A Potential Stucco Time Bomb is Ticking Away 1998

December 16, 2013


As a BRANZ Accredited Advisor in the Auckland Region, I have come across two situations that give me great concern for the long-term durability and structural integrity of houses built in recent times in Auckland.  A modern trend in architecture with domestic dwellings is to produce an exterior solid plaster stucco finish that is considered superior to the alternatives of a foam backed plaster systems or a high build acrylic system such as Harditex.  The cost of this type of construction certainly reflects a higher cost.

There are two clear systems laid down in the New Zealand Building Code Handbook and Approved Documents Section E2 under Acceptable Solutions for rigid and non-rigid backing systems for solid plaster.  The NZBC is further supported by New Zealand Standard Specifications 3604:1990 Code of Practice for Light Timber Frame Buildings Not Required Specific Design, Appendix G and also New Zealand Standards Specification 4251:1974 for solid plastering and its subsequent amendments.  Alternative solutions can also be submitted to the Territorial Authorities for their judgment as to their suitability of performance under the general guidance of the Code, such a solution can be submitted with a Certificate from a qualified engineer or architect or some other similar qualified person.  This alternative solution will then be considered by the Territorial Authority and given approval to proceed or not.  In this case the plans both clearly indicated the use of either Triple S in one case or alternatively NZS3604:1990 or a “sizalkraft system” which indicates a non-rigid backing.

This asks in the question?  Who becomes responsible for the performance of the exterior sheathing as required in the New Zealand Building Code handbook and documents under Section B2 where on Page 3 and Total 1 exterior wall claddings (Claddings/Sheathing) are required to achieve a 15-year durability.  The writer is not able to give legal opinion but has been advised by the legal advisers of the BIA that the person who designed the alternative solution is responsible alongside of the Territorial Authority for their approval of that system and it may be also fair to say that if a builder, or in this case a plasterer sub contractor, felt that the practice was unsafe and did not acknowledge that, they may also be responsible in a matter of taut.

The writer and other BRANZ Accredited Advisers and Technical Advisers throughout New Zealand are becoming increasingly concerned with the practices that are currently undertaken in solid plastering throughout New Zealand.  The writer and others have viewed failures in the plastering systems regardless of whether they are rigid or non-rigid systems.  Equally there are some well-executed plaster finishes.  Failures are often caused by simply not following the requirements of curing, correct fixing of reinforcing, thicknesses of coats, the required standard of mixing of cement plasters and the correct laying out of movement or control joints.  These examples have seen total failures of delamination of plastering surfaces within months, if not early years of their initial construction.

In this case however, the writer wants to concentrate on practices that he has seen in two locations in Auckland of using plaster on a non-rigid backing system and comments by a well-regarded plasterer that “this is what everyone is doing in Auckland currently”.  To understand the concerns that the writer has it must be noted firstly that the two houses with this system inspected, both had reasonably good quality of plastering to the exterior with some signs of minor failure only.  The writer was fortunate in both cases that owners of both properties had drilled holes in the plaster to take an outlet hose for their clothes dryers through the laundry walls.  In both cases, it was found that the plaster was fixed hard against building paper that was itself fixed directly onto timber studs.  These studs would normally be treated to the standard H1 Grade common for light timber frame construction (to protect against insect infestation).  This fixing of the plaster directly onto black breather paper, and that paper fixed directly onto the studs, is incorrect based upon the documents as stated above.

