Our luxury Garden Buildings used as Garden Rooms and Garden Offices are all fully insulated to modern standards. The lower the U-value, the more thermally efficient the wall construction is, so a U value of 0.28 is much better than one of 1.6. 


All construction materials are tested to determine how much they conduct heat (known as the Lambda value), and the combined performance of a set of these materials will determine the overall thermal capacity of, say a wall; this is known as the U-value. 

In simple terms, a U-value is the amount of heat lost per square metre of a building component (wall, roof, floor, windows etc).

The U-value, therefore is the resistance of these materials to heat passing from a warmer environment to a cooler one.

The higher the U-value the worse the thermal performance of the building is because it shows how much heat is being lost through each square metre of internal surface.

The U-value will take into consideration the wall thickness, material and any render or insulation used.  For example, a typical solid wall (9 inch brickwork) used in a Victorian property has a U-value of 2.1 W/m2K. The Table below shows this in comparison to other, more modern elements:

  • Type uv comparison chart.

As you will note, a Victorian house loses nearly 10x as much heat through its Walls as a RUBICON™ Garden Room, whilst a modern (uninsulated) Brick Cavity Wall loses nearly 6x more. 

It should also be noted that, whilst double glazed windows are far more heat efficient than single glazed, you still lose far more heat when a building has lots of glazing, even though we fit Pilkington's 'K' Glass giving a U-Value of 1.6. 

That's why 2010 Building Regulations state that only up to 25% of a buildings exterior fabric should be made up of glazed areas.  For this reason we offer our 'Classic' configurations which are warmer and more energy efficient than our 'Panoramic' options.

Through the use of modern types of insulating materials, the thermal performance of our Garden Rooms is dramatically improved, and U-values of less than 0.30 W/m2K (the 2010-2013 Part L Building Regulation for England) can be achieved.

All the U-values for our Garden Rooms are calculated and certified using the BBA Scheme for Assessing the competency of persons to undertake U-Value and Condensation Risk Calculations. This uses the methods stated in BS/EN ISO 6946 2007 and the conventions set out in BR443 as required by Part L of the Building Regulations. Redacted copies of our certificates are available from our offices showing the U-values achieved, which match or exceed 2010-13 Building Regulations. They are redacted to protect our design rights but customers can be supplied with full copies upon completion by request.

The estimated usage of electricity for heating a typical 12mRUBICON™ Garden Room is around £100 a year at 2015 prices.

So, you stay as warm in Winter and cool in Summer in a RUBICON™ Garden Room as you do in a modern (2013) house….! 

Rubicon Garden Rooms customer testimonials

“John was great at communicating to us what was happening when and the result is something we are really pleased with. Highly recommend!”

Catherine Frith