[Badfish740]

Since the 90s are already here in NJ I am finally getting around to the air sealing/attic insulation project I've been putting off. I have a single story ranch with a simple gable roof. There are four ceiling fans, one ceiling light fixture, six recessed lights and one bathroom ventilation fan penetrating the ceiling so those all need to be sealed up which should be pretty straightforward. I'm going to use some plastic covers I found at Lowes along with Great Stuff to seal around the ceiling boxes for the fans, the hall light fixture, and the bathroom fan, but the recessed lights are going to be a challenge. I don't know whether they are IC rated or not and can't tell because the attic had a mold problem (due to poor ventilation) before we bought the home and it was sprayed to encapsulate what could not be removed-as a result the cans are completely coated. I have read about building a box out of drywall around the cans with 6" clearance all around to ensure that they don't get too hot and then caulking/taping the seams and joints. Does that sound like the best option? Besides the obvious ceiling penetrations what else should I be looking for in terms of leaks? The attic access is in the garage which is unconditioned space so I'm not going to worry about sealing it.

Once the ceiling is air tight I need to address the attic ventilation. Prior to our purchasing the house there was mold in the attic due to the fact that there was no ridge vent, soffit vents, or any type of mechanical ventilation-only two undersized gable vents. We got the seller to agree to have the mold taken care of, as well as install a ridge vent and two attic fans. The problem is that the attic fans now pull conditioned air from the house because there are still no soffit vents. The air sealing will help, but I still need to put in soffit vents of course. I was planning on installing the circular vents about every 4 feet.

Finally, I need to address insulation-the amount of insulation in the ceiling is a joke. I have about 6" of fiberglass and that's it. I figure the ceiling insulation is about R-15 and I want to get to R-60 in the hopes that it will lighten the load on my A/C this summer and keep more heat in during the winter. The question here is unfaced fiberglass batts or blown cellulose? I used the calculator on the Lowes website and found that I would need either 87 bags of cellulose or 32 bags of unfaced fiberglass in order to achieve R-60. Either option will cost about $1000 for the material. Lowes offers a free 24 hour blower rental with the purchase of the cellulose so there's no additional cost there. What is the better option? I'm leaning toward cellulose since it seems like it can really fill in where fiberglass would sort of just sit on top, but there's also the fact that it does settle over time.

 

[gregzoll]

http://buildingscience.com/ has a lot of info for what you are looking for.

 

[federer]

i have a similar insulation project. the 6in space is what i have read too. so nothing catches on fire. as for soffits, i would run it all along the eaves, not just every 4 feet.

 

[jklingel]

FG vs cellulose is not even a contest. Leave the FG at the store, and blow cellulose right over what is there. You are very wise to air seal; do so like a madman. I think the sheet rock boxes for the lights will work, but check w/ a code-freak on that. Ventilation should be 1 sf of vent to every 150-300 sf of attic area. If you have wind, keep soffit openings near the house, to prevent wind washing. Have a good weekend.

 

[HomeInsulation]

Air Sealing your Attic

BadFish740,

Your analysis of the project at hand is dead on! You're asking all the right questions and your attic air sealing, insulating and ventilation project is really going to make your home more comfortable this summer and save you a ton of money.

Let's start off with air sealing your attic. In addition, to any penetration in your attic, like the ceiling light boxes and recessed lights, you need to air seal the gap between the wall framing and the drywall that creates your ceilings. The 2X4s shrink over time leaving a gap where air can leak through. Great Stuff works great here.

Make sure to squirt some foam into the electrical and plumbing holes in the top plates.

Chimney chases and plumbing chases are some of the largest unsealed holes in your attic. They are frequently not air sealed because they look like they're supposed to be there. To air seal a chimney chase, you need to use sheet metal and high temperature caulk.

There's a lot more on air sealing an attic here..

http://howtohomeinsulation.com/insulation_basics_losing_money_sealing_attic_air_leaks.html