have you looked at just blowing in some fiberglass or cellulose over the old insulation. much cheaper and easier.

would you remove the fg batts before installing foam on the attic floor (joists)?

any mechanicals or ducts in the attic?

you do understand that what is being proposed is that with the roofline foam install your attic will now be unvented instead of vented?
have you done any research on unvented attics in your climate?
visit www.buildingscience.com and check what they have to say for your location. this is not a site selling product so the info is unbiased, and an excellent resource.

I'm in a hot climate and just finished the paperwork on an audit nearby. The only upgrade they did was foam insulation (open cell) on both the roofline and under the house (house on piers). Their cost for the less than 1700 sq ft house was around $8,000 payback was 13 years lowered monthly utility cost was $60. As they are all electric and don't have a heat pump winter time savings will be equal to cooling savings.

we do open cell here, when the roof leaks we want the water to pass through the foam and not be trapped agains the roofline (or under floors).

foams won't void shingle warrenties or cause them damage.
(not that shingle mfgs honor warrenties anyway!)

best of luck.

The R value if I blew in cellulose would probably be around 25, a far cry from R 40_50 which is the recommended value for attics in this area. BTW, is this an appropriate R value for this area and temp range or is this on the high side? I am not sure how beneficial this would be but given the cost/benefit ratio, maybe it would. How could I figure this out?
Yes, I would remove the fg batts before installing foam. No, there are no mechanicals or ducts in the attic. Thank you for informing me of the vented vs. unvented space. This was not brought up in our discussion although, the person did recommend to me the building science web site and the book called "Cold Buildings"?. It did say in that book that one could expect a 10% loss of life span for the shingles although much more is lost depending on the color of the shingle and its orientation. In order to get the higher R value, I would have to use CCF otherwise, the R value for OCF and cellulose is about the same so what would be the benefit between using one over the other? I will look into the consequences of having an unvented attic in this area. THANKS YOU. How much additional savings would I experience getting an R 40 over and R 25? I presently have oil heat. The cost for CCF is high, for 1200 sf it was $10,000 !!!! OCF 6700. We use about 800-850 gal/yr for oil. What is my best option? We plan on staying here for 20 yrs..

This question has been so much discussed in the literature and forums that it is almost surprising that it is raised again. The giveaway is "knowledgable sales person" which translates to maximizing profit. This is one application where foam should probably not be used unless the whole attic is needed for conditioned space. Blown cellulose and more fiberglass bats would give any degree of high R value. The Family Handyman in the Dec/Jan 2010 issue has an article "Super-insulate your attic" with many good pointers including the sealing off of air leakage. I think you need to get three or four bids for your work.

this is the trade off Richard.
Time, materials and effort to air seal
vs cost to foam insulate& air seal in one step.
one takes considerable effort and time
although materials are less
the other takes little time little effort
and higher cost.
air sealing is the KEY to insulation performing
as spec'ed.
foam just makes it easier.
And haven't you noticed that FAQ's are ok for
the other guy..but this is MY house ans I have
specific to me questions...LOL!
Just the way it is...

OP, in my cooling climate we insulate to R-38
there is a diminished return on investment with
more insulation..but it starts diminishing when
you insulate over R-19 as the first few inches of
insulation work the best.However most states mandate
R-30 and above and there is a good savings in higer
values. Just how much for above R-38?? Don't know
for heating climates..ask Joe @ bulding science!

I'm glad to hear that you would remove the batts before
foam sealing the attic floor. Personally this is the location I would purchase in your situation. No mechanicals
or ducts in the attic make the roofline install more of a
profit for the foam co than actual benefit to you.
If I were you I would opt for this, but with the specification that the insulation at the eaves of the house
be installed from attic floor to soffits to roof making this an air tight install. (it won't be 100% air tight...even though they sell it as such) This will seal exterior walls at top plates which is always an air infiltration site.
Oh and WELCOME YOU!

Merry Christmas all!

The best way to really cut costs... in our heating climate is to up your insulation R and... to really stop all the airflowing in and out of your home. Get a handheld laser guided temp meter and you will amaze yourself walking around checking your rim joist, bilco doors, windows, doors, receptacles, interior partitions, recessed lights, bath fans, range hoods... attic entrys. I dislike vented attics now that I have used icynene sprayed to the roof and poorly sealed and insulated rim joists... Air flowing through your home is a huge part of your most homes heat loss. I have been in homes where you can feel the breeze blowing from rim joists... and plumbing pipes entering into attics...

Seal up your home first... you can do the rim joist yourself. The attic needs good sealing and then cellulose as deep as you can install it... with venting for roof maintained. Alternatively I do love icynene sprayed right to roof deck eliminating roof venting. I have checked in August roof temp differences... It is consistently 5 degrees different with black asphalt 30 year shingles here in Lake George, NY on a project we completed recently.

Thanks jackupstateny, do you have any good quality brand names for a laser guided temp meter? Thanks for the info and will work on this asap.

We put OCF in the walls and filled in between the rafters in our new build. The foam installers even "wrapped" the rafters in foam -- so basically all you see on the "ceiling" when you are in the attic is foam. Our attic, naturally, is not vented; it stays within 5 or 10 degrees of the inside of the house -- and the a/c has to struggle less because the ducts are in a conditioned space. Our electric bill reflects the fact we used foam: it was $120 last month for 3100 square feet, 3 air conditioning units/heat pumps, and Christmas lights.

Go with the foam -- you won't regret it.

You want an infrared thermometer, that uses a laser for pointing. Get one with something close to a 12:1 spot ratio or less. That means that at 12 inches from target, you are measuring a 1 in diameter around the laser point. At 12 ft away it's 1 ft diameter being read.

This is a good one on Amazon below.

Here is a link that might be useful: KINTREX IRT0421 Non-Contact Infrared Thermometer