Building in winter with the aid of enclosures

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Building in winter with the aid of enclosures

Smith, A. W.

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NATIONAL RESEARCH COUNCIL

GANADA

DIVISION OF BUILD]NG RESEARCH

BUILDING IN WINTER WITH THE AID

OF ENCLOSURES

BY

A. W. SMIITH

A N A L Y Z E T )

Reprinted from

NATIONAL BUILDER

September, October, NoYember, December 1959

TECHNICAL PAPER N.O. 85

OF THE

DIVISION OF BUITDING RESEARCH

OTTAWA

JANUARY 1960

PRICE 25 CENTS

NRC 5537

This publication is being distributed by the Division of Building

Research of the National Research Council as a contribution towards

better building in canada. rt should not be reproduced in whole or in

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S U M M E R B U I L D I N G A L S O H A S I T S H A Z A R D S . H e r e t i m e w o s l o s l o n d e x l r o c o s l s w e r e i n c u r r e d in t h i s o p o r l m e n l s u m m e r - b u i l d i n g p r o i e c l i n O t t o w o w h e n t h e f l o o d e d e x c o v o t i o n h o d l o b e p u m p e d o u t o f l e r r o i n . ( l l l u s t r o t i o n l ) .

How to build in wintertime

with the aid of enclosures

In recent years, extensive studies have been made by the Division of

Building Research, National Research

Council, into the applications, cost

and performance of various types of enclosures

when used in winter for

different kinds o,f building construction.

This month, Mr. A. W. Smith of the DBR staff, who was co-author

of the Armstrong report, begins an exclusive series of four articles in NB

dealing with the use of enclosures

for different {ypes of building

construc-tion in winter.

By A. \il. SIIITH

There are still many in the construc-tion industry who believe that building in winter automatically implies extra costs and low quality.

Those who compare winter work with work done in the summer months often forget the days lost because of iain, slowdowns because of high t€mperatures, delays in the delivery of materials; the pumping out of an excavatiotr, or the moving of vehicles stuck in the mud. (See illustrations I and 2.)

All of these zummer problems rep-resent added costs which are not aearly so apparent as the direct cost of heating materials and providing for fresh con-crete in wintertime. Time lost in warm-ing up, clearwarm-ing up, and sittwarm-ing otrt winter storms appears to be much more signifi-cant than time lost due to heat, rain and slow deliveries in summer.

Only within a complete enclosure can work continue entirely independently of weather under conditions which en-courage the maximum output from labour. Increased productivity will cut construction costs and in many p4rts of Canada will often more than pay for the direct costs of winter construction.

Builders operating on a year-round basis have the opportunity of building up efficient crews of experienced work-men, and can greatly reduce overhead expetrses and operating costs in general, They can take advantage of the seasonal fluctua.tion of material costs and can often avoid the labour and material price increases which occur every spring. It should, be possible for subcontractors to reduce their winter prices knowing they can be assured of work for the duration of the winter.

By heating an enclosure which

sur-A. W. SMITH

rounds the work, the need for giving add,itional protection to the work itself is eliminated. It is also a simple matter to avoid the costly protection of build-ing materials stored on the site by placbuild-ing them inside the enilosure and cloce to their final position.

Hearting of sun enclosures is one of the direct costs of winter construction. This can very often be red,uced by utilizing solar energy.

The plastic films that are now wide-ly used on such structures bave the abili-ty to trap solar heat so that the tempera-ture inside such shelters may be as much

I : ,

A N o T H E R SUMMER BUILDING HAZARD, This olso hoppened in Ollowo ofler roin in summer when tronsport become bogged down orounc o iob-sile' lt could seldom hoppen in winter when the ground would be frozen. (lllurirotion 2),

as 45 F. above outside air temperatures during sunny weather. This alone will often provide all the heat r€quired during the day.

At night, however, and during perriods of cold, windy and cloudy weather, addi-tional heat is required. (See charts-iillus-tration 3.)

Sometimes a double layer of plastic can improve the insulating value of such a film by isolating an inch or so of air between each layer.

