Looking Back at Insulating Advice from 1951

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Looking Back at Insulating Advice from 1951

For at least four decades, the Audels Carpenters and Builders Guide was considered the Builder’s Bible

Posted on Feb 23 2018 by Martin Holladay

Up until the mid-1950s, almost every American carpenter had heard of Audels Carpenters and Builders Guide. Even carpenters who didn’t own all four volumes of the book series had probably studied the Audels books at some point in their careers, or knew someone on the job site who had copies of the books.

In a way, the Audels Guide was the Fine Homebuilding of the 1930s and 1940s. It instructed beginners in the right way to do things; it upheld standards; and it promoted quality work.

First published in 1923, the guide was updated in 1939, 1945, and 1951. As U.S. builders made the transition away from post-and-beam framing to stick framing, Audels dragged its heels, entering the new era with great reluctance. Even in its 1951 edition, the series insisted that a quality building needed a post-and-beam frame with mortise-and-tenon joints.

In an online essay, Tedd Benson credited the Audels books for inspiring his love for the construction method that became Benson’s focus for decades: “Reading the old Audels was, in fact, the first time I became enamored of timberframing. That edition had good illustrations and reasonably good instructions about joinery and particular framing techniques.”

The 1951 edition of Audels, which I own, advised readers that stick framing was inferior to post-and-beam construction. The books refer to stick framing as “balloon framing,” whereas post-and-beam construction (timber framing) is called “full framing.”

According to Audels, a “full frame” consists of “heavy and solid timbers fastened together with mortise and tenon joints secured by pins,” while a balloon frame “is a cheap and as usually put together a more or less objectionable construction. … Since the balloon frame is a type which invites poor work and a certain class of builders cannot resist such a temptation, it has a bad reputation.”

The Audels authors' contempt for stick framing makes for fascinating reading. But I was even more interested in the chapter on insulation.

I have long held certain assumptions about builders’ understanding of insulation in the early 1950s. I assumed that most builders had a limited understanding of modern building science principles; that many new homes had little or no insulation; and that available insulation products were primitive.

I was pleasantly surprised, however, to discover that this 67-year-old book did a pretty good job of introducing the topic of insulation to residential builders.

Heat transfer basics

The Audels chapter on insulation starts out the same way as a modern book would: with a discussion of heat transfer basics. The book notes, “Insulation of a building is usually concerned with the problem of reducing the transfer of heat from one region to another … There are three general methods by which means of which this transfer can be accomplished, called respectively conductionMovement of heat through a material as kinetic energy is transferred from molecule to molecule; the handle of an iron skillet on the stove gets hot due to heat conduction. R-value is a measure of resistance to conductive heat flow., convention, [and] radiation.”

OK — we’re off to a good start.

Why do we insulate?

The two main reasons for insulating a building are to improve occupant comfort and to lower fuel bills. The Audels guide mentions both reasons: “When insulation is properly applied, it keeps the interior of the house at an even comfortable temperature which is obtained by a minimum of fuel consumption.”

The famous John Ruskin quote which appeared as an epigraph to the Audels books for decades. (Ruskin failed to anticipate the fact that women would enter the trades, unfortunately.)

What factors affect payback?

On GBAGreenBuildingAdvisor.com, readers often ask questions about the likely payback period associated with insulation improvements. Here’s what the Audels book had to say about payback: “In certain localities where the winters are usually long and severe, and where the fuel is expensive, the cost of insulation may pay for itself in a comparatively short time, whereas in climates only moderately cold, or where fuel is cheap, this time may be considerably longer.”

Green materials were big

I don’t think that the term “green building” was used much in 1951, but today’s green builders might be surprised at the variety of insulation materials that were available back then.

