U.S. Department of Housing and Urban Development 

Office of Policy Development and Research 

FROST-PROTECTED 

SHALLOW FOUNDATIONS 

Phase II - Final Report 
FROST-PROTECTED SHALLOW FOUNDATIONS 

Phase II - Final Report 

Prepared for: 

U.S. Department of Housing and Urban Development 

Office of Policy Development and Research 

Prepared by: 

NAHB Research Center 

Upper Marlboro, MD 

Instrument No. DU100K000005897 

June 1994 
Notice

The U.S. Government does not endorse products or

manufacturers. Trade or manufacturers' names appear

herein solely because they are considered essential to

the object of this report.

The contents of this report are the views of the
 

contractor and do not necessarily reflect the views or
 
policies of the U.S. Department of Housing and Urban

Development or the U.S. Government.
Acknowledgements

This report was prepared by the NAHB Research Center for the U.S. Department

of Housing and Urban Development. Special appreciation is extended to NAHB

members Bill Eich, Gerald Eid, Tim Duff, Jess Hall and their staffs, for

constructing the five demonstration homes; Richard Morris, National Association

of Home Builders for initiating the technology transfer into the United States;

Peter Steurer, National Oceanic and Atmospheric Administration, for providing

and verifying proper methods of estimating long-term air-freezing indexes; Dow

Chemical Company, Mid-America Molders, U.C. Industries, Inc. and Amoco

Foam Products, for donation of insulation; and William Freeborne, U.S.

Department of Housing and Urban Development, for guidance and review

throughout both phases of the project.

In addition, the NAHB Research Center gives special recognition to The Society of

the Plastics Industry, Inc. for several years of support that has helped to reintroduce this technology to the United States. Their sponsorship has promoted

activities such as technology transfer from Europe, finite element computer

modelling of heat transfer through foundations, analysis of design procedures for

frost protection of foundations, formulation of important climate data for the

United States, and dissemination of information to building code representatives.

 These previous activities have contributed tremendously to this document. 

The NAHB Research Center staff responsible for this document are:

Jay H. Crandell, P.E., principal investigator

Eric M. Lund, technical assistance

Mike G. Bruen, P.E., technical assistance

Mark S. Nowak, reviewer
Contents
 

List of Figures ................................................................................................... vi
 

APPENDIX: Demonstration Site Data ...............................................................A1
 

EXECUTIVE SUMMARy ....................................................................................vii
 

INTRODUCTION............................................................................................... 1
 

BACKGROUND ................................................................................................ 3
 

RESULTS ......................................................................................................... 7
 

RECOMMENDATIONS..................................................................................... 15
 

CONCLUSIONS ............................................................................................... 17
 

BIBLIOGRAPHy............................................................................................... 19
 

v
List of Figures
 

Figures

Figure 1.A frost protected shallow foundation in comparison to a

 conventional house foundation........................................................... 3
 

Figure 2.The effect of various conditions on frost penetration into

Figure 7.Photograph of the FPSF foundation construction at Fargo,

Figure 9.Photograph of the recycled plastic lumber used in the FPSF design at

 the ground ......................................................................................... 4
 

Figure 3.Heat exchange occurring at an insulated building foundation .............. 4
 

Figure 4.Photograph of the Williston, Vermont site............................................. 8
 

Figure 5.Photograph of the Spirit Lake, Iowa site ............................................... 8
 

Figure 6.Photograph of the Fargo, North Dakota site (home #1).......................... 9
 

North Dakota (home #1) ...................................................................... 9
 

Figure 8.Photograph of the Palmer, Alaska site. ............................................... 10
 

the second Fargo, North Dakota site (home #2) ................................. 10
 

vI
 

 

EXECUTIVE SUMMARY
 

This report contains the results of an investigation and demonstration of the

frost-protected shallow foundation (FPSF) technology. Specific tasks include

field performance testing of the technology in five homes in the United States;

investigating the cost-effectiveness of the technology; and developing design and

construction guidelines for builders, designers, and code officials.

A frost-protected shallow foundation is a practical construction method in cold

climates where more costly conventional foundation methods are used. The

most extensive use of the technology has been in the Scandinavian countries,

where over 1 million homes have been constructed successfully over the last 40 * years. The figure below illustrates a frost-protected shallow foundation

compared with a conventional foundation. Briefly, a frost-protected shallow

foundation relies on insulation strategically placed around the foundation to

raise the frost depth around a building, thereby allowing foundation depths as

shallow as 16 inches (0.4 meters) in the most severe U.S. climates.

