Foundation Walls and Footings for Houses (A Survey of Building Code Requirements)

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Technical Note (National Research Council of Canada. Division of Building Research), 1959-06-01

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Foundation Walls and Footings for Houses (A Survey of Building Code Requirements)

Hansen, A. T.

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NATIONAL RESEARCH COUNCIL OF CANADA

7r

［ｉｾ［［ｾ

ｾＺｾｇ

ｒｅＺａｾｾｅｦＣ

No.

281

NOT FOR PUBLICATION

PREPARED BY A. T. Hansen CHECKED BY W.H.B.

FOR INTERNAL USE APPROVED BY ｾｲｌ

PREPARED FOR Subcommittee on Construction, Cladding and ｾ June 1959 Materials, of the Special Committee on

Housing, Associate Committee on the National Building Code SUBJECT

FOUNDATION WALLS AND FOOTINGS FOR HOUSES (A Survey of Building Code Requirements)

The Division of Building Research undertook the publication of HOUSING STANDARDS in January 1958. This document had, previous to this, been published by C.M.H.C. under the title. Building Stan-dards. In keeping with the practice established by the Corporation the Division has met annually with the Research Committee of the National House Builders Association and representatives of C.M.H.C., to discuss changes to the Standards proposed by the Association and other interested parties.

In the course of these discussions a number of details in the requirements for foundation walls and footings were questioned on the grounds that they are unnecessarily restrictive in view of the loads that are imposed on them in residential bUildings, and because there appeared to be a lack of flexibility in the requirements for various conditions of loading.

This report summarizes the results of a survey of the

requirements of a number of reference codes and standards relating to foundation walls and footings. Tables were prepared to permit rapid comparisons of the different requirements. The tables are necessarily a simplification of the actual reqUirements and as such may be incomplete.

Most of the codes or standards studied in this survey permit variations from the stated requirements if evidence is provided to

support the adequacy of proposed designs. Some permit a relaxation of the requirements if approved by a local bUilding official.

This report consists of a series of tables followed by a discussion of them. The discussion relates to the requirements of Housing Standards.

The following is the explanation of the abbreviations used in this report.

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,

ｾ

.

ｾ

.

2

-NBC National Building Code of Canada

DBR Housing

Standards Division of Building Research Housing Standards

ｾｾｓ - FHA Minimum Property Standards of the Federal Housing Administration

NBS - BMS National Bureau of Standards Building Materials and Structures

NY State New York State

BOCA Building Officials Conference of America

MCBO Midwest Congress of Building Officials

SBCC Southern BUilding Code ,Congress

leBO International Congress of Building Officials

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.

3

-TABLE I

6" Solid Concrete Foundations

Authority Maximum Maximum Remarks

Depth Below Height of

Grade Su perstru cture

NBC Not permitted

DBR Housillg _{No limit given} Permitted under

Standards slabs only

MPS - FHA 5f _-Oll _{No limit given} _{Frame construction}

only NBS - BMS 107

-

1 story Basementless construction only NY State 4'-0" 1 story Bldg. Code Basic Bldg.

Code, BOCA Not permitted

Midwest Bldg. _{No limit given} _{1 story} FIB me construction

Code, MCBO only - presumably

3000 lb. cone.

Southern Std. _{1 story} 2000 lb. conc.

Bldg. Codeg

-

basementless houses

SBCC only

Uniform Bldg. _{No limit given} _{1 story} Frame construction

Code, ICBO only

Am. Std. Bldg. Code

Require-ments for ＴｾＭｏｮ No limit given

Masonry

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.

4

-TABLE 2

6" Solid Masonry Foundations

Grade Superstructure

NBC _- Not permitted

DBR Housing

Standards No limit given Permitted

Under slabs only

MPS - FHA 3'-0" Frame construction

only

NBS - BMS 107 Not permitted

NY State Bldg. 12' to eave Wood frame

base-Code 20' to peak mentless houses

only

Basic Bldg. _{Not permitted}

Code, BOCA Midwest Bldg.

