The First Passive House in The Lake District National Park

This project is the first passive house in The Lake District National Park built with super insulation, triple glazing, low air-tightness, passive solar gain & with the benefit of a fully integrated solar thermal hot water & photovoltaic panel roof array. The only heating is via mechanical heat recovery ventilation system which guarantees pre warmed clean fresh air.

Project Introduction. Tim & Sarah moved to Staveley in the summer of 2010 when Sarah was appointed to a teaching post at John Ruskin School in Coniston. They had been living in rented accommodation in Staveley village, but had not found anything tempting to buy. When Middlefell a dilapidated falling down substandard bungalow became available on the edge of the village, they jumped at the chance to demolish it and start the process of building a Passive House. Tim & Sarah are supporters and members of the local Sustainable Energy Network Staveley (SENS) organisation and have friends at the Lancaster Cohousing Passive House project 30 miles down the road.

Tim & Sarah have a long standing interest in sustainable, low energy “green’ buildings, having been frequent visitors to Scandinavia and experienced the ‘norm’ of their highly insulated comfortable homes, and where excited by the opportunity to build one of their own. Tim & Sarah where keen to build and live in the most energy efficient house yet to be constructed in the Lake District and work with Eco Arc Architects with our track record of innovation in low energy Passive House sustainable housing. (it also  helped that our office is just 4 miles from the site.)  In response to the challenges of Climate Change and the depletion of fossil fuel reserves, Tim & Sarah where motivated to demonstrate alternative design and construction solutions that support the shift towards Low Carbon lifestyles and provide a possible new vernacular model for future affordable housing in the protected Nation Park.  It was equally important to Tim & Sarah not to create a lavish building, but to ensure the design concentrated not only on energy efficiency and sustainability, but cost-effectiveness.

first passive house in The Lake District National Park
super insulation, triple glazing, low air-tightness, passive solar gain
use of recycled materials

Having experienced friends struggling through the inevitable delays during long cold winter months building the traditional wide cavity masonry built Lancaster Cohousing Passive House project, Tim & Sarah decided from the outset that they wanted to go for the efficiency and speed of a part off site prefabricated super insulated timber frame construction to achieve the Passive House Standard.

Project Aims: Tim & Sarah set the project aims to demonstrate best practice in: home energy conservation, renewable energy use, water conservation, waste reduction & home food production.

Principles of Design and Construction: It was agreed from the outset the project aims would be achieved through the application of: super high levels of insulation, minimizing thermal bridging, excellent airtightness & heat recovery ventilation, natural daylighting, passive solar gain, renewable energy (solar hot water and photovoltaics,) use of recycled materials & recycling of rainwater along with local resourcing of materials and labour.

Passivhaus Design Standard: The dwelling has been built to the Passivhaus standard working through PHPP design with Andrew Lundberg of Passivate and with initial M&E designs by Alan Clarke. As most readers will know this is a successful European ultra-low energy standard for buildings as Passivhaus buildings use only a fraction of the energy for heating (90% less) compared with houses built to the standards required by current UK building regulations, and deliver low carbon solutions without needing excessive renewable energy. Where Passivhaus differs from UK building regulations and CSH is the requirement for an absolute minimum level of energy consumption instead of improvement over a more basic specification.

The Passivhaus approach has three main strands: 1.To minimise heat loss – via a compact built form, super insulation and triple glazing. 2. To minimise ventilation heat loss – via airtight construction and heat recovery ventilation, & 3.To optimise solar gain for winter heat.

These factors combine to deliver a heating demand that can be met with a minimal heating system (it is recognised that to design a house that needs no heating at all is not economic). As well as very low heating bills, Passivhaus offers comfort and a healthy indoor environment. Attention to detail in design and construction ensures no draughts or cold spots wherever you are in the house. Heat recovery ventilation uses low power fans to provide ample fresh air day and night, warmed to room temperature by a heat exchanger transferring the heat from the exhaust air from kitchen and bathrooms to the incoming air.