Savings Can also be made by providing controls which will set a limit on the temperature within the enclosure.

In many cases, where control is not exercised, the temperature may rise to a very high level. This not only increrases the heating costs but may also have an adverse effect on the quality of the work. Different types of building construction are affected in different ways duLring wintertime.

Prefabricated frameworks of steel or precast concrete are least affected since they can be erected without difficulty in all but the most severe weath€r condi-tions. Cast-in-place reinforced concrete frames and buildings with load-bearing wAlls present greater problems.

ha all cases, best results are achieved when it becomes possible to use the en_ closed building for support and maybe even as part of the enclosure itself.

In the ensuing articles in this series in National Builder, each type of construc_ tion will be oonsid,ered separately and the various methods of enclosing each type will be discussed in some detail.

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T H E S E C H A R T S S H O W h o w i m p o r r o n t con be the solor heoting of o n o r c h e n c l o s u r e . They compore the doily voriotion of the oir t e m p e r o l u r e inside the enclosurds w i t h t h e n o t u r o l voriotion of fhe o i r t e m p e r o l u r e o u l s i d e lh e m .

T I M E ( H O U R S )

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How to solve winter's problems

in multi-story construction

In the second of his series of articles

on buililing in winter with the ald of enclosures, Mr. Smith of the Division of Buildlng Research, N.R.C., deals here wifh multi-story frames. The prefabricated framework of steel or precast concrete, he says, is least af-fected since it can be erected wlthout difficulty in all but the most severe weather conditions. Cast.in:-place re-inforced concrete frames and buildings with load-bearing walls, however, pre-sent greater problems. fn ail cases, best results are achleved, when it be-tomes possible to use the enclosed building for support and maybe even as part of the enclosure itself.

By A. W. SMTIII

Prefabricated frames

Prefabricated frames of steel or pre-cast concrete can be erected without dif-ficulty in all but the most severe weather conditions and then closed in simply and effectively by using a permanent floor construction above and below, and a tern-porary, lightweight wall enclosure sup-ported by the frame itself.

There are two principal methods of enclosing the building skeleton.

The first and best method for taller buildings uses a covered-in suspended scaffold as an external working platform. (Illustration 5.)

This scaftold is suspended from out-riggers at roof level and raised from one story to another as work progresses. (Illustration 6.) It provides the walls of a story-height enclosure. The roof and floor of this enclosure are best formed by precast concrete slabs but iould just

as well be formed by metal pans on bar joists or even timber floor forms.

The metal pans and timber formwork imply a cast-in-place concrete floor slab which will require additional protection on the uppermost outside surface.

The second method of enclosing the skeleton makes use of standard sections of tubular scaffolding and is generally most economical for buildings under four or five stories. The scaffold is braced against the prefabricated framd and covered in by placing plywood, ta4)au-lins, or plastic over a light timber frame-work wired to the outside members. (Il-lustration 7.)

Prefabricated wall panels whether of metal, concrete or plastic can eliminate the need for an outside scaffolding of any kind and provide in thernselves an immediate enclosure of permanenrt mate-rials. 0llustration 8.)

