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Posted by tg on December 18, 2008, 8:01 pm
> > -----------------------
> > I can only answer the very narrow question about the actual structures
> > and their relative merits in terms of (non-renewable) energy
> > efficiency. You clearly get points for walkable and infill, for
> > example, but what are we comparing it to? =A0The same problem exists
> > when you talk about cost---are you going to be using coal-fired
> > electricity with no carbon tax? Are you thinking of resale value in 10
> > years when energy costs may include what are now externalities?
> > All too complicated for me.
> > But I would guess that, even in NC, =A0the house you describe would use
> > twice as much energy as the house I describe here:
> > 1) R30 prefabricated wall panels and R50 prefabricated roof panels.
> I've read mixed reviews (again, I'm very early on in my research and I
> am starting from basically point zero) so far of prefab walls. Most
> recently, I was reading this highly critical analysis:
> http://www.jetsongreen.com/2008/09/prefab-is-not-t.html
> Feel free to add your counter-arguments to theirs if you wish.
I can't add counter-arguments because we are talking about completely
different things. If you read their article, you will see that it says
that most prefab *houses* are still using the same insulation system
as stick-built. I said prefab *panels*, which are a different
technology.
> Secondly, regarding R-levels and insulation, I've talked to several
> insulation experts (i.e., people who are not in any way associated
> with the builders and who would actually be motivated to upsell me),
> and each of them basically said the same thing, which is that anything
> beyond the R19 walls and R38 roofs spec'ed by the builders would be
> overkill and not cost beneficial.
I thought I pretty clearly said that I am talking about relative
energy efficiency *not* cost. If you are generating electricity by
burning coal, then the state standards that you mention are just fine.
If all you care about is cost; just turn the thermostat up and down as
needed like Al Gore. Also, insulation 'experts' are usually interested
in selling their particular technology, and there aren't any
insulation experts that sell prefab panels and wall systems.
> For you people who have for some god-
> forsaken reason made the dubious decision to live in the Arctic zone,
> perhaps the R38 and R50 levels you mentioned might do some good, but I
> really don't know. ;-)
I hardly consider where I live Arctic---I've lived in the Lake Effect
zone, and winter camped in the mountains for years never using a tent.
This is my version of living in Florida.
> I also talked to a local Energy Star certifier, and he went as far as
> to say that the R-levels are not irrelevant, but a comparably minor
> consideration compared to the sealing of the house.
Again, air leakage around openings is the result of shoddy
construction, not design. See below.
> The Healthy Built
> Home certification mandates that these homes are Energy Star certified
> as part of the process, so they would be sealed using the highest
> standards and inspected appropriately.
> In either case, I am pursuing the question with another individual who
> certifies homes for energy efficiency.
> On a side note, according to the individuals I spoke with, NC does
> have mandated residential building codes (R11 for floors, R13 for
> walls, R21 for roofs, if memory serves me right). In either case, the
> levels on the two homes I referred to exceed the minimum levels
> enforced by the State.
> I really can't argue the comments made above; I'm just passing on the
> information. In any case, this is all very good because it makes a
> perfect launching pad for discussion/research on my part.
> > 2) Heat pump
> Check (on House1) ... mini-split a/c on House2
> > 3) Slab foundation perimeter insulation only.
> Check.
> > 4) Interior walls 5/8 gypsum, tile floors where functional.
> I don't think this is feasible with 2X6 framing, is it? Why tile
> floors over concrete?
> > 5) High efficiency lighting.
> Check. Energy Star certified.
> > 6) High efficiency windows with external shutters, skylights.
> Check on windows (Energy Star certified), don't think so on external
> shutters and skylights.
> > 7) Structure orientation and shading non-random.
> Both homes are roughly North/South facing. I don't know what "shading
> non-random" means.
> > You get the most savings with 1, perhaps 30% or more of the heating
> > and cooling.
> That didn't seem to be the opinion of the folks I spoke with, none of
> whom are affiliated with the builders in any way, but I'll keep
> investigating this.
But it is the opinion of physics. If you build two identical houses,
and one has R19 effective walls and one has R30, you will lose and
gain heat at different rates. I have the luxury (heuristic, if not
economic) of moving between 3 space on a daily basis, one of which is
poorly sealed R7, one at R19 well constructed, and one at R30 well
constructed. Today, because of our conversation, I confirmed the test
I've done in the past---placing the palm of my hand on the wall of the
different spaces. In the first case, your palm starts and stays cold,
in the R30 it is just neutral, and the R19 starts cold and ends up
feeling slightly cool after about 15 seconds. What's interesting is
that the R30 air temp is about 52 while the R7 and R19 are around 58.