Passivhaus is a rigorous energy standard; where energy performance must be demonstrated through the use of the Passivhaus energy modelling software, ( PHPP ) which is specifically designed to model ultra-low energy buildings. This is backed up by air leakage tests and commissioning records of the heat recovery ventilation. The standard requires a predicted heating demand of 15kWh/m².a over the usable floor area, adapted for the local climate (average energy use for UK housing stock is around 200kWh/m².a and new-build ranges from 50-100 kWh/m².a).

We developed the design of the 2 storey house as a compact 10.7m X 7.4m south facing plan. This form has minimised the heat loss from the house and enabled gains to be received from its share of winter and summer sunshine. The Passivate PHPP Planning design shows that the house achieves the required targets of Space heating demand of: 15 kWh/m2/yr, a Heat load of: 10 W/m2 & a Primary energy demand of: 112kWh/m2/yr. We worked hard to develop bespoke cold bridge free junction detail designs and Passivate carried out extensive Psi-Therm 2D modelling of all the key junctions to achieve a resultant calculated cold bridge PSI- value 0.02283 W/mK, fRSi-value 0.91.

renewable energy (solar hot water and photovoltaics)
passivhaus
passivhaus interior

The Passivhaus standard requires an airtightness of ≤ 0.6 ach (air changes per hour) @ 50Pa (current Building Regulations require 10.0 ach @ 50Pa). This high standard ensures draught-free comfort, protects the building fabric from condensation due to leakage of humid air, and ensures that the efficiency of the heat recovery ventilation is not bypassed by leakage ventilation. The completion air test by Paul Jennings of Aldas confirmed an Airtightness result (at 50 Pascal’s): 0.58 ACH or 0.52m3/m2/hr

As a bonus to meeting the Passive House standard criteria the house achieved an ‘as Built’ EPC A rating and a numerical SAP figure of 104 making it eligible for a level six Code for Sustainable Homes rating. Tim & Sarah have now moved in, but are still finishing off certain superficial completion tasks and will monitor actual performance against design criteria over the next twelve months. We will report back in due course to let you know how it performs in reality.

Building Fabric: Working with Viking & MBC Timber Frame we developed the low U value, super-insulated, timber building fabric build ups as set out below:

Ground floor:  20mm reclaimed maple flooring, on 50mm battens with Knauf glass wool insulation between, on 100mm thick reinforced concrete floor slab, on 300 mm Aerofloor EPS insulation, on Viking Passive Slab (PHI certified). U-value: 0.105 W/m2K.

Ground floor walls: 10mm thin coat silicone K render, on 100mm Masterblock recycled aggregate concrete block, on 50mm wide drained cavity, on Pro Clima Solitex WA wind-tight membrane, on 12mm thick Panelvent sheathing board, on MBC 300mm stud twin wall with full-fill Warmcel 500 cellulose insulation, on 12mm OSB with taped joints. The walls are finished internally with 50 x 50 battens to form service void insulated with Knauf glass wool insulation, on 12.5mm Gyproc plasterboard internal lining with plaster skim. Dulux Ecosure emulsion paint. (PHI certified). U-value: 0.112 W/m2K.

First floor walls: Eternit Cedral weather boarding on, 50 x 50 mm vertical battens to form ventilated cavity, on Pro Clima Solitex WA wind-tight membrane, on 12mm Panelvent, on MBC 300mm twin stud timber wall with full fill cellulose insulation, on 12mm OSB with taped joints, The walls are finished internally with 50 x 50 battens to form service void insulated with Knauf glass wool insulation, on 12.5 mm Fermacell board with Dulux Ecosure emulsion paint finish. (PHI certified). U-value: 0.110 W/m2K.

