Best Placement of an In-Attic Furnace, Among Roof Trusses

The title of this post is revised, deleting the furnace adjective, gas. Information will apply to a gas furnace with or without air conditioning, and to HVAC heat pump installations having the same footprint and air duct arrangements.

Customer Meyer:

I have called this a good installation. Call it generally parallel to trusses.

Here is the Meyer installation as I found it. Badly installed ducts are in the way of harm, everywhere. Ducking ducts, one could at best get at the furnace access panels. The untrained "professional" installer ruined the side of the furnace, hacking on an oversize return box with no possibility of the imperative return-air high-efficiency filter. 

See outlet Medusa of fully unguided flow losing all kinetic head.

See accommodation of two return air ducts at the narrow inlet D-box.

I will demolish all of this awful ducting less than two years old and blessed as conforming with required methods. Leaky and unstable duct connections to a D-box are hacked-in unsupervised at the job site. I will spend several hours dangerously stripping off goop and screws that might have achieved an airtight assembly. Worse to me, the assembly is hydraulic foolishness. Dampers full-open only add to the wasteful blower head. There is a better way.

It is October 30, 2017 in mild-maritime weather of Portland, Oregon, and the home will lack HVAC for several days. Here the furnace is reset on a raised floor with space below that will pass furnace-output flex ducts, under flooring, buried in the floor insulation. Is there a better way to place ducts in "conditioned space?"

Here trial-fit the new, lined 180° turning plenum. Behind the furnace see bags of fiberlass insulation employed to fully stuff space under flooring, to R60. The new floor supports are up 20 inches from ceiling drywall. There is good return in filling all available space with insulation.

The improved furnace has a  insulated 180° turning plenum on top, directing conditioned air downward with ducts to be buried under a raised attic floor. A couple of vanes in  the second 90° turn might do some good in reducing flow turbulence.

Look down through the progression of wye fittings below the turning plenum, that keep air moving steadily at ideally a constant velocity. All of this guiding steel is with some cost of efficiency. Steel mass that responds to elevated temperature of each furnace cycle, has heat capacity. Heat capacity cooling or heating output furnace air, acts just like leakage of the conditioned air. Do what I can to reduce responding thermal mass, by palm-applying many layers of flexible grout. Flexible grout is insulating ceramic microballoons more than half by volume. I allege that the coating reduces responding thermal mass by more than half, a really good investment of my time with material cost-free.

Framework that supports flooring, and passes buried ducts, can be complicated. There is a good R25 base layer of insulation under this ducting pit. It gets more difficult now, to tightly place insulation.

This is all that will remain visible, of HVAC flex ducts. With planning, excess R8 duct liner pulls up to cover almost all area of the non-lined steel fittings. Full wrapping is of about equal importance, to the internal lining of ceramic microballoons; neither perfect insulation. An in-attic furnace must have been thought necessary. I have perhaps minimized the penalties, while making the attic a well-lighted, useful space. 

Let's look around this now-pretty attic, reviewed in other blog post about its new access hatch cover and R30 insulation of a skylight.




Finished attic, access beyond the skylight, two shelves nestled in trusses. Storage space was needed and affordable. no one may command that attics be left dark and dangerous, with precariously-hung, energy-losing tangles of flex ducts and pretend-only hatch and skylight insulation. Extensive flooring was essential to placing the R60 floor insulation, now protected for sixty years or more. I think flex ducts sheltered from attic heat and yanking in passage should survive far beyond warranted life of not more than 25 years. The creation of useful space was a very good investment and is perhaps affordable for anyone.

An Opportunity Not Yet Resolved, Customer Coleman:

(Someday, maybe with conversion to heat pump elimination of a gas furnace.)

With the deep dimension of the furnace parallel to trusses, the return air at the bottom via a service box efficiently collects two 12" ducts in a wye, to 16" round inlet. The output at top is then blocked by truss elements at sides, and a  return must not obstruct front service doors and air supply and exhaust ducts. Output duct compromises at top are not acceptable. This furnace is only one truss bay distant from an end wall.Set closer to attic centerline and turned 90°, service doors then facing to left, could then be reached with best-headroom access along the attic centerline.