Outside temp is just under 40.
-tg
> > Each other thing contributes some percentage, and that
> > depends on lifestyle to some degree---you might get a total more than
> > 50%. I'm also not familiar with your climate, but as I said somewhere
> > I am thinking that cooling is more important than heating. That would
> > influence my choice, for example, about the radiant floor heat
> > business. Those are getting popular now but
> ...
> read more =BB
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Posted by ta on December 19, 2008, 1:09 pm
> > > -----------------------
> > > I can only answer the very narrow question about the actual structure=
s
> > > and their relative merits in terms of (non-renewable) energy
> > > efficiency. You clearly get points for walkable and infill, for
> > > example, but what are we comparing it to? =A0The same problem exists
> > > when you talk about cost---are you going to be using coal-fired
> > > electricity with no carbon tax? Are you thinking of resale value in 1=
0
> > > years when energy costs may include what are now externalities?
> > > All too complicated for me.
> > > But I would guess that, even in NC, =A0the house you describe would u=
se
> > > twice as much energy as the house I describe here:
> > > 1) R30 prefabricated wall panels and R50 prefabricated roof panels.
> > I've read mixed reviews (again, I'm very early on in my research and I
> > am starting from basically point zero) so far of prefab walls. Most
> > recently, I was reading this highly critical analysis:
> >http://www.jetsongreen.com/2008/09/prefab-is-not-t.html
> > Feel free to add your counter-arguments to theirs if you wish.
> I can't add counter-arguments because we are talking about completely
> different things. If you read their article, you will see that it says
> that most prefab *houses* are still using the same insulation system
> as stick-built. I said prefab *panels*, which are a different
> technology.
Yeah, the terminology is a bit confusing. I've only heard them
referred to as SIPs, so I didn't realize that's what you were
referring to.
> > Secondly, regarding R-levels and insulation, I've talked to several
> > insulation experts (i.e., people who are not in any way associated
> > with the builders and who would actually be motivated to upsell me),
> > and each of them basically said the same thing, which is that anything
> > beyond the R19 walls and R38 roofs spec'ed by the builders would be
> > overkill and not cost beneficial.
> I thought I pretty clearly said that I am talking about relative
> energy efficiency *not* cost. =A0
Right, but my reasoning was that if you weren't going to realize the
cost savings in my lifetime (which is what one person said), then it
would follow that they can't really be *that* much more efficient.
Again, I'm talking about comparing apples to apples -- R19 insulation
in stickbuilt homes with R38 insulation in stickbuilt homes. The SIPs
are another issue altogether.
According to the stuff I've read on SIPs so far and the SIPs reps I've
talked with, there seems to be little doubt about the superior
technology and better efficiency. That's a non-issue. When it comes to
SIPs, the *only* relevant issue is cost.
The builders in charge of these two projects reasoned that in order to
keep their homes affordable for the average Joe, they aren't using
SIPs.
The SIPs people of course claim that the reduced labor costs and lower
utilities bills will mitigate the additional up-front costs, but
again, they are trying to sell product as well. Being the reasonably
intelligent person that I am, I'm fully aware that each party is
probably going to present a slightly different "truth". ;-)
The totally neutral party I've been talking with -- an energy rater
who is building his own home using SIPs, and who has no vested
interested in either technology, had this to say:
"It is a cost issue. SIP's are great and significantly more efficient
than stick-built framing (they use a lot less wood framing), but when
we run the numbers in the energy model, it takes a while for the SIP's
to pay back. For some people, it's worth the upfront cost. For
builders who are watching the bottom line, especially on spec houses,
they can't justify the increased cost. The house I designed for me and
my wife is planning on using 4.5" SIP's (R26) because I understand the
benefits, but I also know that it will take 7-10 years for the energy
savings to pay me back for the increased cost of the panels. I was
originally planning on 6.5" SIP's for the walls, but the payback
jumped to 20 years."
So ultimately, as a matter of necessity, it has to be about cost. If I
could find a way to afford the superior technology and not live in a
300 sq.ft. box, then obviously I would do so. ;-)
> If you are generating electricity by
> burning coal, then the state standards that you mention are just fine.
> If all you care about is cost; just turn the thermostat up and down as
> needed like Al Gore. Also, insulation 'experts' are usually interested
> in selling their particular technology, and there aren't any
> insulation experts that sell prefab panels and wall systems.
