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Concrete Construction Overcomes Leak Problems

Cement & Concrete Association of New Zealand

Media Release 21 November 2001

Concrete Construction Overcomes Leak Problems

Beat the rot, build in concrete – that’s one solution to the problem of leaks being experienced in some new Mediterranean style homes according to the Chief Executive of the Cement and Concrete Association, David Gray.

The issue of weather-tightness has attracted considerable attention in recent months with a Building Industry Association commissioned study showing that houses built in the last ten years may have significantly more cladding defects that older homes. If these textured coatings or modified plaster finishes, which have become very popular, are not correctly detailed and constructed, leaks may develop causing mould and structural damage including rotting timber framing, damage to floorings and interior wall lining, and wet insulation materials.

Mr Gray says these problems have occurred primarily in the residential sector where timber construction is dominant. In the commercial sector where concrete is much more prevalent as a construction material, leak problems are rare.

He says ironically while many of these Mediterranean style houses are being designed to emulate the massive construction of concrete, in New Zealand they are being built using timber - spaced timber studs with a thin cladding of stucco acrylic plaster on rigid board. As a result, because they are not built in concrete they loose the advantages offered by concrete.

“Concrete is not a material that will rot even if it is wet for long periods. Solid concrete construction is what it says it is - solid. It doesn’t have a cavity that can fill up with water and it is strong. It has high impact resistance unlike the polystyrene claddings which have been likened to chilli bin construction.”

Mr Gray says concrete houses generally perform well in terms of weather-tightness due, in large part, to the levels of quality that can be achieved with concrete construction. Most precast concrete panel systems are produced in factory conditions and a number of these systems on the market have been developed and tested overseas, often in harsher environments than New Zealand. These systems don’t leave any gaps for problems to develop, he says.

Additionally fewer trades are involved in the construction of a completed concrete wall which means there are fewer responsibility and accountability gaps. This lack of a clear accountability chain has been identified as contributing to the leak problem.

Weather-tightness problems begin most frequently at openings and penetrations. Concrete, generally more massive and thicker than other wall systems, allows the vulnerable details at doors and windows to be sheltered from the weather. Integral stepped profiles, against which frames are fitted, are also a feature of concrete construction not occurring in other construction systems.

If problems do occur and water gets through the outer cladding, concrete can tolerate moisture much better than most other construction materials.

Mr Gray says there has been resistance to concrete construction in the residential market because of a perception that concrete is expensive. However, a new publication due to be released by the Cement & Concrete Association early next year will address that misconception. Building Comfortable Homes follows earlier CCANZ publications on the design of concrete homes and focuses on the different structural systems suitable for the residential market in the $150,000-$250,000 bracket.

Mr Gray says building in concrete is getting easier all the time and the past five years have seen significant market growth for concrete as people appreciate the advantages offered by concrete. These include:
- increased fire resistance;
- reduced sound transmission;
- thermal comfort and efficiency – concrete homes are warm in winter and cool in summer
- a healthy living environment particularly for allergy sensitive people – concrete does not harbour dust mites or other allergens;
- it is a locally made product;
- it is strong and durable.

In all cases, irrespective of construction system, weather-tightness can be improved through:
- careful consideration of environmental conditions;
- respect for the limitations of particular materials;
- careful detailing at openings, including the proper use of flashings;
- protection of vulnerable areas such as the tops of walls. Parapet walls, which are part of the Mediterranean look, have a statistically higher rate of weather-tightness problems than any wall protected by an overhang.


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