r38?

[MitchellGlass]

whats the best insulation for the money? I havew heard R38 is what you want. is it worth the extra money? I am planniong on building a 2 floor 4200 square foot house, I want to learn all i can about insulation. whats approxiate costs for insulateing the house?

[danh]

No, it isn't worth the extra money.

If you want to improve energy efficiency in roofs, look to improving the taping & sealing of drywall joints.

[rabadger]

Have your HVAC guy run the calculations with your chioce of attic insulation and then R38. See what the difference is. It may change the required equipment size or may not.

[rbisys]

Greetings,

If you want to go for max energy eff, you won't get it with FG, Cel or foam. I have written a paper on the the eff of various insulations. If you want a copy e-m me your address and I'll send it to you. Most common insulations gain/lose up tp to 20-30 btu/hr/sf. Radiant barriers gain/lose about 2-3 btu/hr/sf. You can use ground temp water (not geo) to cool a house with these RB.

[ODDJOB]

You might want to try the owens corning web site, there you can enter your location and they can tell you what thickness is recommend for a particular application.

[tooltroll]

If you want to go for max energy eff, you won't get it with FG, Cel or foam... Most common insulations gain/lose up tp to 20-30 btu/hr/sf. Radiant barriers gain/lose about 2-3 btu/hr/sf.

Depends on where you are. RB's aren't recommended for cold climates. They're an AC improvement and do little to improve heating efficiency. See
http://www.healthgoods.com/Education/Healthy_Home_Information/Building_Design_and_Construction/radiant_barriers.htm
down near the bottom somewhere. It also mentions freezing & condensation problems during heating season.
Check
http://www.sprayfoam.com/
for some interesting info... (I love this stuff :D )

[rbisys]

Greetings,

RB are used in buildings the Artic. If you see a documentary on the Artic and they enter a building, the first thing you see is RB on the walls.

RB were first used in the Artic about 1964 because the Navy CBs had to chip out the ice impacted FG and replace it with new batts. This was a continual process, repeated about every 2-3 weeks. When Rb replaced the FG there was no more replacement. The Navy issued a RB material spec at that time, HH-I-1252.

In 30 yrs I have never heard of water pipes freezing in a RB house, even without heat.

The competitors of RB are the ones who make the claim you have repeated here. If you look in a mechanical engineering handbook you will see that it does not list a differnce in the rate of emissity in any direction. By the way DOE lists this comment on their web site too. Guess why.

However there is a difference in the amount of RE emitted per up or down flow. But this affects ALL insulations. These vague claims also do not include the type of test, the number of foils, the delta T or even a comparison test and other variables. This is why I have been pushing for the amount of btu's radiated from a interior ceil/wall surface to a floor surface, using varioue temperture differences. This takes into account ALL variables, including the structure. IT IS THE ONLY FAIR AND ACCURATE METHOD FOR ALL MATERIALS. This is what the US Senate stopped in 1981 when they cut operational funding to the FTC until the FTC recinded their new regulations. This is on record.

The thing one must ask ones self when reading any specs, particurally insulation specs, is, Who financed the tests. Do the test compare, under installed conditions, the differences. Is the statement devoid of test procedures or comparisons, and so on. Manufacturers are vary guilty of making the type of statement you made and let it hang there for YOUR interpetation. If their products are so good why don't they back them up with truthful facts.

I hope this helps.

[rabadger]

Nice post. Thats why I I told him to have the load calculations run with the different materials. By looking at the different building HVAC load requirements one can see that just because a manufacturer boasts about added savings the required equipment size may not change, therefor payback may not ever be realized. why pay more for insulation when the equipment size remains the same. You could take the savings on insulation and put it into high efficiency equipment.

[rbisys]

Greetings,

I did not include the rate of btu's emitted from the ceil'g for FG and RB.

95 deg day, unshaded roof, mid afternoon. values are approx.

FG ceil'g 110 deg to 75 deg floor. 37 btu/hr/sf.

1 layer RB dividing airspace. 2 btu/hr/ sf to drywall, plus joist conduction.

2 layer RB attached to BOTTOM of joist with 1/2" metal sound channel, about 2 btu's/hr/sf TOTAL. The joist surface becomes a low emittance surface.

Maximun air temp above RB about 11 degs over ambient out side temp.

If house is designed properly you can just about eliminate a/c.
Ranch style houses are easy to heat with low cost passive solar.

I try to elimunate as much HVAC equipment as possible. Could that be why HVAC contractors ignore me?

[danh]

You might want to try the owens corning web site, there you can enter your location and they can tell you what thickness is recommend for a particular application.
I think that Owens Corning are the last people to talk to about improved energy efficiency. Somehow I don't think improving their product is a priority when they have dominant market share. PS R-Value only works if you have no air flow. But that takes money away from Owen's Corning.

RB are used in buildings the Artic. If you see a documentary on the Artic and they enter a building, the first thing you see is RB on the walls.

I'd use RBs as the interior finish on my walls too if I was in the arctic. You get a 1.0 reflectivity reflector and a vapor barrier together. Realistically, radiative & convective transfer are the dominant transfer modes in nature; we pretend that heat travels by conduction but that happens only if we sandwich layers together (to prevent radiation) and cut off all air leakage. How often does that happen? Honestly?

But it's not the reflectivity that is important in hot climate applications; it's the low emissivity. The RB industry has done such a poor job of even explaining how that works. How hard is it to explain to a customer that 1 + 0 + 0 = 1?

But let's talk about the rest of the story. Like the fact that reversable vapor drives put your arctic RBs in prime location to act as a condensation plane under summer conditions in more moderate climes.

Let's talk hot climates, roof deck RBS. Now we have a low emissivity material on the underside of the roof deck, storing solar energy and preventing it from being radiated to the attic floor. Sweet, right?

But how is that heat dissipated? This is where the RB website recommendations for over-ventilation come into play. Oversize the soffit & ridge vents, conduct heat from the RB into the air stream, yada yada yada.

But hot humid climates have no basements. So over-ventilation + attic HVAC = recipe for disaster: condensation issues. We can't win. We really can't.

Who else wants to step up? My work day is over & I'm going home. Heck, I'm not even an expert. I'm just a dude who knows how to think and does google searches.