> > For you people who have for some god-
> > forsaken reason made the dubious decision to live in the Arctic zone,
> > perhaps the R38 and R50 levels you mentioned might do some good, but I
> > really don't know. ;-)
> I hardly consider where I live Arctic---I've lived in the Lake Effect
> zone, and winter camped in the mountains for years never using a tent.
> This is my version of living in Florida.
Hey, to each his own. I wish more people would plan those types of
trips so fewer would haul their RVs and SUVs down the blue ridge
parkway every summer. Eventually, we might be able to actually *see*
the mountains through the smog . . . that is, the ones that the
developers haven't yet shaved off to build McMansions for those rich
yankee retirees who need their 2nd homes to escape the Florida heat in
the summer.
Hey, if this global warming thing really takes off, they might soon be
headed your way. ;-)
> > I also talked to a local Energy Star certifier, and he went as far as
> > to say that the R-levels are not irrelevant, but a comparably minor
> > consideration compared to the sealing of the house.
> Again, air leakage around openings is the result of shoddy
> construction, not design. See below.
Of course -- but Energy Star certification is one way to ensure
quality. The point is that if the house is sealed properly, which
Energy Star certification helps to ensure, then pouring alot of money
into thicker insulation is not necessarily a wise thing to do,
according to these folks. If anything, I would think they'd be
motivated to sell me thicker, more expensive insulation. Again,
talking about stickbuilt here.
> > The Healthy Built
> > Home certification mandates that these homes are Energy Star certified
> > as part of the process, so they would be sealed using the highest
> > standards and inspected appropriately.
> > In either case, I am pursuing the question with another individual who
> > certifies homes for energy efficiency.
> > On a side note, according to the individuals I spoke with, NC does
> > have mandated residential building codes (R11 for floors, R13 for
> > walls, R21 for roofs, if memory serves me right). In either case, the
> > levels on the two homes I referred to exceed the minimum levels
> > enforced by the State.
> > I really can't argue the comments made above; I'm just passing on the
> > information. In any case, this is all very good because it makes a
> > perfect launching pad for discussion/research on my part.
> > > 2) Heat pump
> > Check (on House1) ... mini-split a/c on House2
> > > 3) Slab foundation perimeter insulation only.
> > Check.
> > > 4) Interior walls 5/8 gypsum, tile floors where functional.
> > I don't think this is feasible with 2X6 framing, is it? Why tile
> > floors over concrete?
> > > 5) High efficiency lighting.
> > Check. Energy Star certified.
> > > 6) High efficiency windows with external shutters, skylights.
> > Check on windows (Energy Star certified), don't think so on external
> > shutters and skylights.
> > > 7) Structure orientation and shading non-random.
> > Both homes are roughly North/South facing. I don't know what "shading
> > non-random" means.
> > > You get the most savings with 1, perhaps 30% or more of the heating
> > > and cooling.
> > That didn't seem to be the opinion of the folks I spoke with, none of
> > whom are affiliated with the builders in any way, but I'll keep
> > investigating this.
> But it is the opinion of physics. If you build two identical houses,
> and one has R19 effective walls and one has R30, you will lose and
> gain heat at different rates. I have the luxury (heuristic, if not
> economic) of moving between 3 space on a daily basis, one of which is
> poorly sealed R7, one at R19 well constructed, and one at R30 well
> constructed. =A0Today, because of our conversation, I confirmed the test
> I've done in the past---placing the palm of my hand on the wall of the
> different spaces. In the first case, your palm starts and stays cold,
> in the R30 it is just neutral, and the R19 starts cold and ends up
> feeling slightly cool after about 15 seconds. What's interesting is
> that the R30 air temp is about 52 while the R7 and R19 are around 58.
> Outside temp is just under 40.
> -tg
Are we talking apples and oranges here? In your experiment, are you
comparing three SIPs walls or 3 stickbuilt walls?
> > > Each other thing contributes some percentage, and that
> > > depends on lifestyle to some degree---you might get a total more than
> > > 50%. I'm also not familiar with your climate, but as I said somewhere
> > > I am thinking that cooling is more important than heating. That would
> > > influence my choice, for example, about the radiant floor heat
> > > business. Those are getting popular now but
> > ...
> > read more =BB
|
|
Posted by tg on December 19, 2008, 9:00 pm
> Yeah, the terminology is a bit confusing. I've only heard them
> referred to as SIPs, so I didn't realize that's what you were
> referring to.
> > > Secondly, regarding R-levels and insulation, I've talked to several
> > > insulation experts (i.e., people who are not in any way associated
> > > with the builders and who would actually be motivated to upsell me),
> > > and each of them basically said the same thing, which is that anythin=
g
> > > beyond the R19 walls and R38 roofs spec'ed by the builders would be
> > > overkill and not cost beneficial.
