Attic insulation

[BrianAbington]

Originally Posted by Daox

so let me see if I understand this. The polyiso stuff would be those big sheets of that foam that is usualy put on behind siding. This is then cut into strips and laid in the rafters back into the wedge were the floor and the roof meet?

then the celulosic foam goes in over the top?

It looks like there is an air flow area from the soffit, above the roof insulation and out into the attic?

I'm learning all the time so forgive me for this, I under stand the advantages of air flow in the atic...but what does this do better than filling the entire attic with cellulosic or pink batts?

[larryrose11]

Originally Posted by Binger

so let me see if I understand this. The polyiso stuff would be those big sheets of that foam that is usualy put on behind siding. This is then cut into strips and laid in the rafters back into the wedge were the floor and the roof meet?

Yes

Originally Posted by Binger

then the cellulose goes in over the top?

It can go over the top. In my case, this area was thin on insulation and the only way to get a decent R-value was to use pollyscio foam where they have fiber insulation in the diagram because, the pollyscio foam is R-7/inch, cellulose is half that @ R-3.5/inch. and fiberglass is R-2.3/inch. So, if your are space constrained. use the highest R-value available.

Originally Posted by Binger

It looks like there is an air flow area from the soffit, above the roof insulation and out into the attic?

yes, that is the air passage.

Originally Posted by Binger

I'm learning all the time so forgive me for this, I under stand the advantages of air flow in the atic...but what does this do better than filling the entire attic with cellulosic or pink batts?

As I mentioned, it is best to use this foam board where you are space constrained. In this tight area on the diagram, you only have 3 inches. So, what to you want there? (7*3)= R-21 or (3.5*3) = R-10.5?
R-21 right?
Once you tackle these tight areas, the rest is easy.

Also, do you yourself a favor and avoid the pink bats. they have formaldehyde in them (FEMA Trailer anyone?), they under perform cellulose, and they LOSE 20% of their R-value when the temp drops below 30 F. The stuff sucks.

Before you install the loose fill cellulose, make sure you seal up your attic, like I said earlier in this thread.
Larryrose11

[Daox]

Just to clarify, polyiso is not (I believe) the normal foam board you buy at your local home improvment store. The normal foam board is called polystyrene and is cheaper and isn't quite as good at R-4 per inch of thickness. Polyiso (full name is polyisocyanurate) is a little different and as mentioned is R-7 per inch of thickness.

Also, cellulose is not a foam. It is a mixture of mostly recycled paper.


I'll be getting into the house at the end of the month assuming no hang ups. I'll be sure to post any progress here.

[larryrose11]

Daox,
Polyiso foam is avalable at Home Depot. It goes under the commercial name Super TUFF-R

Did I make a typo and call cellulose a foam? Its power-like Grey fluff. Works great where space is no concern, but wear a mask when installing in an open area.

[Daox]

Binger mentioned something about putting cellulose foam over the top. I was just clarifying for him.

Good to know you can get polyiso at the local chain improvment store. I kinda figured you could, but wanted to note there are more than one type of foam board avaliable. I'll have to check it out for pricing next time I swing by.

[elhigh]

The polyiso will look different, have a different texture. In my experience it's usually kind of an off-amber color, very fine grain.

Don't forget to keep your cellulose away from light fixtures, unless they're rated OK for insulation contact. Make a quick-and-dirty box to drop over the tops of fixtures to keep the insulation 3" away.

[larryrose11]

Daox,
elhigh,
ON recessed lights:
These things look nice, but you couldn't ask for a worse thermal offender. Typically they are double wall, with venting at the top and bottom, so they have a built in air leak. When they are on, the light bulb gets hot (Even CFL will get warm) and heat up the inner can. This heat is transfered into the air between the metal cans, where it rises to the upper vent, where it escapes, and room air is takes its place. This is a thermodynamic air pump. It is throwing your energy (heating or cooling) into the attic. The solution is to make boxes out of drywall (which is a fire rated material) and then cover this with foam board insulation, sealed up with GreatStuff. Drop these boxes over the recessed lights from the attic side, and back fill the gaps with more GreatStuff. You now have a airtight, insulated box with an air gap between the lights and the box, and a 15 min fire-rating.

