Attic insulation options / Home energy efficiency

[stickfigure]

Foam worked well in my house. Electric bills dropped and attic was never more than 10 degrees different than house. I left some of my ridge vent unfoamed so that my gas unit could draw in fresh air.
If you don't go with foam, the next best thing is what bowhntrmatt said. (balanced intake and exhaust vents) continuous soffit vents and ridge vents, although many of todays houses have limited ridges to install vents.

[ken800]

If you go foam, just be sure it is closed cell. My last house was foamed by the builder and while it did keep the attic no more than a few degrees difference from the house, it was open cell foam and held way too much moisture. I ended up having to put a dehumidifier in my attic space to keep mold from growing.

[bowhntrmatt]

Matt if he isn’t totally encapsulated why would he have to change HVAC and add make up air?

If the walls aren’t sealed wouldn’t there likely be enough air infiltration around doors & windows?


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Not talking make-up air for air exchange in a tight structure. What I meant was combustion air for the gas appliances. You don’t want your attic to go negative air pressure and building code says you can’t use conditioned air for combustion.

For example, if you have a gas furnace and water heater in attic and both are running. Furnace uses an induced combustion system, forcing a large amount of air out of the exhaust. If this air isn’t made up in the attic it can backdraft a naturally-drafting water heater. Good way to die in your sleep.

Even if it’s just the furnace up there, if you seal the attic up completely, the only place for make-up air to come from is leaks and penetrations in the ceiling, which can kill overall efficiency of the home. Another reason I hate powered attic fans in otherwise poorly-ventilated attics.

Op, the reason I was talking about system replacement with foam was because your existing equipment will likely be oversized. Also, multi-stage or variable-speed equipment pairs well with encapsulated homes because usually a very high percentage of your heat gain will come from windows (since you have addressed other major heat gain factors with the spray foam). This could mean you need a 4 ton ac in the afternoon, but just 1.5 tons after the sun sets. It’s nice to have a system that can adapt for maximum comfort.

[erikm1981]

Just got three quotes for the same issue. My home is 2750sqft. I got quote breakdowns for adding radiant heat barrier foil, solar attic fans, and added insulation to get to R60.

All quotes were all over the place.
$17,500 this guy was using the paint heat barrier
$6500
$3800

I’m about settled in just adding insulation myself to get to R60. I also have some knee walls in the attic from ceiling height Changes and will add radiant heat barrier wraps to those to keep the heat transfer down. Will probably go with the solar fans next year.


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[Mike D]

If you go foam, just be sure it is closed cell. My last house was foamed by the builder and while it did keep the attic no more than a few degrees difference from the house, it was open cell foam and held way too much moisture. I ended up having to put a dehumidifier in my attic space to keep mold from growing.

Open cell is typical in attics and walls of houses. Closed cell is normally used in more open structures like
metal shop buildings.


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[Mountaineer]

I'm starting to research some different options for cooling down my attic and making my home more energy efficient.

Basically I'm looking for the most bang for my buck in energy savings.

I'd appreciate hearing any feedback / experiences...

There are a lot of factors that go into it. Design of your attic & roof, exposure to the sun, shingle color, age of the home, etc.

Increasing attic ventilation is helpful. Generally, ridge vents with continuous soffit is most efficient if you have long ridges on your home but I would add more soffit intake vents with baffles and a maybe a few more static roof vents if that's what you already have and don't have enough to begin with.

Electric attic fans aren't cost effective and motors commonly burn out. Solar attic fans are probably about even with cost vs. energy savings if they last a long time.

I've seen a lot of attics with the silver spray paint and foil-type radiant barriers. I don't notice much difference with attic temps and you can't see your roof decking and vent terminations to check for water leaks. Radiant barrier-backed decking is good, but not cost effective if you don't already need to replace your shingles and old decking to begin with.

I don't recommend adding foam to encapsulate without planning to replace the HVAC system with high-efficiency gas units or electric. I've seen a few of these installs and they weren't good or safe - with the combustion air issues mentioned above.

Feel free to pm if you want to send me some pics of your roof, attic, and current attic ventilation design.

[mooney_ag]

Understand the soffit vents or continuous soffits but how do I maintain circulation with vaulted tray ceilings?

[ken800]

Open cell is typical in attics and walls of houses. Closed cell is normally used in more open structures like
metal shop buildings.


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That's not universally true. They put closed in the walls and open in the attic on my house and when I got a quote to do my cabin it was the same without asking - closed for the walls and open for the attic.

I'm not going to debate the value of each as I'm not an engineer. I just know that I had a serious issue with open cell trapping moisture. Perhaps it was the installation - poorly mixed, etc.