House framing

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Ser THI B92 no, 23 c . 2

sm:

HOUSE FRAMING by D,B. Dorey BUILDING RESEARCH

i-LIR9nAY-I

\

HATIONAL RFSEAAEH COUHCTL

2

3

_{q c C ;}

~

HOUSE

FRAMING

by D.B. Dorey

The purpose of the house frame is

to

give shape, e%r?cgthr and r i g i d i t y to the f i n i s h e d structure under normal e o c d i t i o n s of uae and c l i m a t i c loadings. H o w w e n any partic-

u?.ar house frame does t h i s depends upon s i z e and grading of

t h e lumber and upon the planning and carpentry. As a secondary

purpose, we might say t h a t the frame provides

a

_{skeleton to} which Insulation and o t h e r e x t e r i o r and interior materials are at-bachsd.

To f u l f i l t h l s purpose, a house m a t have the necessary

s t r e n g t h and r i g i d i t y to resist without damage to i n t e r i o r

finishes :

1. Wind leads;

2. Snow Loads;

3 .

_{Lave loads;}

PEOPLE. E F U R N l S H I M G S L I V E LOAD

4. Dead loads;

I I I

--

-

V E I G H T of STRUCTURE

I53

DEAD LOAU

5.

Earthquake loads

-

h o r i z o n t a l loads which

are

not common to a l l parts of North America.

The loads, or combination of loads, to which we have

j u s t r e f e r r e d must be transrndtted to the foundation by t h e house frame and the various materials which a c t w i t h the

frame in the finished house. These loads are transmitted to

the foundation by the structural components of t h e house: 1. A c t l n g as beams

-

bending loads;

2, Acting

as

columns

-

a x i a l loada;

3.

Acting b o t h as columns and as beams

-

bending loads and

axial Inads;

4. Acting

in

combination as panels

-

bending loads, axial

loads and racking loads.

Having d e a l t v e r y briefly in the way

of

review w l t h

the loads which

are

imposed on a house by use and climatic

loadlrtgs, we might

t u n

now to t h e types of framing we m y f i n d irh various parts of Canada.

T h ~ r e a r e three rnaln types of' house framing in Canada, excluding, of course, plank wall c o n s t r u c t i o n which is q u i t e

common in t h e Province of Quebec. Plank wall constr~ction, to .

my h o w l e d g e , I s n o t being used to any great e x t e n t , if at

all, in house c o n s t r u c t i o n in t h i s area, Therefose, we w i l l

omit i t from this discussion. The three t y p e s of framing a r e :

151

braced-frame constructf on; balloon-frame construct Lon;

western-franc eF platform construction.

Braced-frame construction.

-

The braced-frame construction is

said t o be the o l d e s t method of framing 9n America, havlng been Imported from Europe in c o l o n i a l times. Although in a

somewhat modifled fozrn, it L s still being used in c e r t a i n

areas. Originally this t y p e of framing was characterfzed by

heavy t l m b e r p o s t s at the corners9 often w i t h intermediate posts between, all of which extend c o n t ; i n u ~ u s l y from a heavy foundation sill to an equally heavy plate at the roof LZne.

A t the second a t o r e y , o r second floor l e v e l , heavy timber

g i r t s were introduced running from post to post and carefully

mortised and tenoned w i t h oak pins. These g i r t s supported t h e seeon& f l o o r joists. Knee b m c e s were u s u a l l y well. f l t t e d

and pinned

at

the copper p o s t s . The quality of the materials

and workmanship accounts f o r the number of o l d houses of t h i s type of c o n s t r u c t i o n that a r e s t i l l standing i n many parts of

Eastern Canada and the Eastern United States t o d a y .

Balloon-frame co~struction. - The principal characteristic, of b a l l o o n framing

_-

i a t h e use of s t u d s extending in one piece f r o m the s i l l on $he t o p of the foundation wall-to the pia5e

or roof. J o l s t ends are nailed to $55 s t u d s and are supported by a ribband or l e d g e s board l e t I n t o the studs. Corner

bracing usually sxtends from t h e a l l 1 to _{t h e ribband and f r o m}

t h e r i b b e n d to t h e t o p p l a t e . O p e n i ~ g s in walls must be

adequately framed because

or

the con5inulty of the s t u d d i n g .

