We are very excited to have a special project currently on site - Llama Croft which will (hopefully!) be our first certified Passivhaus made predominantly out of natural, bio-based materials !
Over the coming months, we will be sharing posts both about, how things are progressing on-site, and also explaining key details and design considerations that have gone into this unique Passivhaus Design.
THE WALLS
When designing a Passivhaus, very high levels of insulation, airtightness and minimal thermal bridging are key.
Using a combination of flexible and rigid insulation is a cost effective way of increasing insulation and reducing thermal bridging - the flexible stuff (in this case loose fill Cellulose) can go within the structure between studs and the rigid boards (in this case Woodfibre) can wrap around the outside of the structure, creating a surface to render onto, and reducing
the cold bridge of the structure.
In order to create more space for the Cellulose insulation, a 'deeper' structure is needed. There are a few ways of doing this and here, we have chosen to use a Larsen Truss which is a twin-stud timber frame, with an inner structural stud and an outer stud, connected with a some plywood gussets. This creates lots of space for insulation with reduced contact between inner and outer studs, reducing thermal bridging. Our panels are being designed & built by Broadaxe timber frames
We use thermal modeling to ensure that the amount of thermal bridging is low enough to achieve the passive house standard. The thermal bridging calculations are then fed into PHPP, along with a multitude of other complex parameters (passive house planning package), which will determine weather the building will achieve the passive house standard.
There is an inner layer of coated OSB board (SMARTPLY propassiv) which is the structural sheathing and airtightness layer, along with an insulated service-cavity to reduce penetrations through the airtight layer.
The walls are being built as panels, off-site in Broadaxe's workshop for better quality and will be erected on-site before being filled with, and covered in insulation.
Currently the panels are being fabricated and we are looking forward to seeing them go up in the coming months!
Please get in touch if you would like to know more about this design, we'd be happy to share knowledge
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