An in-attic furnace adversely placed parallel to trusses and handily near an end wall. This time, the home owner has ample garage storage, and desire to cope with the bad furnace installation. I need to convince a reader that this installation is wrong. A builder should keep control over how the necessary in-attic work, is done. Perhaps the architect could have provided an interior furnace location. A builder must cope. So here we are. What could have been done differently, within the control of the builder?


An alternative attic with furnace perpendicular to trusses, has excellent access. The found hatch then interferes with duct paths. A better access is possible. 

Here are found conditions of the badly-oriented furnace and badly-conceived HVAC ducts. I have pinioned my back and legs to move through the trusses in the alley at RHS. Appreciate the needless hostility of this attic, and the consequences to decrepit conditions.

This one of the too-few soffit vents moderating temperature in the attic. The house was built in 2001, and I am the first person to see that the cardboard baffles are already falling-down. Two others are fully detached We must ban all that is not durable. Who now will fix this? How? The HVAC flex ducts will disintegrate within the next twenty years. Perhaps they will last much longer, buried, temperature moderated, not under tension. Shouldn't something be done here, now? 

I hope I will be allowed to fix this attic.I hope then that lessons shared, will cause an end of cheap foolishness. I am up here early in the failure cycle, only because there lately has been a loud clicking in the walls at each furnace startup. A 12" steel pipe connecting the attic to the crawl space and carrying conditioned air to floor registers of the first floor, was pinned against ability of thermal expansion. I was able to hack away the wood interference,.


Look for web consensus that an in-attic furnace should be perpendicular to trusses:
An attic furnace should be oriented perpendicular to trusses for best deployment of ducts. 
Hope that this post will be detected, and will lead a change of direction.

Search results include: https://www.greenbuildingadvisor.com/article/dealing-with-ductwork-in-an-unconditioned-attic  (I have joined this conversation.)

https://www.energyvanguard.com/blog/73245/Go-Up-Go-Small-and-Get-Those-Ducts-Inside-Conditioned-Space    (I don't like that duct Medusa.  I think the USDOE reverse bulkhead idea has no traction. How could you get to ducts for service?

A Yet-Better Replacement Of A Drywall-Plunker Attic Access Hatch

This is a high-end new home. Yet, the access to the attic is standard cheapness and thoughtlessness. The plunker and tied-on R38 batt lift with difficulty and danger. Slight handling errors break the brittle drywall. Allowing for bare areas, the effective value of the burdensome insulation is less than R7.

75% R38. 25% uninsulated.

1/(Reff + 3) = .25/3 + .75/41


Reff = 7

Or, is it even that good? The number 3 in math so far, represents the sum of convection and conduction resistances in a complex wall with at least two convection interfaces, aiming for a highest number, so as to not over-estimate savings with correction. What if the real sum here is only 1.3?
0.17 + 0.45 + 0.68 = 1.3 (Colorado Energy numbers)
1/(Reff + 1.3) = .25/1.3 + .75/(38 + 1.3)


Reff = 3.4, doubling the heat cost as-found. Ueff = Reff = 1/3.4 = 0.29

My insulation math at 95% furnace efficiency and natural gas cost of $2 per therm, says heat cost per year is: $2.4*Area*.88/.95*Ueff.
Area = 3.6 sq ft.
Cost per year: $2.30. Compare to cost of $0.20 per year at 3.6 sq ft of R38 ceiling, U = 1/39.3.

With my usual analysis with that number 3, Reff = 7, cost per year is:
$2.4*3.6*.88/.95/(7 + 3) = $0.80. 

Save $2.10 per year or $1.50 per year with the better hatch cover. Motivation is the same whatever the math. The gob is even more a nuisance and safety hazard, than a false economy. Avoid spending more for the better hatch.

Here is the replacement hatch cover, ready for application of facing drywall. An R19 unfaced  batt was at hand, costs less than R15 and is acceptable where it overfills the space.






















Here is the completed useful attic with the new hatch cover stowed upon a tray.

I intended to use the 1x4 wood frame in the ceiling as-found. Finding that frame unacceptably out-of-square, a repair was instructive The RHS member of the frame was long by 7/16". In the correction by steel-cutting Sawzall, a steel edge frame for drywall was confirmed. The drywall and steel edging formed into the hole reduced possible opening size by more than an inch.

