Insulation When is to much

[henfruit]

I have been reading specs on spray foam ect. They said at r 8 you have reduced heat flow by 90% if you go to r12 you only gain 3% and all the way up t r32 97% are we over insulating and just thinking the higher the r # is that much better? They also said the differance in cost from r8 to r32 wood take 107 years for pay back.

 

[Mcbride]

I have been reading specs on spray foam ect. They said at r 8 you have reduced heat flow by 90% if you go to r12 you only gain 3% and all the way up t r32 97% are we over insulating and just thinking the higher the r # is that much better? They also said the differance in cost from r8 to r32 wood take 107 years for pay back.

Do you have a link to this article?

 

[henfruit]

look up north east spray foam.

 

[tom in maine]

As the article says, it is somewhat relative.
If you are talking about insulating a house, you really need to think about Superinsulation in 2011. Superinsulation used to be R-40 walls and R-60 roof.
As the cost of fuel goes up these numbers increase.
IMHO, I think a house should be R-60 on walls and roof.
I would suggest going to www.builditsolar.com and run the numbers through a heat loss calculator to do a "what-if" in terms of heat loss.

Cheaper fuel like firewood would warrant less insulation, except when one considers the sweat equity that is involved in using wood.

My example would be my own home, which is R-65 sheet foam and spray foam. The energy use is about 250 gallons of oil annually for heat and hot water or about 1.5 cords of wood during the heating season with a heat pump water heater running in the summer.

Spray foam being rated at R-8 per inch is a little optimistic. I think its actual rating is 6-7 based on aged values.

As of now, R-60 seems to be the point of diminishing returns. I am sure it will go up as costs increase, but at this level, the rate of change is minimal.
Also at this insulation value, I think that active solar heating becomes a real viable option, with a very small backup system.

 

[bigburner]

" inherent mass" Any thing that has mass is a good insulator, no a great insulator, but a good insulator. 12 inches of any thing has an R-valve. [normally stated in U-factor] Before everyone starts yelling it's because of the speed that heat will travel threw the mass. When I was making Ice we had block machines that ran a -40F evaporator and put in room temp water, it would bring the water to 32 degrees then start freezing from the bottom. The first inch would freeze in an hour then two hours for the next inch 4 hours for the next inch and three days later it would be on 10 inches thick.[the insulating properties of the ice mass slows down the freezing process, thermal dynamics doesn't care which direction the temp is going up or down] 30F on the top of the block and -40 on the bottom, this process used RO water and was so clear you could read a news paper threw it. {no air bubbles} just ice. Got a bunch more examples will save for another day.

Insulation has a diminishing return on thickness. Spray foams ability to stop air infiltration makes the effective R-value better at a lower installed R-value. Any type of insulation over R-40 with a proper vapor barrier is IMO a waste of money.

 

[pybyr]

I have been reading specs on spray foam ect. They said at r 8 you have reduced heat flow by 90% if you go to r12 you only gain 3% and all the way up t r32 97% are we over insulating and just thinking the higher the r # is that much better? They also said the differance in cost from r8 to r32 wood take 107 years for pay back.

Depends on a lot of things. One factor that is sometimes overlooked is air sealing of the structure as a whole- if you have air leaks at the top and bottom of the structure (even if they're small individually, they cumulatively add up), air will convect up through and out, and, regardless of the R-value, you'll be fighting some form of a losing battle to heat the outdoors.

 

[benjamin]

Good point, I hear this about spray foam a lot. "The first inch is the most important" You have to think of where it's coming from I guess. These guys insulate a pole shed by spraying the inside of the steel siding creating an incredibly efficient building, at least if you compare it to how cold and drafty it was without the foam. I wonder if foam's tendency to crack has anything to do with why they are selling themselves short? Does it crack more if it's thicker?