Code, MCBO Not permitted

Southern Std. Bldg. Code,

SBCC Not permitted

Uniform Bldg. No limit given 1 story Frame construction

Code, ICBO only

Am. Std. Bldg. Code require-Not permitted ments for masonry ASA A41.1.1953

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ｾ

.

-..

5

-TABLE 3

6" Hollow Block Foundations

ｾｵｴｨｯｲｩｴｹ Maximum Maximum

Depth Below Height of Remarks

NBC Not permitted

DBR Housing Permitted under

Standards slabs only

MPS - FHA Not permitted

.

NBS - BMS 107 Not permitted

NY State Bldg. 12' -to eave Wood frame

base-Code 20' to peak mentless houses

only Basic Bldg.

Code, BOCA Not permitted

Midwest Bldg.

Code, MCBO Not permitted

Southern Std.

Bldg. Code, SBCC Not permitted

Uniform Bldg. No limit given 1 ｳｾｯｲｹ Frame construction

Code, rCBO only

Am.

Std. Bldg.

Code

require-ments for Not permitted

masonry

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,

.

..

6 -TABLE 4

ｾｵｴｨｯｲｩｴｹ _{Depth below}Maximum _{Height of}Maximum _Remarks

Grade Su perstru cture _"

NBC 6'-0" 2 stories for frame

or masonry _{2000 lb. concrete}

1 story for brick veneer

DBR Housing Not listed 1 story 2500 lb. concrete

Standards

6'-0" 2 stories (25') 2500 lb. concrete

MPS - FHA 7'-0" No limit given

NBS - BMS 107 No limit l' stories or 20'_2"

given to gable if

sup-porting veneer, or 10" cavity walls

NY State Bldg. 28' to peak or when

Code 7'-Olt supporting 10llcavity

or veneer walls

9'

to eave,15' to peak

Basic Bldg. 6'-Olt _{35' to peak}

Code, BOCA

Midwest Bldg. _{No limit} 2-story frame or Presumably 3000

Code, MCBO _given I-story masonry lb. concrete

or veneer

Southern Std. No limit It story or 20' if

Bldg. Code, given supporting lOllcavity

SBCC or veneer walls. other: 2000 lb.

superstructures not clear

Uniform Bldg. No limit 2 stories F:rame construction

Code, leBO given only

Am. Std. Bldg. No limit given but

Code require- if supporting IOu

ments for No limit ｣ｾｶｩｴｹ or veneer

masonry given ｬｾ stories or 20'

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,

.

·

,

.

7

-TABLE 5

8ft _{Solid :Masonry Foundations}

ｾｵｴｨｯｲｩｴｹ Maximum Maximum

Depth below Height of Remarks

NBC 6'-0" 2 stories

DBR Housing

Standards 3'-Ou 1 story

MPS - FHA 7'-0" No limit given Masonry

construc-tion only

5'-0" No limit given Frame

construc-tion

NBS - BMS 107 5'-0" ｬｾ story or 20'

- - to gable if

sup-porting veneer or lO" cavity wall

NY State Bldg. 5f_-01l _{28' to peak or when}

Code supporting 10" cavity

, or veneer, 9' to eave

and 15' to peak

Basic Bldg. 6'-Otl _{35' to peak}

Code, BOCA

Midwest Bldg. No limit 1 story Frame

construc-Code, MCBO given tion only

Southern Std. ｬｾ story or 20' if

Bldg. Code, 5'-0" supporting 10" cavity

SBCC or brick veneer. Otb2!r'

