Roof Build Up
The pitch of both roofs is 12.5 degrees. The architect choose this in order to optimise the solar gain during the winter months and ensure both buildings receive adequate light.
There is a roof overhang of 1.8 metres in order to control the solar gain during the summer. (See below)
The build up of the roof from the inside is : Plaster Board, 40-100mm service cavity, airtight layer, 400mm metac isover semi rigid 0.34 k insulation, bitumen impregnated wood fibre board, membrane, ventilated cavity, OSB, DELTA®-TRELA membrane and then zinc.
We thermally broke the rafters where possible see above.
Planning Permission Factors
In our planning permission reference was made to standing seam. This restricted the options for controlling costs later on. (A lesson for others). As it turned out for our design there were no variations in the roof (ie no openings, different pitches, etc and this kept the costs under control. )
If one is designing from scratch note that tiles/slate options start with a minimum pitch of approximately 12.5 degrees (example: the melodie single pantile). During the design stage if one can simplify the design of the roof by minimising openings for roof lights, ventilation flues and any architectural details this will keep the costs under control.
An early idea I explored was to use amorphous solar electric panels (PV) built into the roof -I was unable to come up with a solution in the time frame and deal with the potential risks such as Fire/Insurance/Waterproofing and Hygrothermal issues of an intergrated roof solution. I will revisit this idea in the future.
Zinc can be placed on spaced untreated wooden battens without a membrane – a cost saving is possible using this technique.
All fixings nails and screws are either grade 2 or 4 stainless steel.
New Roof Products
In the last month I came across a promising roof and wall facade system that acts as a solar hot water panel and it uses the drainback system (see previous blog on drainback system). The company is called http://www.aventa.no . As previously discussed it is too late for me to plan for this . What needs to be clarified is the cost of storage and panels .
Some test are being carried out on passive houses at http://www.aventa.no/eng/References/Row-houses-at-Mortensrud-Norway .
When one is getting a quote from any zinc installer ensure you specify the same product. I found that the Zintek (be careful there is another name that sounds similar called Zintec but it is not zinc) was cheaper than Rheinzinc and the installers usually know which zinc is good. Ask for their opinion (as they are working with the material). Think whether you can use non patinated (natural) zinc in some places as it is roughly a €1 cheaper per kg. The non patinated zinc eventually returns I believe to the same colour as the patinated zinc. We were advised not to use non patinated zinc in areas where different weathering could occur. So for all the fascias/sofit and edging details visible we used patinated zinc. As zinc is a traded commodity on the stock market prices vary.
The zinc detail for the gutter were as follows. A ventilation/insect grille can be seen below.
The ventilation/Insect grille on the overhang is as shown below. A detail to satisfy the engineer and the zinc installer was agreed as proper ventilation and air flow was required for the roof.
Roof Overhang Zinc Detail Passive House
I must do more research on this as little appears to be available..