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C O V E R E D . I N S U S P E N D E D S C A F F O L D . T h i s c o v e r e d scoffold, enclosing o s l o r y - h i g h s t o g e of consfruclion, w o s used in Toronlo. lt is roised o s f h e w o r k p r o c e e d s . ( l l l u s t r o f i o n 6 . I . . . A N D H E R E ' S W H A T i l l o o k e d l i k e i n s i d e . B r i c k w o r k is g o i n g o h e o d m o n y s t o r i e s u p w i l h f h e m e n o p e r o t i n g u n d e r n e q r - i d e o l con-d i l i o n s con-d e s p i l e s e y e r e w e o l h e r o u t s i con-d e . ( l l l u s t r o f i o n 6,) H E R E ' S A N E X A M P T E f r o m t h e M o r i t i m e s o f h o w s t o n d o r d s c o f f o l d i n g c o n b e e n c l o s e d b y w i r i n g o l i g h t t i m b e r f r o m e w o r k t o t h e o u f s i d e m e m b e r s o n d c o v e r i n g i t w i t h h o r d b o o r d o n d p l o s t i c . T h i s i s l h e M o r i t i m e A u t o P o r f i B u i l d i n g , H o l i f o x . ( l l l u s t r o t i o n 7 , ) . . . A N D H E R E 1 5 A N O T H E R m e t h o d f o r e n c l o s i n g m u l l i s l o r y b u i l d -i n g s , o l s o f r o m H o l -i f o x . l l -i s t h e M o r -i t -i m e T e l e p h o n e o n d T e l e g r o p h B u i l d i n g w h e r e s l o n d o r d s c o f f o l d i n g w o s b r o c e d o g o i n s t t h e b u i l d i n g f i o m e . ( l l l u s l r o t i o n 7 . ! J A C K E D - U P R O O F S T R U C T U R E . D u r i n g c o n s t r u c f i o n o f o n l l - s t o r y o p o r l m e n t b u i l d i n g in Otfowo, this lemporory root struclure wos i o c k e d u p s t o r y b y s f o r y i n s e c t i o n s . A s t h e w h o l e enclosure wos r o i s e d , e o c h f l o o r wos conslrucfed w i t h i n i t . ( l l l u s t r o l i o n ll.)

. . . T H E S A r I E J O B l N C T O S E - U P . T h e m e c h o n i c o l iocking sysfen r o i s e d f h e f e m p o r o r y e n c l o s u r e i n s e c t i o n s o s w o r k p r o c e e d e d . Note h o w t h e iocks ore positioned ond thol lhe nen ore working in com-f o r t d e s p i t e s u b - z e r o l e m p e r o t u r e s o u t s i d e . ( l l l u s l r o t i o n l l . )

cast concrete frame they can eliminate the need for temporary enclosures of any kind and reduce the closing-in time to an absolute minimum. (Illustration 9.)

Gast-in-place frames

The problem of enclosing cast-in-place construction is basically the same in that it revolves around the enclosure of a story-height section of the building but the whole operation is generally much slower and more complicated.

Time is los while waiting for the con-crete frame to gain sufficient strength to support the next "layer" of construction and it is generally necessary to enclose two or even three stories at one time. This means that temporary heating costs are increased and additional materials are required.

The walls of the enclosure are usual-ly formed by hanging tarpaulins and covered, scaffolding as previously describ-ed. Tho roof is provided by ,the floor form, whether of permanent steel sheet-ing or temporary plywood and is sup-ported by column forms and telescopic jacks which rest on the roughly finished floor which has just been oompleted. (Il-lustration 10.)

This method still requires additional protection for the outside surface irf the "roof" slab and this is usually provided by some kindi of insulating blanket.

Some contractors have developed tem-porary roof coverings which can be jack-ed from floor to floor as the work pro-gresses. This method of totally enclosing the working arga provides full protection for the workmen, who are then able 'to form and place each floor in ideal condi-tions. The temporary roof, usually in the form of a steel or timber truss, is sup ported on steel columns which pass through the floor being constructed and rest on the completed floor underneath. (Illustration 11.)

This temporary roof may also be sup-'

ported on temporary columns located outside the walls of the building under construction. This arrangement has the advantage that the supports for the en-closure do not interfere with oonstruc-tion operaoonstruc-tions.

The lift slab method is particularly well suited to wintertime construction. The only enclosure required is a very simple one at ground level. (Illustration 1 3 . )

All the floor slabs are placed within this small enclosure, one on top of the other, and then raised into position by hydraulic jacks on top of steel columns.

Hanging tarpaulins or prefabricated wall panels ca4 be used to close in the entire structurd after the precast floor slabs aie finally positioned. The original enclosure usedr for the concreting opera-tion might be a laminated timber arch structure covered with plastic.