On pages 6, 7 and 8 of the New Zealand Building Code Handbook and Approved Document, under Section 2.3.4 – Non Rigid Backings and 2.4 – Building Paper it gives clear explanation to the requirements and also in Figure 3 on Page 7 it gives a clear section detailing the correct procedure for Non-Rigid Backing.  That procedure is as follows:

Firstly, the type of building paper should comply with Paragraph 4.2 or alternatively be a waterproof building paper complying with B3521 or finally other suitable material complying with the NZS4251.  In Figure 3, noted under Plan B Non Rigid Backing the following details are shown: Building paper, a 25 millimetre batten and building paper, then the normal pattern of reinforcement and plaster as is required under NZS4251.  In Appendix G of NZS3604 it also gives a clear detail similar to that described on Page 7 of Section E2 of the Building Code Handbook.  In this, it further states under G3.5 – ‘Non rigid backing shall be attached to 25 mm battens treated to H3 of MP3640 fixed vertically to faces of the studs over sheathing (or cladding underlay) required by 8.7.  In G5.1 it further states that ‘Where non-rigid backing is used, the cavity between the backing and the building paper shall be ventilated to the outside air with top and bottom openings.  The bottom opening shall serve also as weep holes to drain the moisture to the outside (this matter of ventilation and drainage is of paramount importance in this article).  ‘In G5.2 it further states that the cavity shall be sealed off from the roof space and from sub-floor space.’

In line with the comments above, the concern the writer has, is that a stucco finish that does not have this cavity when using a non-rigid system, that is the plaster hard against the building paper and studs, with the required standards of the Building Code, especially where it states the following in Section 7 of the Building Act.

(1) All building work shall comply with the Building Code to the extent required by this Act whether or not a Building Consent is required in respect of that building work.

In this case, the Code has not been met and yet Code of Compliance Certificates for both properties were issued by the respective Territorial Authorities.

As Solicitors taking normal care there is little doubt that one of the requirements you would have for people purchasing new homes or even recently built existing homes that they have a Code of Compliance Certificate.  However, here are two specific incidents where properties have been given a Code of Compliance Certificate and that there are, in both properties, potential time bombs.

Please note that both jobs had a reasonable standard of finish, the integrity of the plaster seen through the core sample was good, in both places there was some minor cracking and both properties had been painted with what appeared to be a good standard of acrylic paint.

So why the concern about the breaking of the rules?  The answer is simple, when moisture and food (namely timber or even building paper) and air come together over a period of time, fungal rot can develop.  This fungal rot will destroy the structural integrity of the framing that is attacks.  The writer has viewed a property where a conservatory had to be demolished because water was leaking in.  Fungal rot had developed within a five-year period of the dwelling being first constructed.  Behind the Gibraltar board was veritable forest of different varieties of fungi.  The building paper itself had been eaten to a point where it was tissue thin and brittle.  There was clear evidence on both sides of it of the fungal fibres growing in a web like framework.  The strength of the timber was eaten away be the insidious and ferocious eating habits of the fungi.

There are many that will argue that the practice of applying stucco directly to building paper and onto the studs has been around for years, therefore why the fuss?  Let’s just consider that many building products that are applied to the exterior of dwellings are constructed in factory conditions with every effort made to make the product perform to very tight specifications.  Alternatively other products are made, such as timber weatherboards, where the grading of the timber must be of such a standard that it does not allow the ingress of moisture (hence the failure of “Knoty” Cedar to comply with these types of conditions).  Plaster mixed on a site however has not got factory-controlled conditions and the accuracy of measure is more the care of the plasterer and his labourer than a factory controlled mixing condition.  The variation of curing environments is reflected in the daily changes of the weather pattern.  Given this it therefore would be very difficult to accept that the plaster surface could have the same integrity as a factory produced product.  Therefore it is quite correct to assume that plaster surfaces could crack and leaking could occur, and thus design for this possibility.

The Code for Non-Rigid Backing specifically sets out to prevent the danger of trapped moisture against timber studwork that is not treated to a level that it can prevent this type of fungal attack or rot.  It gives a 25 millimetre cavity with vents top and bottom that allows air movement to remove any moisture that has got through either from the inside or more opportunity from the outside with cracks in the paint work and plaster finish.  It allows for the bottom venting holes to act as weep holes to allow any water to drain away.  It further has 25 millimetre battens that are treated to an H3 standard that will not rot.  This situation is designed to prevent the likely attack of fungi rot to a timber frame structure.  In other words it is an insurance scheme to cover leaks through the plaster system.

