How to Identify UFFI - Urea Formaldehyde Building Insulation InspectAPedia® -
How to recognize UFFI Urea Formaldehyde Foam Insulation, where to look for it
Health effects of UFFI in buildings - the original worry, the present concerns
How to distinguish UFFI from other foam insulation products
Photo guide to identification of different building insulation materials
Properties of different building insulation products
This article illustrates and describes UFFI - urea formaldehyde foam building insulation and describes where it is found, when it was used in buildings, how to look for it, how to distinguish this from other building foam insulation products, and its health effects.
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We have
added these examples because of frequent questions about these materials. This document assists building buyers, owners or inspectors who need to identify asbestos materials (or probable-asbestos) in buildings by simple
visual inspection.
Readers concerned about exposure to formaldehyde gas indoors should see Formaldehyde Hazards where we describe the sources of this contaminant, exposure levels, and steps to reduce formaldehyde levels indoors, and see Formaldehyde Gas Hazard Reduction.
UFFI Insulation - What Was the Urea Formaldehyde Insulation Worry
UFFI or Urea Formaldehyde Foam Insulation was an insulation retrofit product used in the 1970's. This expanding foam insulation
was mixed on-site and then pumped into building wall or other cavities in older buildings which were not previously insulated.
Early cancer research on UFFI: Some earlier research on the carcinogenic effect (cancer causing) of urea formaldehyde foam insulation suggested that formaldehyde out gassing from the insulation formed a significant cancer risk. Eventually, additional study
suggested that the initial cancer risk from formaldehyde was not supported, at least in this application.
The level of
formaldehyde that out gassed from UFFI depended in part on how the foam product was mixed at the site, and not all
building insulation projects using this substance produced the same level of formaldehyde.
The level of outgassing formaldehyde from UFFI insulation declined steadily with age. This was an open-cell foam that did not retain its gases long term.
No formaldehyde outgassing found after the foam aged: More interesting was the observation that perhaps largely because this insulation formed an open-celled foam,
even if there were high initial formaldehyde out gassing levels, after months or at most a few years, even careful
measurements were unable to detect any levels of ongoing formaldehyde out gassing from this material.
Only people
hypersensitive to chemicals such as sufferers of MCS (multiple chemical sensitivity) and some people with other respiratory illnesses seem to have any remaining reaction to this material, and even in that case a study of such
reactions is complicated by the observation that higher levels of formaldehyde out gassing from building products occurs
from some furniture padding and from some glues or finishes used in chipboard based cabinets or sub flooring.
Yet at the peak of the UFFI enviro-scare, and exacerbated by inconsistent advice offered by government and private
health experts, some buildings were sold at a significant discount to allow for extensive gutting, cleaning, and
re-insulating of building cavities.
Should You Avoid Buying a UFFI-Insulated Building?
The short answer is no, but there may be some insulating defects (such as shrinkage) and a modest resale impact to consider. Details follow.
In the 1970's we made three successive telephone calls to the US CPSC to inquire about the hazards of UFFI in a home we were evaluating. We received these different answers from three different people answering the CPSC UFFI hotline on the same day:
Do not buy the home under any circumstances. The cost to remove the UFFI and clean the wall cavities will be greater than the value of the home.
Buy the home but remove the UFFI insulation. The remaining scraps in the wall cavities will be insignificant as a formaldehyde source.
Buy the home and don't do anything about the insulation: the health hazards have been exaggerated and are probably very low if any.
Today, in 2008, we add an updated opinion:
Don't refuse to buy a home because of the presence of UFFI in its walls or ceilings;
purchase some test kits and actually measure the formaldehyde level;
realize that the foam is open-celled and that all of the formaldehyde will leave the building;
if the insulation was added more than five years ago there is almost no chance that you will detect any formaldehyde from the insulation;
any remaining formaldehyde problems will probably be from other sources such as carpet padding or some composition wood-product building materials like chipboard shelving.
examine the insulation in wall cavities to see if UFFI shrinkage has left so many gaps that you need to improve the building insulation. Shrinkage of the insulation product produces openings which may permit significant air leakage or simply thermal bypass leaks, reducing the effectiveness of the insulation system - a problem referred to in the industry as thermal drift.
