Comments on risk of flat roof with internal gutter

It is no doubt that flat roof incorporating internal gutters is regarded as a high risk design feature.

The economic risk and return theory is generally applied to building design as well. While risk of leaking is higher, flat roof can often gain higher usage of limited building platform, achieve a better view, achieve desired exterior looking, hide unsighted features, bring more light into interior space and so on.

As long as well designed, well built and well maintained, just as any other exterior features, flat roof with internal gutter can be well performed or even out-performing many other type of roofs. It is problematic only when either design, or construction or maintenance side has got any problems, such as no consideration was taken by the designer for future maintenance and replacement, incorporating overly complex junctions, substandard materials being used during construction, poor construction workmanship, minimum or no maintenance by occupants and so on.

Flat roof incorporating internal gutter is a building element, which inspectors should keep good eyes on rather than simply relying on inspection tools only. It is a typical feature, which to be assessed from design, construction, historical and current performance, likelihood of future major issues, expected serviceable life and other perspectives. A competent building inspector should deliver a lot more comments than simply stating “leaking or not”.

Why there is a common “perception” that stucco houses have “no value” comparing to “other” building finishes?

First of all, common perception does not necessarily mean correct. Otherwise, there is no need to have any scientific study. It is actually more to the other end, i.e. common perception is often wrong.

This common perception comes from a summary of following common misunderstanding:

Most of leaky houses are “monolithic” houses;

Many monolithic houses are clad with “Stucco”;

Stucco is a high maintenance material;

Stucco houses cost fortune to reclad;

Stucco has got poor ventilation ability, therefore moisture can be easily trapped within framing;

If I need to make a correct statement, I would put it in the following way:

A poorly designed, poorly constructed and poorly maintained complex timber framed house clad with direct fixed stucco may have “no value” if exterior wall framing timber is under-treated.

We have to look at a stucco building from many perspectives, such as design, construction, maintenance, building envelope simplicity, timber treatment, cladding system, location, wind zone and etc. before we can make any judgement.

To explain where this common perception comes from, consider the following workout:

Many externally complex houses leaked;

Many externally complex houses used stucco;

So stucco causes leaks.

There are a lot of reasons why complex buildings have used stucco as their cladding system. I will do some separate writings for that topic. But should people somehow decided to use other type of cladding, e.g. weatherboard as the main cladding system back during that leaky building era, we now many have a totally different common perception.

开发商成片开发的新盘，如Universal Home在Rodney以及Long Bay开发的新楼盘，也有问题吗？

Q: Have you found any major issues for houses being built within large developments such as houses built by Universal Homes in Rodney or Long Bay?

A: In general, it is true that well reputable building companies with long building history tend to deliver good quality buildings.

When it is unfair to say that small and newly established building companies tend to build poorly, it is a truth that most of problem new builds are built by un-experienced new-comers or small developers.

Reasons are obvious. Sole traders or small developers tend to cut cost by reducing management inputs or completely ignore construction management. It is also common for some small building companies or spec owners to limit their construction management in price bargaining only.

This finding is not a secret for most buyers. This is why spec house built by large reputable companies are selling more in general. You get what you pay for. This is also a universal rule of thumb for housing industry.

Here is a very interesting topic: Can small building companies, sole traders, individual developers and the like build as good as other well established building companies? I will talk about that during future coming events. 

If the building does not have a cavity, the building will have leaking problem sooner or later. Is that correct?

Of course, not.

Even under current NZ Building Code and related building standards, as long as design risk is low enough (simple plan and form, within low wind zone, single story, wide eave and etc), a building’s exterior wall cladding can still be installed without cavity.

Looking at the whole NZ building history, majority of buildings were built without cladding cavity. Most of those building have been well performed without suffering major weathertightness issues.

Looking at buildings built during so called “leaky building era”, i.e. during 1995-2004, not all buildings built without cladding cavity suffered weathertightness issues. in fact, most buildings built without cladding cavity have been well performed.

Solutions for solving leaky building issues have never been only limited to providing cladding cavity only. Every single recladding project will not just involve providing cladding cavity, but also incorporate some redesign of inadequate details, rectification of defective structural details, repair of non-weathertightness related defects, make good to poor workmanship and etc.

From building inspection point of view, cladding cavity has never been a major factor for us to determine if a building is “leaky”. If we are satisfied in terms of design, construction, workmanship, maintenance and etc for a building, we will regard the building as “weathertight” regardless it contains a cavity or not. 

Post/beam connections – Practice vs. Compliance

Here are some perfect examples to show different results from good building practices vs. details in accordance with NZBC AS1 or NZS 4306.

A good building practice:

Post/beam connections simply sandwiched with nailed 4x2 on each side. The connection was built 35 years ago and showing no deformation at all.

Today if you draw that detail and apply for a building consent, you need specific testing to verify that this detail would meet our Building Code.

A detail in line with NZBC AS1 and NZS 4306:

The post/beam connections are fixed with stainless nail plates on each side. Connections are severely deformed and twisted. By the way the details have formed at 2009.

So, as a pre-purchase building inspector, how do we judge the above details? 

It is simple when you know the first detail has formed some 35 years ago. But what about if same detail is formed today? Do you raise concern due to deviation from our Acceptable Solutions/Standards or happy with that? Do you believe same timber sandwiched post/beam connection formed today will be able to perform for at least 35 years?

Are there leaky type claddings?

A very common question is: the house is clad with xxxx, will it leak?

In my past 6 years of inspection I never found any leaky house, which leaked purely because of cladding type itself.

Similar question is studied in a recent Branz Bulletin – Ventilation drying behind wall claddings, the question is:

Are some cladding types more leaky than others?

The findings are quite surprising for many people:

Low leakage claddings:

New freshly painted weatherboard walls

Well maintained continuous sheet claddings,

Metal and PVC weatherboards with tight-fitting overlaps and effective jointers at corners

Average leakage claddings:

Well maintained painted timber or composite weatherboards with few obvious defects

Leaky claddings:

Warped and cracked unpainted weatherboards

Non-rendered brick veneers

Two interesting notes to be made here:

1. ·         Combination of factors such as build quality and maintenance rather than cladding type itself will determine the leakidity (how likely to be leaky) of a cladding.
2. ·         More publicly accepted leaky types of cladding, such as sheet cladding, are not listed under leaky cladding. Well-reputed cedar weatherboards and brick veneer are summed as leaky claddings.

But there is one fact which is commonly agreed by everybody: Most leaky buildings are monolithic clad buildings. But can we rephrase it as: monolithic cladding likely to leak? Wanted or not, majority of public think that way, and that is the main reason why monolithic clad houses are selling with discounted price. 

I have always enjoyed in challenging public perceptions, here are my questions:

If you simply replace the cladding of leaky buildings with weatherboards, but without redesign junctions, joints, ground clearance, balcony details, will you stop leaks? The answer is No.

Or put the other way: we build two houses, one with direct fixed weatherboards, another one with direct fixed fibre cement sheets, all with untreated timber framing, all with no clearance to ground surface, all with fully enclosed membrane balcony, all with windows without any flashing, all without eave overhang, all with poor workmanship to detailing. Will the weatherboard house be survived when fibre cement house be leaking like shit? The answer is No.

If cladding type is not the one to blame, what to blame? Design? Workmanship? Then the whole Country likely has targeted the wrong thing again. Looks like we no longer building any plaster houses, which itself never been the reason causing leaky building issues. But we have not improved anything from design and workmanship point of view. Will that mean another construction disaster in the near future? We will see.