E2/AS1 and WANZ WIS offer two different solutions to window head flashing details with bevelback weatherboard cladding installed over a drained and ventilated cavity. What are the differences?

E2/AS1 provides an Acceptable Solution for head flashing design with bevelback weatherboards, while WANZ WIS complies with the NZBC Clause E2 External moisture because it has passed the verification method E2/VM1 for this cladding.

The principal difference between the systems is the position of the head flashing. E2/AS1 requires the head flashing to be fixed under the cavity battens against the timber framing and WANZ WIS requires it to be fixed over the cavity battens. As a result, the two systems differ on how water that gets into the cavity is directed to the outside of the cladding, and on the construction sequence.

Detailing the systems

Installation for both systems begins with the wall underlay folded into the window opening followed by flexible flashing tape applied across the sill and at the upper corners. From there the detailing is different.

E2/AS1 DETAILING

E2/AS1 requires the head flashing to be fixed against the timber framing over the underlay (see Figure 1). A second layer of underlay, or flexible flashing tape, is lapped over the head flashing upstand. Cavity battens and a vented cavity closure are then fixed over the head flashing. The flashing has 10 mm stop-ends which finish at the back face of the cladding at both ends (see Figure 1), and has a minimum 15° slope to the exterior.

WANZ WIS DETAILING

WANZ WIS requires a proprietary WANZ cavity closure to be fixed against the timber framing over the underlay, with a second layer of underlay, or flexible flashing tape, lapped over the cavity closure upstand, followed by the cavity battens. The cavity closure must have a camber falling from the middle to the ends and have an overhang of 60 mm minimum at each end of the window unit.

The head flashing is fixed against the cavity battens. It must overhang the window by a minimum of 30 mm at each end and also have a minimum 15° slope to the exterior.

Water management differs

In the E2/AS1 system any water that gets into the cavity above the window, and all water that falls onto the head flashing, will be directed to the exterior by the head flashing. The stop-ends help direct water to the outside rather than past the flashing ends where it would continue down through the cavity.

In the WANZ WIS system the cavity closure closes the cavity above the window and acts as a flashing, directing water in the cavity above to the back face of the cladding on either side of the opening. From there it continues down through the cavity to exit at the next horizontal joint or the bottom of the wall. The head flashing diverts only the water that has fallen onto the flashing directly to the outside.

Comparing buildability

E2/AS1

Although the cavity battens and weatherboards can be fixed up to the level of the top of the opening before the window is installed, the E2/AS1 detail requires the window to be installed before the rest of the weatherboards can be fixed.

Once the window is installed, the head flashing can be fitted over the window flange, followed by an additional layer of underlay lapped over the flashing upstand. Cavity battens and the cavity closure are fixed over the head flashing, and the cladding can then be fixed in place.

WANZ WIS

The first stage of the WANZ WIS detail is to install the proprietary cavity closure. Additional underlay overlaps the closure upstand, then the cavity battens are installed. The cladding can be installed next, although this is not the sequence suggested by WANZ WIS. Weatherboards can be aligned with the trimming studs and cavity battens at the jamb faces, and temporarily tacked in place at the window head, as has traditionally been done with direct-fix weatherboard installation. This allows the insertion of the head flashing later. The window can be installed after the weatherboards have been fixed, and finally, the head flashing installed under the temporarily-fixed weatherboards.

WANZ WIS may be easier to build

In both systems the water is directed away from the window to the outside. The E2/AS1 system directs all water from above a window to the outside face of the cladding, whereas the WANZ WIS system directs the water down the back face of the cladding.

However, the practicality of the WANZ WIS construction sequence may prove easier on-site for window and door installation.

Figure 1 Figure 2

We know from news reports that decks and balconies can be a significant area of concern in terms of the effect they can have on the weathertightness of a building, the durability of the components used to construct them and, over time, their structural adequacy.

E2/AS1, in the risk matrix, classifies two types of decks:

Enclosed (waterproof) decks, over an interior or exterior space, that have an impermeable upper surface and are closed on the underside. There is often a habitable space below, and the deck is likely to incorporate a solid framed balustrade.Open timber-slatted decks, usually constructed with an open barrier.