Realize that a few future buyers may have an irrational fear of the UFFI - a condition that might have a (probably small) impact on property resale - see Enviro-Scare, the Cycle of Public Fear
Inspecting several such projects it was interesting to note that the one real defect
of this insulation product was that depending on how it was mixed, it shrank after installation, leaving gaps of no
actual insulation at the top and sides of wall cavities - it wasn't the perfect insulating seal that was promised, but it
was not the carcinogen that was feared.
How to Identify UFFI or Urea Formaldehyde Foam Insulation in buildings
Our photo (below) shows the dark dusty skin on UFFI insulation where it oozed from a wall cavity opening into a crawl space in the attic over a building garage.
Consider the building age: UFFI is not likely to be found in buildings built after the 1970's; insulation retrofit or add-on projects are more likely to be found in buildings which were built with little or no original insulation, such as homes built before 1960. It is unlikely that you'll find UFFI foam insulation in a building built after the late 1970's.
Look for Oozing-out Foam Insulation: in the attic, basement or crawl space, foamed insulation installation often produces an oozing-out insulation leak at the building sills; in the attic you may find the same oozing insulation shown at the top of gable end walls - as seen in our photograph above.
Look at the foam insulation color and finish skin: UFFI foam is yellowish and not shiny, but may have picked up dirt or dust during installation as it oozed out of a dirty building cavity or due to simple age and exposure its exterior may be darker yellow. The dried surface may have a very light "skin" that will be dull, not shiny.
Probe the foam insulation - a finger tip is fine or if you can only see foam insulation in a tiny wall gap or knothole, try probing with a pencil or even a wire or paper clip: UFFI, urea formaldehyde foam insulation is very soft and crumbly. At the article linked-to just below we explain this unambiguous way to distinguish among UFFI foam insulation, Icynene® spray foam insulation, and latex foam insulation
How to Find & Identify UFFI Insulation in an Older Home by Visual Indoor Inspections: Insulation Retrofit Projects
Below we give specific inspection methods useful in building interiors and exteriors that will help spot the types of insulation that may have been added to a building over its life.
Look at interior or exterior building walls for evidence of openings that were cut or drilled to blow-in building insulation.
Since the same type of round openings are used for blowing in cellulose or at least two different types of foam building insulation, if you see these marks or round hole cuts you will need to investigate further to identify the specific type of insulation that was installed.
Our photo (left) shows interior drill holes in an attic stairwell where insulation was pumped into the building wall cavities. Why so many holes? The first cuts probably hit wood framing.
Look in basements and crawl spaces for evidence of UFFI (crumbly) foam exuding out into the basement or crawl space at the bottom of wall cavities. Often there were gaps that permitted this foam escape - usually it was just left in place. Where balloon framing techniques were used, depending on the adequacy of fire blocking in wall cavities, foam injected into the walls may have passed between floor levels and easily into an attic (as shown in our photo above) or into the basement or crawl space as shown below in the left hand photo.
Look in un-finished areas such as attics and closets where plaster and lath are left incomplete or where drywall has been omitted during a building retrofit. Our photos below show UFFI insulation pushing on a poly plastic vapor barrier. Someone has cut the poly in the left photo, perhaps to sample the material - a step that was unnecessary if the inspector simply looked down at his or her feet (photo below-right).
You may also be able to see UFFI or other types of foam insulation oozing out from large openings at the sill plate between floors (photo below-left) or UFFI foam may have oozed out of even small wall openings as we show in the right hand photo of an un-finished plaster lath wall (below right).
Look for small amounts of soft crumbly foam insulation at tiny openings in wall cavities such as at knot-holes or gaps between siding boards, as we show on our photo (left).
You may need to probe this material to evaluate its density and fragility. If the material easily crumbles to a powder, it is probably Urea Formaldehyde Foam Insulation or UFFI Foam.
Look for scalloped drywall on the inside surface of building exterior walls: often the UFFI foam insulation was sprayed with more water content than specified; because the insulating material could be quite wet when first installed, we found that in some old homes which had been renovated by replacing original plaster with drywall, the drywall became wet, bonded to the UFFI, and then actually became sunken or concave along the building exterior walls as the UFFI insulation cured.
We pose that the drywall had become soft while wet, that it bonded to the UFFI in the wall cavity, and that as the UFFI insulation dried and cured it also shrank, pulling the damp drywall sections inwards.
We first spotted this phenomenon in an 1890 home in Wappingers Falls, NY when the home was insulated with UFFI spray in the 1970's.
