A Deep Energy Retrofit, Fall of 2013

This post absorbs still-relevant content of withdrawn post Working With Cotton Insulation Batts.  At March, 2026, recycled denim as expensive wall insulation or sound treatment is a dead market. Thick batts for floor insulation are no longer sold anywhere.

Some cotton batts continue to be sold at Home Depot, labeled Henry UltraTouch. "R13" and "R19" bags under-fill 2x4 and 2x6 walls. Under-fill is from irregular thickness and extreme difficulty of cutting-to-fit. Odd circumstances are not served by powerfully-stamped perforations. Parting to pass wires is impossible. With my reporting, I seek to discourage all others from thinking that cotton batts are somehow "green."

My experience with cotton batts has relevance now, only as an element in my only experience with a deep energy retrofit. 

A deep-energy retrofit is a comprehensive, whole-building construction process aimed at reducing an existing building’s energy use by at least 40%–50%.

This deep energy retrofit began right in 2008, with a ground-mounted 3.5 KW PV array. The array safely beautifies and might fully electrify a 2.5 acre farm. It seems that the now-old air-source heat bump needs expensive deep-winter electric resistance heat backup. A good ground source heat pump might now be afforded.

Opportunity advances since 2008 include affordable and reliable battery storage permitting off-grid electricity when the sun is down and time-shifted draw from the grid when that is needed.

Proper weatherization of the home to support this early-adopter heat pump energy independence is to my credit. I hope that the air-source heat pump has never again needed backup of electric resistance heat, and that no grid power has been needed. In this there is increasingly now an additional investment in large battery capacity. I hope to learn soon whether all of my work has been durable, and that net-zero has been attained.

Making Right Out of Fright

So much work in home weatherization is with starting conditions that are beyond challenging.

Falling-down insulation in a crawl space MUST BE REPAIRED. Batts out of contact with flooring have no insulation value.

The work is daunting. I credit the workers, very badly instructed, as being willing horses, like me. 

 

Fixing everything on the main floor, attic and roof took 274 hours in the Fall of 2011.

Here are the many details of these repairs as PDF captioned job photo albums:

Real Sealing Fixes HPwES Sealing In An Oregon Attic

Insulation and Decking

Wrap Ducts, Completion Survey

Microwave Fan Wiring and Duct

LED Light Installations

Roof Penetration For Kitchen Fan

Roof Penetration for Bath Fan

Remove Debris

Here are photos of main floor, attic and roof starting conditions. There was very much air leakage to the attic from conditioned spaces, contributing to foolishness of placing cotton batts under the roof deck. I suggest that a token amount odf wasted effort of sealing was accomplished with a few cans of fast-skinning orange spray foam. I call that a "can of foam trick." The ugly foam that was applied sealed almost nothing,

I sealed all air gaps 100% with tough Densarmor drywall and my "flexible grout."

Large attic floor pits exposed first floor walls to attic temperatures. Here, drywall was grouted in the floor about a chimney well.

Sealing involved much work with fans and lights.

Attic photos, work in progress:

Here are achieved conditions in the first floor and attic

I build inventive factory-quality and safely manageable attic hatches. R21 is more than enough. An attic ladder is far safer and for economy need not be more than R5. An attic ladder even at R10 is far too expensive and gets refyused. Here, I coped a lot, managing to stay safe.

To the very end I coped with an R3 leaking and not-insulated attic hatch cover, for my safety with ease of handling.

174 hours of repairs in the crawl space were done in the Fall of 2013.

The found condition in the crawl space was blocked by a no trespassing indication.

Very heavy cotton batts hung down 6" from floor contact against twine restraint, there was zero insulation value, Brave workers persisted against common sense, and an invoice was paid.  A thorougn new Visqueen ground cover was one simple  lasting contribution.

The found all-steel HVAC supply ducts were left horribly leaking, draped with R19 fiberglass batts. The duct insulation batts added much to a feeling of confinement. The same with R11 batts generally wrapped around copper water pipes.

 See that steel duct fittings, wyes, take-offs and reducers hang from 9" rips of 1/2" plywood. after perfecting co,p;ete coverage with insulating jackets, hoist to jam an eye bolt through a 1" hole in the plywood, and pin with a 5/8" dia length of resilient farm property tree branch,

Intimacy of flex ducts with the overhead plywood rips will discourage mouse habitat, I hope. For persons, see freedom to get around, easily sliding under clean and smooth flex ducts.

CS Batts Repair Method:

Someday, say in 25 years, the flex ducts will need replacement. It will be easy to unpin the steel fittings to place new lengths of clean flex duct. Know that absent replacement, the interior plastic conduit will become brittle and leaking, inviting vermin home invasion.

Consider the energy savings in employing flex ducts vs. solid pipes with wrong assumption of zero leakage either way:

Reduce Energy Waste in Thermal Cycles Of Heat Ducts

An important feature of the new ducting is much-reduced thermal mass exposed to each heating cycle. The mass of steel ducts responding is reduced from 200 pounds, to fifty pounds. 

Compute an energy savings for the reduction of duct thermal mass:

Assumptions:

Crawl space at 200-day heating season average of 50°F.

Average air temperature within ducts in a cycle is 90°F.

Wrapped ducts heat inertia is such that temperatures are followed 50%.

The furnace cycles every half hour, 48 times per day.

The total mass of ducts is reduced from 200 pounds, to fifty pounds.

The temperature change of the total mass of heat ducts is 10°F in each cycle.

The heat consumed in each furnace cycle is:

m * Cp * delta T

where m = 200 pounds mass, or reduced to fifty.

Specific Heat Capacity, Cp = 0.12 BTU/pound/°F

delta T = 10°F

BTU wasted in each cycle: 200 * 0.12 * 10 = 240 BTU

Times 48 cycles

Times 200 days

Result: 2,304,000 BTU per year

Times 0.00001 to convert to therms, is 23.0 therms.

Times $2 per therm is $46 per year.

At fifty pounds, this is reduced to $11.50.

Energy savings now with flexible ducts are $34.50 per year, not counting benefits of real duct insulation. I think wrap of unfaced fiberglass batts loses most of its value with air circulation.

I think this is a fair estimate. Under $50 per year is saved. Even with insulation wrap, the steel components without an interior liner may cycle by more than 10°F. However, the number of days and cycles per day, may be high assumptions for this home.

Please just recognize that lower duct thermal mass is a good deal, comparable to benefits of stopped leakage and of keeping fittings and flexible ducts aligned for least flow resistance. The prospect of much easier replacement of flex ducts terminating at fixed-in-place steel elements makes coping with flex duct failure more bearable. Be happy to have ducts renewed, clean.  every 25 years 

Study Details of the Ducts Hanging From Steel Elements

6" Chamfered Straight Take-Off From 12"

Please study my practice of HVAC duct design, and the specific design of the HVAC ducts in this home:  More HVAC Circuitry, In A Crawl Space.