Schematic of FPSF and conventional foundation systems. 

* MorrIs, RIchard A. Frost-Protected Shallow Foundations: Current State-of-the-Art and Potential

Application in the u.S. Prepared for the SocIety of the PlastIcs Industry, Inc., (EPS dIvIsIon) by the

NAHB Research Center (August 1988); dIstrIbuted by SPI LIterature Sales, Waldorf, MD.

vII
 

 

The insulation around the foundation perimeter conserves heat loss from the

foundation and prevents the freezing of soils under the foundation. The frostprotected shallow foundation is also applicable to unheated parts of buildings

such as garages by conserving the geothermal heat reserves in the soil below the

building.

CONSTRUCTION AND MONITORING OF DEMONSTRATION HOMES

Five homes were constructed for this project over a two year period to

demonstrate and test the technology. During the 1992-93 winter heating season

(phase I), one home was constructed and instrumented in each of three sites -

Fargo, North Dakota, Spirit Lake, Iowa, and Williston, Vermont. During the

1993-94 winter season (phase II) two additional homes were built - one in Fargo

and another in Palmer, Alaska. All of the homes were built on slab-on-grade

foundations. The styles of these homes varied from affordable townhomes and

detached residences to custom built homes. The FPSF design for each site was

based on the established practice in Norway. Four sites were constructed with

extruded polystyrene (XPS) insulation, and one site with expanded polystyrene

(EPS).

Temperature sensors and an automated data logger were installed at each site

during the construction of the homes. Sensors were placed to obtain foundation

temperatures, ground temperatures, indoor and outdoor air temperatures and

slab surface temperatures. Soil type, moisture content, and other parameters

were recorded at each site. 

DESIGN PERFORMANCE ANALYSIS

Data from the five homes provided valuable information for the assessment of

the frost-protected shallow foundation performance with respect to the

recommended design guidelines. The frost heave potential at all of the sites was

successfully mitigated for both the heated and unheated areas of the homes and

none of the homes experienced freezing of the subgrade soil supporting the

foundation. Test areas on two homes were purposely under-designed to subject

the technology to a severe test as would be expected should a 100-yr return

period winter event occur. These designs were also successful in preventing the

potential for frost damage, and further validate the integrity of the design

recommendations. 

COST OF FROST-PROTECTED SHALLOW FOUNDATIONS

During phase I of the project, a detailed cost analysis was compiled for the

homes built for the 1992-93 winter season. Although the builders each realized

cost savings compared to their conventional construction practices, there was a

wide variability in costs due primarily to different degrees of familiarity with the

vIII
 

 

 

 

Executive Summary 

technique and to differences in house type. Cost savings ranged from 1.1 to 3.8

percent of the total home sales price. 

Previous cost studies also illustrate the cost savings potential of frost-protected

shallow foundations. A study by Morris compared shallow foundations without

garages or other unheated spaces to conventional deep-foundation practices in

Fargo, ND; Minneapolis/St. Paul, MN; Chicago, IL; Pittsburgh, PA; Washington,

DC; and, St. Louis, MO.** The savings calculated for a frost-protected shallow

foundation in this study were similar to that achieved by the demonstration

homes. Morris has projected a potentially large annual savings in energy and

construction costs if the technology experiences wide-spread acceptance.

DESIGN AND CONSTRUCTION RECOMMENDATIONS

Design and construction recommendations were developed under this project

based on data from a proposed consensus standard by the Comite Europeen de

Normalisation (CEN). The CEN draft standard is based on well-documented

experiences in Europe, covers a broad range of frost-protected shallow

foundation applications, and is also being considered as a standard by the

International Standards Organization. Results from the five homes in this

investigation further validate the proposed CEN design standard for the type of

applications covered in the demonstration homes. The design and construction

guidelines are published under a separate title: Design Guide for Frost-Protected

Shallow Foundations***.

CONCLUSIONS

Findings from this study support the following conclusions:

 1.	 Houses and other structures may be built on shallow, slab-on-grade

foundations in cold-climates when properly insulated to protect against

frost heave.