> > I thought I pretty clearly said that I am talking about relative
> > energy efficiency *not* cost. =A0
> Right, but my reasoning was that if you weren't going to realize the
> cost savings in my lifetime (which is what one person said), then it
> would follow that they can't really be *that* much more efficient.
Why in the world would you think that? You can obviously buy one of
those Tesla cars, and it is far more efficient than anything else, but
with gas at 1.60 per gallon it is a lousy economic choice. Jeez ta, I
guess should give up my quest to get people to think quantitatively
and go back to knocking down windmills with my lance......
> Again, I'm talking about comparing apples to apples -- R19 insulation
> in stickbuilt homes with R38 insulation in stickbuilt homes. The SIPs
> are another issue altogether.
> According to the stuff I've read on SIPs so far and the SIPs reps I've
> talked with, there seems to be little doubt about the superior
> technology and better efficiency. That's a non-issue. When it comes to
> SIPs, the *only* relevant issue is cost.
> The builders in charge of these two projects reasoned that in order to
> keep their homes affordable for the average Joe, they aren't using
> SIPs.
> The SIPs people of course claim that the reduced labor costs and lower
> utilities bills will mitigate the additional up-front costs, but
> again, they are trying to sell product as well. Being the reasonably
> intelligent person that I am, I'm fully aware that each party is
> probably going to present a slightly different "truth". ;-)
> The totally neutral party I've been talking with -- an energy rater
> who is building his own home using SIPs, and who has no vested
> interested in either technology, had this to say:
> "It is a cost issue. SIP's are great and significantly more efficient
> than stick-built framing (they use a lot less wood framing), but when
> we run the numbers in the energy model, it takes a while for the SIP's
> to pay back. For some people, it's worth the upfront cost. For
> builders who are watching the bottom line, especially on spec houses,
> they can't justify the increased cost. The house I designed for me and
> my wife is planning on using 4.5" SIP's (R26) because I understand the
> benefits, but I also know that it will take 7-10 years for the energy
> savings to pay me back for the increased cost of the panels. I was
> originally planning on 6.5" SIP's for the walls, but the payback
> jumped to 20 years."
Again, that is not the right question for two reasons:
1) You are asking about 'what is really green', but you are deciding
based on economics, not green-ness.
2) You can't figure out the payoff period with any certainty because
you are making assumptions about the cost of energy in the future. By
this reasoning, you should have bought a Prius two months ago, but now
you should by a Hummer, since gas is 1.60. That way lies madness.
> So ultimately, as a matter of necessity, it has to be about cost. If I
> could find a way to afford the superior technology and not live in a
> 300 sq.ft. box, then obviously I would do so. ;-)
.......
> > > I also talked to a local Energy Star certifier, and he went as far as
> > > to say that the R-levels are not irrelevant, but a comparably minor
> > > consideration compared to the sealing of the house.
> > Again, air leakage around openings is the result of shoddy
> > construction, not design. See below.
> Of course -- but Energy Star certification is one way to ensure
> quality. The point is that if the house is sealed properly, which
> Energy Star certification helps to ensure, then pouring alot of money
> into thicker insulation is not necessarily a wise thing to do,
> according to these folks. If anything, I would think they'd be
> motivated to sell me thicker, more expensive insulation. Again,
> talking about stickbuilt here.
> > > The Healthy Built
> > > Home certification mandates that these homes are Energy Star certifie=
d
> > > as part of the process, so they would be sealed using the highest
> > > standards and inspected appropriately.
> > > In either case, I am pursuing the question with another individual wh=
o
> > > certifies homes for energy efficiency.
> > > On a side note, according to the individuals I spoke with, NC does
> > > have mandated residential building codes (R11 for floors, R13 for
> > > walls, R21 for roofs, if memory serves me right). In either case, the
> > > levels on the two homes I referred to exceed the minimum levels
> > > enforced by the State.
> > > I really can't argue the comments made above; I'm just passing on the
> > > information. In any case, this is all very good because it makes a
> > > perfect launching pad for discussion/research on my part.
> > > That didn't seem to be the opinion of the folks I spoke with, none of
> > > whom are affiliated with the builders in any way, but I'll keep
> > > investigating this.