The numbers on the website are ridiculous. The starting point of zero insulation is not a relevant comparison. I think they misplaced the decimal point in the annual savings based on $750 a year, if you double the r value, you halve the heat loss, so going from r 8 to r 16 would be half of $750 which is $375 not $37.50 unless they made the assumption that the house was a chimney like Pybyr mentioned and the walls and roof only accounted for 10% of the heat loss, that might work out to $37.50. I'd hate to see the house that lost only 10% of it's heat through r-8 walls. Then again, I had a friend who lived in a very cozy house with r-8 wall that he heated with under 40 lbs of propane a year, the house was on the back of a Toyota though, about a cord of space.

Or maybe I'm giving them way too much credit, they may have multiplied the percent "improvement in efficiency vs r 8" (which is misleading) by their $750 heating cost to get the annual savings, which is just incorrect. You save 50% by doubleing your insulation even if it is only 5% less compared to an irrelevant third number.

I recently did a seat of the pants heat loss (gain) calculation for my passive solar home in progress, and came up with 44 btu/hr/degree F for roof(11"cellulose), 77 for walls (7" cellulose), 220 for windows (lots of clear glass) and somewhere around 100 for air infiltration (wild guess). It wouldn't make sense for me to make 12" walls with this design because there is relatively little heat lost out of the walls, due to the relatively large heat loss and gain from the glass.

You really have to run the numbers for a particular situation to see where your money is best put to use.

 

[bigburner]

built a high end home for a customer last year 6000 sq ft, sip's on the roof 2x6 side walls, average interior ceiling height 15'- this house had all commercial style store front windows, tons of glass with very little solar gain. This place was so weird that a simple energy audit won't pass the energy code and we had to use a heers rating to get a building permit and establish a base line air infiltration number before it was built, if it doesn't pass the blower door test at the end you are screwed. Commercial window systems are crude at best the only good thing about them is the seal. We passed this with 30% glass, buy using 8 inch sip's on roof, 6 inches of open cell foam in all the side walls, foam all the bonds and used wet cellolouse in the walk out wall cavities. If you walked into this place you would think it heats like a barn, just the opposite the heating is about the same as standard walls & windows. The moral of the story is AIR INFILTRATION - PERIOD Build a house with no windows that has 2 or more air changes per hour or one with 30% windows and only 10% air change per hour, the window house will win by miles. Some thing that is cool are Air to Air heat exchangers [just the cube type] These things work great are relatively inexpensive. We build a tight a house as possible and then stick one of these in and now you got the best of both worlds, most have two speeds and draw very little power.

another project that I only consulted on was a large pole barn, we used 1.5 inches of closed cell foam on the walls then put in 6 inch of rolled fiberglass on top of that to finish off the wall cavity. This was VE choice, we wanted the max insulation/air infiltration barrier at the least cost. This type off building is almost impossible to keep air tight with out using spray foam to seal it up. Tall side wall exposure to wind can make even the smallest hole a cyclone. FYI - it has in floor radiant and under floor also in the finished loft areas. Trying to talk the customer into buying a Garn, this is the perfect set up for lots of lower temp water.

 

[Mcbride]

Even using a common house building style, with 6 inch stud walls.
The studs themselves offer a low R value, despite the 6 inches of insulation in between them.

Windows suck as far as insulation.

But wow I see some horrible drafts in so many homes aound electrical boxes and windows, seems some builders just do not care to take the extra few minutes to seal each one correctly.

I did my own renos, and made sure to eal up all the cracks, and insulate around the new windows I installed well, and also changed the outside doors.

No exageration, i cut the wood needed to heat this place in half once I was done.

Spray foam in a can is great stuff, used low expansion around the window and door casings. And high expansion to seal cracks and electrical boxes etc.

 

[btuser]

R40 in the wall seems a little steep. Maybe if you're building with SIPs but you'd have to save a lot of wood to pay for that.