I think this is a much better arrangement of a generally-useful hatch, allowing maximum hole size with 24" framing on-center tolerance of plus or minus  1/2". It will be better that the hatch and its frame are built with precision as a matched set. I think of ways to increase durability while reducing cost.

Show a larger opening where the hatch assembly is installed with least effort, into a simple drywall cut. Show wood veneer banding of the cover drywall edges as thought to reduce cost and improve ruggedness. A high-end cabinet shop finding fill-in work and uses of scrap material, making thousands per year, will find many opportunities of improvement and lowered cost. Energy Trust Of Oregon, and Oregon HBA: Please support this, including better content of IECC Residential Chapter 4, paragraph R402.2.4 at 2019 cycle, timely with showing at 2019 International Builders Show in Las Vegas. Showing would enlist cabinet makers anywhere, at minor cost for the advocacy. Any shop could make improvements, to be shared.

Flexible grout completes the ceiling drywall edge over the hatch frame, with texture match. Think to offer a white melamine plywood facing instead of heavy drywall. In practice, a manufactured hatch of standard size will cost less than drywaller steel-edging of a plunker hole while complying with raised energy-efficiency code requirements.

I do many important things in an attic, and work hard to share with others. In this home, I completed a better example of R30 insulation hard-covering a skylight . Most important to the home owner, I created a useful attic, vastly capable of storage, enabling rental of the ground floor of a grand year-old duplex home. Found conditions were dark and dangerous. Access anywhere was blocked by hanging HVAC ducts. A full report upon the HVAC demolition and replacement is out of place in this blog post, and will be relocated after the ruined new-home furnace is replaced, hopefully in Spring 2018. Place some content now, to be moved to an appropriate post

All HVAC ducts are suspended. This is common, but it is not good practice.

Dangerous passage around the poorly-insulated skylight had trampled floor insulation value.

No passage this way, around the awful furnace installation. See that the furnace is ruined by absence of filtering provision. An entire side of the furnace was hacked open for absurd return-air ducting. The furnace inlet ducting must be modified to provide filtering of the return air. 

















Awful conditions were found in the demolished furnace-outlet D-box. Read more and see more in the associated photo album .

See the improved furnace proud upon a smooth attic floor, in photos at the beginning of this post.

Flawed Measurement Of R-Value With A Certainteed InsulSafe4 Gage

I want to at last dispose a gage saved from a job in which I concluded the following:
The Builders Statement of found insulation states that for intended R38, one bag covers 44 sq ft. 37 bags were applied, sufficient for 1628 sq ft. The installer was unaware of actual area  2315 sq ft, then with 30% under-fill,  R26 before discount for overwhelming consequences of missing insulation.

General fill of insulation was 10", not a goal of about 15".  A greater depth of insulation did not exist at time of construction, then lost by settling. A failure of inspection occurred, on top of a perhaps-conscious failure of math. Was compensation for the job not proportional to cost of materials?

Adjacent to the found access hole where inspection would be expected, the gage is revealed at 10" depth. By human nature, depth is less at a majority of area not accessible for inspection.

Here is a cropped photo of the gage, with marking of depths at values of common interest, a black line and arrow under-lining each named value.  For example, named value R60 is at depth 22.0".The gage corresponds to a table in PDF document InsulSafe® SP Installation Guide - CertainTeed .

Having insulation generally R26 where R38 was wanted, is mean. Call the weighted average of loose fill R24.  The overall effective R value of the attic floor is diminished by areas bare of insulation and by thermal equalization of interior walls through assorted floor openings often large. Bare areas are mainly at edges of the attic, and are typically 5% of floor area.

Do the Insulation Math , of found effective R-value:

Allow for thermal shorts of 2x8@24" framing.

1/(R_eff + 3) = f_joists/(R_joists +3) + f_{insulation in contact}/(R_insulation +3) + f_bare/3

For 2x8 framing, R_joists is  6.8.