Uniform Bldg. No limit 2 stories Frame

construc-Code, rCBO given tion only

Am. Std. Bldg. 28' or-if supporting

Code require- 10" cavity or veneer

ments for 5'-0" ｬｾ story or 20' to

masonry peak

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J •

8 -TABLE 6

8" Hollow Masonry Foundations

ｾｵｴｨｯｲｩｴｹ Iv'Iaximum Maximum

Depth below Height of Remarks

lNBc

Not permitted

IDBR Housing ＳｾＭＰＱｬ 1 story

Standards

MPS

-

FHA 5'-01t No limit given

NBS - BMS 107 4'-Ott

I-b

story or 20' to

gable if supporting veneer or 10ucav11iy

wall

lNy

State Bldg. 4'-Ou 28' to peak, or if

Code supporting 10"

cavity or veneer 9' to eave, 15' to peak

ｾ｡ｳｩ｣ Bldg. 6'-0" 35' to peak Code, BOCA

ｾ､ｷ･ｳｴ Bldg. No limit 1 story ｾ｡ｭ･

construc-Code, MeBO given tion only

Southern Std. ｬｾ story or 20' if

tBldg. Code, 4'-0" supporting lO" cartty

SBCC or brick veneer. Other

IUniform Bldg. No limit 2 stories Frame

cpnf3truc-Code, SBCC given only

ｾＮ Std. Bldg. 28' or 'if supporting

Code require- lOll cavity or veneer

ｾ･ｮｴｳ for ＴｾＭｏｉｬ _ｬｾ story or 20' to

ｾ｡ｳｯｮｲｹ peak

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; .

, .

9

-TABLE 7

Depth below Height of

NBC Not specifically

listed

DBR Housing Not listed

Standards presumably _{2 stories} _{2000 lb. concrete}

more than '6g_-0fl

MJ?S - FHA Not listed

NBS - BMS 107 Not listed

NY State Bldg. _{Not listed}

Code

!Basic Bldg. Not listed

Code, BOCA Midwest Bldg.

Code, MCBO Not listed

Southern Std.

Bldg. Code, Not listed

SBCC

ｾｮｩｦｯｮｮ Bldg. No limit 2 stories Frame construction

Code, ICBO given only

ｾＮ Std. Bldg. Code require-ments for Masonry

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10

-TABLE 8

lAuthority Maximum lV'13ximum _Remarks

NBC Not specifically

listed

DBR Housing ＶｾＭｏｦｴ _{2 stories (25}t )

Standards

IMPs

-

FHA 7i _-Ofl _{No limit given}

tNBs

- BMS 107 Not listed

tNy

State 7'-On No limit given

lBldgo Code lBasic Bldgo

bode, BOCA Not listed

IMidwest Bldgo

Code, MCBO Not listed

Southern Std ..

Bldgo Code, Not listed

SBCC

Uniform Bldgo No limit 2 stories Frame construction

Code, ICBO given only

lAm

0 Stdo Bldg ..

Code

require-ｾ･ｮｴｳ for _{Not listed}

ｾｾ｡ｳｯｮｲｹ

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11

-TABLE 9

10" Hollow Masonry Foundations

Maximum Maximum

Authority Grade Superstructure Remarks

NBC 4'-0" 2 stories Wood frame

construction only

TIBR Housing 6'-0" 2 stories

Standards

MPS - FHA 7'-0" No limit given Masonry

construction only

NBS - BMS 107 Not listed

NY State

6'-0"

No limit given

Bldg. Code

Basic Bldg. Not listed

Code, BOCA

Midwest Bldg. Not listed

Code, MCBO

Southern Std. Not listed

Bldg. Code, SBCC

Uniform-Blag. No limit given 3 stories Frame

Code, ICBO construction only

Am. Std. Bldg. Not listed

Code Require- ' ments for

Masonry

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12

-TABLE 10

Maximum Maximum

NBC 6'-0" 3 stories 2000 lb. concrete

DBR Housing Not listed 3 stories 2000 lb. concrete

Standards

MPS - FHA Not listed

NBS

-

BMS 107 No limit given No limit given

NY State Not listed

Bldg. Code

Basic Bldg. More than 35v to peak

Code, BOCA 6'_0"

Midwest Bldg. No limit given 3 stories

Code, MCBO

Southern Std. No limit given No limit given

Bldg. Code, SBCC

Uniform Bldg. No limit given 3 stories Frame

Code, rCBO construction only

'.