Looking along the top edge of the baseboard trim at the bottom of the wall we saw that the drywall was in contact with the trim only at the location of the wall studs, and that between each pair of studs the drywall was concave.
How to Spot UFFI Building Insulation in an Older Home by Visual Outdoor Inspections: Insulation Retrofit Through Siding
As our photos show below, plugs may be visible in siding boards, but we warn that they also may have been covered by replacement boards or by a new layer of exterior siding. Also this plug and pump method for blowing insulation into building walls was used for more types of insulation than just UFFI.
Look for plugs in the building exterior siding, pull a plug to examine the insulation material. As our photographs show above, you may find evidence of circular wall plugs cut into building exterior siding at regular intervals (one opening per stud bay) at one or more elevations on the building.
Pulling one of these wall -cut plugs will give an opening to the building wall cavity where you may find UFFI urea formaldehyde foam insulation (white crumbly foam) or perhaps blown-in cellulose insulation instead. So don't assume the wall plug means the insulation was UFFI.
Sometimes insulation blow-in holes in walls were covered not with solid materials but with vented or metal plugs, probably just because they were convenient to snap into the hole cut by a hole saw using the same diameter hole cutting blade.
Insulation may also have been blown into building walls by removing and replacing an entire siding board outside, by lifting and replacing aluminum or vinyl exterior siding installed over original walls of another material, or by openings cut into plaster or drywall in the building interior. So absence of wall plugs is not absence of blown-in insulation.
Urea Formaldehyde Foam Insulation UFFI Shrinkage and Thermal Bypass Leaks
Look for UFFI foam spray insulation shrinkage: Neither latex foam spray insulation nor icynene foam spray insulation have the shrinkage problem of UFFI. If you have occasion to open a building wall cavity where UFFI was installed, you'll typically see about an inch of shrinkage at each side of the foam insulation block, and you'll see a couple of inches or more of un insulated space at the top of the column of sprayed foam.
The amount of UFFI insulation shrinkage varied from home to home and was probably the result of how precisely the product was mixed during installation, so the amount of shrinkage may vary among buildings. An expert use of thermography or even infra-red scanning of a building exterior wall in cold weather, with the heat on indoors, may be able to detect this insulation shrinkage too.
See Formaldehyde Hazards where we describe the sources of this contaminant, exposure levels, and steps to reduce formaldehyde levels indoors.
Calculating the Loss in Building Insulation Effectiveness Due to UFFI Insulation Shrinkage
Thanks to recent correspondence from a reader, we provide this "back of the envelope" calculation of the percentage of wall area insulation lost due to UFFI insulation shrinkage. Be sure to measure your own building carefully by opening one or more wall cavities for actual examination, as the amount of UFFI shrinkage may vary significantly from one building to another.
First of all, the UFFI foam insulation shrinkage stops after the foam has fully cured. Typically within the first year or less of installation. So the problem does not continue to worsen over time.
We could calculate, even before an IR scan of the building, the total area of uninsulated space in the exterior walls by examining one or two sample wall cavities to measure the actual UFFI shrinkage.
Typically, where UFFI shrinkage has occurred, we observe 2-4 inches of uninsulated space at the wall cavity top between each pair of wall studs, and about one inch of shrinkage and uninsulated space at each side of the original foam block in the stud bay. This is what we found for a Poughkeepsie NY home investigated in detail during siding renovations.
A back of the envelope calculation suggests that this means we've got roughly (3x16)+(2x96) = (48)+(192) = 240 square inches of uninsulated surface in every 16" wide x 8 foot high wall stud bay cavity (1536 sq.in), or about 240/1536 = 15% of the wall cavity space is not insulated.
If you know the total square feet of wall area (subtract out windows and doors) and if you confirm that your walls were framed with studs 16" on center, you can repeat our calculation with your own UFFI shrinkage measurements. (Contact Us to send photos of what you find).
Using actual measurements from your sample cavity you could calculate the total uninsulated area for the home, and ultimately the probable heating cost savings - but beware, as we comment below, if there are other building air leaks, including thermal convection in interior partitions, the air leaks and convection losses will overwhelm even a well insulated building. More on this later.
You could add blown-in insulation around the UFFI, but it would be labor intensive as drilling to insert the new foam would need to be thoughtfully done.
We *speculate* that it would be possible to inject a new foam product, perhaps icynene, for example, at the top of the cavity - that's where the widest shrinkage will occur as it's over the whole height of the material, leaving smaller gaps at the sides - and that at least some of the new foam would run down the sides of the old material as well.