1/(R_eff + 3) = 0.06/9.8 + .89/27 + .05/3

R_eff = 15

The work of sealing the attic floor is an insulation cost, and I think the expenditure should be encouraged by allowing its result is that of finding another 5% floor bare area:

1/(R_eff + 3) = f_joists/(R_joists +3) + f_{insulation in contact}/(R_insulation +3) + f_bare/3

1/(R_eff + 3) = 0.06/9.8 + .84/27 + .10/3

Found attic floor insulation:

R_eff = 11

The now-accessible attic has a large decked area 18.6" up from ceiling drywall, and much additional area accessible with movable flooring upon raised floor supports. HVAC ducts are more efficient and are buried under floor insulation where allowed. Conditioned space below the attic floor is 2315 sq ft.

A section of hallway ceiling ruined by step-though during electronics wiring is now occupied by a wonderful European attic ladder.

Ladder installation at a 45° diagonal across 2x8 floor joists is supported by 2x18 box beams, a first-ever feat of cleverness.

I imagine a 150 sq ft work room 8' tall from the new flooring level, at the attic space with greatest headroom. The space might be a wood shop or music room, conditioned or not. An attic has congenial temperature a portion of most days of the year.

With dispersed insulation,  f_bare is zero. One bag of R21 insulation, 89 sq ft, 89/2315 = 4% of the floor, is placed over the master bedroom loft ceiling. 5% of the floor at eaves is insulated to R30 with pushed loose fill. The remaining loose fill is 3" to 4" deep everywhere else, called R11.

1/(R_eff + 3) = 0.06/9.8 + .04/24 + .05/33 + 0.85/14

In the now-accessible attic:

R_eff = 11.

This is the same as-found, not diminished. Where this condition must exist for some time, my churn of insulation beyond just creating safe attic access, has not hurt my customer. This finding is very important to me. I hope you agree with my math. Distributing insulation to eliminate bare areas is smart, even where found unstable loose fill insulation is collapsed in the churning.

Find then:
Perfect, fullest placement of insulation is absolutely required in weatherization. Perfect full-filling coverage is far more important than insulation depth or available thickness. Where insulation has been placed carelessly, do not hesitate to trample insulation if necessary, to perfect the installation. Never delegate placement of insulation to be done without caring, in haste. The value of insulation placement is proportional to time spent.

Back to that now-disposed gage then. Don't believe it, even where it reads correctly in perhaps revealing fraud. Diligent work is harder to gage.

Math Assessment Of Poorly-Placed Insulation

Look for  Math of insulation payback assessment and qualification of rebates  . Please follow the link of that Google search, at top finding my work.  It is an important subject, in which there is an absence of academic contribution. Math shows that we can not afford to place insulation carelessly. 

We will find that perfect, fullest placement of insulation is absolutely required in weatherization. Perfect full-filling coverage is far more important than insulation depth or available thickness. Where insulation has been placed carelessly, do not hesitate to trample insulation if necessary, to perfect the installation. Never delegate placement of insulation to be done without caring, in haste. The value of insulation placement is proportional to time spent.

My most-recent customer, May 2017,  wanted storage space in a truss attic, where the home has no basement, and half of the garage is converted to needed living space.

Photos are drawn from a corresponding Google Photos album .

This home had the usual drywall plunker 18" OSB-skirted access hole. There was no safe landing to move between trusses, from the blunt OSB edge. To move, one had to angle feet to opposing angled truss elements, in long steps across trusses.

About 20% of the plunker area was bare about the precariously-stapled R38 batt, and this really mattered to actual insulation value:

1/(Reff + 3) = .8/41 + .2/3

Reff = 8.6.

A batt on a plunker is ridiculous, dangerous, and often temporary. I continue to do good service in safety of attic access, contending for better building codes , and imagining and building very-simple factory-built hatches that cost no more than the plunker-hole. I prefer to install a wonderful attic ladder, then with every safety feature I can imagine.

I am the first person up here since house construction in 2004, and the home owner has cause to trust that I can make this space useful. There is 15" of loose-fill insulation seemingly almost the required R38. HVAC ducts are strapped-up, for the insulation blow, and are very much in the way.

Good lighting and safe access via ladder is accomplished early in a job. A pretty Fakro LTK 22/47 insulated attic ladder is rigidly mounted with the beginning of 18" box beams at both sides. Outer beam faces are 16" rips of 3/4" plywood. There is a step-off well 9" up from the ceiling.