Am. Std. Bldg. Not listed

Code

Require-ｭ･ｮｾｳ for . Masonry

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13

-TABLE 11

Maximum Maximum

NBC 6'-0" 3 stories

Not listed

DBR Housing presumably 2 stories

Standards greater than

6'-0"

,

Not listed,

presumably 3 stories

6'-0"

MPS - FHA Not listed

NBS

_-

BMS 107 No limit given No limit given

NY State Not listed

Bldg. Code

Basic Bldg. More ,than _{35' to peak}

Code, BOCA 6'-0"

Code, MCBO

Southern Std. No limit given No limit given

Bldg. Code, SBCC

Uniform Bldg. No limit given 3 stories Frame "

Code, ICBO construction only

Am. Std. Bldg.

Code Require- Not listed

ments for Masonry

ASA A ＴｬｯｬｾＱＹＵＳ

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14

-TABLE 12

12" Hollow Block Foundations

Maximum Maximum

NBC _4'-0" 2 stories For masonry

superstructure

DBR Housing Not listed, 3 stories

Standards presumably

6'-0"

MPS - FHA 7'_0" No limit given

EBS - BMS 107 No limit given No limit given

NY state Not listed

Bldg. Code

Basic Bldg. More than 35' to peak

Code, BOCA 6'-0"

Code, MCBO

Southern std. No limit given No limit given

Bldg. Code, SBec

Uniform Bldg. No limit given 3 stories Frame

Code, ICBO construction cnly

Am. Std. Bldg.

Code Require- Not listed

ments for masonry

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15

-TABLE 13

Requirements Relating to Capping, Anchorage of Sills, and Clearance of Wood Construction

in

bolts 6' o.c. securely imbedded

(except for dwellings) Authority NBC DBR Housing Standards MPS - FHA

Y

State Bldg. Code NBS, BMS 101 Basic Bldg. Code, BOCA Midwest Bldg. Code, MCBO Southern Std. Bldg. Code, SBCC Uniform Bldg. Code, rCBO Capping required for concrete blocks

2:t

1t _solid masonry

4"

solid masonry

4"

solid concrete or full width wood sill or top course filled with concrete or grout

4"

solid concrete

4"

solid concrete Apparently not reqUired

4"

solid masonry Apparently not required Apparently not Anchorage for sills Shall be securely anchored

:tIt

bolts

6'

o.c.

or

5/8"

bolts

8'

o.c. imbedded

4"

:t"

bolts -

8'

o.c. imbedded

15"

in masonry or 6" in concrete. May be omitted if calcula-tions show them to be unnecessary

i"

bolts - 8' O.C.

imbedded

15"

in masonry or 6" in concrete

Adequate anchorage to be provided

itt

bolts 8' o.c. imbedded 8"

i"

bolts 6' o.c.

imbedded

1"

in

bolts 6' o.c. imbedded

1"

Min. ht. of" foundation wall above grade (wood-frame c onst. ) 12" 12" 8" not given 6" 8U _minimum may be more if reqUired by local snow conditions 6" 6" Minimum clearance in crawl space 18" below the joists 12" below framing or 24" below framing beneath areas that are to be serviced 18" below joists, 12" below beams, or 24" below framing beneath areas that must be serviced 18" below floor framing 18" below framing 18" below framing 18" below joists 18" below framing 18" under joists 12" under beams

Am.

Std. Bldg. Code ReqUire-I

ｾ

ｮｴｳ for sonry ASA A41.1-195

1

ＲｾＢ solid

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16 -TABLE 14

Footing Requirements

Authority Requirements

NBC aft minimum thiclmess1 and must extend at least

4"

from

foundation. Footings required under all foundation walls. DBR Housing 6" minimum thiclmess, and must extend at least 4 ft from

Standards foundation unless evidence of allowable soil pressure shows that other widths are adequate. Footings required under all unit masonry walls but not under poured foundations 1cnless soil conditions require them.