Leaky building statistics have highlighted waterproof decks as a significant cause of problems. Nationally, approximately 14% of new buildings consented have waterproof decks, but in approximately 67% of cases reported to the Weathertight Homes Resolution Service, the leak was attributed to the deck and/or the balustrade walls – a disproportionate rate.

All decks create some risk where they are attached or incorporated into the weatherskin of a building.

Risk areas for waterproof decks

Waterproof decks have a number of features that can make them more susceptible to water entry, but good design, detailing and construction practices can effectively address the known trouble spots. While E2/AS1 is not mandatory, it provides good guidance on the

design parameters for both waterproof and timber-slatted decks.

LEVEL DIFFERENCES AND CLADDING

First, is there a sufficient level difference between the inside floor level and the waterproof deck surface? E2/AS1 requires a minimum difference of 100 mm so that water on the deck is prevented from draining to the inside. Having this level difference (as in the Acceptable Solution), or a means of intercepting and draining water (as an Alternative Solution) seems logical. However, but a number of cases have been investigated where the finished deck level is actually higher than the inside floor level and the only direction water can drain from the deck surface of the door frame is inside.

Have wall claddings been finished hard down onto the deck surface? Where this occurs, water may wick up through the cladding into the framing behind and any water behind the cladding is prevented from draining out. E2/AS1 requires a 35 mm minimum clearance from the bottom of the cladding to the deck surface.

Around the perimeter of the deck, does the waterproofing membrane have sufficient turn up? E2/AS1 requires 150 mm with 115 mm minimum cladding cover so that the framing behind is effectively protected.

An as-built detail where a concrete deck substrate had a tiled finish added over a minimal slab set down. The built-up deck finish caused water to flow inside the building.

Poor detail at the base of a balcony wall where an attempt was made to terminate the butyl membrane into a fibre cement horizontal jointer.

DRAINAGE AND FLASHINGS

Are there drainage outlets big enough to effectively drain the deck area, does the deck design incorporate overflows, and is the deck

constructed so that water will actually drain to the outlets or does it lie on the deck surface? Waterproof decks that are fully enclosed should have a minimum of two outlets (if one blocks, water will still be able to drain off the deck) and the same number of overflows. The capacity of the outlets and the overflows must be designed to suit the area drained. They can be considered similar to an internal gutter, so design them to carry double the rainfall intensity for the building location. Where water does not effectively drain from a deck surface, the waterproofing will deteriorate faster and the risk of water entry through waterproofing membrane joints or a small area of damage is greater. Drainage may also be compromised where a designer determining the slope on the deck has not allowed for deflection in a completed deck.

Do solid framed balcony walls have a flat top textured finish that allows water to sit there? Walls that do not incorporate a cap or under flashing will, over time, allow water into the framing below. For an under-flashed texture-coated balustrade wall the minimum cross-fall under E2/AS1 is 10°. A cross-fall of 5° is permitted when there is a cap flashing of synthetic rubber or metal. A cap flashing can be easily retrofitted to a balcony wall (after the wall structure has been checked to ensure there is no framing damage).

A fully enclosed deck that has a flat topped barrier wall, insufficient inside to deck surface clearance, cladding in contact with the deck surface and no obvious drainage.

Has the junction between the balcony wall and an adjacent wall been constructed with a saddle flashing? Water entry into the wall structure is likely where the junction is not properly flashed and relies on the paint coating or sealant to weatherproof it. Flashings can be retrofitted, but parts of the wall cladding will have to be removed to allow this.

PENETRATIONS OR DAMAGE

Does the balcony wall have handrail stanchions that penetrate (or have fixings that penetrate) the top of the balustrade wall? These features are a major cause of water entry and if water has entered into the framing then significant rot may have occurred without building occupants being aware of it. The rot will significantly weaken the balustrade and may make it unsafe. Good design mounts handrails to the side, not the top of the wall.

