Naturally insulated Wicklow house sets airtightness standard

Introduction:

Ireland's most airtight house was constructed in Co. Wicklow by Jer and Jackie Rynhart.In 2003 Jer and Jackie Rynhart bought an old school house near Rathangan in the hills of west Wicklow. They considered renovating the old school house but Jer reasoned that if they wanted the best build possible, they should start from scratch. 

The Rynhart’s decided to go with a timber frame construction design, where they approached several timber frame companies before choosing Wexford based Shoalwater Timber Frame, who Jer praises for their “wealth of knowledge”, inventiveness and attention to detail.

Super- insulated envelope:

The house features an Isoquick insulated foundation, which is essentially an EPS formwork around and below the concrete slab. The foundations consist of a 250 mm concrete slab with 300 mm of polystyrene underneath and 150 mm around the edges so it is completely insulated on all sides. The system comprises of edge modules and deck modules which come in different thicknesses depending on the thermal requirements, also the different thickness of deck modules allows the thickness of the concrete to be varied depending on the structural demands. This system provided the ground floor with a U-value of 0.11 W/m²K.

Shoalwater then erected the timber frame which was insulated on site. The walls feature 80 mm of Gutex Ultratherm wood fibre board externally, inside the outer Gutex layer is a Panelvent which is a diffusion open external sheathing board which provides structural racking strength and wind resistance, 220mm of cellulose insulation in the stud plus a 100mm service cavity insulated with Gutex Thermoflex, Fermacell boards made from gypsum, cellulose and water line the walls internally. This wall design provides a U-value of 0.11 W/m²K.

Gutex uses a tongued and grooved system for fast construction which can be seen in the above picture.

The roof construction consists of 310mm of cellulose insulation and 100 mm of Gutex Thermoflex. The roof  has a U-value of 0.11 W/m²K.

Ecological Building Services supplied many of the green material used in this build and engineer Niall Crosson says that the primary advantage of using Gutex Ultratherm externally was to increase the thermal mass of the construction, while putting a significant proportion of the insulation to the outside of the frame to reduce non-repeating thermal bridges.

Ecoglaze supplied the windows, triple glazed Internorm Edition with an overall U-value of 0.79 W/m²K.

Ground Breaking Airtightness:

The most impressive aspect of Rynharts house is the airtightness. Intello Plus ‘intelligent’ membrane was used troughout the walls and roof just inside the main cellulose insulated cavity which provided the air tight envelope and vapour diffusion layer. In Winter Intello plus is highly resistant to diffusion and thus protects the building structure, however, in Summer it becomes up to 50 times more vapour permeable allowing the vapour that may have entered the building to dry out.

Pro-Clima’s Solitex plus wind tight membrane was used in the roof, taped and sealed with wind tightness tapes. It is completely air impervious yet has an extremely low vapour resistance to maximise vapour diffusion to the outside.

The most recent airtightness test performed produced phenomenal results of 0.15 air changes per hour (ACH) and a Q50 figure of 0.19 m³/hr/m². The Q50 figure is the best Construct Ireland has ever published.

Space heating:

Jer Rynhart is so confident in the thermal performance of the build, he is not installing central heating, although he is considering electric underfloor heating in the kitchen. The space heating will be provided through the ventilation where he is planning to install a Genvex Combi L-S unit which can provide both space heating and hot water. This system is certified by the Passive House Institute. Domestic hot water is provided from the 185 litre tank which has heat pump priority and can be supplemented by solar or other heat sources through the internal coil. The Rynharts are installing solar thermal, Solar Focus CPC system and and are considering solar PV and wind power into the future.

Conclusion:

The attention to detail during this build was very impressive and an outstanding airtightness result was achieved. Rynhart even put Pro Clima Elasto tape over the staples used to attach Pro Clima membranes in the wall and roof. Niall Crosson from Ecological Building Services says this isn’t necessary to achieve passive airtightness levels but says Rynhart was keen to see if it made a difference nonetheless. Airtightness before taping the staples was 0.22 ACH and after it was 0.15 ACH but other holes were found in the intervening time so Niall Crosson reckons sealing the staples made negligible difference.

