Beginners’ Guide to Building a Low-Energy Home Series – Part 3.
Being a self-builder gives you total control over choosing a plot, designing the architectural style of your house and its layout to suit your specific needs. When designing your Self Build you will also have control over how much you will pay for the day-to-day running of the house. Whether you want to have a house that is environmentally friendly or you want to pay the less for your bills, it is advisable to review your options and what you may get in return for your investment.
This is the last of three articles in our series ‘Beginners Guide to Building a Low-Energy Home’ – the series takes you through the main stages in developing an energy efficient house. The first part introduced the idea of a low-energy home, and described the concept of a Zero-carbon house. The second part explained the principles of building a Passivhaus. In the last part we describe the Fabric First approach. Taking you through the key stages, which will help you build a highly insulated home – without spending money on expensive ‘eco-bling’ that you may not need!
The Fabric First Approach

The last part of our guide to building a low-energy home is a back to basics approach which will concentrate on the fabric of the building first, before focusing on the installation of expensive heating systems – that you may not actually need.
There is a set of basic design principles (or rules) you must follow in order to achieve a Fabric First design. At the heart of your Self Build design will be a highly insulated building envelope with limited cold bridges and high specification windows and doors. You need to use air tight membranes and tapes in order to limit the air leakage from your building at all construction junctions. The next thing you need is to install an MVHR system, this will provide fresh heated air throughout the home. In order to maximise the sun’s natural solar gains, you have to make sure that the house’s design and orientation make the best use of the site. Finally and only once you have got the fabric bit right – you start looking at the renewable heating options.
Now that we know about the basics, we will focus on its six key elements in a bit more detail:
There are many different construction types that will provide an air tight, low-energy house, but there are some construction methods that achieve it in a simpler, more cost effective way. You need to choose a construction type which is naturally air tight, highly insulated and ideally produced in a factory environment rather than on site. We recommend you choose one of following types, all can easily achieve a u-value of 0.10 to 0.15 W/m2k:
– Timber frame – although it is a traditional construction method, it is cost effective and can be easily used to achieve a low energy house. It is advised to add extra airtightness membranes and external insulation.
– SIPS – is a rigid system with insulation bonded to OSB. This is a very air-tight product.
– ICF – is a really good product for achieving an air-tight low-energy house. When using ICF you create a large area of thermal mass.
The thermal mass in ICF will effectively store the heat during the day and then release it throughout the night. Material with low thermal mass will just transfer heat, instead of storing it. If you use timber frame or SIPS, you can compensate for this lack of mass by using the concrete floor slab. If you design your building correctly to the Fabric First principles, you may only need to heat the ground floor, with no heating required on the first floor.

Firstly, let us put to rest one common misconception with Airtight homes. Many people think: ‘I have got an air-tight house, so I must close my windows and doors all the time’ – this is not true! In a passive house the method of ventilation in summer is purge ventilation i.e. opening your windows or doors.
In order to increase air tightness, we advise that you tape the junctions of the panels on the external walls. Also tape around the windows and door reveals. Then, you can wrap the whole building in an airtight membrane (increasing the airtightness of a timber frame construction type). It is important to communicate to all the workers on your site, that if they need to make a hole in the building, they need to advise you so that you can seal it. Remember, that the squidgy foam used around the windows has no airtightness, so those areas have to be taped with the correct products.

3 – LIMIT COLD BRIDGING
Cold bridges or thermal bridges are areas where construction elements have direct contact from the inside to the outside, for example a timber batten in an external wall. These elements are usually poorer performing elements and can create heat transfer through the building. So, if you want to have an energy-efficient house, you need to eliminate or reduce cold bridging as much as you can. One easy way to reduce this is to go from Timber frame construction to SIPS, as the SIPS construction has twice as few poor perfroming timber battens (timber batten centres are generally 600mm and SIPS are 1200mm) In order to achieve a design where thermal bridges are limited, your architect will need to detail all of the major construction elements.