Preview the accomplished attic improvement equally for usefulness, and energy conservation. Up 18.6" from ceiling drywall, there is very much useful space. New and more-efficient HVAC ducts are almost entirely buried, for their safety and better insulation value, without compromise of floor insulation value.  Effective R value of the entire attic floor is now better than R49. Four 900 lumens Sylvania LED disk downlights brightly illuminate the safe, clean, useful attic.

Finished features include a strong, level shelf over a loft cathedral ceiling, making that space useful and safe. Find and exploit every advantage for walking between truss elements. The shelf and flooring constitute a large box beam that restrains this gable wall and adjacent trusses against roll-over in a tornado.

Braces set for alignments during construction are not intended to guard against roll-over of trusses and great tragedy in a tornado. Useful new braces are not in the way of access.

Diagonal bracing against truss rollover is by example of MiTek, USA, MII-GE90-001 .

I have provided the safe, useful storage space that the home owner needed.

Now step back to the work in progress, with demonstration that easily-achieved energy savings are the best reason for the attic conversion. We all can and must afford the best energy efficiencies achievable in our lives. Where one is able to find an honest craftsman or is able to follow freely-offered example, an investment in a durable sixty years and more, chunk of energy independence in our homes, is a significant increment of personal wealth.

This home had complex found conditions. 43% of floor area had askew thick batts, 51% was between trusses with poured loose-fill fiberglass, and 6% was with thermal shorting of truss framing. Two loft cathedral ceilings add elegance to second-floor rooms without the compromise of roof integrity and access limitations of common cathedral construction. Loft cathedrals are easy with truss design but seem to need evolution for improved weatherization.

This collage is of found conditions of R31 and R38 batts of the West loft cathedral.

This collage is of found conditions of R31 batts of the East loft cathedral, and of repair underway under tight hostile conditions with nasty roof nails and danger of falling through drywall. Temporary wood-strip supports and access via a new storage table over the loft were important to holding a good attitude for repairs completed in a half day.

Among the R38 batts of the West loft cathedral, see awful consequence of poor batt placement and failure to block thermal shorts at framing. With 50% contact, the weighted average insulation level is only R3.

1/(R_eff + 3) = f_joists/(R_joists +3) + f_{batts in contact}/(R_batts +3) + f_bare/3

For 2x4 framing, R_joists is 3.3 .

1/(R_eff + 3) = 0.06/6.3 + .47/41 + .47/3

R_eff = 2.6

Find the same result, ignoring joist thermal shorts.

1/(R_eff + 3) = .5/3 + .5/41

R_eff = 2.6

Bare areas dominate the math, overwhelming significance of the framing thermal shorts. Therefore, apply the formula above for the entire attic floor, with glib allowance for joist thermal shorting, whether or not there may be insulation "atop" conductive complex truss framing. Joist thermal shorts remain important in most cathedral ceilings, where a rare reader might amend the math with larger value of R_joists . Consistent math is achieved by use of an OpenOfficeCalc spreadsheet. Please find that spreadsheet for the first computed result, with 2x4 @24 joists, f_bare=, 0, R19, at Google Drive .

About half of intended insulation value is lost where the bare area fraction is just 5%. About two thirds is lost where bare area fraction is 10%.  About three fourths is lost where bare area fraction is 15%. Even 5% sloppiness is an unbearable insult to home occupants, not justified by any offsetting construction economy.

The table above applies in general, for a floor with a single layer of batts, or a floor with loose fill insulation. In the table, 6% of floor area is treated as 2x4 joist thermal shorts, R = 3.3. Where bare areas strongly dominate the math, the treatment of thermal shorts is of no consequence. My immediate self interest in the table treats the question whether my rebates organization, Energy Trust Of Oregon , will grant my customer an insulation rebate. Rebate offers are the only offered encouragement of actions by my customers. A rebate is offered only where found insulation has value less than R12.

In another edit of the example spreadsheet , imagine compromise of insulation in a 2x10@24 cathedral ceiling with R19 batts 50% bypassed. Find R_eff = 2.3. All insulation that doesn't fill enclosing space has questionable value. Try out your own favorite worry. I wait with skepticism, to study methods in new USDOE Home Energy Score software, hoping that penalties will cause end of ruinous venting with deliberate under-fill of cathedral ceilings.