T o equalize o v e r - a l l s h ~ i n k a g e s e t tlernsnt

,

part it ion studs

must extend from joist-supporting b a n s to p a r t i t i o n plates

and between past it i o n p l a t e s .

W e s t e r n - f r m ~ or platform construction. - Of these three

types of frzming, west e m - f r m e or platform construct Ion i~ undoubtedly the m o s t w i d e l y used in this a r e a , Unlike braced-

frame Qr bal1oor1-f rm,e construction, 5t is characterized by platforms independently framed and supported by studs one

s t o r e y in h e i g h t , F l a t f o ~ m construction 1s a convenient

method of framing because walls m y be constructed on each floor Level and t i l t e d i n t o place.

A l l t h r e e types of f r a m i n g have been developed by

experience and good p r a c t i c e t o eliminate p o s s i b l e shrinkage d i f f i c u l t i e s in the Lumber. O v e r - a l l shrinkzge settlement

d:~e to the d r y i n g out oZ t h e lmbber kas been equalizzd where p o a s l b l e , Wood f r o m the t r e e my c o n t a i n from 30 t o 300 p s r o m ?

water

based cn the weight of t 5 e oven d r y wood. Th2s

W E t e may ~ be separated s c u g h l p I n t o t w o p a s t a ; the F r e e

water

i'cr fbe cell c z v i t i e s and t h s water held absorbed in the

~apiflarizs of t h e walls cf such wood elementa 5s fibres an6

z a g cells. The absorbed watcr I s of most i n t e r e s t w h e ~

c c i ~ s t 2 e r i n g shrinkage, Whex t.he fsee water h z s k e n ~ ~ e m c v e d and t h e absorbed water r a m l n s , w3ad 1% said to have ~ e a c h e d

the _{?%>re saturation p c i n t}

.

_{The krSre sat~u-at ifin} pciiqt is

a p p ~ o - u l a s t z l y 30 p e r cenZ mobsfure ~ o n t e 2 t f o ~ a21 apesles.

Shrfnkage aqsass the g r a i n can 'sn as high as I ~ r l - ? pzz fc'ot

DP w i d t k : , i? 5% moistux cofltcnt ~f the wood chaz~gzs fr~m

say 2 1 g e r c e 2 t 2 0 12 pey cent, L o n g i t u d i n a l sh-inkage on

the o t h e r hand 3s r e l a t i v e l y n e g l i g i b l e .

BksLcally

a

house is made up OZ component3 wklc?,

r v h m icte~zonnected, impar? the necessary s t ~ e n g t h and r . j , g X < ~ c > - f o t k e f i n i s h e d house, These components Ere:

the r o o f ; the walls;

the _floors.

IY we f o l l o w in order of design, we can deal w l 3 h

sach of t h e s e comp~nents sepa~ztely. In doing s o , the rocf

may be thought of as b e i n g made up of panels. The roof

sheathing resists the r a c k i n g l o a d s and transmits t h e loads

t o t h e rafters, which, 2n turn, carry bending and a x i a l loads,. C o l l a r t l e s m d e r wind loads f r e q u e n t l y act In tension, but

under a c e w n u l a t ~ d sr-ow loads may act in compression,

S H E A T H I N G

C O L L A R T I E

In

s structu~al t e s t on a full-acale house 5y t h z

DivLsLan of Building Research, it was found t h a t mde? a

slnulated

snow

lose on %he r o o f , the c o l l a r ties wera

in

';orcpsession. The r a f t e ~ s d e f l e c t e d

or

bent tc t 3 e e x t e r ~ t ci+ pushing out t h e n i d e walls at p o i n t s where the ceiling j o i s t s were not adeqaately f a s t e n e d tc t h e b u t t s of the rafters snd

where th,e-e were no Z n t e r t x cross p a r t i t i ~ n s .

Trussed-roof a~stsas & r e belng used more s o ~ m o n l y .

I7

a!lcb sy-skems do

away

with b k e r i o ~ - l ~ a d bearing p a r t i t l ~ g ~ , 2nd g r e a t e r T l e x l b i l i t ~ is m d e possible f o r i n t e r i o r 1ayc1dt. 9 t h - advantages a l e p o s s l 5 l e , b u t many of t h e s e a d v a ~ t a g e s

depend !)-pan each b u i l d e z 9 soperat i o n s .