MPS - FHA Footings not mandatory in all cases but depend on soil

conditions. Must be at least 6" thick or not less than 1.4 times the footing projection. In lieu of more precise data, the following are suggested:

Frame Masonry

Depth Projeotion Depth Projection

1 story basementless 6" 2 ft 6" 3"

1 story basement 6" 3"

6

ft _4"

2 story basementless

6"

3"

6

ft

4ft

2 story basement 6" 4" aft 5"

NY State Footings not required except for hollow unit masonry walls Bldg. Code or if soil conditions require them. Must be at least 6"

thick and wide enough to suit soil conditions.

NBS, BMS 107 Footings must be designed for the existing soil conditions with no minimum thiclmess or projection listed.

Basic Bldg. 6t1 _{minimum thiclmess for I-story frame and veneer.} Code, BOCA au minimum thickness for other types of houses.

No minimum footing projections reqUired as all footing widths are determined from soil conditions.

Midwest Bldg. 6" minimum thickness for wood frame houses, S" for masonry Code, MCBO and veneer. 16" width for 1 story, 20" for 3 stories,

masonry and veneer construction. 12" width for I-story, 14ft for 2-storY9 IS" for 3-story frame.

Southern Std. No limits given ｾ footings must be designed on the basis of Bldg. Code, soil conditions.

SBCC

Uniform 6" minimum thickness for I-story; 7" for 2-story; Stl for Bldg. Code,

3

story-frame. 12" minimum width for I-story, 15" for ICBO 2-story and laft for 3-story frame construction.

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17

-Summary of ｒ･ｾｵｩｲ･ｭ･ｮｴｳ and Discussion

1. Six-inch solid concrete foundation walls.- Of the ten codes investigated only two, including the

NBC

of Canada, do not permit the use of 6-inch concrete foundation walls. Of the remaining eight codes, five limit the use of 6-inch concrete walls to one-story structures, and three have no limits. Three codes limit the use to frame construction only and five do not make a distinction. Of the eight codes three limit the use to basementless houses. The remaining five permit allowable

depths of backfill of from 4 to 5 feet or do not state any limit. 2. Six-inch solid masonry foundation walls.- Of the ten codes,

six do not permit the use of 5-inch masonry foundation walls, while four, including the FHA standards, will permit their use. Two of these allow them to be used with basementless houses only, one with basements down to 3 feet below grade, and the remaining code gives no limits.

It is difficult to explain why 6-inch solid masonry walls are not permitted more generally, especially for base-mentless construction, since there is little doubt that the strength of a 6-inch wall in compression is adequate to resist the usual structural loads in a house. In basementless houses there is usually little or no soil pressure involved as the difference in elevation between the outside grade and inside

grade is seldom more than I foot. Therefore the lateral strength of the wall has little importance.

3.

Six-inch hollow masonry foundation walls.- Seven codes out of ten do not permit the use of 5-inch hollow masonry. One code permits its use in wood-frame basementless houses, one code permits its use beneath slabs and one permits its use in one-story frame houses but gives no figures on the permitted depth below grade.

Here again it is difficult to explain why 6-inch hollow masonry is not permitted for basementless houses because of the absence of significant soil pressures. The bearing strength of such walls is more than adequate to support any vertical force one might expect.

4.

t-inch concrete foundation walls. All of the codes permit t e use 0 8-inc concre e oun a ions. Three of these,

inclu-ding the DBR Housing Standards and the NBC of Canada, permit a maximum depth of backfill of 6 feet and two permit a 7-foot depth. The remaining five list no depth requirements.

Many codes are not specific as to what superstructure may be carried on such walls, but two codes limit the structure

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18

-to two s-tories; three do not mention frame construction but limit the height of 10-inch cavity wallar brick veneer super-structures to ｬｾ stories or 20 feet in height. One code allows a superstructure height of 35 feet, one allows 28 feet except when supporting veneer or 10-inch cavity walls in which case the maximum allowable height is listed as

9

feet at the eaves or 15 feet at the peak, and one code allows two-story frame construction or one-story masonry or veneer construction. One code lists no limits. The National Building Code has a peculiar requirement in that two stories are permitted for frame or

masonry construction but only one story for brick veneer. The present

depth limitations. depth of 7 feet for realistic. This is Standards.