Bare areas in an attic add up fast. In most homes, expect 5% of the floor area bare, at carelessly insulated eaves. See attic walls in the photo above, with loft cathedrals at left and right, insulation uselessly bridging the wall framing.Those uninsulated  attic walls at interior sides of loft cathedrals alone are more than 10% of floor area, and treatment of those walls can not be separated from overall attic improvement.

Bare areas under floor insulation are another 10% of the attic floor, mainly in awful result of blindly stuffing oversize batts before setting drywall, at the loft cathedrals.

Carelessness is the cause of energy waste in this home, in defiance of building codes in effect at home construction in 2004. And, until I showed up to imagine a useful attic, all seemed well. Any inspector or other weatherization contractor would have seen a good-looking attic with no corrections needed. The attic is a dangerous place. Stay out! 









I move further beyond the R12 threshold for a rebate, at f_bare = 0.15 (see table above), if a bare area equivalent 5% of the attic floor area, is added. This is proposed as a standard allowance to encourage sealing of attic floors. 

Payback Math, Insulation Improved Effective Insulation Value Starting  R10, Ending R49:
Apply Insulation Math that gives understandable dollar values then easily scaled for a home, heating means and climate, that matters to you. Basis math is for a home with 88%-efficient natural gas heating, 4400 heating degree days, energy cost $2 per therm.

Annual Cost of Heat =  (.00002 * 4400 * 24  / .88) * (Area/R)  = 2.4* (Area/R)

Let Area = 1200 sf, and R = 1/U = Reff +3.

For the attic floor, the first-year saving of heating cost is $222 - 55 = $167.

Attic walls, the exposed ends of loft cathedrals are another 100 sf, improved from less than R4, to R30. Here the first-year saving of heating cost is $34 - 7 = $27.

Total first-year savings are $194.

In considering savings on into the future, one must account for the rising cost of easy energy through scarcity. Apply Perpetuity Math . The present value of an investment yielding $194 in the first year and continuing indefinitely, is more than $8500, first-year times 44, with a twenty-year outlook and true cost of energy rising at 10% per year. My invoice of $6100 was a bearable cost for wonderful new storage space. All of the cost, including a bit of excess for the storage, is in fact a very profitable investment.

Rebates As Incentive
Once again a rebate application is in process with Energy Trust Of Oregon, for my work. I have asked $296 for the floor insulation, and $30 for the attic wall insulation. $326 total, 5% of job cost. This is a small return of the home owners' thirteen years of contribution to Oregon's Public Purpose fund, a 3% tax upon natural gas and electricity bills.

As I understand it, rebates in fact are not needed as incentives. We just want to know priority of the things-to-do, to be able to afford the work and to trust that it is done honestly, to endure. Incentives are not working to drive weatherization of existing homes, where Energy Trust will promote fewer than 1000 attic insulation improvements in 2017.

Despite need to multiply its productivity times fifty, or go out of business, Energy Trust definitely wills that the described attic would have been left alone. I am commanded in Specifications , that:

IN 1.13—Determination of Existing R-Values

The total R-Value for a floor or an attic shall be calculated based on the depth of the insulation (in inches) multiplied by the recognized R-Value per inch of the insulation material.
15" times R2.2 per inch for loose-fill, is R33. Rebate Denied. And that is the end of a conversation. My customer may receive the asked rebate, but Energy Trust will learn nothing, and will not contact me, for its benefit or as a disciplinary action. Meantime there is some strange complexity  offered in Specifications Appendix A:

APPENDIX A: WEIGHTED ATTIC R-VALUE TABLES
These tables shall be used to determine the weighted R-Value of a single attic space with varying levels of insulation. These figures are determined by using a weighted average R-Value calculation without including framing assembly U-Values:
U-Value (U) = 1 ÷ R-Value
Area (A) = area in sq. ft.
Weighted R-Value = 1 ÷ [(U1A1 + U2A2) ÷ (A1 + A2)]

In cases where the existing insulation level is R-0, an R-Value of R-1 is used in its place to determine weighted R-Value.

