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12 Passive house made from hemp in Central Brittany. Key dates Designing and building permits : 2010 Demolition : 2011 Construction : April 2012 to October 2014. Jacques and Martine have spent most of their professional careers in the family construction company. When they planned to build a house for their retirement, it seemed natural to them to aim high in terms of energy performance, environmental quality and interior comfort. That is why they chose to build a passive house, built using lime and hemp. Introduction Saint Brieuc Quimper Vannes Rennes Loudéac Carimalo Overview - Photo © études ET chantiers

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Passive house made from hemp in Central Brittany.

Key dates Designing and building permits : 2010Demolition : 2011Construction : April 2012 to October 2014.

Jacques and Martine have spent most of their professional careers in the family construction company. When they planned to build a house for their retirement, it seemed natural to them to aim high in terms of energy performance, environmental quality and interior comfort. That is why they chose to build a passive house, built using lime and hemp.

Introduction

Saint Brieuc

Quimper

Vannes

RennesLoudéac

Carimalo

Overview - Photo © études ET chantiers

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The client discovered all the qualities of hemp in construction at the European project Inater (www.inater.net). In contact with international experts in sustainable building, he realized that the house of the future would be highly energy efficient, comfortable, healthy and environmentally friendly. The project specifications were ambitious: a plot of 625 sq m, very narrow, in the city centre (population of 10 000 inhabitants) ; the desire to bring together all stakeholders in a process of integrated design ; the need to train workers in green building and a desire to work in partnership with a non-profit organisation for social insertion.In collaboration with the architect, a building with 280 sq m of living space was planned, facing south- south west, without openings to the east (property line). Bay windows and skylights are positioned to the south. Despite the goal of energy efficiency, which could constrain the architectural design, the Menguy firm managed to design an original building. The entire building, including the basement, is passive and the entire ground floor is accessible to people with reduced mobility.

Context

Ground plane © Menguy Architectes

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Building overviewThe basement concrete was poured in an insulating jacket of extruded polystyrene rigid foam, specially designed for concrete foundations (JACKODUR - Germany). It rests on a drainage pump. On the surface, a wooden frame (300 mm) was erected to serve as the structure, coupled with a second frame made of «I» beams (Steico wall). An insulating concrete made of lime and hemp was laid manually using the traditional shuttering method and was integrated into the framework, both in the vertical walls and the roof. The implementation of these techniques complied with the professional regulations and French standards for concrete hemp structures. The insulation of the exterior of the main walls was reinforced with wood fibre in the form of wood wool. Interior walls are insulated with wood wool and finished with gypsum board (fermacell).

In the inside, the vertical walls are mostly finished with a lime render or in Douglas Fir panelling.Outside they have used pigmented spruce cladding (20 mm - natural class 3) or a thin ‘Parex Lanco’ coating (12 mm) covering the wall surface, depending on which facade it is on. The windows are triple glazed, different types depending on exposure. Heating is provided by a low temperature under-floor heating powered by a air to water heat pump (Viessman) sized correctly. The hot water is produced by solar thermal panels in conjunction with the heat pump. The double-flow ventilation is provided by a German unit (Paul) that recovers 93% of the energy from the extracted air. The building is equipped with a home automation system (My Home / Legrand) that handles: audio sound, safety, smoke alarm, lighting and general electrical consumption.

Insulating composition - Photo © Jacques Carimalo

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Electrical boxes are airtight thanks to the installation of adhesive tapes (ProClima).

It was not possible to harvest or store materials from the site because of its small size. The wood wool was manufactured in France and Poland. The Douglas Fir wood comes from France. The Jackodur and Steico beams were produced in Germany. The Hemp comes from Belgium.

Details of the roof (inside to outside) : douglas fir panelling with counter batten - dust film – vapour screen - lime and hemp concrete (15 cm) – hemp wool (30 cm ) - batten (2 cm) - membrane - zinc.

Detail of exterior walls : lime plaster or cladding - concrete lime-hemp and wood frame (300 mm) – wood wool and Steico beam-wall (160 mm) - wood fibres (grooved panel tabs) - thin coating of Parex Lanco (12 mm) or wood cladding (20 mm).

Technical focus : Lime and hemp concrete.The hemp used on site comes from Belgium (Prohemp) because it was easier to certify the data required by the office of thermal studies from the Belgian industry. This is a hemp straw (55% chippings and 28% fibres) with a particularly long length of hemp chipping (35 mm). The lime used is a pre-formatted mixture of lime (70%), pozzolan (15%), cement (10%) and limestone (5%), sold under the name «PF 70 Tradical». It is referenced in the professional rules of construction for hemp.