> > But it is the opinion of physics. If you build two identical houses,
> > and one has R19 effective walls and one has R30, you will lose and
> > gain heat at different rates. I have the luxury (heuristic, if not
> > economic) of moving between 3 space on a daily basis, one of which is
> > poorly sealed R7, one at R19 well constructed, and one at R30 well
> > constructed. =A0Today, because of our conversation, I confirmed the tes=
t
> > I've done in the past---placing the palm of my hand on the wall of the
> > different spaces. In the first case, your palm starts and stays cold,
> > in the R30 it is just neutral, and the R19 starts cold and ends up
> > feeling slightly cool after about 15 seconds. What's interesting is
> > that the R30 air temp is about 52 while the R7 and R19 are around 58.
> > Outside temp is just under 40.
> > -tg
> Are we talking apples and oranges here? In your experiment, are you
> comparing three SIPs walls or 3 stickbuilt walls?
Yes, ta, the guy who has been reminding people on this group for years
about comparing apples to apples is comparing apples to apples.
<grrrrr>
I know the 'data' is hard to believe---it is one of those neat things
where the physics really comes home to you through a simple physical
experience; these are all conventional walls of different thicknesses.
The only difference is that 4 inch wall (R7 insulation) has different
stud spacing 16" v 24", which brings us to a little discussion that
may illustrate my basic point. This will require carefully reading and
very simple math.
Consider a nominal 6" standard wall (5.5" actual) as described in your
second house, which is claimed to be R19. Every 24", there is a stud,
which is 1.5" wide. So for a 32 foot section of wall, assuming no
doors or windows, there are 16 studs, yielding a total of 24" (2
feet) which is wood, and 30 feet which is insulation. Now the studs
aren't quite 8 feet high, but let's round up, and multiply 2ft wide by
8ft high, which yields 16 square feet. This would be the same area as
a 4ft by 4ft window!
If you add in the horizontal pieces of wood that tie the vertical
studs together, and the extra pieces that go around doors and (actual)
windows, the usual estimates are that 19-24% of a wall is wood, not
insulation. Now, the R-value for that thickness of wood is in the R7-8
range, which is only slightly better than an actual window, So,
conservatively, about 80% of our wall is the R19 insulation, *but*
20% is the R8 wood.
So how do we tell if the builder is serious about green-ness, and what
are the economics? You can nail some siding on and *claim* that you
have an R19 wall, which is what your second house seems to be. Or you
can first apply a 1" layer of isocyanurate rigid foam, which has an R-
value of about 6.5-7.5. What that does is raise the value for the 80%
that is fiberglas insulation to say 26, but also bridges over the 20%
that is just wood, raising that to 14---which is above your state
mandatory minimum. Going by *retail* prices, the cost of doing that
for a 32ft section of wall is 8 pieces times $18 or $144 (in reality
less because of windows and doors). I think you can do the math to
extrapolate to whatever size house you are looking at, and see that
compared to the total price, the difference is trivial.
Now we can look at some of the other features I've mentioned, and
there will be similar (relative) numbers. But those small numbers add
up to profit margin for the builder; even on 12 homes, a few K per
house is a big deal, and they have little motivation to give that up.
FWIW, I'm just trying to make you aware that if you wish to be
greener, and/or don't believe that there will be a magic cheap energy
source discovered in the next few years, it might be worthwhile to
study up on the details *and the actual numbers*.
-tg
> > > ...
> > > read more =BB
|
|
Posted by ta on December 22, 2008, 11:14 am
e:
> > Yeah, the terminology is a bit confusing. I've only heard them
> > referred to as SIPs, so I didn't realize that's what you were
> > referring to.
> > > > Secondly, regarding R-levels and insulation, I've talked to several
> > > > insulation experts (i.e., people who are not in any way associated
> > > > with the builders and who would actually be motivated to upsell me)=
,
> > > > and each of them basically said the same thing, which is that anyth=
ing
> > > > beyond the R19 walls and R38 roofs spec'ed by the builders would be
> > > > overkill and not cost beneficial.
> > > I thought I pretty clearly said that I am talking about relative
> > > energy efficiency *not* cost. =A0
> > Right, but my reasoning was that if you weren't going to realize the
> > cost savings in my lifetime (which is what one person said), then it
> > would follow that they can't really be *that* much more efficient.
> Why in the world would you think that? You can obviously buy one of
> those Tesla cars,
No, I obviously can't, since I can't afford them.
> and it is far more efficient than anything else, but
> with gas at 1.60 per gallon it is a lousy economic choice.
It wouldn't be a lousy economic choice for someone who could afford
it, but it certainly would be a lousy economic choice for me.
Actually, there's no choice involved at all, because they are
obscenely expensive, by my standards (which are the only standards
that are relevant, since this is my house we're talking about). You
cannot determine what are good and bad economic choices unless you
consider the financial state of the buyer.
