(More) pre-cladding preparations...
August 7, 2015
This post describes the preparations to the supporting batten zone undertaken before we can begin the cladding on any one elevation.
We began by removing the temporary protective breather membrane we have had over the battens since the start of the year and taping new fresh Pro Clima Solitex Fronta Quattro into the window reveals.
Much like the process of applying the Extoseal there are several steps involved; straightforward in principle but like most passivhaus details requiring a degree of patience, correct sequencing, and attention to detail to ensure proper sealing to the window frame and the Gutex itself.
There is, of course, more than one way to execute this detail but the sequence we undertook was as follows:
1. Prime the surface of the Gutex to take the tape (using Pro Clima Tescon Primer RP).
2. Tape a band of Tescon Invis (black tape with the branding on the back specifically designed for open rain screen cladding so that the branding is not visible between the boards) between the Gutex and the window frame. We created our own 2-part release paper on this tape to allow us to fold it 5-10mm onto the frame before sticking it onto the Gutex. At first this was a little tricky to get right without cutting right through but 7 years of model making experience each at the Mac with a scalpel and a 10A blade was put to good use once again!
We worked our way around the window doing this process on both sides and the header, and inserting an additional small corner piece of tape to ensure complete overlap at the internal corners, much like the internal airtightness taping.
3. We then taped another band of Invis half over the first one and half over the Solitex Fronta Quattro membrane (which again is black and UV resistant enough over the long term to be specifically used behind open rain screen cladding).
As an alternative we could just have taped the Gutex to the window frame and then taped over the non-tongued and grooved joints as the tape and membrane combination is really for wind-tightness here, but given that we had made the reveal insulation from multiple pieces of Gutex this method seemed quicker and more straightforward. It also has the advantage of extra robustness in the places that have maybe less drying potential than the main elevation. The advantage of the Gutex specifically is that it is impregnated all of the way through so the water-resisting qualities are also present when the boards are cut; not all rigid wood fibre boards are like this as some have a surface treatment to create a water resisting surface which means that the ‘end-grain’ has to be protected with a membrane, so this is something to look out for when specifying and detailing.
4. We then wrapped this membrane out of the window reveal and taped it onto a pre-primed band of Gutex on the main face of the elevation.
5. At the base of each window cill and the doors on the ground floor the membrane was overlapped with the Extoseal, and the junctions taped with another strip of Invis.
6. We then had to fit some cladding battens to take the cladding as it returns into the reveals. We are using min. 25mm reduced thickness battens to better balance the overlap of the cladding in front of the window frame with the overall size of the structural opening. These are fitted with a drainage gap at the base and a bevel to create a drip at the 'front' face.
The soffit of each opening receives battens as well.
7. The penultimate part of the process is to fit the insect mesh everywhere to stop any bugs from getting in. We are using stainless steel soffit mesh at the base of the wall, the head of the wall, and the base of the windows for a more robust protection as this is where water will either be dripping or running out from behind the cladding during heavy / wind-driven rain, and a fine ‘midge’ grade black fly-screen style mesh over the whole elevation behind all of the cladding. We selected a black mesh to also darken the appearance of all of the materials behind the cladding and make this layer recede so the cladding stands out rather than the various lines of tape, membrane, grommets, etc. behind.
8. The final step was to grommet and tape around two cables for external lights. This is done in a very similar manner to the internal grommets: these were applied directly to a square-ish area of pre-primed Gutex and the edges taped using Invis. We then sealed around the centre of the grommet with some orcon-f for 'belts and braces', and popped the cable through a neat hole in the insect mesh to maintain the continuity of this layer over the elevation.
Phew, now we are ready to start the cladding!