C L E A R SPAN

-

OTHER TRUsSE-5

I

Roof trusaes r e q u i r e englneerfng designing, but provex d e s i g n s nay be used where loading c o n d i t i o n s and speclf i c a t l c n s p e ~ m i t

.

A recent test ot two W-trinsses

In

the P i v i s i o m z f s

l a b o r a t s r y iFdicated t h a t even at the point of f a i l w e , t h e

laves c b o ~ d a did n o t reach the maximum allowable deflection oi'

~ 1 3 6 3 o f the span for a p l a s 2 e r ceiling. B o l t s and s p l i + L - ~ 5 ~ - ~

s c ~ ~ e c t o r s were used f o r joining the t r u s s members. O ? h e ~

m ~ t h o d s q f iastening j o t 2 t s have been used suc:essfully,

p s ~ t , . ~ c u l a r l y i~ the United S t a t e s .

Work _{w a s r e c e n t l y undertaken by the Division to obtaLn}

c o i l p a r a t l u e information cn t h e s t m n g t h s of convsnti~nel r a i ' t e r constructioc and asvera3 types of truss constructl~c w i % h the hope t h a t a b e t t e r basis yay be e s t a b l i s h e d f o r t h i s

evsluatlon of the s t r e n g t h of truss c o n s t r u c t i o n .

Walls may be congtruct;ed in a number of ways. Whole

wall sections or panels may Be t i l t e d i n t o position. Regardl~ss

cf the techr.J.que, adequate s5sength auat be b u i l t i n t o wall

7 1. Racking loads and axial

Icads;

2 BendZng l o a d s .

If t h e type of exterior sheathing d o e s not a f f o r d enaugh ~ a c k i n g s t r e n g t h when applied to the wall f~arnLng,

a

S r s c l n g method must be employed t o make the wall nore zigid z.gaZna+ the f c r c e of tSe wind, i.e., wfnd l o a d s , Ot?.erwis~,

o ~ a c k s -my appear In t 9 3 f n t e r l o r f i n i s h e s . The e f f e c t i v e ~ e s s n f %he b?acz9 whether i5 Zs a l e t - i n 1 inch by 4 i n c h e s , a

2-icoh th3-ck c u t - i n brace, or a continuous 2-inch t h i c k bracz,

depends upon the skill and judgment of t h e carpeats?.

As a -mattes or Z z ~ t o s e s t , it might be mentioned that

:E 1950 aad

1951

the S i v i f i l o n made a survey of stud spacing ln 3.ouses under ecnstxuctfon in nine cities acrCisa Canada. T h i a slnvey z e v e s l e d that, I r i t is seasonable to expect t k a t i n the avepage Canadian f ~ m e house of today, up t o 34 p e r

cznt of %he e x t e r i o r wall a r e a w i l l be found t o h a ~ ~ e st.udd:ng

so spaced as to be unsuited to t h e Zncosporation of factor&:

,=cl",e b u i l d i n g materials designed on a 16-inch module". (The

exteyior wail aFea referred t o is exclusive of window and

d ~ c r opsnings

.

) T h l s meam, f o r instance, t h a t i n a u l a t i o : 3

n7:.s? be cu5, and e x t r a t i m e taken tc s e t s p e c i a l p i e c e s i n t s t h e g e

s~sax.

Openings in walls are not d i f f i c u l t to frame if the problem of shrinkage

in

t h e studs, l i n t e l s and p l a t e s is kept

in mind. By way of r e v i e w , it m i g h t se useful t o illustrate

t h - I s as f o l l o w s :

1. C o ~ r e c t method of framing around wall opening;

Floors m y be regarded

in

much t h e aame way as walls

and roof systems. F l o o r j o i s t s , cross b r i d g i n g , s u b - f l o o r i n g a ~ d f i n l s h e d f l o o r i n g , when adequately deslgned and constru-,ted, a r e strong and f r e e from uncomfortable vibrations when walked upon. Bending loads a r e in t h i s case o f t e n t h e most

significant, E D L/lEtd

c r r r

r i

r r r

J o t 5 7

! I t 4

t t

I $ . +

#

t

i

i t

t f t

S I D E . VIEW - ~ J Q J ~ T

t

t

The r i g h t size and the grade of lumber in a f l o o r j o i s t w i l l g i v e the requfred s t r e n g t h ; cross b r i d g l n g and sub-flooring

w i l l give the r e q u i r e d stiffness.