 2.	 The demonstration homes performed well and provide substantiating

evidence for the frost-protected shallow foundation techniques design

**MorrIs, RIchard A. Frost-Protected Shallow Foundations: Current State-of-the-Art and Potential

Application in the u.S. Prepared for the SocIety of the PlastIcs Industry, Inc., (EPS dIvIsIon) by the

NAHB Research Center (August 1988); dIstrIbuted by SPI LIterature Sales, Waldorf, MD.

*** NAHB Research Center. Design Guide for Frost-Protected Shallow Foundations. Prepared for

the UnIted States Department of HousIng and Urban Development, WashIngton, DCC GPP, 1994.

II
Executive Summary 

recommendations.

 3.	 Frost-protected shallow foundation construction provides a cost-effective

alternative to conventional foundation construction in the United States. 

Cost savings to the home buyer range from approximately 1 to 4 percent of

the cost of a conventional slab-on-grade home and are even greater when

compared to basement construction.

 4.	 Experience has shown that the frost-protected shallow foundation

technology may be used to increase the energy efficiency of new houses at

a minimal or reduced construction cost.

I
1

 

 

 

 

INTRODUCTION
 

This report addresses one of a series of projects conducted for the U.S.

Department of Housing and Urban Development (HUD) to investigate

technologies that may reduce the construction costs of housing. Specifically,

this document reports on findings from a two-phase investigation of frostprotected shallow foundations (FPSF).

In the Phase I report2 to HUD, it was verified that the FPSF technology was

capable of reducing the cost of foundation construction and successfully

preventing frost heave of foundations. A detailed presentation of the

performance of the first three homes during the 1992-93 winter season is

presented in that report. Construction cost savings of 1 to 4 percent of the total

home sales price are also reported. These findings are in agreement with the

European experience over the last 40 years which is exemplified in over 1 million

homes built using FPSF techniques.

While the Phase I study was instrumental in demonstrating the feasibility of the

FPSF technology, it did not provide conclusive test results of the performance

limit of FPSF homes during an extreme winter event.

The main objectives of this second phase study were

 1.	 to provide a stringent field test of the frost-protected shallow foundation

technology on homes built in severe climatic and soil conditions of the

United States;

 2.	 to demonstrate and investigate alternative applications of the technology;

 3.	 to provide a concise, yet comprehensive, design and construction

document for builders, designers, and code officials; and

 4.	 to initiate changes to the model U.S. building codes as supported by

substantiating evidence from this project.

The tasks conducted during this Phase II investigation of frost-protected shallow

foundations were:

NAHB Research Center. Frost-Protected Shallow Foundations in Residential Construction -

Phase L. Prepared for the UnIted States Department of HousIng and Urban Development,

WashIngton, DCC GPP, 1993.

2
�

 

 1.	 Monitoring of Phase I demonstration homes. The continued monitoring

of the three demonstration homes in North Dakota, Iowa, and Vermont

required maintenance of automated data acquisition systems at the sites,

periodic data quality/operational checks, and performance analysis of the

FPSF designs during two winter seasons (1992-94).

 2.	 Construction and monitoring of additional test homes. Two additional

homes were constructed to demonstrate alternative uses of the FPSF

technology. Special test areas on the foundations were designed and

instrumented to simulate relatively extreme environmental conditions. 

Performance was monitored and analyzed during the 1993-94 winter

season.

 3.	 Preparation of final design and construction recommendations. The

preliminary design recommendations of the Phase I study were updated in

accordance with site monitoring results, construction experience, and

development of consensus standards. The final design guidelines are

published separately as Design Guide for Frost-Protected Shallow

Foundations. In addition, return period estimates of the air-freezing index,

an important climatic parameter required for the design procedure, were

validated by investigations using reliable long-term weather records.
3

BACKGROUND
 

CONCEPT

A frost protected shallow foundation (FPSF) is a practical and cost-effective

alternative to conventional residential foundations which, in practice, require

excavations to prescribed frost depths. Figure 1 shows a typical FPSF

application compared to a conventional foundation. Briefly, a FPSF relies on

strategically placed insulation to raise the frost depth adjacent to a building

foundation, thereby allowing foundation depths as shallow as 16 inches (0.4

meters) in severe climates.