But because the old UFFI is quite fragile, very easily compressed to a powder, blowing in new foam might also, depending on its pressure, actually crush the old material, causing it to collapse, leaving a larger uninsulated hole than before you started.
Therefore what we recommend is that an owner of a UFFI insulated building should try to convince a foam insulator (probably more effective at spreading down gaps than cellulose blow in) to help me do an experiment. It's an experiment because we are not going to insulate the entire home (and pay that high cost) before we know exactly what is going to happen when foam is injected into the UFFI-insulated wall cavities.
Select two or three typical wall cavities that are easily accessible, blow in the foam from whichever building side is easiest - outside or inside.
Let the new foam dry and cure completely.
Cut open the entire wall cavity on one side, probably the inside as drywall or plaster are easier to replace, and see what happened - checking for old foam collapse and the extent of remaining voids.
Take photographs of both a treated and an un-treated cavity - and please send us copies so that we can comment further, and also so that we can help others who face this question.
IF we find that the addition of another insulation causes more harm than good, or does not appear cost justified, I would focus my strategy on sealing air leaks - that will give by far the most bang for the buck - see these articles for more detailed help with air leaks and building insulation retrofits.
UFFI Urea Formaldehyde Insulation Class Action Lawsuit in Canada 2009 - update
The Spring 2009 issue of The Canadian Home Inspector, published by the CAHI, the Canadian Association of Home Inspectors, reports on a lawsuit involving contemporary installation of UFFI urea formaldehyde foam insulation in a Canadian home during 2008 despite the fact, as CAHI reports, that the Canadian government has banned the use of UFFI in homes since 1980. The Canadian Home Inspector indicated that Rob and Michelle Cecile are plaintiffs in a $500-million class-action lawsuit against RetroFoam, a foam retrofit insulation product that Health Canada says contains "... a toxic substance ...".
The Cecile family indicated that the AmeriSpec home inspector, licensed through the Canadian federal EcoEnergy program, had a financial interest in the local RetroFoam franchise. Our understanding is that the inspector was hired as Federally licensed energy auditor, not as a home inspector. He was not doing a home inspection. There are many inspectors and contractors who recommend products in which they have a financial interest in the energy audit business. We are informed that one energy audit company pays its auditors nothing for the audit work. The auditor only gets a percentage for the stuff that they get the homeowner to buy. The Canadian Association of Home Inspectors includes a code of ethics that may have precluded a home inspector from making such a recommendation.
According to CAHI, the Canadian federal government has issued a cease and desist order to RetroFoam Canada, a company based on Breslau Ontario, and has issued a cease and desist order to the company's dealer-installers as well, prohibiting the insulation companies from installing RetroFoam.
Retrofoam, according to Health Canada, contains urea formaldehyde - UFFI. "The substance causes respiratory problems and cancer" the article continues. "A posting on retroFoam's website does not deny the presence of UFFI, but says its product is safe." As it was reported, U.S. manufacturer did not disclose to the Canadian company importing the product that there was any UFFI in the product.
Robert and Michelle Cecile also assert that the installation of UFFI in their home using the Retrofoam product that contains urea formaldehyde foam insulation has stigmatized their property and thus reduces its property value. See ENVIRO-SCARE Defined, Effects for more information about the common effects of environmental hazards and scares on property values and property resale time.
Beginning at Urea Formaldehyde Foam Insulation UFFI we provide history and information about the health concerns associated with this product. A rough summary: early research suggesting a cancer link with UFFI was later found not to be substantiated; a possible formaldehyde sensitivity remains for people suffering from MCS. Where UFFI contained measurable formaldehyde outgassing, that process was found to diminish to below the limits of detection as the foam cured. Current sources of formaldehyde in buildings where old UFFI is present can be expected to be traced to other materials than the UFFI, such as laminated or pressed-wood products.
However, regardless of any ongoing argument about the level of health risk with a UFFI installation, as reported by CAHI, a home inspector, having a financial interest in the insulation company, recommended home insulation retrofit installation of a material banned in Canada.
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Additional technical contributors & reference sources for this article are listed below.