 

[goosegunner]

My house is 13 years old, 2X6 walls fiberglass R19 walls wrapped with Tyvek. If I could go back I would use spray foam on a least the North and West walls. I have bad air infiltration on the outlets and switches on the North side.

Not sure how to seal it up now. Can you drill and spray foam behind boxes?

Otherwise I am considering pulling vinyl siding, cutting open OSB and spraying the entire back of the problem outlets. The 3 gang switch by my piece of junk Anderson patio door is the worst offender.

gg

 

[tom in maine]

R40 in the wall seems a little steep. Maybe if you're building with SIPs but you'd have to save a lot of wood to pay for that.

Perhaps, but you will use more energy otherwise.
I recall years ago, a friend who worked for a foam insulation manufacturer telling me that his energy auditor friends (hey. I amone of those!!) saying that walls should never be more than R-30.
They felt there was no payback.

As energy costs go up, R-40 makes perfect sense. You need to balance your investment against heating costs and insulation costs.
That is why I suggested running the numbers for different scenarios.

You buy insulation only once. If you have to go back and add it after the fact, it will cost you 10x as much to retrofit.

I think R-60 with good sealing (a lot simpler to do with foam) makes sense. I would probably not do it with spray foam, which is going to be your most expensive option.
I would be using sheet foam with some spray foam for sealing. SIPS are ideal. The incremental cost of foam to get to R-40 or 60 is solely the cost of the extra sheet foam--one of the best deals around. You will spend more on trim but it is worth it.

Some people drive Fords, some Mercedes. Some insulate a lot, some a little. Even if I am burning wood, I prefer to use as little fuel as possible.

 

[DaveBP]

I think this Fog of Diminishing Returns question is best answered by considering the perspective of the owner.

Europeans have a different view, on average, than Americans. I think they look more at the very long term costs of a building, both to the owner and to the community. Over a much longer term than our society does. They tend to build houses to last centuries, not decades like over here.
They have much more stringent and overall efficient construction standards because they know it's cheaper in the very long run. Maybe not to the owner up front but to everybody over the long haul.

We Americans just don't think about our homes as legacies to our children and communities.
It's too easy to think about them as monthly payments.

Compared to no insulation and big air gaps in the wall on a windy day, a film of polyethylene might be 900% better. That doesn't mean that is the point of diminishing returns.

"Diminishing Returns" doesn't have a POINT.

I guess that's my point.

 

[RobC]

GG. I think you could remove outlet or switch and foam behind box while in place, even if you had to drill small holes in box. They do make a low % expanding foam. If you could get box out of wall then you could wrap box and add more insulation behind.
They also make foam inserts that go between the cover plate and the finish wall. These work very well for what they are.

 

[goosegunner]

GG. I think you could remove outlet or switch and foam behind box while in place, even if you had to drill small holes in box. They do make a low % expanding foam. If you could get box out of wall then you could wrap box and add more insulation behind.
They also make foam inserts that go between the cover plate and the finish wall. These work very well for what they are.

Thanks, I need to do something this summer. I have the foam sheets under the outlet covers but I can still feel the air blowing through. Yesterday there was actually condensation on the 3 gang switch plate.

This morning I was thinking about it. I want to add a tile backsplash in that area. I can cut the drywall open and spray the entire back of the boxes in the area of concern.


gg

 

[Nofossil]

The diminishing returns argument clouds the issue. Pybyr is right about infiltration, so deal with that before going wild on insulation.

IMHO, the easiest way to think about it is this: Every time you double your insulation, you cut your heat loss (through the insulation) in half. Twice the insulation, half the heat loss. As someone mentioned, this is a good place to take the long view - you'll be losing that heat every year forever.

That having been said, there is obviously a point where the cost of doubling the insulation just doesn't make sense. In most homes the bulk of the heat loss is through the windows and through infiltration. If loss through your insulation is 30% of your total, cutting it in half will only be a 15% savings on total heat loss.

This is a place where hard data will help arrive at the best approach.

