11 May 2017

How we built our walls ... its different

Our tiny house uses nontraditional systems in terms of structure, bracing, weather proofing and cladding. We are using a form of structurally insulated panels (SIPs) for the structure which is based of the Pop Up House design. The tiny house uses an open joint cladding system using US products which is not common in New Zealand. The cladding was pulled from the rubbish pile and turned into a free and lightweight cladding system. Yes we like to do things a bit differently, read on for more detail.

Structure


The floor, walls and roof are constructed from rigid polyurethane foam (imported from china) and plywood glued together. Sections were glued together on a level ground surface and assembled to the house floor.


This is a form of SIPs system which minimises thermal bridging creating a very well insulated house. The floor roof and walls have an R-value of 4.2m²K/W which is well over NZ building.

Image result for insulation building code nz


In the design of mobile tiny houses weight is a big issue and has to be considered for every material choice. An advantage with this system is its light and strong and incorporates the insulation into the structure.

Rainscreen 


The whole structure is warped in a rainscreen membrane by DuPont under their Tyvek range called UV Facade. This lightweight product from Pink Batts is water and UV resistant and vapour permeable. Meaning its keeps the weather out and-enhances air tightness while being able to breath. 

Cavity Batten


The cavity battens are 25mm thick pine from Mitre 10 painted black using Resene paint. They are attached to the 25mm plywood via screws which bracers the polyurethane. The top surface of the battens have a mitre cut so water does not form on this surface improving life of timber. 


Cladding


The cladding is recycled pine extrusion packaging we sourced for free. At around 8mm thick makes this a light and very cheap material. The cladding is attached to the cavity battens via screws which again help brace the structure. The cladding is stained using resence woodsman 'woody bay'. The cladding has a 12mm gap between each vertical piece crating a gap known as open joint cladding. We also took advantage of second hand corrugated iron by painted the same colour. The idea here is to reduce weight and break up the wooden cladding around the back of the house. 

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Open joint cladding 


Open joint cladding is not common in New Zealand but more widely used in the US and Europe. The idea is the Rainscreen, cavity battens and cladding all work together as a system. The open joints between the cladding has two stages. Firstly instead of fighting to keep the moisture out at the cladding this system simply lets a small amount in. The house is protected from the incoming moisture via the rainsreen. Now stage two kicks in with the open joints that let the sun and wind to quickly dry out the moisture. The second benefit of this system is the negative detail aesthetic from the black rainsreen. 

Cavity Battern inside


We used 12mm plywood ripped down to 25mm wide and screwed and glued to 25mm think structure ply. This braces the inside of the walls and creates a cavity to run wires and plumbing. 


Lining


7mm lightweight plywood lining is glued and pinned to the battens create cross bracing element. 


At time of writing the system has been installed for a year and half and we have has no problems. The UV facade it still the same black colour and showing no signs of giving up in the hot Hawkes Bay sun. Some of the cladding has warped and blown a few screws a month or two after installing. This is due to immature pine timber twisting in the heat and rain. In hindsight better material section would have avoided this. 

Another reason we could be a bit more riskily in terms of design is because this is a tiny house. For example we can re clad it if we had to and its not a massive job. 

The warm inside the structure seems excellent with living it at as of yet. We have not considered a heat source us of yet and taking the wait and see approach. We suspect we may need a small heat source or just turn the oven on! 

A lot of what we have done is new and even unproven in some regards, but that is whole idea. This has all taken a great deal of time but the whole idea for use was to learn and think and about things differently. Would we do it again this way? For the most part yes, off course they are things we would do differently but we are real happy how its all turned out. 

Please ask any questions you have.



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