How it Works

Prevent leaks with weatherproof window and door flashings.  We maintain that to prevent leaks around windows and doors in any conditions, there are three flashings that must be fitted to all window and door installations.

They are:
  • Cavity Head Flashing
  • Jamb Flashing
  • Sill

Conventional of aluminium window flashings and door flashings depend very much (and often entirely) on sealant. This is not a good idea as the  history of leaky homes and buildings attests. The NZ Building Code focuses on minimum standards rather than Best Practice and  does not insist on the installation of these essential three window and door flashings. We believe and can prove, that this is major flaw in the NZ Building Code and have made submissions to the Department of Building and Housing on this point (and may others besides).

We maintain that to ensure weathertightness in any conditions there are three flashings that must be fitted to all window flashing and door flashing installations. They are Cavity Head Flashing, the Jamb and the Flashing Sill.

Cavity Head Flashing


  1. One piece cavity head and drainage and drying vent. Flashman has patented rights on this design which normally requires two flashings, one of metal and one of plastic which are hard to fit and do not provide the straight and sturdy lines of the Flashman Cavity Head Flashing.
  2. Aluminium Stop End does away with the highly leak prone slot that is required to be cut in the cladding to accommodate the ends of any conventional head flashing. The Flashman head flashing completely eradicates such leaks or potential leaks.
  3. Good safe cover over the window or door head.
  4. Vent holes in the flashing allow drying and drainage should any moisture enter above a window or door from some other source and allows this water to drain away harmlessly from the sloping head flashing.

Jamb Flashing


  1. Revolutionary T shaped Flashman Jamb (side) flashing catches any water that might over time penetrate behind the window to jamb junction and the cladding to Jamb junction and direct it to the sill where it is harmlessly dispersed.
  2. The Flashman Jamb does away with the need for timber facings and scribers providing a clean architectural line and much faster and cheaper flashing system. However facings and scribers can easily be fitted for aesthetic reasons to achieve a traditional (but weathertight) look.



  1. Flashman Sill
  2. Full support to the window or door directly under the glazing line where all the weight is concentrated. There is no need for any additional support. High support upstand prevents water being blown up behind the window.
  3. 3mm gap between the window and sill to allow water to escape.
  4. High support upstand prevents water being blown up behind the door.

To read more in detail about how the Flashman flashing system works, download the PDF

Flashing Fabrication Design and Installation

Flashing design has historically been the domain of Architects, Draughtsman, Builders and plumbers as well as roofers. However there is now far less practical knowledge available about how these flashings should be designed, drawn and formed. Then there is the issue of who is responsible for them. Flashings are often very poorly designed and fitted. Skill levels have dropped enormously in the last 20 years or so. Builders do considerably less building these days, as the construction business has increasingly become more disjointed with various trades undertaking small “specialist” tasks. This  largely unsupervised production line trendappears to be unstoppable and is unlikely to change as builders, owners and architects seek quicker and cheaper methods and materials to reduce construction and labour costs.

Unfortunately, because flashings are not highly visible or well understood, their importance is overlooked and often not even costed. The result of poor flashing practice has proven to be disastrous and very expensive to remedy. The entire leaky home crisis in our view is almost entirely caused by poor flashing design, fabrication and installation. We know it is a very serious problem and that is why we have invented the Flashman System and insist that it is only installed by our own Distributors and their trained installers.
Many flashings such as the commonly used uPVC  plastic flashings used in monolithic construction do not comply in any way with the 4 “D’s” but actually trap water under the plastic surface. The  weathertightness of  these common monlithic cladding types actually depends  on microns of paint and approximately  8mm or less of plaster.

Cavity Construction

This form of building was introduced to provide a solution to the leaky home crisis. The principle is simple: create a gap between the back of the cladding and the timber framing by fixing a timber batten direct to the framing over the building wrap ( paper). It is a cheap and efficient means of accommodating a small amount of water that might periodically penetrate behind the cladding. Such small amounts of water are able to drain out at the bottom of the wall. However…many builders, designers and building inspectors treat this cavity as an internal downpipe which has lead to significant numbers of failures in cavity construction.

Our point is this; cavity construction was  intended to be a back-up means of escape for an occasional unforeseen leak, not a main line of defence. Sound flashing design is still needed and should be always given top priority due to the danger of massive remediation costs and damage if a small fault in the flashing design or installation occurs. We know only too well the effects of poor flashing practice. We are involved in the remediation market in a major way.

Flashing Materials

Materials expand and contract at different rates and this can cause problems. Plastics for example are not suitable for long term use or exposure to the elements as they break down and cause cracking in plaster construction because of differential contraction which causes leaks. Sealant has been used as a main means of flashing cladding at window and door openings with most cladding types.

This method of flashing requires no skill, is cheap and DOES NOT WORK!