UPDATING OF BUILDING CODE NEEDED

Press, Volume CXIV, Issue 33614, 16 August 1974, Page 7

UPDATING OF BUILDING CODE NEEDED

Just a year after the big snow of August last year a group of interested people gathered at the New Zealand Agricultural Engineering Institute at Lincoln last week to consider a report prepared by Mr G. C. Pinnell, an assistant engineer with the Ministry’ of Agriculture and Fisheries, in which he proposes amendments to the New Zealand standard model building by-laws for determining design snow loadings for buildings.

Mr Pinnell said in the report that the damage caused to farm buildings in Canterbury had prompted a closer look at the capacity of buildings to withstand snow loads. The current code required a design snow density which was less than typical of New Zealand values and contained no information on design snow depths, but new data had since become available. He noted that under existing and’ draft pro-

visions, where snow was prevalent, roofs should be designed for snow loads assessed at 61b per sq. ft for each foot of fresh snow, the design depth of snow being based on local records and to the approval of tire engineer. But Mr Pinnell said that the information on snow densities was quite erroneous and related only to high altitude continental snow conditions.

The low densities associated with this type of snow were extremely rare in New Zealand and for snowfalls up to an altitude of 1000 metres of a sufficient depth to cause damage the density was about twice the code value.

Also there was no information as to the design snow loadings to be used in a particular region for a particular shape of building.

Mr Pinnell has proposed that the design density of snow should be increased to about double the present figure, which he says is to “the best of our knowledge” typical of New Zealand conditions.

He has also proposed that more information be included in the code relative to the design for snow loadings. This would include such factors as the likely variation in snow loads between regions, and in his report Mr Pinnell includes a map showing the open-

field snow load in New Zealand based on the maximum snow depth to be expected once in 50 years and an average snow density.

Mr A. I. Tomlinson, a climatologist of the Meteorological Service, noted that the map showing maximum snow depth to be expected once in 50 years represented the best estimates available from all the data accumulated by the service since the middle of last century. There was some discussion as to how this information could best be presented so as to be used in local body regions. Mr Pinnell said that other information which should be included would be the influence of the shape of the building and also the effect of shelter belts or neighbouring buildings. In areas where there were obstructions to wind speed, such as shelter belts, which caused snow drifts, Mr Pinnell said that there could be up to three times the snow load.

Mr G. W. Butcher. 8 consulting engineer, of Wellington, who is deputy-chairman of the loadings committee of the Standards Association of New Zealand, said that this Investigation had come at an appropriate time. The draft code had been sent out last year for comment, he said. The second part of this dealt with dead and live loads, with a very’ small paragraph about snow.

They were now getting to the stage where they would be looking at part 2, and the Lincoln investigation would be a basis for looking at the snow provisions in the code. The comments relating to snow had varied from ones proposing that the code be left as it was to others that it was completely inadequate and needed much more detailed provisions. "We do need much better snow loading provisions,” said Mr Butcher. Mr Pinnell told the meeting that to construct a 60ft implement shed with three closed sides for two times and a half the present snow load requirement would increase the cost by about 5 per cent. In proposing a vote of thanks to Mr Pinnell and others who had done a lot of work on this project, Mr D. G. Thomson, the Ashburton County engineer, said that Mr Pinnell’s remarks on the extra cost warranted publicity when the situation could arise where manufacturers faced with having to erect stronger buildings would tell the farmer that the county was putting the cost up.

The chairman, Mr I. Calvert, said that the documents would be forwarded to the Standards Association with a request that they consider some action on snow loadings.