If you want to create an air-tight house you have to manage the ventilation, You cannot just rely on the old fashioned trickle vents. Traditionally, windows have little holes with plastic covers in the top frame, We open and close them in order to bring cold air into our house – It is impossible to manage this process.
However, with a heat recovery system you can manage and control the amount of heated air which is moved around the house. It allows you to recirculate the air up to 10 times more than through trickle ventilators, which means much cleaner air in your Self Build home. Mechanical Ventilation with Heat Recovery (MVHR) system is usually recommended when you are planning to build a low-energy home, but it is important to make sure that you have appointed a professional to instal and commission it. For more information about MVHR systems you can read our article here.

The next crucial part of designing a low-energy house is solar gain. It is important to correctly orientate the building, ensuring there are large openings on the southerly windows, with smaller openings on the north side. It may not be practical to design all your views to the south, but you need to have a trade off between how energy efficient you want to be and making the most your views. We would also recommend you to consider accommodation of shading or brise soleil as (even) the UK can experience overheating during the summer.

The last thing to consider when designing your home with the Fabric First approach is the heating strategy – it is achievable to get the heating demand down as low as 3 or 5 KW even in the UK. The most cost effective ways to provide the heating demand is through a small boiler and underfloor heating (on the ground floor only). There are some renewable heat incentives that you get from using air source or ground source, but the upfront purchase cost is still huge given the low heating demand required. We would suggest using the PHPP or SAP calculations to work out what the heating requirments are for your individual home, then getting a heating company to design the system you require.

“Integrate Fabric First with everything you are going to do. Take the principles of Fabric First and use it, because it will save you a lot of money in construction process and in the long-term of the project”.
Allan Corfield
If you follow all the stages of the Fabric First approach to your Self Build, you will achieve a low-energy home for a reasonable cost. And if everything is applied correctly, your effort and investments will payback in low energy bills and the satisfaction that your home is good for the environment.
More guides based on Allan’s talks from the Homebuilding & Renovating Shows available below:
Beginners’ guide to building a low-energy home series is based on a talk created and delivered by Allan Corfield for Homebuilding and Renovating Magazine, at the 2016 Shows. If you have any questions for Allan and the rest of the team, send your suggestions to us via email, or social media using #asktheselfbuildexperts.
I am very interested in the concept of the Passivhaus having spent time in a cousin’s Passivhaus on the outskirts of Frankfurt Germany albeit in mild early summer temperatures and designed and built my present house. The vast majority of your comments and information understandably relate to cold climate and retaining internal warmth. I live in sub-tropical Australia where the daytime temperature can be 30C+ almost continuously for several weeks or months and the evening temperature rarely dips much below sea temperature which is currently 24C.
As I understand it, the alternative word for insulation ‘lagging’ is because most commercially available insulation does little more than slow the transmission of heat or cold. So my question really relates to the period of time that it will take before the interior of the house fabric becomes close to the exterior temperature and the house becomes an unbearable thermal mass which will take time to re-cool or reheat to an acceptable temperature.
By, comparison my present house is built on a hillside just in view of the ocean uses a totally contrasting approach. It is a two storey Queenslander of sandstone cavity block construction with a 2.7 metre wide veranda all around and sliding French doors to all rooms. During summer evenings and early morning we open all doors to allow the cooling westerly counter sea breeze to blow through the house. The lower floor of the building is half built into the hillside and never drops below 18C in winter or rises above 25C in summer. The roof space is insulated immediately under the corrugated steel roof and then above the ceiling and the air space is ventilated to expel excess heat. During the late morning the sea breeze blows from the north east and the doors remain open until the air temperature increases at which time the house is closed until the evening cooling breeze. Ceiling fans are used for cooling if required.
In the winter the north facing veranda creates a heat trap for the low sun and the north easterly sea breeze blows the warmed air through the house. If occasional evening heating is required this is provided by a wood heater from timber grown on our property. After 50 years of living in this climate we have just installed air conditioning for a little extra comfort but it is rarely used.
I have often thought that if I was to build a new house I would use the principle of the lower floor of our house and build it half underground. However, I would be very interested in your views on the suitability of the Passivhaus design for warmer temperatures.