Insulation: The R value myth

[Hl.house]

Happened to read the following article. Would love to know what you all think about it?

The R Value Myth

One of the fairy tales of our time is the "R-value." The "R-value" is touted to the American consumer to the point where it has taken a "chiseled in stone" status. The saddest part of the fairy tale is the R-value by itself is almost a worthless number.

It is impossible to define an insulation with a single number. It is imperative we know more than a single "R" number. So why do we allow the R-value fairy tale to be perpetuated? I don't know. I don't know if anybody knows. It obviously favors fiber insulation. Consider the R-value of an insulation after it has been submersed in water or with a 20 mile per hour wind blowing through it. Obviously the R-value of fiber insulations would go to zero. Under the same conditions, the solid insulations would be largely unaffected. Again R-value numbers are "funny" numbers. They are meaningless unless we know other characteristics.

We are told, with very good reason, that insulation should have a vapor barrier on the warm side. Which is the warm side of the wall of a house? Obviously, it changes from summer to winter -- even from day to night. If it is 20 F below zero outside, the inside of an occupied house is certainly the warm side. During the summer months, when the sun is shining, very obviously the warm side is the outside. Sometimes the novice will try to put vapor barriers on both sides of the insulation. Vapor barriers on both sides of fiber insulation generally prove to be disastrous. It seems the vapor barriers will stop most of the moisture but not all. Small amounts of moisture will move into the fiber insulation between the two vapor barriers and be trapped. It will accumulate as the temperature swings back and forth. This accumulation can become a huge problem. We have re-insulated a number of potato storages which originally were insulated with fiberglass having a vapor barrier on both sides. Within a year or two the insulation would completely fail to insulate. The moisture would get trapped between the vapor barriers and saturate the fiberglass insulation to the point of holding buckets of water. Fiber insulation needs ventilation on one side; therefore, the vapor barrier should go on the side where it will do the most good.

 

[motorbiking]

In any system design you have to have some constants.. Its not unreasonable to work with norms and design around them. At a Macro level you could plot the typical conditions a house will face in a given location on a chart and most will cluster around a norm. Its therefore not unreasonable to design systems and specifications with those in mind.

The article also seems to be based around the design of American houses which are often SIPS based.

 

[^woody^]

Thats all American crap.

 

[John D v2.0]

Well our architect did a condensation risk analysis for every month of the year based on internal and external temperatures and made sure there was no accumulation of moisture.
So yes if you get it wrong, all sorts can happen that you don't want, so that's why you should check first.
Moisture coming overnight and going during the day isn't a problem, it's when it hangs around and never evaporates for whatever reason.

 

[JohnD]

Consider the R-value of an insulation after it has been submersed in water or with a 20 mile per hour wind blowing through it.

if my house was submerged in water, or if the walls and roof fell down leaving just the insulation exposed to the wind, R-values would be the least of my problems.

Some nutty yank with an axe to grind wrote that garbage.

 

[^woody^]

Well our architect did a condensation risk analysis

Why?
Didn't they know how to design?

I've never heard such nonsnense as "Condensation risk analysis" , but the sad thing is that I'm hearing it more and more, and invariablly for the wrong reasons.

 

[bernardgreen]

Walls that breathe can have high insulation and do not need vapour barriers.....

[/B]

I also wanted to mention that when it comes to thermal insulation, it is the thickness that counts. Thirty-five centimetres means approximately 14 inches of insulation. Wood wool gets used a lot. It still does not exist here, but there is a mill that is going to open in the National Capital Region. There is also a lot of cellulose used in insulating products that they use, but that means you end up with very, very thick walls, which needs to be factored in.

I should also stress that under the Swiss and Austrian criteria, and to a large extent in France too, those that are at the forefront of the green revolution build walls that although very thick and very well insulated, nevertheless let the humidity escape from the building, they breathe. Just like you would not go cross-country skiing in a rain jacket — there are materials like GORE-TEX, for example, that allow the body's moisture to escape when you are engaged in these activities — we want to develop a housing environment that allows moisture to escape just like a GORE-TEX coat does. And as far as that is concerned I can speak frankly when I say that in Quebec and in Canada there is still a lot to be learned.

We are behind on that score, and we are still using type 1 vapour barriers, plastic and aluminum, and there are better ways of keeping moisture levels at an appropriate level in houses. I am not saying that you can snap your fingers and change things overnight, but things are moving on that front. Back home, in our architectural practice, we have been making walls that breathe for the past 20 years. Now let us be clear, having walls breathe does not mean that they are full of holes. I am talking about walls, just like GORE-TEX, which keep you warm, but which let the humidity out. And even if your rainproof coat had air holes where your armpits are, you would still be extremely uncomfortable. The same is true in a house, it is good to have something to circulate the air, but not just to control moisture.

read a great deal more http://www.parl.gc.ca/Content/SEN/Committee/403/agri/02eva-e.htm?Language=E&Parl=40&Ses=3&comm_id=2

 

[motorbiking]

I think we have got to a point though where U-values are getting so low that we are introducing other problems. Personally anything with U-value sub 0.1 is a bit pointless unless you've also excluded drafts, minimised windows etc.

 

[Doggit]

The person writing the initial article shows he has a little knowledge of a lot of things, and shows he doesn't understand the reasoning behind the testing procedures to determine an insulation value. In the summer when it's hot outside, it'll be immaterial which side the vapour barrier is, but in the winter, when the insulation is needed, the vapour barrier needs to be as specified in the manufacturers fitting instructions.

I suspect he was the person that overthought the problems, and put vapour barriers both sides, but won't admit that he screws up.

As to continually lowering the U-values, I've heard reports where the over insulated houses can't soak up the summer heat, and are unbearably hot.

 

[endecotp]

I love that the advert appearing in this thread is for

"EcoQuilt Foil Insulation - equivalent to 120mm of fibre but only 15mm thick"

 

[cjard]

minimised windows etc.

That's something you do when you've got too many programs running an need a bit of clear screen space, right?

On a serious note, it's not necessarily about minimising glazing, it's about orienting and shading it correctly so it naturally provides good solar gain in winter when e sun angle is low, and low gain in summer at higher angles. It's possible to desi windows that admit as much heat as they lose, so when it is buffered sensibly it makes no overall difference

 

[cjard]

.

As to continually lowering the U-values, I've heard reports where the over insulated houses can't soak up the summer heat, and are unbearably hot.

Insulation does work both ways though.. it keeps your paid for heat in in winter and keeps the radiant heat from the sun beating on the tiles out in summer. If there's a problem with the equation it's simply that the design of the house lets the wrong amount in in the wrong context.. it's not correct to say "oh my loft conversion overheats in summer because of all the insulation", it's more a case of "my massive roof lantern in the midday summer heat is the equivalent of having a 16kw fire blazing away in my polystyrene box"

The solution is not to find a way to get rid of the heat accumulated inside, it's to keep it out in the first place..

 

[Malc]

The americans have a problem we in uk don't though. They can have air conditioning in the summer and heating in the winter. In uk the vapour barrier goes to the inside. Warm air holds more moisture so what you want to control is warm air leaking out since as it gets colder it will then condense somewhere in the wall. Or control where it condense to the outside face of the cavity. In USA, winter, heating same applies. In summer it is reversed, outside can be hotter and have more moisture so damp occurs on the outside surface of the vapour barrier.