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Sustainable Design - Take the Passivhaus approach

If you're thinking about undertaking some building works in 2022, why not consider building to Passive House standards? Research has shown that the overall lifetime costs of a passive house project would be equal if not cheaper than a traditional build, and this becoming increasingly more true now that energy costs are continuing to rise around the world. We have plenty of experience designing homes to passive house principles in Bristol and the south west, and have the skills & software (PHPP) necessary to produce the energy model for certification. Feel free to contact us to discuss how we can deliver your passive house project.


What is Passive House?

Passive house is a design methodology in construction that ensures buildings have a very low environmental impact whilst ensuring an exceptionally comfortable living environment year round. The Passive house standard is founded on energy conservation achieved through the use of high performance insulation, high performance windows and doors, mechanical ventilation with heat recovery, an airtight barrier around the building, thermal bridge free design, and approriate solar orientation. A conventional heating system is not required as the heating demand is met by electrical heat recovery and passive re-heating from the sun.


These design considerations help to ensure that heat generated within the building stays inside for as long as possible leading to substantially lower heating and cooling bills across the year. Its very important to implement these design considerations early on in the design process as revisiting a design to fit them in retrospectively can become time consuming and costly.


We've previously written articles on many of the above mentioned topics in detail which you can read on our blog. We have implemented these principles on a previous project, Wellington Lane, a dwelling in Bristol built to Passive house standards.


Advantages of Passivhaus

Beyond energy consumption, the standard has many other advantages for the occupants of a passive house building. Occupants record higher levels of comfort due to the prevention of drafts and more stable internal temperatures and ventilation rates. High levels of insulation and a mechanical ventilation system means that there is much less risk of condensation forming on internal surfaces which can lead to mould growth and respiratory problems.


Construction Material Options

When it comes to construction materials, there are many approaches that can be taken, all of which will affect the speed of construction, the quantity of materials required, and the overall cost of a project. We have highlighted three of the most common approaches below.


Oak Frame / Engineered I-joist Timber Frame / Stick Frame

Timber frame sketch with external insulation

In this approach, the timber frame provides the structural form of the building with the gaps between the frame filled with insulation. The timber structure sits on a masonry wall which is also heavily insulated. Extra layers of insulation are added around the entire building to improve its thermal efficiency. These extra layers of insulation are typically added to the exterior of the structure to eliminate thermal bridging through the structure itself.


Depending on the design, a layer of insulation may also located against the inside face of the structure. An airtight barrier is also fitted according to the design to eliminate unintentional drafts. An interior wall finish is applied and finally an exterior weatherproof layer of either render or cladding creates an envelope to keep the elements out.


Structurally Insulated Panels (SIPS)


A SIP consists of two OSB panels sandwiching an insulation core. These panels create the structural form of the building whilst also providing a good level of insulation. The SIP frame sit on a masonry wall which is heavily insulated to reduce thermal bridging. SIPs are fabricated in a factory to the appropriate size for the project and craned in to place. A SIP house can be erected and made watertight very quickly. The increased levels of insulation, airtightness, and weather proofing can then be installed to passivhaus standards


We have previously written an article about SIPS as we were preparing to use them for a project.



Insulated Concrete Form (ICF)

Insulated concrete form comprises of two layers of insulation with a gap between to accommodate the concrete that will later be poured in. The gap between the two layers of insulation is formed by a pre-installed plastic clips which hold the two layers of insulation in place. This construction system joins directly with the foundation unlike the two systems mentioned above.


ICF panels are small, lightweight, and designed to be installed by hand. They are stacked in rows, in a similar manner to bricks, to create the wall formwork. When ready, concrete is poured in to form the structure. Once the concrete has cured, extra levels of insulation and an airtight barrier are then installed along with a render or cladding system to form a weatherproof envelope.


Conclusions

There are many other approaches to constructing the building form. The nature of the building site and its accessibility could be a factor in which construction material is most appropriate for you. There are also a multitude of different insulation options, weatherproofing materials, high performance windows and doors, interior finish materials, mechanical ventilation systems with heat recovery, and other design options that could alter the outcome of the design and affect the cost.


We have a passion for working closely with individuals, self-builders and community groups to help them turn their architectural dreams into a reality. This means designing collaboratively with clients, builders, and other consultants to deliver high quality, well considered buildings which do not cost the earth.

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