Obviously Larry Hagman can afford to be a lot more "green" than I can.
You seem to think that efficiency is the only relevant factor and that
economics are irrelevant (in my original post, I said "bang for your
**buck**). That's fine if you're an academician writing a paper or
preparing a lecture about some theory or ideal. However, for those of
us actually dealing in reality, we have real housing needs with real
budgetary constraints that must be considered.
> Jeez ta, I
> guess should give up my quest to get people to think quantitatively
> and go back to knocking down windmills with my lance......
> > Again, I'm talking about comparing apples to apples -- R19 insulation
> > in stickbuilt homes with R38 insulation in stickbuilt homes. The SIPs
> > are another issue altogether.
> > According to the stuff I've read on SIPs so far and the SIPs reps I've
> > talked with, there seems to be little doubt about the superior
> > technology and better efficiency. That's a non-issue. When it comes to
> > SIPs, the *only* relevant issue is cost.
> > The builders in charge of these two projects reasoned that in order to
> > keep their homes affordable for the average Joe, they aren't using
> > SIPs.
> > The SIPs people of course claim that the reduced labor costs and lower
> > utilities bills will mitigate the additional up-front costs, but
> > again, they are trying to sell product as well. Being the reasonably
> > intelligent person that I am, I'm fully aware that each party is
> > probably going to present a slightly different "truth". ;-)
> > The totally neutral party I've been talking with -- an energy rater
> > who is building his own home using SIPs, and who has no vested
> > interested in either technology, had this to say:
> > "It is a cost issue. SIP's are great and significantly more efficient
> > than stick-built framing (they use a lot less wood framing), but when
> > we run the numbers in the energy model, it takes a while for the SIP's
> > to pay back. For some people, it's worth the upfront cost. For
> > builders who are watching the bottom line, especially on spec houses,
> > they can't justify the increased cost. The house I designed for me and
> > my wife is planning on using 4.5" SIP's (R26) because I understand the
> > benefits, but I also know that it will take 7-10 years for the energy
> > savings to pay me back for the increased cost of the panels. I was
> > originally planning on 6.5" SIP's for the walls, but the payback
> > jumped to 20 years."
> Again, that is not the right question for two reasons:
The right question is: how efficient can I get within my financial and
other constraints. All other questions are strictly academic and of
absolutely no interest to me.
The guy who wrote the paragraph above has his own criteria, which may
or may not be different from mine (I really don't know his financial
condition, so it's not for me to judge). If I were in his place, I may
or may not choose to install the 6.5" SIPs, depending on how much more
they cost (i.e., if I could afford to take the hit, the extra green-
ness might be worth it . . . just as if I could afford to buy the
Tesla, then the added efficiency/green-ness might be worth it --
"worth" being used generically, not strictly financially).
> 1) You are asking about 'what is really green', but you are deciding
> based on economics, not green-ness.
No. I am deciding on *both* economics and green-ness. I don't think
it's that complicated a question really. I have X amount of money and
I want to achieve maximum efficiency within that real-world
constraint. Other real-world constraints/factors include geography and
size.
> 2) You can't figure out the payoff period with any certainty because
> you are making assumptions about the cost of energy in the future.
That's true. I have no idea what kind of model he used, tbh.
> By
> this reasoning, you should have bought a Prius two months ago, but now
> you should by a Hummer, since gas is 1.60. =A0That way lies madness.
Nonsense. I wouldn't buy a hummer if gas was .60/gallon.
> > So ultimately, as a matter of necessity, it has to be about cost. If I
> > could find a way to afford the superior technology and not live in a
> > 300 sq.ft. box, then obviously I would do so. ;-)
> .......
> > > > I also talked to a local Energy Star certifier, and he went as far =
as
> > > > to say that the R-levels are not irrelevant, but a comparably minor
> > > > consideration compared to the sealing of the house.
> > > Again, air leakage around openings is the result of shoddy
> > > construction, not design. See below.
> > Of course -- but Energy Star certification is one way to ensure
> > quality. The point is that if the house is sealed properly, which
> > Energy Star certification helps to ensure, then pouring alot of money
> > into thicker insulation is not necessarily a wise thing to do,
> > according to these folks. If anything, I would think they'd be
> > motivated to sell me thicker, more expensive insulation. Again,
> > talking about stickbuilt here.
> > > > The Healthy Built
> > > > Home certification mandates that these homes are Energy Star certif=
ied
> > > > as part of the process, so they would be sealed using the highest
> > > > standards and inspected appropriately.