Two stage-by.stage Plans

for winter building

Prefobricoted fromes of sleel or preco,sl concrele con be erecled w i t h o u t d i f f i c u l f Y i n o l l b u t the most severe weolher c o n d i t i o n s . T h e y c o n l h e n b e c l o s e d i n s i m P l Y o n d e f f e c t i v e l Y b Y u s i n g o p e r m o n e n l f l o o r c o n s l r u c l i o n , o b o v e o n d b e l o w , o n d o l e n p o r o r y , l i g h t w e i g h t w o l l enclosure suPPorted bY t h e f r o m e i f s e l f . ( l l l u s t r o t i o n 5 ) T h e p r o b l e m o f e n c l o s i n g c o s l - i n - p l o c e c o n s l r u c f i o n i s b o s i c o l l y l h e s o m e i n l h o t i t r e v o l v e s o r o u n d t h e e n c l o s u r e o f o s t o r y - h e i g h l s e c l i o n b u t l h e w h o l e o P e r o t i o n i s g e n e r o l l y m u c h s l o w e r o n d m o r e c o m P l i c o l e d . ( l l l u s t r o t i o n l 0 l T h e s e i l l u s t r o l e o m e t h o d o f e n c l o s i n g f h e w o r k i n g o r e o s o n d s u g g e s l o s e q u e n c e o f o p e r o l i o n s w h i c h c o n r e d u c e l h e d i r e c l c o s l s of o temporory enclosure. I T € M P O R A R Y R O O F - - r

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STEEI FRAME BUITDING

STAGE 5 wALL CONSTRUCTIOI}I

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-Herets when total enclosure pays off

for one-storey winter building

T H I S S I M P L E E N C T O S U R E wos used on o fhree-story office building in Oilowo fo pro_ t e c l l h e c o n s i r u c f i o n o f o lo<id-beoring woll.

( l l l u s l r o f i o n I 6 l

By A. W. SMITII

. Methods of enclosing toad-bearing walls and single-story conshnction for winter building ls the theme of this month's ar-ticle on the use of enclosures by Mr. A. W. Smith of the Division of Building Reseqrch, NRC. In this, the thirrl of his series for National Builder, ltdr. Smith. says: 'Repeated use of standard sections makes it possible to think in terms of geodesic domes and other forms of alu-minum space frames capable of covering the largest of construction sites.,

The slip-form method of construction. in which a working platform covering

the whole building area is raised on jackrods imbedded in the cast-in-place load-bearing walls, is easily enclosed.

A tgmporary roof can be erected on top of the working platform and con-sequently carried up to roof level as an integral part of fhis platform.

Other methods of bearing-wall con-struction present much greater difficulties unless the building is low enough or narrow enough to be completely enclos_ ed, roof construction and all.

Total enclosure is much more expen-sive in both materials and in heating requirements but repeated use of stand-ard sec.tions makes it possible to think

HERE'S AN EXAMPLE of lhe oir-supporled enclosure. "Monufqcfurers _{of oir-supported rents cloim thot fhey con .roof, on qreo rhe size of o}

in terms of geodesic domes and other forms of aluminum space frames capa-ble of covering the largest of construc-tion sites. Such enclosures can be easily moved as a complete package from one site to another by crane or helicopter and may be light enough to position manually.

A rented framework of standard scafiolding may prove more economical than a temporary timber structure when salvage value and capital outlay are taken into account. In most cases, it is possible to uSe the scafiolding for its normal purpose - that of a working platform for wall construOtion.

The most efficient way of enclosing a given ground area is probably by means of a lamihated arch Structure. For larg-er spans, howwlarg-er, headroom at the edges becomes a limiting factor and for this reason arch eaclosures have proved most successful for foundation work and basement construction (Illustrations 14).

Generally column footings and strip footings require a relatively small amount of concrete in localized areas and so total enclosure of die whole work-ing site is not necessart' until the frame itself is erected. An insulating layer of straq for example, pldced on top of these footings immediately af,ter the concrete has hardened is usually all that is required.

Manufacturers of air-suplrorted tents claim that they can "roof" an area the size of a football ffeld antl they have developed a heating system to go with the air blower that Eaintains the pres-sure differential necessary to support the, whole structure.