Figure 1. A frost protected shallow foundation in comparison to a conventional house 

foundation. 
Background 

Figure 2 illustrates the effect of ground covering and other conditions on frost 

penetration. It is important to note that the frost line rises near a foundation if the 

building is heated. This effect is magnified when insulation is strategically placed 

around the foundation. 

Figure 3 illustrates the heat exchange process of a FPSF, which acts to prevent soil 

freezing below the foundation. The vertical (wall) insulation and horizontal (wing) 

around the foundation perimeter conserves heat loss through the slab and redirects it 

toward the soil below the foundation. Energy efficiency is increased by limited heat 

loss through the above ground portion of the foundation wall where the most sever 

losses occur in conventional foundations. Stored geothermal heat released from the 

underlying ground also helps to raise the frost depth around the building. 
7

 

Background 

By increasing insulation under the entire slab and improving the conservation of

existing geothermal heat, the FPSF concept can also effectively protect unheated

buildings as well. Unheated areas of homes such as garages, porches, and

stairwells may be protected in this manner.

FPSFs are most suitable for slab-on-grade homes on sites with moderate to low

sloping grades. The method may also be used effectively with walk-out

basements by insulating the foundation on the downhill side of the house, thus

eliminating the need for a stepped footing. FPSFs are also useful for remodeling

projects and sites with difficult ground conditions because they minimize site

disturbance and excavation depth. They are also useful to solve existing frostheave problems by retrofitting foundations with a protective FPSF insulation

design.

While this report focuses on slab-on-grade construction methods, the technology

may also be applied to crawlspace foundations with some added considerations

such as ventilation control. In addition to residential, commercial, and

agricultural buildings, the technology has been applied to control frost-heave

damage in highways, dams, underground utilities, railroads, and earth

embankments.

It is estimated that FPSF techniques could provide 590,000,000 kilowatt-hours

in energy savings annually and nearly $300,000,000 savings in annual

construction costs3.

HISTORY

In the United States, slab-on-grade houses were constructed around the turn of

the century in cold climates near Chicago, Illinois. During the Depression,

Frank Lloyd Wright designed and built a type of FPSF to meet affordability needs

and used FPSF techniques in his "Usonian" style homes with shallow slab-ongrade foundations. However, the technology was never developed or applied to

the degree realized in Europe.

3 MorrIs, RIchard A. Frost-Protected Shallow Foundations: Current State-of-the-Art and Potential

Application in the u.S. NAHB Research Center. Prepared for the SocIety of the PlastIcs Industry,

Inc. (EPS DIvIsIon), WashIngton, DC. (1988).
8

 

 

 

Background 

In the 1950s, Swedish and Norwegian researchers constructed the first

experimental houses using insulated shallow foundations. These homes

provided practical experience and empirical data on the FPSF technology. By

1972, nearly 50,000 slab-on-grade foundations had been built in Sweden, and

the FPSF technology had gained wide acceptance. In the 1970s, the

Scandinavian countries consolidated their research efforts in an attempt to

address cold regions engineering topics. The effort led to the 1976 publication of

Frost I Jord ("Frost Action in the Ground")4. Scandinavian engineers consider

Frost I Jord a reliable guide for design against frost action in soils. Based on the

results of the Frost I Jord Project, the Norwegian Building Research Institute

started publication in 1978 of "Building Details" specifically detailing FPSF

design and construction methods. The FPSF technology is now considered

standard practice in Norway, Sweden, and Finland.

CURRENT STATUS

It is estimated that several thousand homes and other structures have been built

in the United States using the FPSF technology, but only in circumstances where

building codes are non-existent, special engineering was performed, or local

conditions (e.g. Alaska) necessitate consideration of insulated foundations placed

at depths above the maximum seasonal frost penetration. 

The major model building codes in the U.S. do not specifically address the FPSF

technology. However, recent amendments to the CABO One and Two Family

Dwelling Code and the BOCA National Building Code recognize performancebased criteria for frost protection of foundations. The ICBO Uniform Building

Code (common to many northern states) and the SBCCI Standard Building Code

do not permit any alternate methods of protecting foundations from frost heave. 

Foundation insulation is required by national energy codes (e.g., CABO Model

Energy Code), but it is not recognized for its frost-protection benefits.