This math is of course in error, where convection heat transfer coefficients and resistance to heat conduction through surface materials add up always to nearly 3. A low number for convection and surface resistances is a bad idea, for it leads to over-estimate of savings achieved where there was little or no insulation at found conditions. A modestly high value, 3, gives desired under-estimate of savings achieved. Add 3 to all insulation effective R-values and then invert the result, to obtain U-Values. Please see discussion of such concerns at Wikipedia , and ColoradoEnergy.org . Compare savings from insulating a 1200 sf attic from no insulation to R49, assigning 1 or 3 as found effective R-value, 1/U, U = 1 or U = 1/3

$2.4*1200*(1 or 1/3) = $2880 or $960, at found conditions.
$2.4*1200/50 = $58 at R49.

No one would think to mislead, in offering that another $2000 per year is saved. The only math offered by Energy Trust for mixes of insulation then is incorrect. No correspondence to dollar savings is suggested. There are internet links at Fine HomeBuilding and elsewhere to USDOE math of payback calculation, now broken. The missing information handicaps decision making for weatherization. In particular, the treatment of out-of-contact insulation is not addressed, leaving some to think contact doesn't matter. Surely the correct treatment of insulation out of contact and permissive of air bypass driven by heat input and rejection, is to fully discount any value of the insulation.

Tragedy In A Typical 1970s Town Home

Many 1970s homes are dominated by cathedral ceilings that have no actual insulation value. This is the first home I will address with USDOE Home Energy Assessment software. What direction will I find for this condition in 2x10@24 ceilings? I have seen clues that the insulation will not be counted.

The exterior walls of 2x4@16 construction have insulation nearly as poor.This small area at a removed air conditioner, fixed with removal of exterior sheathing, may be the model, unaffordable repair, saving $6 per year at cost of $600.

It may be evident that this home has a personal connection to me. Bitterness about the cathedral ceiling and wall insulation seemingly not treatable, motivated two of the ten proposals for 2018 revision of the International Energy Conservation Code, at Louisville , that I offered and personally defended at great cost. Please find a February 2016 summary of my correspondence with IECC , where I responded at the best of my ability to all editing suggestions. At this code cycle IECC newly offered an online submittal process, cdpAccess, and supported my telephone and email newbie needs. At the conference, I relied on my own printing of proposals vs. existing 2015 code, as in this abbreviated printing for followup discussion with NAIMA. I sorted through a tall stack of paper-printed code and revision in competition with experienced professionals using laptop computers, trying to follow all proceedings that mattered to me.

My proposal 11881 offered:
R402.2.1 Over-fill of insulation. Wherever possible, insulation shall be confined on all six sides. Insulation fill shall be complete and without voids that could allow air bypass of the insulation. Overfill of insulation shall be required to achieve complete insulation fill. In addition to installation methods that prevent voids within the insulation, the methods shall prevent the presence of air spaces between a barrier film such as the kraft facing of a batt or the containment mesh for blown cellulose, and hard wall coverings such as drywall.


At the eaves of an attic, insulation installation methods shall achieve as much insulation R-value as possible toward exterior wall headers. The eaves shall be packed tight with insulation and overfilled except the resulting R-value at these locations shall not be required to exceed R-value required for the adjacent ceiling.

My proposal 11882 offered:
R402.2.2 (N1102.2.2)  Ceilings without attic spaces. Such spaces, commonly called cathedral ceilings, have depth limited to that of practical roof framing. They are to be crafted with all of the seriousness of any other conditioned attic, concerned for roof rot in insulation at temperature below the dew point where moist air may pass. A solution for insulation, in well-applied closed-cell foam, must be seen as risky in the event of roofing failure. These spaces shall not be violated by can lights or provisions for attic ventilation and foolish wish to cool composition shingles. There shall be no compromise of required insulation value.


With these provisions, any persisting construction of cathedral ceilings shall be with acceptance composition shingle roofing is not allowed.

My proposal 11859 offered:
R402.2.3 Eave baffle and insulation provisions. Where needed at soffit vents, a solid baffle durable for service of at least sixty years, shall hold insulation at bay, while allowing a stable maximum amount of insulation to be placed. The airflow resistance of each baffled path shall be less than that of its screened vent. Soffit vent paths installed as pre-made "bird block" and designed for placement at every frame bay, shall be placed in every frame bay.  