DBR Housing Standards have the' It would appear that a maximum 8-inch concrete walls would be the depth that is permitted in

most severe allowable more the FHA

5.

6.

7.

8.

Ei foundation walls.- All of the

co es permi € use a -inc so 1 masonry oundations. One

permits a depth of backfill of

7

feet for masonry superstruc-tures only, two permit 6 feet, 4 permit 5v_{-0", one permits}

3 feet and two list no limits. As in the case with 8-inch concrete walls, the limiting superstructure requirements vary considerably. Only two codes, including the DBR Standards, limit the superstructure to one story.

Eight-inch hollow unit masoOfY foundation walls. Only one code, the National BUilding Code a Canada, does not permit the use of 8-inch hollow block walls. One code limits the depth of backfill to 3 feet, four to 4 feet, one to 5 feet and one to 6 feet; two others list no limits. The superstructure require-ments vary considerably but the majority permit two-story frame construction with a number of codes having further restrictions for brick veneer or cavity wall constructions.

Ten-inch concrete foundation walls. Only two codes, including the Housing standards, specifically list requirements for la-inch concrete walls. Three codes do not have requirements for walls greater than 8 inches, while five codes jump from 8-inch to l2-inch walls. Two codes limit the superstructure to two stories.

Ten-inch solid unit ｭ｡ｳｯｾ foundation walls.- Only four codes, including the Housing ｳｴｾ｡ｲ､ｳＬ list requirements for la-inch solid masonry. One code does not have reqUirements above 8-inch solid blocks, while five jump from 8-inch to l2-inch blocks. Of the four codes which have requirements, one limits the back-fill to 6 feet (DBR Standards), two limit it to 7 feet, while the third gives no limit. Two of these codes limit the super-structure to two stories and two give no limit.

(20)

10.

II.

12,.

19

-Ten-inch hollow unit masonib foundation walls.- Five codes do not list requirements for -inch hollow block walls. Of the five that do, one lists the allowable foundation depth to

4

feet (NBC), two, including the DBR Standards, list 6 feet, one lists 7 feet and the fifth gives no limit. Two limit the superstructure height to two stories, one to three stories and the remaining two give no limits. Four of these codes that have no requirements jump from 8- to l2-inch blocks; the remaining code does not have reqUirements above 8 inches. Twelve-inch concrete foundation walls.- Of the ten codes,

seven have requirements for 12-inch concrete walls. Of these, only one, the National BUilding Code, limits the depth of

foundation walls to 6 feet below grade while the remainder have no specific limits. All codes either limit the height of superstructure to three stories or else provide no limit.

Twelve-inch solid unit ｭ｡ｳｯｮｾ foundation walls.- Of the ten codes, eight have ｲ･ｱｵｩｲ･ｭ･ｮｾ for l2-incli masonry. Of these only the National Building Code limits the depth of wall below grade to 6 feet; the remaining six do not list specific limits. The limiting heights for supported superstructures vary from two to three stories.

Twelve-inch hollow unit masonry foundation walls.- Two of the ten codes have no requirements that go as liigh as 12 inches for hollow block walls. Of the other eight codes, only the National BUilding Code imposes limits on the allowable depth below grade (4 feet) for such walls. Three of the eight give no ,limiting height of superstructure while the remaining five list from two to three stories.

Maximum spacing between lateral supports.- Although several codes require walls to be supported laterally when the ratio of wall thickness to unsupported height exceeds a certain limit, the unsupported height for most basement walls is well within the required limits so that intermediate lateral supports would not be required. No other code contained reqUirements similar to those in the DBR Housing Standards which require intermediate supports such as cross walls or buttresses for various types of foundations.

