Real risks associated with over-cladding


We both have a background as builders and we share Mike Fox’s concern with the cost of recladding buildings.

We are also both members of the New Zealand Institute of Building Surveyors. Members of this organisation were instrumental in the changes from untreated back to treated framing, and from direct fix to cavity construction.

Unfortunately there are real risks associated with over-cladding, which did not get a fair airing in Mr Fox’s article. There is no dispute over the time period in question — all monolithic-clad houses, especially those built from 1993 to 2005 tend to be stigmatised, especially in the main centres.

Mr Fox expresses his opinion that “tens of thousands” of these homes are, in fact, sound, but offers nothing to back up this claim. We all know by now that “no sign of moisture ingress” does not equate with “no problem”.

Part of the explanation for the stigma is that many of these houses have failed to perform despite no outward signs, and that creates doubt regarding the rest. It is worth looking at what has gone wrong, as this provides the backdrop to considering the merits and risks of over-cladding similar homes.

Some background to the problem

At the beginning of the decade in question, treatment applied to pine framing was undergoing significant changes. Prior to 1993, green, or wet, Radiata pine was well treated with boron, which provided not only protection against borer and other such insects, but also some protection against fungal decay.

Shortly after the introduction of the first Building Act, the new building code requirement for framing to be dry before linings were installed was one trigger for change.

Builders were soon sick of using blow dryers so merchants started supplying kiln-dried framing for them — but most of the boron came out with the water during the drying process.

The NZ Standard was amended to allow lower levels of boron in kiln-dried pine that were intended only to prevent insect attack, or Permethrin could be added after drying. This also satisfied the requirement to stop insects eating the framing but, unfortunately, added no protection against fungal decay.

So houses were being built with “H1” treated framing which was nearly or equally as vulnerable to fungal decay as untreated pine.

Coincidentally, the export market of Radiata pine took off, resulting in a shortage at home, which the Douglas fir suppliers were happy to fill — even with sapwood, which lacks the natural protection Douglas fir is famous for, making it also more vulnerable to fungal decay.

Timber in houses at this time could come from a wide variety of sources — a merchant would have one supplier for wall framing, another for lintels, another for joists, another for roof trusses and so on.

And substitution was common, especially after kiln dried “chemical-free” timber was sanctioned in 1995. So while treated timber might be specified and even ordered, frequently, the new kiln-dried untreated timber was used instead.

This means that while some framing in a house built during this era might be treated, that is no guarantee it all is.

Then there is the building paper. At this time most claddings were still installed over kraft-based product — the black stuff. This is an ideal medium for growing moulds as it contains cellulose, a basic food for many moulds and all decay fungi.

When monolithic claddings came back into fashion in the mid-1980s, there was very little residual knowledge (from the 1950s) of previous problems and how to do this type of cladding well, and the result was some very poor weathertightness detailing.

BRANZ responded in 1996 with the Good Stucco Practice Guide, but this, too, contained some poor detailing, and there was no requirement for a cavity between the stucco and the framing until 2005.

Plastered polystyrene (EIFS) and plastered fibre cement detailing improved dramatically during the 10 years in question, but it wasn’t until around 2004/05 that the general move to cavities was completed.

Specific problems that can arise with over-cladding

If the over-cladding is successful, the old black building paper behind the original cladding will dry out. Some of the moulds which have been growing on the previously wet building paper are potentially harmful, and drying out releases their spores. Once airborne, they can be carried inside, creating health problems.

Ground level issues are common, and in many cases the most efficient solution is to raise the bottom plate on a new concrete nib contained within the wall.

The alternatives commonly used when over-cladding include lowering the ground outside, or installing surface drains which tend to be less satisfactory.

In particular, surface drains directly under the new cladding are generally a bad idea for several reasons — they are maintenance intensive and water ponds when cleaning is not done frequently.

Cavities are designed for rapid air movement and water vapour is drawn up inside, condensing at a higher level and potentially creating new problems. 

In addition, if the new cladding stops close to the grill on top of the surface drain, water inevitably bounces up off the grill and can soak into the new work.

Perhaps the most obvious risk with over-cladding is that until technology delivers a machine that can fully disclose what is hidden within the walls, we will never know exactly what we are covering up — and experience has shown there can be many hidden problems which are not directly related to weathertightness failures, on top of damage due to leaks, which is not discovered until all the cladding comes off.

Structural issues are only too common in houses built during that era — structural steel without bolts, bracing not tied down, beams not properly supported, missing lintels, missing insulation, electrical mistakes — the list is endless.

Of course there were good builders, and not all houses built then have these problems. In particular, monolithically-clad houses which are only one storey high, on protected sites, with wide protecting roofs all around are obviously less likely to have weathertightness-related problems than a house with two or more storeys, enclosed decks and no eaves on an exposed site.

But, again, until you take the cladding off, in all cases there is a whole lot of unknowns.

With respect to the money saved, there is no doubt that it is cheaper to simply over-clad.

Actually, the short-term savings should be significant as you are not replacing any decayed timber, not treating the rest to protect it going forward, nor confirming and/or bringing up to code the structure, bracing, insulation, electrical etc.

Longer term, the savings are less certain. Depending on how the junctions between the cladding and joinery, cladding and roof, and ground level issues are detailed, over-cladding may not solve all the weathertightness problems.

Even if successful, given all the questions which remain unanswered regarding the condition of the structural components, you have to wonder — how much of the stigma has actually been removed?

And then there are the risks associated with the law. Unfortunately, the Government which passed the first Building Act in 1991 enshrined litigation as an acceptable way to resolve construction disputes, and as a society we have embraced this concept wholeheartedly, much to the delight of legions of lawyers and their experts.

Mr Fox complains that councils are risk averse. Who can blame them, considering how often they have been sued?

Until the law regarding joint and several liability is changed and New Zealand embraces a fully effective home warranty scheme like the British one — see — everyone involved, including builders, inspectors, experts, conveyancing lawyers and councils alike, cannot afford to forget how easily they can be taken to court, and the many business which have been bankrupted should serve as a warning.

If (or when) problems appear after over-cladding, litigation will follow as night follows day, and everyone involved will have to justify the limited approach that was taken.

“Saving money” is no defence if the works have not met the performance requirements of the building code.

One possibility which has always existed under the Building Act is to reduce the expected life of the proposed work. While the default is 50 years, there is nothing to stop an applicant using a lower number.

If the over-cladding is only meant to protect the existing building for 10 or 15 years, before the building is fully reclad or completely rebuilt, that would reduce the risk considerably, but the stigma and loss of value may remain.

And now there are over-clad jobs that have failed, with everyone including the unfortunate builder being sued. And all those involved, including the owners, now regret the (very) short term solution. The old adage applies — better to be safe than sorry.