It must also be noted that plaster dwellings for a variety of reasons from a lack of good control joints, ground movement, poor curling, attack over long period by the sun, slow breakdown in the strength of the plaster, poor plaster consistency, or simply a weak point can crack as stated previously.  Even if the surface is painted with a high quality acrylic paint it is most probable that the crack will form right through the painted surface.  This crack will allow moisture in and this is what the time bomb is all about.  This moisture, if allowed to sit behind the plaster wall surface against the building paper and even finding its way into the timber framing, will, in all probability, start the formation of fungal rot and thereby attack the integral structure of a dwelling.  It would also be fair to say that this scenario might not happen in all cases, however the Code sets out, as well as does the New Zealand Standard Specifications to prevent the likelihood or the chance of it occurring.  This is a method of stucco practice by plasterers common in Auckland today.  It completely contravenes the New Zealand Building Code and also sets up the scenario of houses in Auckland today that could have potential failures, with forms of fungal rot already growing in their wall frames.  The writer knows of a thirty-year dwelling where massive damage was caused by fungal rot.  The walls were stucco and were hard against the studs without a vented cavity.

Fungal rot it not only dangerous to the structure in that it weakens it, it is also potentially a health hazard for the occupants of these homes especially those who have allergy or asthma problems and further the moisture ingress is likely to increase mould growths in other parts of the home.

As Solicitors, you are carrying out your duty of care in checking that the Code of Compliance for the dwelling is in place prior to purchase.  Unfortunately, there are those that should deliver a sound house, bound by the Building Code, to your clients that are not doing so.  In discussing this with the BIA’s legal advisers, it is clear that different scenarios can exist.  Does the client have a contract with the builder?  Therefore the builder, under the terms of that contract is responsible for these matters and further is the plasterer also responsible, not from contractual obligations by taut.  It also brings out the responsibility of the Territorial Authorities, especially where in both these cases, the vendors purchased the properties from a builder who was the owner and thus responsible directly to complying with the Code.  It is the responsibility of the Territorial Authority who are required to act with reasonable care when it comes to checking dwellings.  The writer does not attempt to try and spell out or look at the full extent of legal implications, as this is not his field, however the writer does suggest that before a house is purchased, that has been constructed with a stucco surface, that the plans and specifications are perused and the Council documents are checked to see that they have undertaken inspections, including the exterior cladding, and that these groups, namely the builders, solid plasterers and Territorial Authorities give an undertaking that the house has been built to conform with the correct Codes.  If no undertaking is forthcoming then it may be a matter of requiring a core sample to be taken of the plaster structure to check that it has been built to conform.  When the purchaser has the opportunity to purchase or arrange for purchase of the dwelling, before the exterior systems have been fixed on site, it is definitely suggested that they require the builder and or ownership of the property being built to meet the standard of the New Zealand Building Code and have independent people confirm that these standards have been met.  The decision for doing this is entirely in yours and your client’s hands.  The fact that this poor practice has occurred in dwellings and that a good system has been devised in the relevant Codes and Standards, that does overcome the likelihood of future problems does ask questions as whether those currently building are following the NZBC or rather simply ignoring its requirements.  It also asks the question of the Territorial Authorities as to why this blatant code breaking is occurring.

You may also like

Presenting Our New Prendos Associates

Presenting Our New Prendos Associates

Case Study: Conspec Structural Upgrade

Case Study: Conspec Structural Upgrade

Exploring the Benefits and Costs of Mass Timber Solutions

Exploring the Benefits and Costs of Mass Timber Solutions

Meet with us

If you’d like to talk to us about an existing building, new build project or future property venture, get in touch. We’d love to find out more about your objectives and help you achieve the best possible property solution.

Contact Us.

0800 773 636)

[email protected]

Business Hours.
9am - 5pm

  • This field is for validation purposes and should be left unchanged.

Copyright 2022, All Right Reserved

Prendos New Zealand Limited