Door thresholds

In a house that has been well insulated externally, the opportunities for heat loss from the house are greatly reduced. Most of the heat loss that does occur is concentrated around the weakest points, such as those locations where a non-insulating part of the structure passes through the insulation or is poorly insulated.

One tricky area where cold bridging is difficult to minimise is the door threshold. No matter how good the door (these are passive house suitable triple glazed doors called 'EcoPassiv'), the positioning of the door and the cold bridge detailing is still critical.

We have done our best with the back door by placing it in a ply box which protrudes beyond the brickwork and into the insulation. However, it is important that the flow screed does not come into direct contact with the brick walls which are exposed at the door opening.

In this case, we removed a course of bricks and placed highly insulating Marmox thermoblocks on top instead. (These will be covered when the flow screed is poured).

The photo shows 4 grey Marmox blocks which sit directly on top of the brickwork. These will reduce heat loss from the screed into the brickwork below. On either side of the Marmox blocks, silver EPS and white external insulation can be seen. Below the slab in the foreground is a 300mm thickness of silver EPS.

Elsewhere, around the edge of every room, up-stands of insulation will form a barrier preventing heat in the screed from transferring horizontally into the brick walls and from there into the ground.