Unfortunately the sub-contractors on site omitted to install the specified Pro Clima Intello Plus vapour control membrane assuming the 12mm OSB with taped joints would suffice. This goes some way to explain the marginal pass rate at the final airtest, when compared to other subsequent timber frame projects, where we have come to expect a result of 0.2 to 0.3 ARC (at 50 Pascal’s) as standard.

Roof: Bob tail fink truss rafters at 600 c/c with 620mm full fill Warmcel insulation, followed underneath by Pro Clima Intello vapour control layer / air tightness barrier, 25 x 50 battens to form a services void, 12.5mm drylining Gyproc board, Dulux Ecosure white emulsion paint finish. (PHI certified). U Value: 0.065 W/m2 K.

Unfortunately the sub-contractors on site failed to install the specified OSB ceiling board to support the loft insulation, so we had significant sagging of the air tightness membrane between the service battens which made taping difficult.

Windows: Ecohaus Internorm KF410 triple-glazed aluminium clad windows and doors with, ISO glazing spacers (Overall U-value: 0.72W/m2K) were supplied & installed with air tight tape seals by Ecohaus to a very good standard. We certainly recommend a similar supply and install package on all our other PH projects to retain a single point of responsibility and high levels of quality assurance.

Passive and Active Solar Design: A large percentage of the high performance solar glazing is orientated due south to the private courtyard back garden to obtain the benefit of passive solar gain to the living spaces. Shading prevents summertime overheating but permits low level winter sun to penetrate to the heart of the house. Windows to the north, east and west elevations that have less passive solar gain potential and are in comparison deliberately kept more traditional in scale and modest in size to reduce heat loss.

Site Generated Solar Hot Water: One the largest consumers of energy within any house is the heating of domestic hot water to service the kitchen and bathrooms. As part of the sustainable development, 7.8 square metres of 3No Consolar Plano 27H flat plate integrated solar Panels are located on the south-facing roof of the house and are connected to an Akvatherm 500litre  solar plus thermal store located in the centre of the house off the landing. 

Site Generated Solar Electricity: A 4kWp Solar photovoltaic integrated array, consisting of 16No Hyundai 250W modules are mounted on the south-facing roof of the house to convert sunlight to domestic use electricity and hot water via a Immersun controller unit to transfer excess electric to the Akvaterm solar thermal store.

Low Energy Appliances: All appliances have been carefully considered to eliminate unnecessary electrical demand and to optimize the efficiency of the essential items (cooker, fridge, low energy LED lighting etc).

Mechanical Ventilation With Heat Recovery: In winter months when the outside air is cold relative to the required inside temperature, a Passive House Institute certified Paul Focus 200 whole house clean air comfort ventilation system is fitted with a 1kW electric supply duct heater which includes the controller, programmable room thermostat and duct insulation (note: all of the supply ductwork was insulating with 50mm of foil backed fibre glass insulation. (Heat Recovery rate 91%.) All the duct work was installed by the local Cumbrian plumbing sub-contractor, who had little previous experience and the final installation was commissioned by the suppliers, The Green Building Store.  Tim and Sarah have the option to not use the mechanical ventilation system in the summer months in favour of natural ventilation.

Water Use: Presently we spend an enormous amount of energy and money collecting and purifying fresh water to a high standard suitable for drinking. We then use this very inefficiently for purposes that do not require this level of purification. In this proposal, household and garden non-potable water requirements are met by collecting rainwater from the main roof via galvanized steel gutters and downpipes and storing it in water butts and a 2000 litre ‘Rainharvester’ underground storage tank. Water from underground storage is filtered and used for flushing toilets and the washing machine. The water butts are used for garden irrigation. Mains top-up water is available from the mains system, but due to the relatively high rainfall in Cumbria this has not been required. Efficient low water use dual flush toilets with a maximum flush of 4 litres and aerated flow restricted taps and shower heads have been installed.

Healthy Internal Environment: Scatter rugs over reclaimed maple timber boarded floors, organic non-volatile solvent paints, avoidance of formaldehyde and other toxic equivalents combined with natural materials along with summer natural ventilation and a winter heat recovery mechanical ventilation system has l lead to a healthy internal air quality which Tim & Sarah are very pleased with.

