Publisher’s version / Version de l'éditeur:
Engineering News-Record, 171, 25, pp. 58-61, 1964-02-01
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In winter: under-cover construction speeds projects
Legget, R. F.
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CANADA
D I V I S I O N O F B U I L D I N G R E S E A R C H
IN WINTER:
UNDER.
COVER
CONSTRUCTION
SPEEDS
PROJECTS
ROBERT
LEGGET
A N A L Y Z E I I
R E P R I N T E D F R O M E N G I N E E R I N G N E W S . R E C O R D , V O L . I 7 t , N O . 2 5 , D E C E M B E R 1 9 . 1 9 6 3 , P . 5 A - 6 1 . T E C H N I C A L P A P E R N O . 1 7 I O F T H ED I V I S I O N O F B U I L D I N G R E S E A R C H
BY
F.
F U R T H E R D E T A I L S O F S O M E O F W I L L B E F O U N D I N C A N A D I A N C O N S T R U C T I O N A N D W H I C H T H E R E C E N T B U I L D I N G J O B S M E N T I O N E D I N T H I S A R T I C L E B U I L D E R F O R O C T O B E R 1 9 6 3 W H I C H F E A T U R E S W I N T E R l s c o M M E N D E D T o r H o s E l N T E R E r t r E o e y o e R / N n c .18:JG
OTTAWA
F E B R U A R Y I 9 6 4
N R C 7 A s 2 P R I C E I O C E N T Ss6 //6,25
like o greenhouse, plostic enclosure keeps building site comforloble in cold weolher, so work moves
By Robert F. legget
Winter bLrilding is paying off in Can-ada. Cost figures shorv that the slight extra cost for cold-weather provisions is nrorc thnlr offset bl tirne s:rved :rnd reduced interest on cauital.
Wide acloption of'nerv techniques and the stimulus of a nationu,ide edu-cational campaign spur a steadv advance in the :rmount of buildine eacl'r u,inter. \\/ork ou horrsing, nrultistorv buildings. bridges, danrs and excavation norv goes on despite freezing tenrperatures. This is having substantial influencc on sczl-sonal unenplovment in Canada.
Most significant of the ncrv tech-niques is nse of tenrporan' shelters of strong, lightu,eight, transparent plastic sheets. This rnaterial can ofterr be sal-vaged, and its transparencv abets heat-ing of errclosed spaces bv solnr radintiorr. \\rith modern portable gas and oil-fired heating units, working conditions rvithin rvinter enclosures can be made com-fortable at a reasonablv lorv cost.
Mr. Legget is director, Division of Bvilding Reseorch, Notionql Reseorch Council of Conodo, Oltowrr, Ont.
Such practices continued on many rna jor Canadian construction projects during the war years. Much of the great Shipsh:rrv l-rnillion-hp project in Que-bec vvas constructed in 1941-42, during one of the most severe winters.
o Cheap enclosure is the key-ln the last l0 vears. Canada has made a con-certed drive to increase the volume of r.vinter building. During tl-ris period, use of enclosures to protect construction oper:rtions has spre'ad rapidly.
Conplete enclosure, not only of a site but :rlso the entire building, how-ever, is not often possible in general buildine construction. But Robert N{c-Alpine -Ltd., Toronto general contrac-tor, used this method to meet :rn eight-week sclredule for construction of a 22,-000-sq-ft, single-storv plant at Bramp-ton, C)nt.
Work on the 129 x 161-ft structure started last December. While the sirn-ole steel frame was erected and the inetal roof deck welded, carpenters framed 14 x l6-ft panels of 2 x 4s for the enclosure, designed for reuse on a later iob. The panels were dowelled into the ground around the steel frarne
December 19, 1963
All rights rclerved. Printad in U. S. A.
In \ffinter: Under-C over Construction
o It started way back-Building inwin-ter is not nerv for Canadians. Records show that the first bridge to be built in eastern Czrnada (in 1826) was con-structed during an unusuallv severe win-tcr rrrrd tn,rsotirt rvns laid undcr cot'er.
In the 1920's, a multistory office building in 1\4ontreal rvas completelv constructed under cover. Winter build-ing of large civil engirieerbuild-ing works was thcn begirrning. A notable hvdroelec-tric plant in northeastern C)ntario, tl.re Uppbr Notch plant on the Montreal River. u'as completed in l9l0 after 75% of all rnasi concrete on the job had been placed at subfreezing temper-rtures. Sorne concrete rvas olaced at a lorv tenrperature of -40F. All concrcte rvas heated at the mixing plant and ternDorirrv shelters, covered lvitlr tar-pauiins and heated with coke salaman-ilers, rvere used for all structures.
All the mass concrete for one of the most notable and beautiful bridses in u'cstern Canrda, the seven-span, con-crete-arch Broadwal' Bridge across the South Saskatchewan River at Saskatoon, rvas placed during one of western Can-ada's most severe winters (1912). The bridge is in perfect condition today.
