Increase R value for closed cell attic/ roof ventilation?s
I currently have what I believe is a closed cell foam on the roof underside. Resulting in my attic being the most comfortable space in my home. There is a heat exchanger with insulated ducts for forced air heat (which i hate). After consulting with the HVAC installer he claims that since his exchanger has freon and the ducts are insulated there really is no need for the conditioned space. What I would like to accomplish is to retain more heat in my living space below by adding blown in cellulose to the floor of the attic where none exists currently. I have 9 or 10 inch floor joists o.c.16 inch. I already know I won’t meet code but my main objective is to stop loosing ALL my heat to the attic. Please advise…..sorry there are lots of moving parts. Additionally I am replacing the roof. My contractor wants to know if I want a ridge vent and GAFs linear soffet vents since I have neither right now. My gut tells me to stay with the original non-vented system. Note I am in New Jersey. Currently no signs of moisture, mold etc. Perfect environment in that darn attic all year round!
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Susan,
The attic is comfortable now because it was deliberately made a part of the conditioned area of the house by placing the insulation at the roofline. If you want to exclude the attic from the conditioned area you need to insulate and air-seal the ceiling, and vent to the outdoors to prevent the (now unconditioned) attic from accumulating moisture.
If you go that route you will lose all the benefit of the insulation at the roofline. But more importantly the equipment and ducts will no longer be in the conditioned space - which despite your HVAC installer's advice is a bad idea, and why the attic roof was insulated in the first place.
https://www.greenbuildingadvisor.com/article/ducts-in-an-unconditioned-attic
So let me ask you this. In Colorado my contractor buddies do spray foam then add fiberglass batts secured by some kind of blanket. Adding more foam to increase the R-value was cost prohibitive. No one has heard of that hear. My other alternative is to add rigid board on the roof decking when I replace my roof shingles. Any thoughts with these approaches?
You can use a mix of materials to insulate a roof, and it's not uncommon to use closed cell spray foam for some of the R value, typically applied right under the roof sheathing, and then to fill the remainder of the rafter bays with cheaper fiberglass batts to get the final R value required. That method is often recommended here. Sometimes a mix of spray foam materials is used too, with closed cell against the roof sheathing and open cell to fill the remainder of the space. The reason for these combinations is because closed cell spray foam is expensive, but has advantages for moisture control, so it's used right under the roof sheathing where it's required, but once a thick enough layer of that has been applied, cheaper materials can be used for the rest of the R value.
It is better to keep the attic conditioned, especially since you have mechanicals (your HVAC system) in there. You can insulate the floor to thermally seperate the spaces somewhat, but you'd be better off increasing air circulation in the conditioned attic space so that the spread the heat out more evenly throughout your home. It think you have more of a stratification problem here than a "heat loss" problem.
Bill
Susan,
Adding permeable insulation below the foam works well, as long as you keep the ratio of foam to batts high enough you don’t get condensation in the inside face of the foam. The assembly you are suggesting is #5 in this link: https://www.greenbuildingadvisor.com/article/five-cathedral-ceilings-that-work
Ditto on what Malcolm said.
The large temperature difference between the living space and the attic above is probably due to air leaks. Warm air constantly leaking out at the top of the house will be replaced by cold outside air drawn in below.
A blower door test will confirm whether your house is leaky or not. Some utility companies offer free or discounted blower door tests. If you house is leaky, then insulating the attic floor will do little to stop that flow of warm air. You will likely get a lot more comfort for the buck by locating and sealing the air leaks. That type of work is done by a weatherization contractor. They can also do the blower door test, but it's nice to have that done by a 3rd party if possible.
Here's an article on what is involved. Note the cautions at the end related to combustion appliances and radon testing:
https://www.finehomebuilding.com/project-guides/insulation/blower-door-directed-air-sealing
Bill please enlighten me and defined stratification? I have already had input to seal all leaks from fixtures etc. Sounds to me like a systems approach to my problem. Note my basement and attic are the perfect environments as compared to my living area!
"Stratification" is when a fluid (like air) seperates into layers of different temperatures within a confined space. In your case, the warm air is getting up into your attic, and presumably cooler air in in the lower levels. What you want to do in a situation like this is to "stir" the air, and since you have several levels, the way to do this with an HVAC system is with air returns and vents that are configured to pull air from where you don't want it and blow it to where you do want it. The classic example of this is using a ceiling fan to keep temperatures even throughout a room.
What you want to try in your particular situation is to have an air return in the attic, then use dampers to shut off airflow to the attic and blow mostly to the lower levels. This is "countercurrent", which means against convection in this case (you're pulling warm air from up high and blowing it out down low). This should be easy and cheap to try with your existing system, and it might solve your problem.
It's common to have a winter and summer configuration for ductwork in multilevel houses. The way you do this is to use dampers to open and close duct runs so that in the winter you put the heat into the lower part of the house, and in the summer you put your air conditioned air into the upper part of the house. Convection then acts to help even things out for you by way of convection currents.
Bill
Your idea would result in your attic being an interstitial space, cooler than the living level but sharing the same air so relative humidity levels would be higher, resulting in elevated risk of mold and microbial action. You could address that by conditioning the space, but if you're going to do that, you would be better off putting all insulation at the rafter level.