" T e s t s at t h e F o r e s t P r o d u c t s L a b o r a t o r y indicate

t h a t loads up t o 400 pounds concentrated on an area of

113

square ft. of a conventional dwelling flooring system a r e

distributed laterally for

a

considerable d i s t a n c e w i t h only

2 0 or 30 per cent carried d i r e c t l y by the j o i s t under the

load. The flooring system in the t e s t s consisted of joists, bridging, a diagonally l a i d s u b - f l o o r , and a 1-inch finished

f l o o r l a i d across t h e j o i s t s . The l o a d was applied at m i d -

span. "

*

One aspect of' p u t t i n g b a f l o o r j o i s t t h a t is well

to guard against is l a r g e knots on the bottom edge of a j o i s t .

Knots OP t h e lower edge weaken a j o i s t c o n s i d e r a b l y . This

s s p e c t is a q u e s t i o n of t h e grade of lumber, Lumher th?,t l a a h a Q or checked or cross grained is n u t s u i t a b l e . Notshes and holes in j o i s t s for plumbing pipes and e l ~ c t r i c w i r i n g d1.m weaken J o l s t a and should be guarded a g a i n s t . Notching oi' t h e t ~ o r p bottom of the j o i s t s for piping, in g e n e r a l ,

s k a u l d not be more than o n e - a b t h of the j o i s t depth and

should be l o c a t e d only in the end t h i r d of t h e span. Hole8

mq 4e b o r e d i l z the joists if t h e diameter is no greater than

2% i n o h e 3 agd the edge of t h e h o l e is n o t iesz t h a n 2 ifichee f ~ c m t h e t o p or bottom edge 'of t h e j o i s t , This usually l i m i % s rhe J c l a t s i z e t o

a

_{2 by 8 or larger,}

*

_{Wood Handbook No. 7 2 , U . S , Department of A g r i c u l t u r e ,}

The l a s t d e t a i l t h a t might be d e a l t with i a where

s p l i c e s may be made

in

laminated beams supporting f l o o r j o i s t s . L i k e a roof truss, a Laminated beam r e q u i r e s the appllcat

Ion

of engineering p r i n c i p l e s

in

the design, unless

d e t a i l s of

a

proven beam t h a t will f u l f i l the requirements a r e available. The advantage of knowing where to spli2e

a

heam is t h a t shorter l e n g t h s of 2-inch lumber may 5e used

?.I? put t o g e t h e r p r o p e r l y , thereby s a v l n g a little on ths

c c a t ,

Computetions have been made f o r the splicing OS l m i n a t i c n z in t h e beams g i v e n i n t h e t a b l e on P, 55 of

C e n t r a l Mastgage and Housing Corporation's B u i l d i n g Stzndasda,

1954,

and t h e f o l l o w i n g applies:

(I)

For 3-span beams, s p l i c e s in one lamination may bs

made as shown in the following dlagram.

EMP WALL C o t u M d G O L U M ~ E M D WALL

3 - S P A N

B E A M

Note: S p l i c e s in one lamination may be made o v e r

c e n t r e aupport s

.

32) F o r 4-span beams, s p l f c e s in one l a n i n a t i o n may 5 e made as shown in the following diagram.

f N U \VAL1 C O L V M ~ COLUMN E ~ W WALL

4 -

S P A N BEAM

N o t a : Splice IE one lamination pay be made o v e r a e n t ~ e suppoZt.

( 3 )

F o r 5-span beams, s p l i c e s

in

one l a r n l n a t i o ~ m y be made as shown in %he following diagram.

5 - S P A N BEAM

Note: Splices

in

one 1am;lnation m y be made o v e r

t w o centre s u p p o r t s

.

In a l l t h r e e of the beams for which- possible locations f o r splices have been given, adequate apiking t o g e t h e r of the

2 i n c h materlal is very important. Also, imperfections such

as large h o t s , checks, shakes, and s h o r t pieces of lumber

should be guarded against.

The purpose in good house framing is to p r o v i d e

adequate s t r e n g t h and stiffness in the f i n i s h e d structure

under normal c o n d i t i o n s of use and climatic loadings. T h i s purpose

can

only be fulfilled by:

(1) c a r e f u l s e l e c t i o n of size and grade of lumber;

(2) proper arrangement and fastening of members and components which a c t together; and