At pf,esent, these air-supported tents are made of lightweight plastic - coated fabric and the initial cost is in the region of $6,000 for a structure large enough to enclose a house.

However, the manufacturers of poly-ethylene are developing a similar struc-ture of this material which should sell for approximately $1,000; The covering is removed from the completed building by unzipping standard segments and the whole enclosure can be moved from one site to ailother in a light truck or station wagon.

If the workiug arca is too large to cover with a single enclosure or if the roof system is prefabricated and re-quires little in the way of winter protec-tion, it may be more economical to enclose the bearing'wirll construction by itself. Sometimes a windbreak is all that is necessary although it is easy enough to enclose a short length of scaffolding which can be moved from one position to another along the line of the wall

(Illustration 16).

Insulated forms can be used to main-tain the temperature of heated concrete long enough to prevent frost damage when these forms are finallv removed.

T o p e r m i f l h e e o s y e n t r y o n d e x i l o f r e o d y - m i x l r u c k s , e l c . , t h i s v e h i c u l o r o c c e s s w o s o v o i l o b l e o s r e q u i r e d . l l w o s o b o u f l 5 ' s q u o r e . T h i s i s o n e x l e r i o r v i e w o f l h e h u g e i n o t e d o r c h e n c l o s u r - 2 5 O ' l o n g , 7 0 ' w i d e , 2 0 ' h i g h - u s e d t o p r o l e c t f O l t o w o . ( l l l u s l r o l i o n l 4 ) w o r k o f o s u p e r s o n i c w i n d t u n n e l o l U p l o n d s , A n d t h i s i s h o w i l l o o k e d o n t h e i n r l d e w i l h l h e m e n w o r k i n g n o r m o l l y i n g o o d l i g h t o n d c o m f o r t o b l e l e m p e r o t u r c s d e s P i t e f r o s t o u l s i d e . t t N o t e l h e l o n g i t u d i n o l b r o c i n g u s e d d u r i n g c o n s l r u c t i o n o f t h e e n c l o s u r e u n t i l l h e o r c h J s l r u c l u r e h o d b e e n c o v e r e d o n d o d d i t i o n o l d i o g o n o l b r o c i n g p l o c e d .

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HERE lS AN EXAMPTE of o ploslic-covered lominofed orch slruclure which wos used lo protect fhe construction during winter of o 2 4 ' b y 4 0 ' b u n g o l o w . W h e n f h e r e p l o c e m e n l volue of such o slruclure wos spreod over five houses, il showed lhdt lhe soving in f h e b u i l d e r ' s l o b o r e x o c t l y e q u o l l e d t h e o p e r o l i o n o l c o s l o f l h e e n i l o s u r e : $ 4 0 0 p e r h o u s e . ( l l l u s t r o l i o n l 8 . l

How winter housebuilding can score

by using standard enclosures

In the last of his series of four articles for National Builder on building in winter with the aid of enclosrres, Mr. A. W. Smith of the Dividon of Building Research, l\lRC, deals spe-cifically with housebuilding. And he emphasizes that the type of enclosure used for house building depends on the size and type of the buildefs own operation.

By A. W, SMITH

Division of Buildtng Research, \lRC The number of houses you build in a winter season will have a direct bear-ing on the type of enclosure rnost suit-able to your operation.

When a building is a standard form (like a single family house) which is re-peated many times, it becomeq posqible to think in terms of a standard form of enclosure to shelter it.

The emphasis shifts from material costs and heating costs to erection and transportation costs. There is a balance between low cost, expendable materials and more expensive, longer lasting ones that can be re-used. Labor costs become a greater percentage of the unit cost charged to each job and may warrant the use of mechanical erection equipment.

A laminated timber arch structure whose replacement value was spread over five houses showed that the saving in the builders' labor exactly equaled the operational cost of the enclosure itself - _{$400 per house (See illustration l8).} The cost of erecting and dismantling this enclosure was 60Vo of the unit cost and could have been greatly reduced by slight modification. (fhis, was described in Mr. Smith's article on the DBR study of a bungalow built under a plastic

A . W , S M I T H

-tt-shelter which appeared in the November and December issues, 1958, of Natlonal Builder.)