 

[DaveBP]

Heat loss calculators can help a lot to estimate insulation cost effectiveness/dollar. But, as we all agree, air infiltration is still a major factor and very hard to 'calculate'. A blower door test when you're done is best. But by then it's too late to effectively improve sealing the building envelope easily if it's not what you hoped for.

In my case, I've used a lot of can foam and sheet urethane to make a close-to-airtight envelope inside a conventional 6" stud and fiberglass wall. 15" of cellulose in the attic and 4" of styrofoam outside the basement walls. Pretty low heat load, right? But I happen to like window walls facing south. So I have 250 sq.ft. of lowE argon-filled glass facing down the hill to the south. I also have gone the insulated foam shutter routine at night in my first cabin and learned that I'm not that devoted to all the inconvenience. I'd rather cut a little more firewood.

That same window wall during a sunny day will gain a lot of heat. I never burn wood during a sunny day. But at night it is only an R3 surface and by leaving it at R3 it doesn't make sense to continue adding more and more insulation to the walls without dealing with that R3.

I made a spreadsheet to calculate my heat loss in the new house when I started building and learned, as Nofossil suggested, that the heat loss through the windows at night quickly become a larger and larger fraction of the heat loss.Let's see if this chart will post...

You can see that if I add only 1" of foam to those window walls (maybe R6) I would lower the heat loss from those larger rooms by a lot more that adding lots more to the walls. There is no exact point where this changes, it just is a continual slope. I drew the line at not adding any more to the walls AND not bothering with insulation over the windows at night. That's my personal point of diminishing convenience.

The 3 columns are heat loss with just the 6" walls, with 1.5" foam added to walls, and putting 1" foam on windows.

 

[Fred61]

There is one more thing that enters into the equation and that is comfort temperature. Discomfort due to the radiation from the windows. At any given "comfort temperature," say 70F the human body will be more comfortable at the low end of the range if that radiation is blocked. It doesn't take much insulation to slow it down. Just a double thickness of fabric will instantly reduce the radiation affecting the body. But if you apply a cover on the window you may as well configure it so that the glass isn't a convector. This means blocking the top or the bottom or both to keep that air that is in contact with the glass from dropping out on to the floor to be reheated. Killing two birds with one stone!

 

[benjamin]

Nice chart Dave. That's what I was getting at with my heat loss numbers, but mine would be even more dramatic with over 400sf of clear glass instead of low e.

The low e glass sure helps for comfort as Fred was describing, if you're too lazy to use movable insulation. Maybe I'll retrofit some soap bubble insulated glass panels someday when firewood becomes too much of a hassle.

I agree with Tom that the cost of adding additional insulation to new construction is almost trivial, which makes his r40 or 60 practical. We will pay one way or the other, whether its paying for the insulation, or the energy, or through discomfort. You do have to have awefully good windows, doors and other details, or a lack of them to make that amount of insulation make sense.

 

[barnartist]

My 2 cents, spray foam is great for doors and windows, but every one of those areas I used the stuff they are fog houses. I had a guy warn me and I did not believe him until seeing it first hand.

 

[ihookem]

What do you mean by a fog house?

 

[Duetech]

I believe he means high internal humidity

 

[Nofossil]

Any reasonably tight house needs an air-to-air heat exchanger to keep humidity down.

 

[goosegunner]

Any reasonably tight house needs an air-to-air heat exchanger to keep humidity down.

What is ideal humidity?

gg

 

[benjamin]

Humidity is usually limited by window condensation. The recomended humidity goes down with the outside temperature.

Here is a chart of the window condensation point at different temps and relative humidities
http://www.ag.ndsu.edu/pubs/ageng/structu/ae1204-2b.gif

Personally around 40% is ideal but that will cause more condensation than most people want on their wood windows. If you have vinyl or don't care then you can get away with it. Of course the higher you keep the humidity then the more risk you have of moisture damage from air leaks into the building structure.