R E P R I N T E D F R O l , l E N G I N E E R I N G N E W S - R E C O R D Copyrighf 1953 ilcGrow-Hill Publishing Conpony, Inc.
Under o plostic orch, excovslion goes on, free of snow.
foster thqn
usuol.
Sp"eds Projects
and covered with polyethylene sheet toenclose the stnrcture completelv. Three portable heaters kept the inside at a comfortable temperature.
Sixteen men then comoleted the block walls within five davs.^and finish-ing work proceeded without delay. Cost of the temporary enclosure, not allowing for salvage value (for all of it could be used on other jobs) was $2,000.
o Two enclosure concepts-A contrast between extreme approaches to enclo-sure design for winter building was pro-vided last winter in Winnipeg, Man., renowned for its bitter winters. One contractor used an enclosed exterior working platform, which he moved from story to story. Another completely en-closed a six-story building in a tempo-rary shelter.
In walling the steel frame of the eight-story Wheat Board Building, Peter Leitch Contractors developed an enclosed swinging scaffold, supported by steel cables from outriggers at the roof of the building. The working platform could be moved from floor to floor by operating hoisting units at the platform level. The platform was completely
en-closed with polyethylene and heated to permit masonry work and glazing throuehout the winter.
Foi the Credit Foncier building, also in Winnipeg, Baert Construction Co., Ltd., completely enclosed the six-story reinforced concrete frame with polv-ethylene and wood-fiber board. Coil-creting proceeded without delay throughout the winter, with workmen operating in shirt-sleeve comfort. o Big enclosures-Some temporary structures are so large that they are themselves noteworthy. Bowstring trusses of glue-laminated timber, for ex-ample, supported a plastic-sheet roof for the temporary structures erected by Commonwealth Construction Co.. Ltd.. for a l0-story nurses residence at Foot-hills General Hospital, near Calgary, Al-berta. Commonwealth estimates that the actual cost of such temDorary shel-ter adds l0 cents per sq ft t6 the-build-ing costs. Against this can be set the gain in productivity arising from the comfortable workins conditions and the savings in overheadcosts due to earlier completion of a project.
As with all construction methods, use
Bridge work proceeds, housed from obutment to qbulment.
TRANSTUCENT ENCTOSURE, three stories high, permits finishing work in a building.
of lightweight enclosures for winter building erection sometimes leads to unexpected results. For a four-story ex-tension of Qu'Appellc Hall at thc Urri-versitv of Saskatchewan durins the wirr-ter oi 1962, Poole Construc"tion Co., Ltd., completely enclosed the rein-forced concrete frame with a 6-mil-plastic-covered lurnber frarrework, 60 x 130 ft by 40 ft high, and capped it with a tarpaulin roof. Temperatures in the enclosure were keDt between 50 to 60F' with heat from steam fronr thc univcr-sity's heating plant. As a result, snow melted on the roof and froze later at colder air temperatures. T'he rveight of the ice thus formed provided necded stability under 55-mph-winds.
o Moving shelter-In the New Bruns-wick port, Saint fohn, owner-builder fames A. Robar, to erect a six-storv apartment building with 54 units, buift a one-story-high temporary enclosure of well braced lumber, 90 x 90 ft in plan. A crew iacked it up 4 x 4 wood posts as a complete unit from floor to floor as the concrete frame advanced. Only four men working three hours rvere needed for a lift.
Heating was with an oil-fired boiler and four hot-water unit heaters. Solar heat alone, on sunnv davs. raised the temperature within'the' polyethylene sheeted enclosure as high as 60F. The shelter withstood winds-up to 65 mph. Mr. Robar estimated that his firm would gain $35,000 extra in rental reve-nue by having his apartments ready earlier. Although building costs were slightly higher than normal because of the special shelter, the saving in over-head costs ofiset the extra costs. o Winter earthmoving-Earthwork, too, is carried out in winter in Canada. but sometimes it is limited to cuts. Winter earthwork construction at the South Saskatchewan River Dam, for example,
has been confined generally to excava-tions for embankment foundaexcava-tions and cutofts. Materials excavated, shale and wet clav overburden. were hauled to waste oi to stability berms at extremi-ties of the embankment.
Frost often assisted by providing bet-ter footing and traction. It allowed ex-cavations to be made with scrapers, whereas draglines were needed in sum-rner. But excavators had to loosen the frozen material by ripping prior to ex-c:rvating.
Placing of compacted embankment n.raterials usuallv has been conFned to frost-free periods from April I to Oc-tober 31. Select impervious material has not been placed in the embankment during frcezing weather, whereas some granular materials have been, with sat-isfactory results. Generallv, when the temperature falls below 28F, it has been impossible to obtain relative densities in excess of 50Vo with the normal sands and gravels encountered at the site.