Household Waste: Kitchen waste and garden debris material is composted until dry and inert and then returned as a valuable non-toxic fertilizer to the food growing areas of the garden and conservatory greenhouse.

Organic Home Produce: The carbon footprint of most households is greatly increased by the reliance on industrial food processing systems and the food miles required to get food to our tables. The lean too conservatory / greenhouse facilitates the propagation of seeds and growing of organic home produce combined with the vegetable garden on the site, which goes some way towards reducing Tim & Sarah’s carbon footprint over an extended time period.

Costs: The overall building spend was £220K which included for a 72m2 one & a half story workshop / utility store and a 15m2 conservatory greenhouse outside the thermal envelop of the 3 bedroom main house. So the actual spend on the passive house thermal envelope was in the region of £1,370m2, which is exceptionally good value for any one off architect designed house never mind a eco house to the passive house standard. Tim & Sarah will have minimal utility bills for life; in fact at the time of writing they have surplus income after paying bills due to the FIT & RHI tariff payments received.

Build Procurement Route: The high quality/good value for money construction was achieved by Tim & Sarah acting as fully engaged active clients, employing two local Cumbrian builders; Sam Nelson & Jim Crawford on a labour only basis (Sam has done a lot of previous work with Eco Arc before; including building our architects office and private home, so he was highly trusted from the outset.) The timber frame element was sourced directly from MBC in Ireland at a good price. Sam opened direct trade accounts in the clients name with several local merchants and most materials were paid for direct to the merchant by Tim & Sarah at the end of each month along with Sam & Jims labor costs based on time sheets.  Most other sub-contractor trades submitted competitive fix price quotes which were agreed en-route through the build process. We have used this procurement route many times before, to avoid risk averse over pricing by main contractors who are not familiar with passive house construction and tend to put up tender figures to a super inflated level to cover the un-know risks. Sam had never built a Passive House before, and learnt on the job with some gentle tuition from us, he finished this one on time & on  budget without a cross word. Sam has now almost finished his second Passive House in Kendal and has agreed to go on and do a third house in Windermere on the same procurement basis, as it seems to be a winning formula for all parties.

Timber Verses Masonry. We have now finished 45No masonry passive houses across five different sites in North England and are currently working on 18No individual timber frame passive houses across a similar geographical region. Clearly there are pros and cons for both options which vary from site to site and client to client depending upon specific circumstances. Tim & Sarah’s house was a steep learning curve down the timber frame route but it was a success. We have now fine-tuned a timber I beam and Cellulose system with a local Cumbria based timber frame fabricator Trevor Lowis of Eden Insulation and Cumbria based Ecological Building Solutions which has allowed us to erect the whole timber frame thermal envelop consisting of all the pre-insulated walls and roof for a four bedroom house in one day, and follow on with installing the triple glazed windows with air tight seals over two further days and deliver consistent air tightness results in the region of 0.2 to 0.3 ACH at 50 Pascal’s.  In comparison our last wide cavity wall masonry passive house project in Cumbria for two affordable passive houses finished 4 months late due to bad weather delays and struggled to achieve the required 0.6 air tightness results with a wet plaster approach.  So from a range of experiences in terms of quality control and time certainty we are leaning towards timber frame as a quality assured route to passive house certification delivery. We are currently working on our first single block work leaf with external wall insulation passive house in Chester so that may put the cat amongst the pigeons and knock timber frame off its perch ?

CONCLUSION: The Staveley passive house is an appropriate and high quality / good value development that provides a possible model for the way our new homes may need to operate within a Low Carbon Society and show a route whereby we can live our individual lives in a more sustainable way.

Photos Text by Andrew Yeats & Vincent Fierkens of Eco Arc Architects.

(With input text from Alan Clarke on the Passive House Standard article text)