A lot of people ask me about the detail of how my house is built so I thought it worth a thread to explain things.
First off, I didn't want an "ordinary" timber framed house with a cavity then a brick or block outer skin. That outer skin just costs a lot of money and adds nothing to the insulation of the house, it's just an expensive rain shield.
I still wanted the traditional Scottish look of a white rendered finish but I want all elements of the wall make up to add to the insulation and air tightness of the property.
The solution is a timber frame, clad with 100mm thick wood fibre external wall insulation boards (I used Pavatex, but other makes are available), and the render goes straight onto the wood fibre board.
Here's a picture to make it clear:
In that picture I only have a few of the fixing screws in place. A lot more were added and then driven fully home. The board is fixed to the frame with long screws with big plastic spreaders to stop the screws pulling through the board.
There are a few twists to the frame however. First thing you will notice is that it is not an "ordinary" timber frame. For a start it's built with much thicker timbers than normal to allow more insulation in the walls. But secondly people keep telling me i have put the frame up "inside out" The OSB racking layer is on the inside of the frame. That's done for vapour permeability reasons with the least vapour permeable layer on the inside.
With this build method you can either fill the frame with blown in insulation from the inside once the wood fibre cladding is fitted, or in my case I have chosen to use Frametherm 35 as it's less than half the cost of blown in insulation but gives the same U value. So I am fitting the insulation from the outside as I fit the wood fibre cladding. Insulating only that bit of frame I expect to get clad in that day as I don't want the insulation left exposed to get wet if it rains.
The render is a lime based system from baumit.com. It has 3 layers, a base coat that is mixed from dry powder, then a primer that is painted on, then the top coat comes pre mixed in tubs. A fibreglass mesh gets pressed in to the base coat before it is dry.
Overall benefits of this approach Vs an ordinary timber frame with blockwork outer skin:
Simpler foundations (no need for provision to support the outer brick or block wall)
More insulation for a given wall thickness
More of the job can be DIY done, perfect for self builders.
And an unexpected one, because there is no cavity, there is no need to pepper the wall with weep ventilators, so you get a clean render finish with no "warts"
And here is what the finished and rendered front of the house looks like.