> > > > In either case, I am pursuing the question with another individual =
who
> > > > certifies homes for energy efficiency.
> > > > On a side note, according to the individuals I spoke with, NC does
> > > > have mandated residential building codes (R11 for floors, R13 for
> > > > walls, R21 for roofs, if memory serves me right). In either case, t=
he
> > > > levels on the two homes I referred to exceed the minimum levels
> > > > enforced by the State.
> > > > I really can't argue the comments made above; I'm just passing on t=
he
> > > > information. In any case, this is all very good because it makes a
> > > > perfect launching pad for discussion/research on my part.
> > > > That didn't seem to be the opinion of the folks I spoke with, none =
of
> > > > whom are affiliated with the builders in any way, but I'll keep
> > > > investigating this.
> > > But it is the opinion of physics. If you build two identical houses,
> > > and one has R19 effective walls and one has R30, you will lose and
> > > gain heat at different rates. I have the luxury (heuristic, if not
> > > economic) of moving between 3 space on a daily basis, one of which is
> > > poorly sealed R7, one at R19 well constructed, and one at R30 well
> > > constructed. =A0Today, because of our conversation, I confirmed the t=
est
> > > I've done in the past---placing the palm of my hand on the wall of th=
e
> > > different spaces. In the first case, your palm starts and stays cold,
> > > in the R30 it is just neutral, and the R19 starts cold and ends up
> > > feeling slightly cool after about 15 seconds. What's interesting is
> > > that the R30 air temp is about 52 while the R7 and R19 are around 58.
> > > Outside temp is just under 40.
> > > -tg
> > Are we talking apples and oranges here? In your experiment, are you
> > comparing three SIPs walls or 3 stickbuilt walls?
> Yes, ta, the guy who has been reminding people on this group for years
> about comparing apples to apples is comparing apples to apples.
You misunderstood. I said are **we** talking apples and oranges. That
is, are you talking about one thing (SIPs) and I'm talking about
another (stickbuilt).
> I know the 'data' is hard to believe---it is one of those neat things
> where the physics really comes home to you through a simple physical
> experience; these are all conventional walls of different thicknesses.
> The only difference is that 4 inch wall (R7 insulation) has different
> stud spacing 16" v 24", which brings us to a little discussion that
> may illustrate my basic point. This will require carefully reading and
> very simple math.
> Consider a nominal 6" standard wall (5.5" actual) as described in your
> second house, which is claimed to be R19. Every 24", there is a stud,
> which is 1.5" wide. So for a 32 foot section of wall, assuming no
> doors or windows, =A0there are 16 studs, yielding a total of 24" (2
> feet) =A0which is wood, and 30 feet which is insulation. Now the studs
> aren't quite 8 feet high, but let's round up, and multiply 2ft wide by
> 8ft high, which yields 16 square feet. This would be the same area as
> a 4ft by 4ft window!
> If you add in the horizontal pieces of wood that tie the vertical
> studs together, and the extra pieces that go around doors and (actual)
> windows, the usual estimates are that 19-24% of a wall is wood, not
> insulation. Now, the R-value for that thickness of wood is in the R7-8
> range, which is only slightly better than an actual window, So,
> conservatively, =A0about 80% of our wall is the R19 insulation, *but*
> 20% is the R8 wood.
Right, so all this an argument for SIPs, which I am already familiar
with. No studs =3D more efficient.
> So how do we tell if the builder is serious about green-ness, and what
> are the economics? =A0You can nail some siding on and *claim* that you
> have an R19 wall, which is what your second house seems to be. Or you
> can first apply a 1" layer of isocyanurate rigid foam, which has an R-
> value of about 6.5-7.5. What that does is raise the value for the 80%
> that is fiberglas insulation to say 26, but also bridges over the 20%
> that is just wood, raising that to 14---which is above your state
> mandatory minimum. Going by *retail* prices, the cost of doing that
> for a 32ft section of wall is 8 pieces times $18 or $144 (in reality
> less because of windows and doors). =A0I think you can do the math to
> extrapolate to whatever size house you are looking at, and see that
> compared to the total price, the difference is trivial.
Ok, that's good to know. These are things I can investigate.
> Now we can look at some of the other features I've mentioned, and
> there will be similar (relative) numbers. But those small numbers add
> up to profit margin for the builder; even on 12 homes, a few K per
> house is a big deal, and they have little motivation to give that up.
> FWIW, =A0I'm just trying to make you aware that if you wish to be
> greener, and/or don't believe that there will be a magic cheap energy
> source discovered in the next few years, it might be worthwhile to
> study up on the details *and the actual numbers*.