It is interesting to note that in the National Concrete Masonry Association publication "Concrete Masonry Foundation Walls", curves are prOVided showing that the intermediate

lateral supports have very little effect in increasing the wall strength by distributing the vertical stresses unless the

supports are spaced quite close together. It is shown, for example, that even with the supports spaced at only three times the wall height apart (about 20 feet), the vertical stresses caused by earth pressure would be about 93 per cent of the stress for walls without any intermediate supports.

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20

-140 Allowable height of superstructureo- The weight of masonry or wood-frame superstructures

of

two or three stories plus the design loads produce compression loads in the foundation walls well below the safe limitso For house construction, therefore, the vertical load-carrying capacity of masonry walls is rarely an important considerationo On the other hand the weight of the superstructure may significantly affect the strength of a wall in resisting lateral forces caused by earth pressureo The greater the superstructure load, the stronger the wall will be in resisting earth pressures (which is the prime consideration in the design of masonry foundation walls) 0

The following is an excerpt from the American Standards Building Code requirement,s for masonry (ASA A410101953):

"Vertical compression loads on foundation walls resulting from the weight of the building and its contents tend to prevent the development or to reduce the magnitude of the vertical tensile stresses caused by earth pressureso The resistance to lateral pressures of a given foundation wall is therefore

increased by the increase in weight of the superstructureo ooo The use of thinner foundation walls for light structures than for heavy structures as permitted by some codes is not justified by a consideration of lateral stabilitYolt

Capping for hollow unit ｭ｡ｳｯｾ foundation walls o- Three codes do not have any requirements or capping the top of hollow block walls o Five of the remaining seven require 4 inches of solid masonry or concreteo Two codes require only 2t inches of solid concrete or masonryo One permits, as an alternative to solid capping, the use of a sill that bears on both face shell$ or the filling of the top course with grout or concreteo It is hard to determine why capping blocks are required0 It can be

shown, for example, that if a full width of sill was used on top of block walls, the allowable bearing strength of the wood would be many times that required to support the superstructure loado

Anchorage for sills to foundation wallso- Of the nine codes mentioning requirements for anchorage, two simply state that the superstructure be securely anchored, two list t-inch bolts, 6 feet OoC o imbedded

7

inches in concrete or masonry, one

lists ｾＭｩｮ｣ｨ anchor bolts, 6 feet OoCo or 5/8-inch bolts,

8 feet ooco, imbedded 4 inches 0 One code requires t-inch bolts, 8 feet ooco, imbedded 8 inches, one requires i-inch bolts,

8 feet ooc o, securely imbedded, and two list ｾＭｩｮ｣ｨ｢ｯｬｾＬ

8 feet ooc o, imbedded 15 inches in masonry or 6 inches in concrete0

Minimum height of foundation walls above ｾ｡､･ for wood-frame constructiono- Two codes, the DBR Housing tandards apd the National Building Code, require a minimum of 12-inch clearance

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-from the ground. Four codes require a clearance of 6 inches while three require a clearance of 8 inches. The remaining two codes give no limit.

18. Minimum clearance in crawl space. - Eight of the nine codes having such requirements, require a minimum clearance of 18 incheso

9f these, two permit 12-inch clearance under the beams. The other code requires a clearance of 12'inches, or 24 inches beneath areas that have to be serviced.

190 Footings.- The majority of codes permit considerable scope for design of footing sizes based on soil conditions. Some codes do, however, have certain minimum requirements that must be met if no bearing pressure data are available. The National Building Code, although permitting some degree of flexibility, prOVides requirements for certain minimum footing width regard-less of the soil conditions. For example, it is stated that the footing must extend a minimum of 4 inches from the founda-tion wallo Although footings are required by the National

Building Code, the Housing Standards permit concrete foundation walls without footings if the allowable soil pressure is not exceeded. The minimum thickness of footings varied from 6 inches to 8 inches with many codes requiring an 8-inch thick-ness for two- and three-story buildingso