Case Study

Case Study

Introduction

Our client wanted extra accommodation, and we undertook this project to build a 2 Bedroom garden house to see how  achievable it is to build accommodation at a cost effective price.  We wanted to build a building that followed the principle of a lodge, but delivered better performance and a better look.  If we could achieve this, this could solve how to achieve affordable housing.

The Design Brief

2 bedrooms, with 2 bathrooms and an open plan kitchen and living area.  Client requested bi-fold doors to all rooms, which were made from Accoya® along with the front doors and all other windows to match.  This was done by 414 Timber & Fencing.
The customer also requested a bath, which we also installed.  
It is worth noting, that we would not normally propose these things as they make the building less energy efficient due to increased air leakage from the doors, and more energy to heat the water required for a bath.
Performance Values

We originally wanted to build this building to passivhaus standard, as we felt this would help us demonstrate the off-grid potential of what we can do; but in the end opted for a performance level that would stay focused on affordable housing, which also included buildings that satisfy the planning permission/permitted development and could be categorised as a lodge.  

The U-values for the buildings are as follows - 
  • Floor   =  0.21
  • Walls   =  0.21
  • Roof    =  0.17
The Y-values were also considered very carefully, and all openings had insulation preventing cold bridging to the lintels.  Again, we could use air tightness tape in these areas to further reinforce the performance of these joints, and would do if we had a client that wanted either a passivhaus or off-grid solution.

In terms of the airtightness, again we wanted to go for a level of 0.6 arch, but as the customer wanted to have bi-fold doors to all rooms we knew this would not be realistic for the budget we had. All joints of the SIP panels were glued using special expanding PU glue, and screwed. We can further improve the air tightness by using air tightness tape to the inside of the building on all joints.
We used LightwaveRF wireless lighting to avoid chasing out the walls and affecting the airtightness, and the electric sockets ran around the subfloor and up the plasterboard.
We fitted a HRV system to make the building feel comfortable, which will allow fresh air into the building without losing heat.
The Alternatives

At the moment, the main types of buildings in this market are static caravans and park homes/mobile homes.  We believe that based on the costings of this project, this could be a viable alternative to these types of buildings which both have challenges.
  1. Static caravans have a real problem with them being very hot in the summer, and very cold in the winter as the buildings are very lightweight.  The layouts are not always conducive to full time living as they can soon feel cramped if lived in by a family.
  2. Mobile homes/lodges have a similar challenge to static caravans, although not as bad.  They feel much more homely and are more suitable as a full time home.  From experience, the electric bills can be quite substantive during the winter months, so for affordable living this is a challenge as electricity is becoming more and more expensive.

Proposed Solution

We believe that our Garden-Haus buildings can be the viable option to the two traditional options.  We now know that we can offer -  
  • Family friendly layouts, that are modern and feel homely and spacious.
  • Options that minimise summertime overheating by increasing the decrement delay and can add thermal mass to your building.
  • Options to minimise heating bills, with the ability to upgrade to passivhaus or go off grid - this means no heating bills if designed and sited correctly for your plot.
  • Affordable!  We can deliver, or erect on site, 2 and 3 bed units, starting from under £100,000.

Recommendations

From this exercise, we have learned that for buildings to be both economical to build and to run, there should be some considerations by the clients on what is really needed, and how the building is going to be used.  In this building, we put in a bath which has the knock on effect of storing and heating more water.  
As mentioned earlier, we would also avoid increasing the risk of air leakage by bifold doors.
In terms of services, we opted to not use gas, but also avoided the temptation to fit a wood/log burning stove.  In future I would recommend that we stick to this strategy as we do not understand the users and adding these services could potentially be dangerous.

Using electric only, it becomes much easier to monitor and take action to save money.  Here is a guide to how much electric is used in buildings - https://www.cse.org.uk/advice/advice-and-support/how-much-electricity-am-i-using 

Figures are similar when it comes to baths versus showers, but consensus is average bath is 80 litres, and a shower is 30 litres. By having a shower only arrangement it not only is more environmentally friendly, but more economical both at the building phase and the occupancy phase. Figures here are taken from http://www.southeastwater.co.uk/faqs/saving-water/how-can-i-save-water-in-the-home

On this project, we didn't look at rainwater harvesting and the use of grey water, this would be something we are interested in introducing in future buildings or indeed would do if we have the chance to do a research and development project.


Conclusion

This exercise has enabled us to see the potential of what we can achieve with these buildings, and as such can have conversations with more people in terms of providing accommodation for all sorts of people, on a short or long term basis.
We hope to introduce a range of pre-designed buildings that can easily be customised to the client, which can be either pre-fabricated or erected on site offering a choice of either clad or rendered finishes.
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