A significant current activity is a proposed Comite Europeen de Normalisation

(CEN) consensus standard that is based on the extensive European experiences

of the past four decades. This European community standard, also being

considered by the International Standards Organization (ISO), will likely become

a U.S. consensus standard.

4 HeIersted, R.S. Frost I Jord (Frost ActIon In Ground), Nr. 17. CommIttee on Frost ActIon In

SoIls. Prepared In NorregIan for the Royal NorregIan CouncIl for ScIentIfIc and IndustrIal

Research (Pslo, Norray). 1976.



9

 

RESULTS
 

DESCRIPTION OF DEMONSTRATION HOMES

During Phase I of this project (1992-93), three FPSF demonstration homes were

constructed, monitored and evaluated for foundation performance and

construction costs. These homes were located in Vermont, Iowa, and North

Dakota. The homes varied in style from a 4-unit townhome complex, to a

custom single-family detached home (see Figures 4 through 7). In each case, the

foundations were constructed with 12 inch deep monolithic slab footings (plus

an additional 4 inch depth of gravel). The foundations were protected against

frost heave according to European FPSF design guidelines. Two homes used 1.6

pcf extruded polystyrene (XPS) insulation, and one used 1.8 pcf molded or

expanded polystyrene (EPS). Construction details are shown in Appendix A for

each site. 

Because the foundations in Phase I were designed for a 100-year return period

winter freezing event, the average winters experienced during 1992-93 did not

provide a stringent performance test of the FPSF designs. Consequently, two

additional demonstration homes were built in Phase II with the intention of

subjecting the FPSF designs to a severe design event. The foundations were

designed using the normal 100 year return period, with exception of a test zone

created in each design. The insulation in the test zone was sized for an average

winter event for that climate, instead of the 100-yr return period as normally

required in the design guidelines.

The Phase II homes are located in Palmer, Alaska and Fargo, North Dakota. The

Alaska home was an affordable, single-story ranch style home constructed on a

monolithic slab-on-grade. The North Dakota site (#2) was an affordable, singlestory 3-unit townhome complex on a slab-on-grade and stem wall foundation. 

The foundation stem wall was constructed of recycled plastic lumber in a

manner similar to permanent wood foundations. The sites are shown in Figures

8 and 9. Except for the special test areas, the foundations were protected

against frost according to European FPSF guidelines, specifically the proposed

CEN standard method. Both sites were built with 1.6 pcf XPS insulation

products, one of which incorporated post-consumer wastes. Construction

details are provided in Appendix A for each Phase II site.

INSTRUMENTATION OF DEMONSTRATION HOMES

Each of the five demonstration homes were outfitted with automated data

acquisition systems to record and download performance data to the NAHB

Research Center in Upper Marlboro, MD. Temperature sensors were installed in

the ground and around the foundations during construction in the summer of

1992 (Phase I homes) and the summer/fall of 1993 (Phase II homes). Other

sensors were placed to obtain indoor air temperatures and slab surface
1�

 

Results
 

temperatures. A weather station that measured ambient air temperature, wind

speed, and frost penetration into undisturbed soil was also deployed at each site.

 Both thermocouple and thermistor sensors were used and, at some locations,

sensors were duplicated to allow simple data quality checks. Automated

dataloggers were installed when the homes were completed.
17

Results 

PERFORMANCE OF DEMONSTRATION HOMES

An analysis of the winter events experienced at each of the sites is needed to

accurately assess the FPSF performance. The air-freezing index (AFI) is a

climatic index used to determine the magnitude of the ground freezing potential

experienced during a winter season. In fact, the 100 year return period of the

AFI is used to size insulation requirements in the FPSF design procedure. A

detailed discussion of the AFI is included in the Phase I report as well as other

technical reports referenced in this document. While the AFI is the primary

factor in determining the ground freezing potential (frost depth), other important

variables include ground cover, snow depth, soil type, and amount of soil

moisture. These key environmental parameters are summarized for each site in

the Appendix. For all but the Alaska site, the most severe winter was recorded in

the 1993-94 season. In terms of the air-freezing index the North Dakota, Iowa,

and Vermont sites experienced approximately a 4-yr return period event during

the 1993-94 winter season. Short duration freezing episodes of 1-day and 7-day

average temperatures broke previous 30-yr extreme low temperature records in

Fargo, North Dakota and challenged previous records in Iowa and Vermont.

