Off grid living, part two — building envelope

This is the second in a series of blog posts by the architect Mark Stephens on taking a traditional Irish cottage off grid. The first post is here.

OK, so here's the first main blog post - where are we going to do it? I'm going to concentrate on an actual built structure rather than the other forms of off-grid living such as yurts, camper vans etc which are discussed in Nick Rosen's excellent book How to Live Off-Grid .

The first form of structure I'll be looking at is the derelict, traditional small cottage which would have been prevalent across the whole of Ireland, though most are now are disintegrating through decay because of exposure to the elements.

There are two stages in making such a structure habitable before we even consider how we then get that dwelling off-grid:

1. Increasing the size. Although we don't want to return to the McMansion sizes of the Celtic Tiger days, we will still need to increase the floor area to make it a more practicable solution for the family of today. Normally the biggest 'traditional cottage' size would have been a single room either side of a communal eating, living/sleeping space. So unless you are a very small family you will need to increase the house by at least another bedroom, and frequently these derelict cottages were without bathrooms, so a new bathroom will also need to be included.

Some older cottages would have been even smaller — I am currently restoring two cottages that were just single rooms where entire families were raised!

I'm not going to discuss here the problems associated with planning for converting properties of this type into habitable dwellings; for more details on this visit my website .

2. Upgrading the buildings fabric to a current standard.

The standard I would suggest trying to achieve is the passive house standard, devised by the Passive House Institute in Germany. Again going into depth on this standard is beyond the scope of this blog post but we can have a look at typical insulation standards that will need to be achieved in order to get close.

The roof should be the most straightforward area as typically the roof will have to be reconstructed anew with new rafters, slates etc. This is generally because the increased weight of slating the roof (frequently the roof would have been metal sheeting that would have replaced thatch) requires the rafters to be increased in size; larger sections of timber would have been impossible to obtain when the house was originally constructed.

This means that we can create a roof with the desired level of insulation. The u-value for a certified passive house  is less than 0.15 W/(m2K), which could be achieved with a warm-roof construction with sufficient insulation between the rafters, and then further insulation under them to prevent cold bridging. The amount of insulation needed will vary depending on the type used.

The walls of the cottage will be more problematic. A typical U-value for a 2' stone wall is over 2 W/m2K; to achieve 0.15W/m2K will require a rendered external insulation of around 200mm of EPS (expanded polystyrene). The good news is that cottages of this type would have been normally been rendered with a lime render and white lime wash which is not a million miles from a modern white, mono-couche external render.

As well as calculating the U-values you should also take care to avoid the risk of condensation; the correct way to do this is with a dew point graph which graphically shows the area in any construction build-up where condensation can occur. A condensation analysis  can be carried out using simulation software such as WUFI, which is based on EN 15026, a European standard for simulating condensation risk.  

Any new structure that extends the existing cottage will be easier to insulate to a high standard as we are constructing anew as per the roof.

The next logical step in thinking is to jump from the derelict cottages that are dotted throughout the country to the derelict houses in the ghost estates throughout every county. Theoretically they should be easier to upgrade to a better standard than the older cottages but their poor location and lack of infrastructure will remain an issue.

So, we have somewhere to live in to conduct our off-grid experiment — the next step is obtaining heat and power to the house. Trying to obtain passive house standards will drastically reduce the heat requirement for the house but it will not eliminate it entirely. The next blog post therefore will address this key aspect of off-grid living.