You will be able to rent these house enclosures

A number of scaffolding distributors and aluminum fabricators are at present developing standard enclosirres specific-ally for house construction. These shciuld be available on a rental basis shortly.

The type of enclosure used for house building depends on the builder's own operation.

Those builders who build only four or five houses in a winter season may prefer to enclose the whole house and do everything, including the painting, within the enclosure.

The larger project builder will usu-ally prefabricate most of his work and may prefer to use the enclosure for the basement and subfloor construction only. Once the furnace is instdlled iir the fin-ished basement, it can be used to heat the prefabricated shell. (See illustration 19.) The larger operator is not so con-cerned about getting his final payments and can often leave the painting and brickwork till spring. Some of these briilders believe they could use a single enclosure ten times during one winter. Keep design loads down

to the needs of the job

As the enclosure is a temporary shel-ter, it would be impractical to use the design loads for snow and wind as they are set ouf in our building codes. The main purpose of the enclosure is to provide a simple shelter at the low-est possible cost and, although it would be easy to build a strong, heavy struc-ture ,that could withstiand any storm, the extra cost of labor and materials would not be warranted for such a tem-porary building, whose effectiveness is determined'by its easy erection and dis-mantling.

It should be possible to design the enclosure for a definite wind speed (say 40 mph) and a definite snow load (say 15 psf) and to make provision for extra bracing at higher wind speeds and for removing extra snow. The figure of 15 psf suggested as a snow load represents a l2-inch fall of wet snow.

During Canada's severe winter, it is not enough to protect the work alone. Such protection merely involves an extra cost for pr<itective materials and has no eftect on the workman's reduced effi-ciency. In any case, the workman himself has a definite limit and will find it im-possible to work whcn exposed to ex-treme temperatures and high winds.

In these circumstances, total enclosure of the working site is essential and can often more than pay for itself with in-creased productivity which reaches maxi-mum levels in a controlled climate.

( A ) P R O J E C T B U I L D E R S T A G E I

/-B A S E M E N T C O N S T R U C T I O N U N D E R L O W A R C H O R D O M E P R E F A B R I C A T E D H O U S E U N I T S A S S E M B L E D I N M I N I M U M T I M E W I T H O U T P R O T E C T I O N STAGE 2 /.TEMPORY r/ ENCLOSURE \ FOR BRTCKWORK ( B ) S M A L L E R B U I L D E R S H E L T E R E N C L O S E S W H O L E H O U S E . L E F T I N P L A C E U N T I L P A I N T I N G A N D B R I C K W O R K A R E F I N I S H E D T H I S D I A G R A M D E M O N S T R A T E S h o w l h e l y p e o f e n c l o s u r e u s e d f o r h o u s e b u i l d i n g d e p e n d s o n t h e b u i l d e r ' s o w n o p e r o l i o n . T h e s m o l l e r b u i l d e r m o y p r e f e r l o e n t l o s e l h e w h o l e h o u s e o n d d o e v e r y l h i n g w i t h i n t h e e n c l o s u r e . T h e p r o i e c t b u i l d e r , p r e f o b r i c o l i n g m o s l w o r k , m o y u s e l h e e n c l o s u r e o n l y f o r b o s e m e n t o n d s u b f l o o r c o n s l r u c l i o n . ( l l l u s t r o l i o n l9 l

, . T O I A L ENCTOSURE of the working sile con oflen more lhon Poy for itself wiih incrmsed p r o d u c l i v i l y , " - s c y s M r . S m i t h , o u t h o r o f l h e s e o r l i c l e s . T h i s i s o n e x o m p l e o f l o l o l e n c l o s u r e u s e d t o p r o l e c l l h e c o n s t r u c l i o n o f q l w o - b o y s e r v i c e s l o t i o n o n C u m b e r l o n d S l r e e l , O l l o w o '