To assess the performance of each foundation design, records of the minimum

daily average temperatures were plotted at every sensor for the period of record

at each site. For simplicity in judging the maximum frost line penetration

around the foundations, the 32°F (0°C) isotherm was also plotted. Selected data

is shown in the Appendix. It is realized that this provides a conservative criteria

for assessing the onset of frost damage since freezing of soil water will actually

begin at a somewhat depressed temperature. Other factors, such as a late

completion of some of the test foundations, the angle of the frost line, amount of

penetration underneath the footings required for significant heave forces to

develop, and the actual amount of soil moisture in terms of latent heat content,

add further to a conservative assessment. These factors may be offset to a large

degree by the amount of snow accumulation at each site. Since these factors

cannot be easily controlled by design, the FPSF design method assumes the

worst case of a severe winter in combination with no snow accumulation and a

minimum amount of soil water sufficient to allow frost heave to occur but

minimizing the latent heat contribution. For this reason, the insulation

requirements may be applied to all soil types and successfully prevent frost

heave from occurring as was evidenced by the variety of soil types at the

demonstration sites (see the Appendix). 

The homes constructed during Phase II in Palmer, Alaska and Fargo, North

Dakota (home #2) are of particular interest in assessing the integrity of the frostprotected shallow foundation technology. As described previously, these homes

were designed with a test zone which had undersized insulation to withstand

only the average freezing index for that site. In effect, a near average winter

event would simulate a 100-yr return period test of the frost protection provided

by the design guidelines. In North Dakota, where the 1993-94 winter was

particularly severe, the frost line was successfully withheld from penetrating into
18

 

 

Results
 

the subgrade underneath the perimeter of the building in the test zone. The

frost penetration was significantly less in the remaining areas of the foundation

where normal levels of insulation were utilized for frost protection. This finding

indicates that the insulation requirements specified in the design guidelines

provide a high degree of protection against frost heave, as intended. Similarly

the test was successful at the Alaska site, but the winter there was relatively

mild.

As reported for the Phase I demonstration homes, the foundation performance

was satisfactory and the foundation soils were protected against freezing

temperatures5. The homes constructed during Phase I were monitored

continuously for two winter seasons. This allowed a more thorough investigation

of the long-term performance of frost-protected shallow foundations with respect

to the thermal impact of a building on ground temperatures and freezing. In

spite of a more severe winter at each of the sites in the second season of

monitoring, the general increase in ground temperatures in the vicinity of the

building indicates that buildings provide a significant increase in the thermal

storage of heat in the ground. In turn, this thermal mass in the soil under the

building contributes to greater frost protection and increased comfort for slabson-grade in cold climates.

While all of the sites were successful in preventing frost penetration in the soil

underneath the footings, one home experienced a frost penetration at the corner

of the foundation greater than expected for a near average winter. Highly

conductive soil thermal properties and/or a low moisture content may have

contributed to a greater frost penetration, but the maximum frost depth recorded

at the weather station doesn't appear to support this hypothesis. The proper

specification of insulation products, paramount to the success of any FPSF

application, could also have contributed to the performance at this site. Because

few insulation products are able to maintain a dry R-value in a moist, belowgrade environment over any great length of time, insulation products specified

for a FPSF must be rated with an effective R-value, determined by their ability to

maintain a certified R-value in such an environment for the expected life of the

structure. Because some insulation materials resist water absorption less

effectively than others, which in turn degrades their thermal resistance (Rvalues), insulation material should be specified carefully. Interestingly, EPS

insulation (Type IX) was used at this site, for both the vertical and horizontal

insulation, and a modestly reduced effective R-value was used to determine the

required material thicknesses. The reader is directed to related references listed

in the bibliography for greater detail on this issue. 

Slab surface temperatures at the building perimeter were monitored to

NAHB Research Center. Frost-Protected Shallow Foundations in Residential Construction.

Prepared for the U.S. Department of HousIng and Urban Development (WashIngton, DCCGPP,

1993).

5
19

 

 

 

Results 

investigate the level of comfort provided by the minimum insulation

requirements for frost protection. A sufficiently high slab surface temperature at

the perimeter must also be maintained to prevent moisture condensation. The

interior areas of the slab are affected very little by the perimeter insulation levels.