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06/07: thanks for photographs of transite asbestos heating ducts, courtesy of Thomas Hauswirth, Managing Member of Beacon Fine Home Inspections, LLC and (in 2007) Vice President, Connecticut Association of Home Inspectors
Ph. 860-526-3355 Fax 860-526-2942 beaconinspections@sbcglobal.net
Thanks to reader Anna Marron for discussion of UFFI-insulated building retrofit options 05/29/2010
Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair
Our recommended books about building & mechanical systems design, inspection, problem diagnosis, and repair, and about indoor environment and IAQ testing, diagnosis, and cleanup are at the InspectAPedia Bookstore. Also see our Book Reviews - InspectAPedia.
The Home Reference Book - the Encyclopedia of Homes, Carson Dunlop & Associates, Toronto, Ontario, 2010, $69.00 U.S., is available from Carson Dunlop. The Home Reference Book is a bound volume of more than 450 illustrated pages that assist home inspectors and home owners in the inspection and detection of problems on buildings. The text is intended as a reference guide to help building owners operate and maintain their home effectively. InspectAPedia.com ® author/editor Daniel Friedman is a contributing author. Field inspection worksheets are included at the back of the volume.
"The Elimination of Unsafe Guardrails, a Progress Report," Elliott O. Stephenson, Building Standards, March-April 1993
"Are Functional Handrails Within Our Grasp" Jake Pauls, Building Standards, January-February 1991
Access Ramp building codes:
UBC 1003.3.4.3
BOCA 1016.3
ADA 4.8.2
IBC 1010.2
Access Ramp Standards:
ADA (Americans with Disabilities Act), Public Law 101-336. 7/26/90 is very often cited by other sources for good design of stairs and ramps etc. even where disabled individuals are not the design target.
ANSI A117.4 Accessible and Usable buildings and Facilities (earlier version was incorporated into the ADA)
ASTM F 1637, Standard Practice for Safe Walking Surfaces, (Similar to the above standards)
American Plywood Association, APA, "Portland Manufacturing Company, No. 1, a series of monographs on the history of plywood manufacturing",Plywood Pioneers Association, 31 March, 1967, www.apawood.org
Asbestos products and their history and use in various building materials such as asphalt and vinyl flooring includes discussion which draws on Asbestos, Its Industrial Applications, D.V. Rosato, engineering consultant, Newton, MA, Reinhold Publishing, 1959 Library of Congress Catalog Card No.: 59-12535 (out of print).
Building Research Council, BRC, nee Small Homes Council, SHC, School of Architecture, University of Illinois at Urbana-Champaign, brc.arch.uiuc.edu. "The Small Homes Council (our original name) was organized in 1944 during the war at the request of the President of the University of Illinois to consider the role of the university in meeting the demand for housing in the United States. Soldiers would be coming home after the war and would be needing good low-cost housing. ... In 1993, the Council became part of the School of Architecture, and since then has been known as the School of Architecture-Building Research Council. ... The Council's researchers answered many critical questions that would affect the quality of the nation's housing stock.
How could homes be designed and built more efficiently?
What kinds of construction and production techniques worked well and which did not?
How did people use different kinds of spaces in their homes?
What roles did community planning, zoning, and interior design play in how neighborhoods worked
"An Example of Colonial Paneling", Norman Morrison Isham, The Metropolitan Museum of Art Bulletin, Vol. 6, No. 5 (May, 1911), pp. 112-116, available by JSTOR.
"Energy Savers: Whole-House Supply Ventilation Systems [copy on file as /interiors/Energy_Savers_Whole-House_Supply_Vent.pdf ] - ", U.S. Department of Energy energysavers.gov/your_home/insulation_airsealing/index.cfm/mytopic=11880?print
"Energy Savers: Whole-House Exhaust Ventilation Systems [copy on file as /interiors/Energy_Savers_Whole-House_Exhaust.pdf ] - ", U.S. Department of Energy energysavers.gov/your_home/insulation_airsealing/index.cfm/mytopic=11870
"Energy Savers: Ventilation [copy on file as /interiors/Energy_Savers_Ventilation.pdf ] - ", U.S. Department of Energy
"Energy Savers: Natural Ventilation [copy on file as /interiors/Energy_Savers_Natural_Ventilation.pdf ] - ", U.S. Department of Energy
"Energy Savers: Energy Recovery Ventilation Systems [copy on file as /interiors/Energy_Savers_Energy_Recovery_Venting.pdf ] - ", U.S. Department of Energy energysavers.gov/your_home/insulation_airsealing/index.cfm/mytopic=11900
"Energy Savers: Detecting Air Leaks [copy on file as /interiors/Energy_Savers_Detect_Air_Leaks.pdf ] - ", U.S. Department of Energy
"Energy Savers: Air Sealing [copy on file as /interiors/Energy_Savers_Air_Sealing_1.pdf ] - ", U.S. Department of Energy
Falls and Related Injuries: Slips, Trips, Missteps, and Their Consequences, Lawyers & Judges Publishing, (June 2002), ISBN-10: 0913875430 ISBN-13: 978-0913875438 "Falls in the home and public places are the second leading cause of unintentional injury deaths in the United States, but are overlooked in most literature. This book is unique in that it is entirely devoted to falls. Of use to primary care physicians, nurses, insurance adjusters, architects, writers of building codes, attorneys, or anyone who cares for the elderly, this book will tell you how, why, and when people will likely fall, what most likely will be injured, and how such injuries come about. "
Humidity: What indoor humidity should we maintain in order to avoid a mold problem?