The airtightness of this house is very impressive and that is down to the attention to detail and careful workmanship through out the build but I would be interested to see a feasibility study done on the house to determine if the almost fanatic attention to detail resulting in extra time, labour and product costs are economically worth while compared to if the house was still Passive but achieving airtightness closer to 0.3 ACH.

CEPHEUS – measurement results from more than 100 dwelling units in passive houses

INTRODUCTION:

An EU demonstration project was carried out called CEPHEUS (Cost Efficient Passive Houses as European Standards).14 passive houses with 221 dwellings were built at different sites, with different planners and users and using different construction methods. 11 of these dwellings were assessed in the CEPHEUS project.

All projects showed exceptional low space heating consumption up to 80% less than houses complying with local legal standards valid in 1999. The aim of the CEPHEUS project was to keep the total primary energy requirement for space heating, domestic hot water and household appliances below 120kWh(m²a).

Passive houses offer a cost efficient way of reducing the energy demand of new houses by optimising the efficiency of the building envelope, windows, ventilation system but the heating load cannot exceed 10W/m² or 0.6ac/h. This is achieved by using modern technologies and designs.

Passive houses rely on superinsulation where U-values usually range between 0.1-0.15W/(m²K). High efficiency heat recovery systems are needed to bring the space heating requirement below 15 kWh/(m²k).

Solar gains are an important source of heating for passive houses. Suitable glazing needs to be selected to minimise heat losses and southward orientation is preferable. Thermal bridges need to be eliminated and windows and frames must have U-value of less than 0.8W/(m²K).

PROJECT RESULTS:

The results presented by CEPHEUS may show some inaccuracies as many dwellings were unoccupied during the measurement stage and continuous measurements over a long period of time are not available for some of these.

The CEPHEUS project measured 11 properties in its study. It determined that for 9 of the 11 projects had air leakage rates between 0.3-0.6h^-1.Remedial works could be carried out on the houses that exceeded the limit of 0.6 air changes per hour. Below a video explaining air tightness can be seen.

Space heating consumption varied significantly and this was attributed to different construction types and occupancy levels in the buildings. Given the reduced space heating consumption of passive houses the share of electricity consumption can be higher. The installation of energy efficient appliances is essential and in Hannover an incentive was put in place where buyers were entitled to €2000 rebate if their annual demand was less than 18kWh(m²a).

In all CEPHEUS buildings the mean indoor temperature was above 20⁰C. The mean indoor temperature was below this in some unoccupied dwellings. User comfort is key, and comfortable indoor temperatures are achieved in both summer and winter. CEPHEUS found that users can attain comfortable room temperatures in summer and winter through appropriate ventilation management. Occupancy ratios and shading elements are important during the summer however these are secondary to ventilation behaviour. The cost of heat saved in these projects was 6.2cent/kWh.

CONCLUSIONS:

CEPHEUS has tested and proven the viability of the passive house concept at the European level. The project demonstrated the functional viability of the passive house concept on all sites, the actual achievement of the space heat savings target, practical implementation of passive houses in a broad variety of building styles and constructions, project-level economic  viability and a high degree of satisfaction of building occupants.

Passive house technology has triggered a fresh burst of innovation in the construction industry and CEPHEUS has made available all experience gained and the key planning tools for the passive house concept.

First Steps:What can be a Passive House in Your region with your climate

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The Passive House Institute have developed several Passive house building techniques to suit the central European climate, however theses techniques need  to be adjusted to suit the location and climate that the passive house is being constructed in. the local building traditions and specific climatic conditions must be considered for each  region. Mistakes have been made in the past of copying passive house design from one region for another region with different climatic conditions and have resulted in poor performance. When designing a passive house, the passive house method should be used which determines the appropriate passive house solution.

The principal behind all passive houses is the same, reducing investment through energy efficient design. For a passive house the peak heating load should be projected to a lower level than 10 W/m². There is very little extra benefit increasing efficiencies past this as constructions costs increase too much.

Some rules of thumb include, comfort levels should be high, insulation heat recovery and shading is recommended in all climates. In many cases thee ground is used as a heat or cold buffer. A traditional building type can be used as a starting point and then each element can be modified accordingly.

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