 However, the slab surface temperatures along the perimeter are affected by the

insulation levels, particularly the vertical wall insulation R-value. Quality of

installation with respect to air-infiltration and elimination of cold-bridges also

affect the slab temperatures. Given the extreme cold temperatures experienced

during the 1993-94 winter (exceeding the 30-year extreme cold on record), the

minimum slab surface temperatures recorded were generally within an

acceptable range. As expected, the lowest temperatures were recorded near the

corners of the foundations were heat loss is greatest. The coldest slab surface

temperatures were recorded at 1 foot (0.3 meters) in from the slab edge at the

corner, and they ranged from 37 to 48°F (3 to 9°C) for all but the Alaska site. At

midwall locations and 3 foot from the edge, the coldest slab surface temperatures

ranged from 52 to 64°F (11 to 18°C). The most uniform and warm slab surface

temperatures were recorded at the Alaska site where insulated hot water lines for

baseboard heating were run in the slab around the perimeter of the home. The

minimum surface temperatures at all monitoring locations around the perimeter

of this slab ranged from 57 to 61°F (14 to 16°C). 

DESIGN AND CONSTRUCTION RECOMMENDATIONS

The frost-protected shallow foundation design and construction

recommendations resulting from this project rely extensively on data from a

proposed consensus standard by the Comite Europeen de Normalisation (CEN). 

The CEN draft standard for frost-protected shallow foundation design is based

on well-documented experiences in Europe, covers a broad range of frostprotected shallow foundation applications, and is also being considered as a

standard by the International Standards Organization. The results of this

investigation further validate the proposed CEN design standard for the type of

applications covered in the demonstration homes. The design and construction

guidelines for the United States are published under a separate title: Design

Guide for Frost-Protected Shallow Foundations6. The design guide provides both

a detailed and a simplified procedure which includes the necessary climate data,

construction recommendations, details, and examples. The simplified method is

based on a code change recently proposed to the CABO One- and Two- Family

Dwelling Code. The outcome of this proposal will not be known until late 1994. 

NAHB Research Center. Design Guide for Frost-Protected Shallow Foundations. Prepared for

the UnIted States Department of HousIng and Urban Development, WashIngton, DCC GPP, 1994.

6
�1

RECOMMENDATIONS
 

The frost-protected shallow foundation technology has seen tremendous growth

in the Scandinavian housing industry after first being discovered in the United

States. While the technology has been highly developed and proven in Europe,

great effort will be required to re-introduce it to the United States. Even then,

with such a "new" construction concept, building code adoption will be quite

unpredictable and time-consuming. The following recommendations are offered:

 1.	 Efforts to encourage adoption of this technology by the major building

code organizations in the United States should continue.

 2.	 Educational seminars and materials should be established for building

officials, builders, engineers, and architects.

 3.	 Building energy codes should be encouraged to recognize the use of frostprotected shallow foundations as a means of meeting minimum insulation

requirements for energy conservation.

 4.	 A material test standard to define the effect of moisture absorption on the

thermal resistance (R-value) of various insulation products is needed. The

standard should identify a range of typical ground-use conditions which

may promote moisture absorption and thermal degradation of insulation. 

The standard will help with correctly specifying and rating insulation for

use on foundations to protect against frost heave and excessive heat loss.

 5.	 Future research should investigate alternative foundation materials to be

used for frost protection which provide structural support as well as

significant thermal resistance. Some materials might include plastics,

light-weight insulated concrete and blocks, permanent wood foundations,

and others. 
��
�3

CONCLUSIONS

Findings from this study support the following conclusions:

 1.	 Houses and other structures may be built on shallow, slab-on-grade

foundations in cold-climates when properly insulated to protect against

frost heave.

 2.	 The demonstration homes performed well and provide substantiating

evidence for the frost-protected shallow foundation techniques.

 3.	 Frost-protected shallow foundation construction provides a cost-effective

alternative to conventional foundation construction in the United States. 

Cost savings to the home buyer range from approximately 1 to 4 percent of

the cost of a conventional slab-on-grade home and are even greater when

compared to basement construction.

 4.	 Experience has shown that the frost-protected shallow foundation

technology may be used to increase the energy efficiency of new houses at

a minimal or reduced construction cost.
�4
��

 

 

 

BIBLIOGRAPHY
 

American Society for Testing and Materials. Standard Specification for Rigid,

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