Pergo AB, division of Perstorp AB, is a Swedish manufacturer or modern laminate flooring products. Information about the U.S. company can be found at http://www.pergo.com where we obtained historical data used in our discussion of the age of flooring materials in buildings.
Plank House Construction: weblog from plankhouse.wordpress.com/2009/01/25/plank-house-construction/ and where plank houses were built by native Americans, see
Large 1:6 Scale Plank House Construction / P8094228,
Photographer: Mike Meuser
06/12/2007 documented at yurokplankhouse.com where scale model Museum quality Yurok Plank Houses are being sold to raise money for the Blue Creek - Ah Pah Traditional Yurok Village project.
Re-Bath, tub lining products is a bath tub relining manufacturer and distributor located in Tempe, Arizona - see rebath.com
Slips, Trips, Missteps and Their Consequences, Second Edition, Gary M. Bakken, H. Harvey Cohen,A. S. Hyde, Jon R. Abele, ISBN-13: 978-1-933264-01-1 or
ISBN 10: 1-933264-01-2,
available from the publisher, Lawyers ^ Judges Publishing Company,Inc., www.lawyersandjudges.com sales@lawyersandjudges.com and also from the InspectAPedia Bookstore (Amazon.com)
The Stairway Manufacturers' Association, (877) 500-5759, provides a pictorial guide to the stair and railing portion of the International Residential Code. [copy on file as http://www.stairways.org/pdf/2006%20Stair%20IRC%20SCREEN.pdf ] -
How to Clean Moldy Wood Framing & Sheathing How to clean/seal mold from/on exposed lumber or plywood subfloor or roof sheathing indoors - some suggestions based on our field and laboratory research
Lighting, proper use of: proper aiming of a good flashlight can disclose hard to see but toxic light or white mold colonies on walls.
Manufactured & Modular Homes: Modular Building Systems Association, MBSA, modularhousing.com, is a trade association promoting and providing links to contact modular builders in North America. Also see the Manufactured Home Owners Association, MHOAA, at www.mhoaa.us. The Manufactured Home Owners Association of America is a National Organization dedicated to the protection of the rights of all people living in Manufactured Housing in the United States.
Stuff that is not mold but is often mistaken for it - things you may not want to test. Also, not all "black mold" is toxic - here are examples of harmless black mold.
Mold-Resistant Building Practices, advice from an expert on how to prevent mold after a building flood and how to prevent mold growth in buildings by selection of building materials and by anti-mold construction details.
Slips, Trips, Missteps and Their Consequences, Gary M. Bakken, H. Harvey Cohen, Jon R. Abele, Alvin S. Hyde, Cindy A. LaRue, Lawyers and Judges Publishing; 2 edition (April 2006), ISBN-10: 1933264012 ISBN-13: 978-1933264011
Steps and Stairways, Cleo Baldon & Ib Melchior, Rizzoli, 1989.
"The Dimensions of Stairs", J. M. Fitch et al., Scientific American, October 1974.
"Weather-Resistive Barriers [copy on file as /interiors/Weather_Resistant_Barriers_DOE.pdf ] - ", how to select and install housewrap and other types of weather resistive barriers, U.S. DOE
Weaver: Beaver Board and Upson Board:
Beaver Board and Upson Board: History and Conservation of Early Wallboard, Shelby Weaver,
APT Bulletin, Vol. 28, No. 2/3 (1997), pp. 71-78, Association for Preservation Technology International (APT), available online at JSTOR.
