi,
No, if the space above the current insulation is ventilated to the outside, then you won't get much of any benefit out of insulating the roof rafters.

It would be better just to add more insulation on top of the current insulation. Blown in cellulose works well and is cheap and easy to do.

Gary
energy_rater_la
15 years ago
search www.buildingscience.com for info on unvented attics
lots of foam insulation companies sell a 'total enapsulated' attic package.
best of luck.
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I see someone has been doing some reading.. Yeah lzearc, unfortunately I dont think any state has adopted it yet. Heck, most areas still dont enforce some of the 2006 requirements. NC has a hybrid that is mainly the 2009 versions with a few of the easy 2012 details. Most of our homes do use the performance path, but all our homes use third party certifiers. The software can be used by anyone but the final result is best served by a third party professional. The performance method is necessary to not stifle innovation. Its intended to allow freedom of design and is a great tool for achieving a balance for designs that may do something that doesnt quite meet the prescriptive guidelines but is still an efficient and comfortable design. It is NOT intended as a way to circumvent the basics set forth in the prescriptive guidelines. The performance software is a great and amazingly accurate tool in the hands of the experienced and knowledgable. Its also easily manipulated and can lead to very bad design, performance and comfort by those unfamiliar with the many variables of the program. The software is looking for the same R values as the prescriptive guidelines. Skimping in one area can be made up for by adding in another. If someone is making their home pass the 2012 IECC in RESFEN or other modeling software with only 7" of Open Cell foam at the roof deck, they must have some seriously efficient (and not cost effective) mechanical systems going on or are using the software wrong. For the most part, following the prescriptive guidelines is the most cost-effective way to achieve the intended code which most experts feel is the sweet spot in balance of upfront costs and energy use/comfort.
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I didn't address wall or sole plate leakage as the questions were for unvented attic. you handled the air tight drywall approach nicely, btw. for my clients..I always recommend sill seal or a double bead of caulk between slab & sole plate..even on second floors we caulk sole plate to subfloor. I've tried to make it work where if someone made a hole for example a hole cut in the ceiling for a supply box that they were responsible to properly seal the hole. too hard to ride heard over a bunch of tradespeople. this is where our situations differ..you run the job, I'm just there for efficiency recommendations, installs and performance. I never ever recommend foam in walls. roi is too high..and we seal walls ok..its the ceilings & floors (on piers)! instead I recommend a 1" hi density foam sheathing board to exterior..conventional insulation and ada. air sealing such as sole plates, around windows doors etc. caulk is a wonderful product..my clients usually start with a case. most quickly understand that it is in their best interest to take an active part in the air sealing. but for our climate..and the many mistakes in air barriers ducts & returns...foam for the roofline is a no brainer. in a perfect world...houses would be designed in the south with ducts in cond space. every tradesperson would seal each hole they make. I'm going to have to think about this for a bit! "Also in a heating climate homes can dry in either direction. Its where you place your moisture barrier (if using one) that helps dictate that direction."
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You need a cold roof. To make this happen, you have to stop all air flow from living space to attic, and you should insulate your living room ceiling and bedroom wall to R38. To stop the air flow, look at every fixture in the ceiling and find every pipe and electric wire and other penetration. Some penetrations may be found by searching the insulation on your ceiling for black marks. The insulation acts as a filter and catches particles from the air flowing through. Seal every hole with a fire resistant canned foam product. Dap makes one that is water soluble. When all holes are sealed and insulation is done, I think you should strip the insulation from the roof and leave it bare. But know this: I have no experience with ice dams. I am not qualified to give you any advice regarding attic and roof insulation. However, I do know that it is critical to seal all penetrations through your ceiling and bedroom wall. This includes the door! Copy and paste this to your browser for more info: http://www.umass.edu/bmatwt/publications/articles/ice_dams.html
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garymunson-2008
15 years ago
foam....a good way to rot your roof deck and trusses
happycthulhu
Original Author
15 years ago
Ok, well I guess that's nixed that idea.

How about insulating under my wood floors in the crawl space?
Would that help my energy costs any?
rjoh878646
15 years ago
You would need closed cell foam sprayed in your crawlspace.
bill_bg6
15 years ago
Can't tell where you are located from the pics of your house, but if your concern is summertime heat gain you might consider radiant barrier installed on your rafters. It will help considerably in the summer. But to have any positive impact in the winter it needs to be installed right over the existing insulation and it looks like a large section of your attic is floored and you use it for storage.
You can google radiant barrier and find plenty of sites that show how to install. It should be a pretty easy diy project in that attic,
g'luck
lindamarie
15 years ago
You do not say where you are or if you have heat/AC ducts in your attic.

You can use styrofoam panels with a foil heat barrier installed on your rafters.

Those whirly-gigs are useless. I had mine removed when we put on the new roof.

The conditioned crawl space is a great idea. Close your vents off.
happycthulhu
Original Author
15 years ago
Our ducts are in the crawl space.
I can't close off my crawl space though because my house is balloon framed.
I can look up from inside the crawlspace all the way into the attic because of the space between the outside brick and the wood frame for the interior.
The cold air would just flow up into the attic and out the vents.
As for whirly-gigs, ours work real well.
We have two of them plus gable vents and it's cooler up there than it was before we had the whirly-gigs installed.

I wonder if styrofoam panels with foil would be a good idea for between the floor joists in the crawl space?
CTFoamInsulation
11 years ago
Hi Happycthulhu. Yes! Spray foam insulation would do a tremendous job for your application(s). I provided a link below that has good information for anyone interested.
Thanks,
Mike

Here is a link that might be useful: Spray Foam Insulation
ionized_gw
11 years ago
Spammers dig up old threads.

There is lots of bad information in this thread. Nothing good can come without climate/location information.
PRO
Windows on Washington Ltd
10 years ago
+1

Hopefully future readers will not get steered in the wrong direction.

Get to Building Science.com and get educated folks before you invest big money in SPF.
Mandy13
10 years ago
Two years ago, I had foam sprayed into my roof, trying to live more comfortably. This did not seem to be helping so I installed 3 whirly gigs thinking it would ventilate the attic. This is an older home. After reading some posts now I don't know what to do. I'm older but I climbed into the attic and put styrofoam in the openings to close them, now I'm worried if rain will come into the opening where the WGs are! Input please!!
User
10 years ago
Cap them from above.
PRO
Windows on Washington Ltd
10 years ago
+1

If the roof is now insulated, pull the attic vents and close them up.

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