The lime and hemp concrete is more or less determined by the type of construction and insulating performance sought. Examples : 220 kg of binder per m3 in walls against 110 kg for roofs and 600 kg for wall coating. According to the regulations, the lime hemp concrete is not an insulator (thermal conductivity of 0.06 in roofs and 0.072 for walls). It was therefore supplemented with wood wool outside, because the the strict passive construction guidelines would have imposed an excessive thickness of hemp.

The lime-hemp concrete is a

Shuttered hemp - Photo © Jacques Carimalo

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very good acoustic insulator and is effective against high temperatures in the summer thanks to the its thermal mass. It is also considered as having negative embodied energy because hemp is the plant that absorbs the highest concentration of CO2 for growth (135 kg of CO2 hemp chipping per m3 of concrete hemp) and the lime and hemp mixture requires very little embodied energy for its preparation. The shuttering method was chosen for its simplicity and its proximity to the traditional methods of masonry.

The implementation was also carried out, in part, by people who had not done it before, as part of a project of experimental training. Training sessions on site were led by a Belgian expert in hemp.

Lime coating is used as the sealing membrane as lime-hemp concrete is permeable to water and air. The most important constraint in the use of concrete is the hemp moisture management. Given its ability to store water and long drying time, it is absolutely necessary to perform the installation in dry weather or over long dry summer periods.

Timber frame and shuttered lime and hemp - Photo © Jacques Carimalo

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Barriers and solutionsThe main challenge was to design a dynamic and aesthetic building, whilst not limiting its thermal performance because of its cube-like shape. A further difficulty, on site, was the site itself : because of its narrow width of 12 m, its position in the city centre and a dividing wall, certain phases of construction were performed on the neighbour’s property. Moreover, the available space imposed strict control of the thickness of the walls, and therefore excluded the use of straw bales in favour of the hemp-concrete and wood-wool combination.

Lime and hemp shuttering - Photo © Nicolas Le Duin - Constructys Bretagne

On the technical side, many points of detail were the subject of special attention. For example, Douglas fir generates natural acidity (pH 2.9) which can cause the degradation of fixing nails or zinc roofing. Special nails and polyethylene sheeting were therefore used. In terms of safety, one permanent scaffold was made available for general use, approved by an official body in France.

The construction took place over a long period of time, allowing time to evaluate technical solutions and time for

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personal training for the workers. On the economic front, the installation of security measures, access and training time all increased costs. Concerning professional skills: the architect was trained in the «Passivhaus» standard and the «PHPP» (Passive House Planning Package) tool, in addition to numerous other trips and meetings (Association Bâtiment Santé Plus, HQE Association etc ). Carpenters, electricians, plumbers and masons on site, in addition to the construction workers, benefited from training in the use of lime-hemp concrete. The roofer also took an improvement class on zinc and

sealing (Sika) for green roof terraces.

All the workers from the general building company completed training in energy consumption in the building trade (FEE Bat). Some were trained in fitting windows (fitted “between” the walls) and fixing them to lime plaster and installation of controlled double-flow ventilation mechanisms (supplier). The integrated design process has promoted discussion, particularly between the design office and the various technicians, for example in the analysis of thermal bridges. The client, himself a technician, got training in eco-construction through the European green building project ‘Inater’and the PHPP tool.

Inside - Photo © Jacques Carimalo

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Stakeholders Owner : Martine and Jacques Carimalo Architect : Menguy Architectes (Vannes) General contractor : Carimalo constructions (Loudéac) Experimental site training : Etudes et chantiers (Rennes) Expert in hemp concrete : Evia Partners (Ottignies - Belgium) Thermal study office : Energelio (Seclin)

Costs Plot : £25,496. Contract manufacturer : £292,300 inc VAT is £1,044 / sq m TT

The house is designed to be passive (energy requirements for heating and hot water 13 kWh / m² year ; airtightness : N50 <0.6 h-1 ; «total» home energy consumption <120 kWhep / m² year). The project design was based on a thermal study. A dynamic simulation of moisture migration in the walls was performed with the software WUFI. Finally, a study of the construction system was carried out by calculating the dew point temperature, Sd (standard deviation) calculation for the walls and an acoustic study for the basement were added.

PerformanceLiving-room - Perspective © Myriam Tomas - Intérieur AV

ContactConstructys Bretagnewww.constructys-bretagne.fr