COLD BRIDGING DETAILS FOR 2009

Since late 2008, all new houses are required by law to be built using a new set of construction guidelines.  These new guidelines have increased the level of detailing required in all new buildings.

The most obvious changes are in relation to the AIR-TIGHTNESS of buildings and the higher insulation requirements.

One area that isn’t so obvious to solve  is the area of cold-bridging of the various elements of a building.

Cold briging? what is it?

Cold bridging is a term used in civil engineering and damp proofing. It is the situation when the inside walls of a building become cold enough for condensation to occur. A well insulated and ventilated building can avoid this problem.

You may see the analogy with clothing. Cold bridging occurs easily on all thin, non-insulating waterproofs in cold and wet conditions (particularly when the outer fabric saturates).

In relation to buildings, the various manufacturers of windows etc. have started to tackle this problematic  issue, with the introduction of new aluminium and pvc windows which have a double frame construction, separting the outer frame and interior frame with an insulating compound. For passive house levels of coldbridging it is necessary to use a triple glazing specification on the window combined with the high-tec frames.

The big question now is this:

How do I reduce the thermal bridging between the foundations and the rising walls of a typical new house? as this is where there is a huge amount of cold-bridging, between the foundations, which are in direct contact with the ground, and the rising interior walls of the house. Typically, this is the location of a room which has the poorest thermal bridging performance.  Easily seen on a thermographic camera, as a dark blue/green area, it represents the one area of a wall which has the potential for the formation of condensation.

Thankfully, there are solutions which don’t need to break the bank:

The following are a number of articles posted on line in relation to the issue of breaking the thermal bridge between the ground and the rising walls:

The above article relates to the use of a type of glass foam block, used in the blockwork, at ground floor level.  The 100mm glass foam block is built in during the blockwork phase and provides a thermal break between the concrete floor and the rising blockwork from the ground. It appears to be an ingenious system, but one which needs further testing to ascertain its true potential.

The glass foam block has a lambda value of 0.3 so a 4 inch glass foam block has the same insulation effect as 10mm of Polysterene which is not so much.
Trying to modify a partial cavity wall to build an energy efficient house is like putting a new engine into a Ford Escort.

Here are the product specifications for the glass foam block. This is just for informational purposes. Further testing of thses concepts wil be necessary in order to ascertain the true benefit of this approach to detailing.

__________________________________________________________________________________________________________________________________________________

Alternative 2:

Another approach to this detail is to completely separate the concrete foundations and floor from the ground level by use of 300mm structural polystyrene insulation.

This is the system we are presently using giving a Swedish U-value of 0.11.
(1.1 U-value Swedish windows are 0.8 here.)

The house sits on a 300mm bed of structural Polysterene with no part of the house or foundations touching the soil. The external walls sit on the insulated ring beam designed to take the loads.
It completly eliminates all cold bridging between the floor and the wall when used with Poroton + external insulation or timber frame. The external wall insulation connects with the insulation around the ring beam and stops all cold bridging.
It offers the highest U-value in the world for a similar amount of insulation because all the thermographic lines are concentrated to the Polysterene upstand between the ring beam and the floor slab as you can see in the two images below.

This is the Thermograph (above) for the older L-element with 300mm Polysterene under slab.

This is the Thermograph (above) for the latest Swedish U-min foundation system with 300mm Polysterene under slab.

The U-value improves by 0.08 with no increase in material.
Scan Homes are keen to use this foundation system on all their new houses as they see the value.
The ring beam can take loads of up to 35 tonnes/linear metre.