Good day all, I will be building a ICF building in the next year, and have a qeustion about placement of icynene insulation. The home is apx. 2500 sqft, vaulted ceilings, but not common with the roof decking. Truss roof system. My qeustion is, do i spray the icynene on the underside of the roof decking, down to the top plate, then apply bat or blow in insulation to the topside of the sheet rock?. Any input would be helpfull. Thanks in advance. E.Jones

I use Icynene applied to the bottom of the roof sheathing, which effectively moves the envelope to the exterior plane of the building. This works extremely well when you use Attic storage trusses for the room in the attic to finish later.

Adding other batt insulation is a redundant unneccessary step.

E. Jones
3' or 4"" of foam are enough to take care of most applications. All you will need to do is to spray the roof sheathing.
Close off the soffits and spray the area over the top of the exterior wall up to the roof sheathing.
Do not use a roof vent.
Put a positive air exchanger in the HVAC system. This is very important.
Keep a slight positive air pressure inside the house so that air tends to move outward when a door is opened.
Have your HVAC contractor do a Manual J calculation on each room or you will oversize the system.
Use insulated glass in the windows with a Low E coating that is designed for your area.

Your electric bill will be about 1/3 of that of a similiar block house..
Regards,
Joe

Joe, I am in the process now of building a 5000 square foot ICF home in the Houston TX area. I plan to use the spray foam to seal my attic. However, Richard Rue of EnergyWise Structures says that I do not need an air exchanger. Everything I read says I do yet he is the expert and has many homes out there built his way. What are your thoughts? Mike

I guess that would depend on his location. In a cold climate that would be a big mistake. In my area, he'd have the only roof in the area with no snow on it.

Mike,
An air-tight home, whether built with ICFs, SIPS, or any other method that will assure such an air tight condition, needs a source of outside 'fresh' air.  Your expert may be the only person I've heard of who does not preach the use of some type of fresh air introduction.  Otherwise the air inside the structure becomes stale--loaded with CO2 and other indoor air pollutants that are very bad for your health.  The introduction of outside air dilutes and removes these pollutants.  This leads to less problems with allergies, asthma, and other illnesses associated with 'stale' air. 
Bottom line--ALWAYS include some type of fresh air introduction in your projects.

I think everyone is missing the point! It doesn't matter if you have an ERV or an HRV, what matters is how the building and it's associated systems works together.

I agree that you don't need an expensive fresh air interchange unit, in fact I haven't used one yet, and I doubt I will. I do allow for some fresh air exchange, typically using programmable electronic timers on specific exhaust fans. Then, before you worry about how old style burners function, why not use "direct vent" units which have their own air supply?

I guess what I'm saying is as long as a product is made...it doesn't mean you have to use it! Look at the complete package and determine a functional path to better living!

Mike,
One outfit here in SW Florida built three ICF spec houses and did not even seal the attic nor did they put in an air exchanger., The first family that lived in their house got sore throats, upset stomachs and terrible sinus headaches within 6 weeks. The other two would not sell because of the adverse publicity. They sued the builder and he had to buy the house back. I told him to put in the air exchanger and the problem went away. All three are now occupied.
Think about the situation a little bit. If you take a house and seal it so that they is no air infiltration, and that means little air exchange from the outside except when a door is opened and shut. What happens to the cooking smells and the people orders and the out gassing from the cabinets and the carpet and the paint?
There are a lot more experts in air quality design that tell you to put in an air exchanger than there are expert builders who don't want to spend the money and tell you not to bother. They don't have to live with the results, you do.
Also, an air exchanger is just that, a fan blows fresh air through a filter and the duct system distributes it around the house. It is NOT an ERV or an HRV.
I happen to live in an ICF house with a sealed attic and an air exchanger so I have more than a little first hand knowledge of that which I speak. My HVAC sub would not install the unit without the air exchanger nor would I live in the house without it.
Regards,
Joe

Joe
I see by my previous post that I may have worded it ambigiously.

I agree that some air exchange is necessary, that is why I do it the way I do. I do not agree on the forced use of an HRV or ERV to achieve that air exchange when there are both passive and inexpensive active ways to achieve that air exchange!

MikeICF... We used Richard Rue for our Amvic block home here in Dallas. I must admit that we were surprised about the "no need for erv/hrv" thing, but James makes a valid point re: what matters is how you get air changes, fresh air, etc. We have lived in our home for 16 months now and have never had any air issues -- and this is with 4 cats too... ;-) We insulated as per the EnergyWise recommendations. Our one attic on one end of the house has one of our small furnaces in it and is gable vented, with Sealection foam on the attic floor joists and the exposed ductwork up there. Our indoor humidity levels are consistant at 46-48%. We keep our temp at 77F in cooling season and 71F in heating season. You live (obviously) in a much more humid area than Dallas, so your mileage may vary, and you may use heat pumps and have no need to place a furnace somewhere. If I had to do it over again, I would seriously look at a sealed attic, but I am not unhappy that we do not have one. It would be interesting to know if/how it could be done now, and what that would really give us, as we are more than happy with our energy bills so far. Anyway, those are the thoughts of a homeowner that has lived with Richard Rue's spec for over a year now. Best of luck -- there's some great info here on this forum and we used it a lot at the pre-build stage!