Where an open or glazed balustrade is incorporated into a waterproof deck, do the fixings that secure the balustrade penetrate the membrane weatherskin? Fixings through a membrane provide a point for water to enter. Side mounting barriers locate fixings in a less risky part of the weatherskin.

DAMAGE AND MAINTENANCE

Is the deck membrane showing signs of damage or deterioration? Membranes can be damaged during deck use and allow water into the structure below, with resulting damage. Also, membranes which are stretched or stressed, such as at joints in the substrate which have not been taped to allow the membrane to accommodate movement, will deteriorate along the lines of the joints more quickly.

Has a liquid-applied membrane been regularly recoated as recommended by the supplier? Typically, liquid-applied coatings should be recoated every 7–10 years to ensure they continue to perform.

Risk areas for open timber-slatted decks

Open timber-slatted decks have a higher risk of problems where:

the deck is cantilevered, as the cantilevered joists create a penetration through the weatherskinbearer or stringer fixings penetrate the claddingthere is no drainage gap provided between the bearer/stringer or the decking and the claddingbrackets, bolts and joist hangers used in conjunction with H3.2 timber have insufficient resistance to corrosion – typically, deck situations are damp and stainless steel should be used for structural components (see page 18).

Insufficient timber treatment of cantilevered joists, and therefore deterioration of the timber, can be a potential problem where the joists have been notched on site to provide a set down (E2/AS1 requires 50 mm for cantilevered decks). Cantilevered joists are, in BRANZ’s view, best avoided or, if unavoidable, used in a situation where they are fully protected by a verandah roof. To ensure appropriate treatment of the cantilevered joists, the cantilevered portion should be a smaller member fixed to the side of the floor joists.

This completed deck does not have a 10 to 12 mm drainage gap between the deck structure and the cladding, and water is being trapped in the junction. Also the barrier will not meet current Code performance requirements.

Barriers around decks must be capable of taking the load of people leaning against them. Balustrades that do not have enough fixings, undersized fixings, barriers fixed to deck joist less than 125 mm deep or incorrectly located fixings could mean that the balustrade may not provide sufficient resistance to an applied load. B1/AS1 gives one solution for the construction of a timber barrier (note that B1/AS1 specifies fixings that may not achieve 50 year durability with copper-based timber treatments). All other barrier construction must be specifically designed.

Timber-slatted deck members can be susceptible to rotting where water is trapped between two timber deck components, such as at decking/joist junctions.

Warning signs for deck problems

There is a range of indicators that identify problems with a completed deck. For some, immediate action is required to ensure the deck is not dangerous.

Sponginess felt when walking across the deck may indicate water damage to, and deterioration of, supporting joists. When this is noticed, the deck should not be used until a thorough investigation of the cause of the sponginess is carried out and, if necessary, the deck fixed. Flexibility or movement may also indicate that the joist depth/span ratio is incorrect.

Cracks in coatings, particularly at junctions, create a water entry path. Water can enter through cracks as small as 0.2 mm. Any water that is getting into the structure can result in damage – the amount and speed of the development of rots in framing will depend on the level of timber treatment, and temperature conditions within the wall.

Signs of water entry behind the weatherskin can also be:

staining on the ceiling below a waterproof deck or on walls adjacent to cantilevered joists penetrating the claddingmusty smell or mould on inside walls, particularly adjacent to a balustrade wall junctionbubbles in paint work or a change in paint colour.

Other problem indicators can include:

visible rusting of bolts, nails and brackets. Rusting will ultimately compromise the performance of the item as the deterioration causes loss of strengthvisible rot where timber is continually damp, such as the contact points between the timber slats and the joists below.

Remedy the problem, then repair

Before any repair work is carried out on a deck structure, checks should be carried out to:

identify the source of the water entryremedy the water entry problemdetermine the extent, if any, of damage as a result of water entry into the wall, deck and ceiling framing.

Too often a leak is sealed without the full extent of the damage being determined. As a result, the damage that is hidden will get worse.

Significant reconstruction is often required where a waterproof deck has allowed water into the framing, or where insufficient drainage from the deck has been provided.