A two-man team from our factory was appointed to install the additional layer of 100mm Kingspan Kooltherm insulation we needed to meet the performance levels given in our Passive House Planning Package (PHPP) analysis.
They also fitted the timber battens to support the external cladding. The timber cladding boards, which were fixed vertically, were supplied by Vincent Timber.
We selected prefinished western red cedar in a lozenge-shaped profile with 7mm face gaps between them. Additionally, we mocked up several different gap widths to determine which looked best and, after much deliberation, selected 7mm as the most visually appealing option.
It’s important to note that if you are opting for a “gapped” cladding effect, you must use a membrane behind it that is capable of withstanding permanent exposure to UV light — most breathable membranes cannot do this. We used Protect 5000 Façade Wall Membrane.
One of the slightly unusual things about our Passivhaus show home is that it features masonry cladding too, in the form of Terca Megaline Grey Multi bricks from Wienerberger.
The long, narrow format brick with 8mm mortar joints provides a contemporary appearance, with a nod to the traditional brickwork elevations of the vernacular. A common aspect of all new builds is making sure a planning condition relates to the appearance of the external finish, so before starting work on-site, we mocked up several brickwork panels with different coloured mortars and mortar finishes (flush, bucket handle and recessed), and selected the one that appealed the most. One thing we did know already is that the very pale cement we selected is quite tricky to work with as it can swiftly go sloppy if overworked.
Most SIPs (structural insulated panels) and timber frame Passivhaus builds exclusively use lightweight cladding systems, which are carried by or fixed back to the building structure. To use the masonry cladding and not introduce any thermal bridging, we needed to construct a separate foundation just to carry the brickwork façade. This was a simple strip foundation — it is completely isolated from the main insulated raft.
The brickwork support channels, which provide restraint, were screwed back through the external insulation into the 15mm OSB (oriented strand board) face of the Kingspan TEK® Building System of SIPs-based panels. The impact of the repeating screw fixings was added into the U value calculations for the external wall and, in this instance, it had little impact because of the large amount of insulation in the wall. This would not be the case in constructions with lower levels of insulation.