I am still in the "deciding what to do" stage on the air exchange. It is very difficult when people are at both ends of the spectrum. I talked to someone here in Houston the other day who overheard Richard Rue talking to Tom Tynan (Houston and Dallas Homeshow Radio talk show host) about ICF construction, venting of walls and attic, etc. Tom Tynan is a believer that energy efficency can be equally achieved with venting the walls (vent skinning) and venting the attic with ridgevents and soffit vents. Richard asked Tom if he thought all structures used to provide shelter for humans must be vented and must breath. Tom said absolutely they must. Richard then asked him how it was possible for the first astronauts to go in space were able to survive in an "air tight" container. I was told that Tom just had a stunned look on his face, turned red, and did not answer his question. I have yet to talk to Richard in person and see why he thinks the air exchange in my ICF home is not needed. I will see what is reasoning is and try and pass it on if anyone is interested in why he believes they are NOT necessary. Mike

James & Mike
It would be a very dull world if everybody had the same opinion. You presented yours in a professional manner and I respect that. My opinion is based on what I read and what happens here in SW Florida. I hope I come across as well as you two have.

Here in Paradise I have a 2016 sq ft house with 9'4" ceilings and my actual electric bill for August was $92 for the electric and $73 for the fuel chares , taxes etc. My attic never gets over 87 degrees. I have a hot tub that runs 24-7 also. It costs me $11 a month because I had it sprayed on the inside with foam.
Regards,
Joe

Mike... I used to listen to Tynan a lot, and I did learn some stuff from him, like great paint (S-W Duration), always make sure you get a TXV-based, VS-speed HVAC, and a few others. The one thing I knew to take with a huge grain of salt is this: he is a traditional stick builder and he has a 'bought time' radio show. That's radio where the guy BUYS the time from the station(s). 75% of weekend AM radio advice shows are bought time. They solicit sponsors to pay for it. Central City Air is a Tynan sponsor. CCA sells ERVs and HRVs and does indoor air quality testing. Now, connect those dots to get Tynan's advice. If you paid Richard Rue for your audit, then call him and talk. I talked to him a LOT about our home and how he marked up our plans. Due to the nature of the design -- a 28ft lofted living/dining/kitchen space in between two sleeping/media areas -- we required two heat & A/C systems. They needed to be small enough, but not too small; or too big on the heat side that we would dry things out. He was most helpful as I ran numbers and stuff by him. 80% vs 90% furnaces, 13 SEER vs 16 SEER vs our insulation and ICF walls and payback and comfort. He was awesome and I never once thought that he was trying to "get me off the phone." Bottom line with him is you have vents and windows and doors and all of them run or are open during the day. Your house is never sealed. Windows that open are never completely sealed when shut. There is always freash air leakage unless you wrap the thing in cellophane! FWIW, our 3000 sq ft 1.5 story home, with the 22 x 28 ft, 28 ft lofted ceiling living/dining area, and 10ft ceiling main and 9ft upstairs wing, electricity for a/c is listed below -- in our hottest summer in 10 years. And I'm doing consumption because rates in Texas (as you know) are outrageous and you can't compare $$ - we pay 14.7 cents a KwH! June/890, July/1589, Aug/2077, Sept/1388. Dollars ran a range from a $130-$305. Happy investigating!

Just curious Bill, did Richard not suggest a sealed attic for the Dallas area? He told me that without question on the Gulf Coast (hot humid climate) it was a must. I had already learned on the Building Science website that for this climate it was the recommended way to build. Do you think your home would have been more efficent had you gone with a sealed attic? It just makes sense to me to have the attic be a part of the conditioned space. Heck, I might even sleep up there if Anna kicks me out of the house! Mike

Bill, I forgot to mention that my walls are complete and we are going to pour/pump concrete at 10AM tomorrow! It is so excited after two years of waiting and planning!!!! Mike

No, Mike... it never came up.  North Texas is a LOT different than where you are.  You have two weeks where you do not have to mow your grass.... we have Nov-April!  We had a high of 34F today and will have our second night of 25F in a row.  The lawns and roofs are scattered with white and ice.

I fully understand the benefits of a sealed attic -- I don't regret it here in retrospect.  Our consumption numbers, as I posted, are fine.
Congrats on the pour!

Bill

Yes I know it is different there. I grew up near Lake Texoma in Sadler TX. I do remember the the dead grass and the snow and ice. I rarely see that since living in Houston for the last 31 years. My ICF pour went great today and the walls are now solid. It was funny as they completed the walls on one side of the house my wife and I were talking. She made the comment that they had quite working so we walked over to a door to see why. However, they were still working. We were unable to hear the noise of the concrete flowing and the loud vibrator they were using to settle the concrete in the walls. We both know we will appreciate the quite these new ICF walls will provide. Can't wait to move in next year!