According to Audels, “Insulating products are manufactured from a great variety of raw materials. Those most commonly used are: asbestosMineral fiber once commonly used in many building materials, including insulation, fireproof siding, and resilient flooring. Inhalation of invisible asbestos fibers can lead to chest and abdominal cancers as well as scarring of the lungs. The use of asbestos in some products has been banned by the EPA and the U.S. Consumer Products Safety Commission; manufacturers also have adopted voluntary limitations on its use. When found in older buildings (most commonly in floor tiles, pipe and furnace insulation, or asbestos shingles), the product's friability is a major determinant in how it must be handled during renovations. More information: http://www.epa.gov/iaq/asbestos.html, cork, corn-stalks, cotton, gypsum, hair, jute, limestone, moss, paper pulp, wheat straw, wood, aluminum, etc.”

OK, green builders will probably skip the asbestos and aluminum products. But everything else listed in Audels could be displayed at a “green materials” booth at the next NESEANorth East Sustainable Energy Association. A regional membership organization promoting sustainable energy solutions. NESEA is committed to advancing three core elements: sustainable solutions, proven results and cutting-edge development in the field. States included in this region stretch from Maine to Maryland. www.nesea.org trade show.

Two types of attics

The Audels guide discusses two types of attics: vented unconditioned attics and unvented conditioned attics.

Here’s the advice for a vented unconditioned attic: “In a house with an unfinished attic, insulation may be installed … between the top story ceiling joists…”

Here’s the advice for an unvented conditioned attic: “An attic with a heated room should be insulated by installing the insulation between the rafters…” Admittedly, this last description leaves out an important detail: the need for a ventilation gap between the top of the insulation and the underside of the roof sheathingMaterial, usually plywood or oriented strand board (OSB), but sometimes wooden boards, installed on the exterior of wall studs, rafters, or roof trusses; siding or roofing installed on the sheathing—sometimes over strapping to create a rainscreen. . But at least the existence of conditioned attics was noted.

There’s even a mention of triple glazing

Amazingly, triple-glazed windows are mentioned in Audels: “In locations where the weather is frigid, a common method to prevent air leakage through the window glass is to double up the glass either by installing storm windows or by insertion of an additional glass in the original frame. … In some cases triple glazing with dead air spaces between the panes has been found to be a most satisfactory method of insulation.”

You can choose to use rigid insulation, batts, or loose-fill

Even in 1951, builders could choose between rigid insulation, loose-fill insulation, and batt (or blanket) insulation.

This detail from Audels shows the use of continuous exterior rigid insulation under brick veneer.

According to Audels, “Rigid type insulation … is often utilized as a combination insulating and structural material, such as sheathing on the outside of framing members, and as a plaster base within. … When rigid insulation be used as wall sheathing under wood siding, shingles, brick veneer or stucco, large panels are preferred.”

Loose-fill insulation is referred to in Audels as “fill type insulation.” The book says that fill type insulation “is powdered, granulated, or shredded material. … Fill material can be applied in houses under construction or those already completed by packing or blowing it into spaces between framing members. Its insulating value varies with the properties of the raw materials used and according to the density with which the material is packed.”

In the early 1950s, insulation batts installed between studs were usually quite thin. These thin batts didn't fill the entire stud cavity.

Audels refers to batts as “flexible type insulation,” which “consists of a loosely felted, fibrous mat, usually covered on both sides with a layer of paper or fabric. It is sometimes referred to as ‘blanket’ and ‘quilt’ insulation. … When flexible insulation is employed between framing members, a common method of installing it is to place it in the center of the air space between the studs of the wall… In this case the insulation is cut slightly larger than the openings in which they are to be installed; in this way the surplus material will fold back and form flanges, which are fastened to the studs…”

While the Audels book accurately describes the manner in which batts were installed between studs in 1951, it failed to note a major drawback to the described technique: the batts weren't thick enough to fill the entire stud space.

Interestingly, 19th-century builders of ice houses (who were faced with the challenge of making blocks of ice cut from frozen lakes last for eight months in storage) had a better grasp of insulation basics than residential builders. Typically, an ice house had very thick framed walls filled with sawdust. Ice house builders undoubtedly developed this superinsulation method out of necessity: since electrical refrigeration did not exist in the 19th century, the only way to keep ice from melting was with thick insulation.

