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.

Which gas boiler?

On the long list of decisions to make is the choice of gas boiler.

Given that hot water use will probably be higher than our heating requirements (and we are low water users to boot), we'll want a boiler that is very, very small. I'm hoping we'll be using less than 5000 kWh per year of gas in total.

A top of the price range, super-efficient boiler won't save us much, given how little gas we will use. A small and basic combi boiler at a correspondingly basic price sounds attractive right now!

Any suggestions?

Air tightness and insulation coming soon

The long gap since the post about insulation below the damp proof course does not indicate a lack of activity - just my lack of interest in groundworks.

Once the groundworks are complete (and essential things like gas, electricity and water which for various reasons are being moved into the garage) we are on to the main external wall insulation and lots of air tightness work - hurray. June will be busy!

One thing to consider if embarking on a refurbishment project is that there are chickens and eggs all over the place, making life complicated and slowing things down.

For example, if the gas meter is on the external wall and you don't want to create a major thermal bridge by only insulating round it, you have to move it. But if you want to put it on the external house wall, that has to be insulated before re-instating the gas meter. So what to do in the meantime? Live without gas? Pay to disconnect and then reinstate, which costs more?

In our case, we decided to move the gas meter to the garage wall. Which would have been very simple if the garage had been in a fit state, but with the whole structure sinking badly, we decided to rebuild. Only now is the new garage wall in place to receive the gas meter. The rest of the garage can't be built until the external wall insulation is complete. So installation of the gas boiler and MVHR unit will have to wait until we have a garage roof. And so it goes on.

For more detail about this project...

There is more detail about this project in the 'Homes Behaving Badly' (HOBBS) report - it is the 1950's case study in section 2.3.3.

To view, click here. The report can be downloaded for free as well, and is easier to navigate via the contents page once downloaded.