[lgtech]

Hi guys,

Great thread! Sealing the air leaks and insulating the attic is top on my to-do list - the car has to wait. I'll be sure to take pics and post. I used 1186 gal of heating oil last year here in NH.

On the Great Stuff, I read in Family Handyman magazine the Great Stuff is *not* fire rated and should not be used for service penetrations between floors. In some cases, it is against code to use it; check with your local building inspector to be sure. Use something that meets ASTM E-84 Specifications and classified as a fire-rated foam insulation.

Have fun!
LG

[RH77]

Great thread

To expand the topic a bit, my biggest problem is the summer heat...

Aside from the built-in air vent / soffit setup, would it be beneficial to install an exhaust fan and inlet? I recall seeing one years ago that was hooked to a thermostat.

Also, do any new homes have attic fans anymore?

Last item: when it's hot on the second floor, I usually run the bathroom fans to pull the hot air out and let the cooler air from the A/C sink (the top floor ducts run through the attic and exit through the ceiling). The fans have a decent CFM rating (forget the number at the moment). The exhaust essentially looks like a dryer hose sticking out of the attic space. Is there a benefit vs. cost to this practice?

The house design is a traditional rectangle-on-rectangle 2 story (no level splits).

RH77

[larryrose11]

Originally Posted by RH77

To expand the topic a bit, my biggest problem is the summer heat...

Aside from the built-in air vent / soffit setup, would it be beneficial to install an exhaust fan and inlet? I recall seeing one years ago that was hooked to a thermostat.

Yes, these can be bennifical at cooling the attic, but generally, where the heat is coming in (summer)is where the heat is leaving (Winter), so a good sealing job (See above posts) is always in order. Also pay attention to the attic hatch. Think of it like a door. It my house, it was just a piece of plywood. I reinforced it with 2*4, heavily insulated it (I love foam board.) and put EPDM foam strip on both surfaces, the hatch and the ledge it sits on when in place. It seals nice.

If you have ducts running through the attic area, they need to be well insulated and sealed at the beginning and end. PILE cellulose insulation on top of the ducts. Make walls out of cardboard to hold the loose fill in place. If the ducts are metal, then I know that there are leaks along the path. Where they join are obvious problems. You can find the leaks by turning on the furnace blower, and with a stick of incense and a flashlight shining on the smoke. If the smoke moves at all while you slowly move the incense stick along the surface of the duct, then you found a leak. Seal up the duct leaks with aluminum tape, NOT duct tape. AL tape rocks!

Aside,
I would seal up all the duct work in a house you have access to. You can use Mastic, (furnace caulk) or AL tape. Use the incense method to find the leaks. you will be surprised at how many leaks you find. doing this ensures that the heated/cooled air goes to its intended location. In general, 30-50% of air in a HVAC system is lost due to leaks.

Originally Posted by RH77

Also, do any new homes have attic fans anymore?

Some do, but they are not std.
Unless directed otherwise, new house ae built to code, which is the bare minimum, and no where near good.

Originally Posted by RH77

Last item: when it's hot on the second floor, I usually run the bathroom fans to pull the hot air out and let the cooler air from the A/C sink (the top floor ducts run through the attic and exit through the ceiling). The fans have a decent CFM rating (forget the number at the moment). The exhaust essentially looks like a dryer hose sticking out of the attic space. Is there a benefit vs. cost to this practice?

The house design is a traditional rectangle-on-rectangle 2 story (no level splits).
RH77

What I did when I lived in a bi-level, is to use a house or window fan at night on exhaust on the upper level with the lower windows open. If you use a window fan, make sure that the openings around the fan are covered up so the air doesn't just circulate. Cool of the house as much as posable while the outside is colder than the inside, then close up the windows in the morning. When A/C was needed, cover up the send and receive ducts on the lower floor. leave 1 return open in the basement, but no supply's open in the basement. That way, the returns are open upstairs, the air that needs the most cooling. The supply upstairs get all the flow, and the cold air flows down the stairs via gravity.

When I say cover up the supply and return ducts, the built in louvers are a joke. Use a ex-shopping bag, stuffed full with other ex-shopping bags, and shove this in the supply duct under the grate. If this is not an option, use the flexible magnet material, available at your local hardware store to cover up the ducts.

Larryrose11