For new home construction and in tear-down remodels, eave baffles and at least all eave-edge ceiling insulation shall be placed before installation of ceiling-edge drywall, if needed to assure thorough  insulation, in areas that become inaccessible. Where an attic eave extends to a cathedral ceiling or other roof-over-conditioned spaces, do not employ the insulated cathedral ceiling cavity as passage to admit air for attic venting. 

Altogether, these three proposals dealt with my concerns of deficient and irreparable poor construction of the 1970s depicted in the town home photos above.

All ten of my proposals were unanimously disapproved, sometimes with enmity and sometimes with sympathy expressed by other conference attendees. It was awful. Seeking solace from ICC long after, I was chided for not doubling my investment in another try at the final hearings in Kansas City. My goal instead is to develop alliances for another try in submissions for 2021 IECC. Alliances are needed to combat a little army of obstructors seasonally hired to work the hearings, by the National Association Of Home Builders, aiming to squirrel every possible nickel to pockets of big-time builders. I especially need to find a working relationship with NAIMA , the successful obstructor of the batt-overfill proposal. NAIMA must admit for example, that R13 batts are grandly inappropriate in 2x4 exterior walls, never being 3.5" thick as-placed, and possibly of no value.

Please see that math is integral to my contributions for USA responsibility to conserve energy now wasted in our generally-shoddy homes. Please see that regulation in building codes applies only to new homes and major renovation. Energy conservation is not regulated thereafter.

Note to Self: Anticipate a review in Summer 2017, of consequences of 2018 IECC changes approved, by US Department Of Energy. The report may be like that issued for 2015 changes, in August 2014, which did not reveal any useful math.
PNNL-23438
https://www.energycodes.gov/sites/default/files/documents/2015_IECC_preliminaryDeterminationAnalysis.pdf 

Issued by Battelle Pacific Northwest National Laboratory, Richland, WA.

Note to self fulfilled, August 2018:

See what US Department of Energy has to say about 2018 IECC. 
Search  energycodes.gov + 2018 IECC 

Examine two search results:

What You Need to Know about the 2018 IECC | Building Energy ...

https://www.energycodes.gov/resource-center/.../what-you-need-know-about-2018-ie...

Mar 8, 2018 - This webinar, which is part of DOE's Building Energy Codes Program Energy CodesCommentator webinar-based training series, provided an overview of the 2018 IECC residential provisions. The presentation focused on the highlights of what has changed in the residential requirements ...

Here, we are invited to a March 8, 2018, 1 PM webinar. 

The webinar consists of 101 slides.

Content of the March 8th webinar shares this set of 120 slides:

Residential Provisions of the 2018 IECC - Building Energy Codes ...

https://www.energycodes.gov/sites/default/files/becu/2018_IECC_residential.pdf

www.energycodes.gov. BUILDING ENERGY ... IECC addresses both residential and commercial; IRC addresses subset of ... Considered part of the requirements of the code, but IECC provisions take .... Climate Zones for the 2018 IECC ...

I believe that these slide sets have been studied by extremely few new-home builders and have little value. They are agnostic of my expressed wishes of better code, where I have work only in existing homes. Monster homes are illustrated, where some wealthy buyers just might act upon new code prescriptions. There is no beginning yet of imagining affordable smaller homes of the future. I comment only on this slide:

I gave up on finding meaning in USDOE Home Energy Scores. Where IECC should promote scoring as ERI, I wonder if my 1955 home now better than new as an example affordable construction, again, is it now better than ERI 62, I wonder. As an exemplar worker and  USA taxpayer, I think I should freely try out ERI. How can that happen?

Where code is interpreted by USDOE in this suggestive detail for better ceiling construction under an unconditioned attic, I am appalled. Surely there is no continuous air tight hard covering over stuffed-up batts within very-deep truss joists that enable HVAC duct placement within the heated envelope. I am not contradicted in my advocacy that batts shall fill framing space with six sides air tight containment. Open space under batts will have convective heat exchange with the attic, probably then effectively not insulated. In teaching beyond code prescription, USDOE misleads us. I teach better ways of having attic HVAC ducts under insulation.

USDOE intent to promote ugly mercury-contaminating CFL bulbs against the public interest for three more years, is given emphasis: