To the best of my knowledge, every weathtertightness claim I have been involved with has included issues with window and door openings.
At least 50% of leaks in leaky homes occur at window and door openings — and they are still occurring.
It is essential that attention is paid to the detailing and installation of windows and doors. In my opinion this is often not happening, and litigation as a result of the consequential leaks is a natural and expensive result.
Cavity construction, pressure equalisation of the trim cavity and even the most excellent flashing system will not allow for the inevitable leaks at the window or door junction that I want to focus on here.
New cause of leaks
This article is intended to bring to the attention of builders yet another issue affecting window and door installations which has created a new cause of window and door leaks in aluminium joinery installations.
The new leakage point has been brought about by the extensive use of double glazing to comply with H1 requirements and the need to cantilever windows and doors out beyond the framing line as much as 50mm. This occurs with direct and cavity construction.
What is needed is full window support along the length of the window and door. This requirement, in the main, is not being insisted upon by building consent officers, nor is it being widely enforced on site. As a consequence, builders are not fitting these essential support bars.
This is not entirely an oversight of building inspectors as E2/AS1, the External Moisture clause of the New Zealand Building Code, is not clear on the essential requirement to provide critical support in any of the window drawings.
There is not one drawing in E2/AS1 which shows a support bar under windows or doors, let alone states that it is an essential part of the window installation.
However, there is, in Note 3 attached to all window drawings, regardless of which cladding is used, this statement:
“Make allowance between packer and sills for support brackets for large windows. Such brackets require specific design, and shall be supplied by the window manufacturer.”
This lack of clarity regarding the importance of supplying the window support has raised a potential gold mine for lawyers with future new litigation claims caused by early failure of windows and doors which do not have the required support as stated in Note 3 mentioned above.
Window manufacturers themselves are in a state of confusion as to what is needed. In my discussions with the WANZ technical committee on the issue of support to windows, their answer was clear and adamant. “All windows require full support.”
This is not happening. Where support is being provided it is inadequate or contrary to WANZ’s own recommendations to their members.
E2 was produced with great haste to provide some prescriptive solutions to the leaky home epidemic, and the requirement for window support was not fully addressed.
However, the WANZ web site is very clear on the matter.
Can’t fit window support with direct fix construction
Let me ask this question at this point. How is it possible to fit and support bar to a direct fixed installation where there is a sill tray? Answer, it is not possible.
That point alone should put an end to the entire practice of direct fix! The cheapest insurance available is the price of cavity construction at a cost of approximately $1000 to batten out an average-sized house.
On my independent inspection of window and door installation, I discovered that often the support bar or brackets did not support anything at all!
A bit like the many huge beams I have seen in roof spaces where load bearing walls have been removed and a beam installed on top of the ceiling joists but not landing on any load bearing walls. In other words, the support bars have added expense for no purpose whatever.
In many of the remediated leaky homes where existing window and door joinery remains (a practice I do not recommend), the now essential support blocks were never fitted by the window manufacturer because no one had thought of window support.
It is clearly impossible to provide support via a WANZ bar by some other means, if there is nothing to support!
Builders face litigation if windows and doors leak due to sagging and the opening up of mitres and mullion connections which cause leaks well inside the framing line (a cavity won’t help).