How have building lines changed with H1?

Advances in the requirements prescribed by H1 Acceptable Solution have changed the finishes and locations of fixtures on the building line. Insulated slabs and the location of the glazing suite have raised details when it comes to interacting with threshold drains and perimeter channels.

The impact on level threshold design

The threshold drain will require a minimum 150mm deep by 200mm wide channel (CH 7.4.2 E2/AS1) to be formed at the edge of the slab. Then a removable grate is required, to be self supporting and separated from building elements by a continuous 12mm gap, or allowance of a drip line.

This grating system is always a variable dimension, and can often be required to be wider than the 200mm channel, for reasons I will go into below. This is where designers can feel a challenge to be able to step the gratings as required and keep the area functional, looking good and compliant with E2, E1 and also, importantly, D1 accessibility requirements. Making this detailing simple, and not overly customised is where a perimeter drain will offer you these solutions.

Achieving compliant level access design

A couple of challenges that are raised by H1 details is the addition of an insulated panel being brought against the slab upstand, and the glazing suite or panels being recessed in, aligning with the plasterboard, rather than stepping out from the cladding system.

Insulated panel being brought against the slab upstand

In the case of an insulated slab, the detailing will result in an interaction between the insulated panel system and a channel drain, and creation of an over-width grate, which I will go into later. The build-up of the system between panel and channel is quite easily dealt with, and accepted by all the leading insulated panel (XPS typically) suppliers. The panels will generally have a cement-type scrim as the facing. This scrim will give a good substrate for a liquid applied, UV stable membrane to be installed onto the face. Once applied, this membrane will separate the insulated panel, and the internal slab, from any perceived moisture in the channel. Then the perimeter drain can be installed up against the membraned panel as usual. Once the perimeter drains have been placed and the screed laid into it, this will allow for the membrane to be lapped from the vertical edge of slab into the base of the channel, creating a space that will keep moisture away from building features and protect screeded elements, with an easy-to-clean finish.

Glazing suites recessed back from the building line

With glazing suites being pulled back in from the building line, often seen in education projects with a brick veneer and a slab rebated at doorways, an overwidth grate will often be required as the threshold drain will be set to 200mm off the foundation, but at the doorway the reveal may over-extend to 250 or 300mm. For this reason the perimeter drain system has a 300mm wide recycled GFP grate that will allow for the over width reveal, without relying on a custom grate to be fabricated. This keeps the system as an off-the-shelf stock solution, with the installer able to cut the grate down to suit the reveal width. If a Wedgewire grate is selected, then this can be fabricated to any real width. At Commercial bay in Auckland there are regular set-ins of over 600mm that were accommodated by an over-width grate.

With set-in joinery, attention must be given to the detail and clearances to the sill or base of the rebate. If a full depth slab rebate is not allowed for, there must be enough depth clearance for the grating and leg to be installed and provide support over the sill and keep the entrance accessible, meeting E2 requirements. Generally a minimum of 40mm would allow for this, but the more depth clearance the better.

Conclusion

In summary, interacting with building elements created by H1 requirements is made easier by the use of a system-based threshold solution. Use of off-the-shelf elements will ensure a speedy install, particularly at the end of the project. Economy and compliance is also easily achieved with the perimeter drain having published installs, confirmed between multiple suppliers of insulation, membranes and cladding systems. Allproof's system has been proven over hundreds of kilometres of installed product, ensuring that product specified will be accepted by consenting authorities and stakeholders alike.