What about air leakage?

While older carpentry books often advised builders to include insulation, they usually fell flat when it came to discussing air leakage. But the Audels book did a better-than-expected job for its era.

The book explains: “The two predominant ways in which heat is lost is by in-leakage of cold air around and through doors, windows and walls of the building and by transmission through the material constituting the walls, floors and roof.” Of course, the author didn’t mention infiltration through basement cracks or exfiltrationAirflow outward through a wall or building envelope; the opposite of infiltration. through ceiling cracks — but that omission was typical in the 1950s.

Unfortunately, this misguided focus on leaks near the neutral pressure plane rather than more important leaks lower down (in the basement) or higher up (at the top-floor ceiling) persisted, even among educated builders, into the early 1970s.

The Audels guide noted that older homes are often leakier than newer homes: “It is evident therefore that even though the house was tight when built, a few years of usage will permit a considerable amount of leakage. In addition, in masonry walls, small cracks often develop which in time may become sufficiently large to permit a considerable air leakage. The most common remedy against this air leakage is found in calking or filling of the leaks. … In the same manner as calking mitigates air leakage around window and door frames, so do weather strips minimize leakage due to loose fittings around windows and doors.”

These references to “calking” and “weather strips” were ahead of their time.

Martin Holladay’s previous blog: “Using a Bath Fan to Equalize Room Temperatures.”

Click here to follow Martin Holladay on Twitter.

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Feb 23, 2018 4:24 PM ET

Edited Feb 23, 2018 6:20 PM ET.

Aluminum insulation?
by Charlie Sullivan

Thanks for this perspective, accurately reflecting what has been learned, as well as as showing what has been known for many years.

One thing stood out as a mystery. Aluminum insulation? Like steel wool, but made of aluminum? Or was this an early radiant barrier approach?

Feb 23, 2018 4:49 PM ET

Edited Feb 23, 2018 4:58 PM ET.

Response to Charlie Sullivan
by Martin Holladay

It was common in the 1940s and early 1950s to refer to radiant barriers as a type of insulation. These radiant barriers were made of either aluminum or galvanized steel.

I have a copy of the February 1947 issue of House & Garden magazine that includes an advertisement for flexible steel sheets that are touted as "insulation." The ad reads, "Insulate with Ferro-Therm once and you insulate forever!" The ad further boasts that Ferro-Therm sheets reflect "90% to 95% of all radiant heat."

Right now, I can't find my House & Garden -- I'm quoting from notes I took for an Energy Design Update article. But after an online search, I found the image below -- an advertisement for "Ferro-Therm Metal Insulation for Homes."


Ferro-Therm metal insulation.jpg

Feb 23, 2018 5:40 PM ET

Math, typo, custom Delorean powered w/ flux capacitors, or...?
by Dana Dorsett

"I was pleasantly surprised, however, to discover that this 57-year-old book did a pretty good job of introducing the topic of insulation to residential builders."

Last time I looked at my watch it was 2018, not 2008. That would make a circa 1951 publication 67 years old, not 57.

The great thing about radiant barrier advertisements from the 1940s & 1950s is that they don't include pictures of satellites or the Space Shuttle or written references to the space program, unlike some more recent hype. I've yet to encounter mid-century house with radiant barrier insulation in the field, but it's probably lurking out there somewhere...

Half -inch thick broad-sheet horsehair insulation with heavy kraft on both sides was around in the early 1920s. The only installation I've seen had it woven through the studs prior to installing the sheathing, bisecting the stud bays on the diagonal. Installed that way it's a total PITA to deal with for retrofitting dense packed cellulose without first gutting the walls. (Ask me how I know... :-( ). It's definitely better than totally empty stud bays, and a reasonably effective air barrier compared to just plank sheathing w/ rosin paper or felt. It's not clear how popular it ever was, having seen but a single example.