For the river diversion scheduled for this winter, about 500,000 cu yd of ex-cavation will be required. Of this amount, 360,000 cu vd will be granu-lar material that will be placed in 6-in. lifts in the closure section of the coffer-dam in fanuary and February. The bal-ance of ihls w6tt will consisl of remov-ing plugs, and buildremov-ing closure dikes. o Planning is essential-Canadian expe-rience confirms that the key to success in winter building is adequ-ate prelimi-nary planning. One example is a recent project in Regina, Sask. The new head office buildine of the Saskatchewan Power Coqp.,-a l3-story, gl7-million project, had the steel for five floors erected when the prairie winter arrived. The general contractor, Commonwealth Construction Co., Ltd., decided to "work downward," to finish the ground floor and the large basement before the upper stories.
STORY-HIGH SHETTER is iacked up on
In this finished space, subcontractors set up suitably heated workhops and most bf the pipe and ductwork ior the entire building was precut before spring. With the turn in the weather, steelwork was completed and the entire building closed in before the second winter. Bv that time. services had been completed in the first five stories. Win-dows were temporarily closed with poly-ethylene sheet and then glazed from the inside as part of the second winter's operations. All extra costs were said to have been more than ofiset by savings from continuity of work and'speeding the iob.
o Things to watch for-Building during the winter does present some unusual hazards. One of the most important of these is the possibility of frost heaval of soils beneath buildings. Several cases occurred in Canada when base. ments of buildings under construction were not properly heated. Every pre-caution must always be taken to insure that soil beneath any structure being built during subfreezing conditions does not fieeze.
Another hazard is the possibility of freshly placed concrete mortar freezing due to failure of temporary heating or of the enclosure. Damage also can be done to other sensitive iraterials. such as paint and bitumens. Thus, prelimi-nary planning is vital to ascertain that extra heating units are always available. In addition, temporary structures must be properly designed to withstand win-ter wind and snow loads.
High concentrations of carbon di-oxide from unvented heaters will dam-age the surface of freshly placed con-crete. This can be prevented by proper ventilation. Dampness during concret-ing and plasterconcret-ing is a more serious danger. Damage can result from freea ing of condensation. This hazard, too, can be avoided with ventilation.
wood posts as work proceeds upward. With temporary heaters, the hazard of fires on construction is unusually se-rious. But again, proper preliminary planning of fire-fighting equipment and
fire-prevention measures can insure safety.
o Cost experience-Costs of temporary enclosures and heating are a relatively minor part of total construction cost. A recent survey by the Canadian Con-struction Association of over 100 con-tractors showed that the average extra cost of winter construction rans;d from a b o u t 0 . 7 5 t o l L V o , d e p e n d i n f o n size of contract. But the extia revenue from earlier completion far more than ofiset the extra coit.
Studies carried out by the Division of Building Research of the National Re-search Council of Canada (DBR) of homebuilding costs in winter in eastern Canada indicated a total cost of 9850 for a temporary enclosure. The cost av. eraged $400 per house after enclosure re-use for five structures. Because of the comfortable workine conditions- actual construction cost o'f each house was over $400 less than normal. So, the temporary enclosure for winter work more than paid for itself.
In Hull, Quebec, a contractor erected two almost identical schools, one in summer, one in winter. The additional cost of the winter job was $4,800, or ?% of the total building cost, but it was finished four months ahead of the original schedule, because of the excel-lent working conditions provided bv the temporary enclosure.
In early studies of light temporary enclosures, DBR erected a small experi-mental structure in Ottawa and kept careful records of its performance. The effect of solar radiation was notable. No extra internal heat was needed on many winter days to majntain comfortable working conditions inside. DBR gave the results of this experiment to local
PIASTIC cover over site for a house permits it to be built in cold weather. builders and continued experiments on
larger jobs. There still remain many questions that call for research, and work in these fields is proceeding in Canada.
o Winter-construction promof ion-Much of the recent advance in winter construction throughout Canada and the corresponding reduction in seasonal unemployment has resulted from the work of the National foint Committee on Wintertime Construction. This body includes representatives from eight national associations representing the construction industry, buyers of construction, designers, labor, and three agencies of the federal government. Act-ing as an advisory body to the govern-ment, it encourages and coordinates pro-motion of winter construction.
Most of the committee's recommen-dations have been adopted, in whole or in part, by the federal government. These include a Municipal Winter Works Incentive Program.
As a further eftort Io promote winter
construction in the residential field, the government recently instituted a "win-ter bonus" scheme. The Special Serv-ices Branch of the Department of La-bour will pay $500 for "each dwelling unit in a residential structure substanti-ally completed during the winter months." It is too earlv vet to antici-pate the efiect of the iclieme but re-action in the homebuilding industry is favorable.
Much resistance to wiirter construc-tion has come from owners, some of whom have the idea that such construc-tion has poorer quality. Great efiorts bave been made to counter this wrong impression.
To assist, DBR has prepared two l6-mm films, "It Can be Done" and "House Building in Winter", to show how winter constrlction is done and how it benefits the economy. These films are loaned to anvone interested. DBR also has prepared a pocket pam-phlet, Wintertime Construction, and a bibliography of over 300 items on worldwide practice.