Yes, I agree -- that's why I'm asking these questions. ;-) And again,
I do appreciate the information. I'm simply trying to discover optimal
efficiency at a price I can afford and in a location and size that is
suitable to me.
I have no allegiance to these two examples that I've given -- they're
just the first two that I have come across. I was talking with another
builder this weekend who may be able to sell me a house using SIPs
that I can actually afford (the two that I had investigated prior were
way out of my price range).
> -tg> > > ...
> > > > read more =BB
|
|
Posted by tg on December 22, 2008, 1:09 pm
<snip>
> Right, so all this an argument for SIPs, which I am already familiar
> with. No studs =3D more efficient.
> > So how do we tell if the builder is serious about green-ness, and what
> > are the economics? =A0You can nail some siding on and *claim* that you
> > have an R19 wall, which is what your second house seems to be. Or you
> > can first apply a 1" layer of isocyanurate rigid foam, which has an R-
> > value of about 6.5-7.5. What that does is raise the value for the 80%
> > that is fiberglas insulation to say 26, but also bridges over the 20%
> > that is just wood, raising that to 14---which is above your state
> > mandatory minimum. Going by *retail* prices, the cost of doing that
> > for a 32ft section of wall is 8 pieces times $18 or $144 (in reality
> > less because of windows and doors). =A0I think you can do the math to
> > extrapolate to whatever size house you are looking at, and see that
> > compared to the total price, the difference is trivial.
> Ok, that's good to know. These are things I can investigate.
> > Now we can look at some of the other features I've mentioned, and
> > there will be similar (relative) numbers. But those small numbers add
> > up to profit margin for the builder; even on 12 homes, a few K per
> > house is a big deal, and they have little motivation to give that up.
> > FWIW, =A0I'm just trying to make you aware that if you wish to be
> > greener, and/or don't believe that there will be a magic cheap energy
> > source discovered in the next few years, it might be worthwhile to
> > study up on the details *and the actual numbers*.
> Yes, I agree -- that's why I'm asking these questions. ;-) And again,
> I do appreciate the information. I'm simply trying to discover optimal
> efficiency at a price I can afford and in a location and size that is
> suitable to me.
Ok, I've finally figured out what I've been trying to say and perhaps
can now do it in (somewhat) fewer words.
One is obviously constrained by one's budget, location, and size
requirements, and you are obviously more conscientious than most
because you are doing the research. But I am concerned that everyone
treats efficiency by a different standard than they do all the other
factors *other than* budget, location, and size.
The problem is that there is no other feature of the house which is
required to 'pay for itself' in some number of years in order to be a
desirable choice.
Let's say you are buying/building a 64x32 house (I don't think you are
going to buy a McMansion any more than I think you are going to buy a
Hummer.) That would be 6 of the above wall sections, and let's say
the cost to add those rigid foam sheets comes out to $1000. Not SIP,
but a similar effect by bridging over the framing members.
Well, lots of people would gladly spend $1000 to get, say, a nice
front door---maybe with one of those little semicircular windows over
the top. But they would never even think to ask whether that was going
to 'pay for itself' in 6 years or 12 years. They simply accept some
risk v benefit, since when they sell the house such doors may be out
of fashion, or maybe there's a revival, so they could lose or win, but
probably they just like knowing that they have a nice door and are
happy to spend the 1K.
But then, why don't we apply the same approach to energy efficiency?
Why do people have to see some calculation that the choice of extra
insulation is going to be economically neutral, and in a specific time
frame? Why not apply similar reasoning: It could be that energy will
become cheaper, or more expensive, and you could lose or win, but by
making that choice you will at least be a bit more physically
comfortable and have contributed something to the future.
So my question is, why is spending that $1000 such a big deal in one
case, but not in the other? I'm not saying someone should choose (if
the choice were available) the insulation over the door, or vice
versa. But it should be a matter of preference, without the double
standard that seems to have been created involving 'pay-back periods'.
Does this make sense yet?
-tg
|
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> > I can only answer the very narrow question about the actual structures
> > and their relative merits in terms of (non-renewable) energy
> > efficiency. You clearly get points for walkable and infill, for
> > example, but what are we comparing it to? =A0The same problem exists
> > when you talk about cost---are you going to be using coal-fired
> > electricity with no carbon tax? Are you thinking of resale value in 10
> > years when energy costs may include what are now externalities?
> > All too complicated for me.
> > But I would guess that, even in NC, =A0the house you describe would use
> > twice as much energy as the house I describe here:
> > 1) R30 prefabricated wall panels and R50 prefabricated roof panels.