I'm not sure when foil-faced batts were first invented, blending the batt & metal insulation concepts, but they're pretty common in early 1960s houses. Is foil faced batt insulation mentioned anywhere in the book(s)?

Feb 23, 2018 5:58 PM ET

You blink, and another decade passess...
by Martin Holladay

Thanks for catching my math error. I'm older than I think.

Feb 23, 2018 6:19 PM ET

Edited Feb 23, 2018 6:21 PM ET.

Old insulation ads
by Martin Holladay

Here's a screen shot from a 1922 brochure for Lith, a rigid insulation product manufactured by the Union Fibre Company.

For access to a wealth of fascinating old insulation brochures, see this web site:



Feb 23, 2018 6:25 PM ET

Aluminum insulation
by Charlie Sullivan

Some more tidbits on the history of the radiant barrier approach:

According to the Insulation Handbook by Richard T. Bynum (2001), reflective metal surfaces for insulation were first patented in 1804, and became somewhat commercially popular in the 1930s. The source for that information is given as Paul Dunham Close, Thermal Insulation of Buildings,1947.

A 1950 book, "Heat Insulation" by Gordon Ball Wilkes, mentions using a configuration with four air spaces, and a reflective surface facing each of them.

A Google n-gram search of the terms "aluminum insulation", "reflective insulation", and "radiant barrier" shows that aluminum and reflective insulation were quite popular--at least popular to write about--between 1945 and 1960, more so than fiberglass insulation or mineral wool insulation. But it wasn't until the mid 1980s that "radiant barrier" became a popular term.

There's also an article called "Aluminum Foil for Insulation: A Research Report", by John Hancock Callender in Architectural Forum, Volume 60, Issues 1-3, Whitney Publications, 1934 that sounds like it would would be interesting.

Feb 23, 2018 6:48 PM ET

by Charlie Sullivan

Wow, thanks for the link that that archive, Martin. That could be many hours of entertainment. I found brochures from two "reflective insulation" companies, and they were generally considerably more accurate than modern radiant barrier sales brochures or web sites tend to be. A notable difference is that they are very clear about needing multiple air gaps to get significant R-value, recommending as many as 8 layers for insulating a cold-storage room!

Feb 23, 2018 6:59 PM ET

Thanks Martin!
by Dana Dorsett

The stuff I was fighting was similar to Cabot's Quilt, but with horse hair rather than eel grass between the sewn heavy kraft sheets, and much wider- about 10' wide (full height in the stud bays.)


Feb 24, 2018 8:03 AM ET

by Bill Rose

The archive that Martin linked to in comment #5 was largely the work of Mike Jackson. Mike has retired from his position with the Illinois State Historic Preservation Office, but he remains very active in APT, the Association for Preservation Technology. APT has a quarterly Bulletin journal that is an amazing resource. Mike was largely responsible for promoting energy and climate issues within the organization, and he guest edited a 2005 issue of the Bulletin on energy.

May I offer to the GBA community a big shoutout to Mike and APT.

Feb 24, 2018 9:28 AM ET

Response to Bill Rose
by Martin Holladay

Thanks for providing the information on how the archive came to be. And I'd like to join you in extending thanks to Mike Jackson for his work. It's a wonderful resource, and is a great example of one of the ways that the Web has changed researchers' lives.

Feb 26, 2018 12:03 PM ET

1923 model
by Dan Kolbert

I've got the complete set from, as far as I can tell, 1923. No mention of insulation that I can find. But it does have helpful info on mixing your own lead paint.

Mar 4, 2018 1:11 PM ET

The touch the feel
by Andy Kosick

I grew up in a neighborhood built in the 50's and have since worked on quite a few houses there. Many were insulated with cotton. This stuff was plush, you could have cuddled up with it at night.

IMG_1804 1.6mb.jpg

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