As structural engineers, we play an essential role in the design of a self-build home. Without us, you run the risk of being trampled by structural defects and numerous safety concerns.

When it comes to designing a passive house, however, we’re presented with a level of complexity that complicates the design of the building structure and adds time to the design process. It’s important to keep this in mind as a client.

An architect with experience in passive house design is crucial, but what about your engineer? We’re here to give you an insight into the role of a structural engineer in a passive house project, and why low-energy experience matters.

OUR ROLE IN A PASSIVE HOUSE PROJECT

As always, our first point of call is to look at the Architect’s designs, building materials and the site, and design a structural support system that fits that design. Passive Houses are more challenging to detail, so the process generally takes longer.

To give an example, architects love to use big overhanging eaves. Those become easier if we’re allowed to run ridge beams over the top of the wall with a big cantilever. If this isn’t an option for us, getting your dwelling to passive house standard becomes a lot more complex.

As is true with all self-builds, the more complicated your home is, the more complicated the structural design process will be. In our experience it’s best to decide whether you are pursuing the passive house standard as early in the process as you can, to avoid going back to the drawing board.

 

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THE MAIN DIFFERENCES FROM A REGULAR PROJECT

Passive Houses are a little different to regular projects. The detailing process takes longer, and a lot of this process can prove challenging for engineers who aren’t familiar with this low-energy standard.

We play a more involved role in the thermal requirements of the building. The architect will contact us with their energy & design requirements, and from this, we begin designing the structure.

The material that the house is made of is hugely significant. The first thing we would advise is using a modern construction method such as Timber or SIPs. It’s theoretically possible to build a passive house with traditional construction, but good luck.

We also advise avoiding the use of any steel in your walls, which runs the risk of Cold bridging. This is a phenomenon that interrupts the continuity of insulation and promotes heat loss.

One of the big things is solar gains and heat loss. In an ideal scenario, the architect always turns the house to face the winter sun while shading themselves from the summer sun. Catching winter sun doesn’t bother us, but adding design features to provide shade? That would complicate our design.

Despite not needing a structural certifier, A passive house certifier includes our recommendations as part of their calculations. The project may be different, but our presence in the design process remains significant.

DOES MY ENGINEER NEED TO BE SPECIALISED IN LOW-ENERGY DESIGN?

It certainly helps to have a structural engineer with experience in designing low-energy structures. Having prior knowledge of the requirements and the correct products to mitigate heat loss will save you a lot of time.

The most important thing is to get us involved as early as possible, as it allows us to prevent features that will complicate and add unneeded expenses to your project.

As a company, our default is to design low-energy buildings anyway, as no one wants a home that’s hard to heat.

THE COSTS OF A STRUCTURAL ENGINEER FOR A PASSIVE HOUSE PROJECT

Due to the specialised work and longer detailing process, the costs of our services tend to be slightly higher than a regular project.

 

“Detailing and coordination is always important in any successful project, However, on passive house projects it’s critical to achieve the desired accreditation. This requires additional design input and expertise increasing the time required and therefore the fee of the structural design process.”

– David Gallagher, AC Structures Technical Director

The exact impact on your project will depend on the number and complexity of details that potentially introduce thermal bridging into the structure.

To minimise any redesign costs, the passive House Certifier and the Architect need to clearly identify their detailing assumptions and proposals to the Engineer before any detailed design.

WORKING WITH AC ARCHITECTS ON PASSIVE HOUSES

 

We work closely with AC Architects to advise on what materials and specifications best suit the client’s requirements and the form of the proposed house.

Working on Passivhaus projects was a bit of a learning curve for us, but our newfound knowledge of passive house principles in a structural setting makes the self-build process smoother for everyone involved.

“What fascinates me is the way self-builders future-proof their homes. I’ve seen a client build a lift shaft in their home in preparation for getting old! You’re only building your dream home once after all.” 

– Susan Anderson, Senior Structural Engineer

Overall, a structural engineer plays a vital role in designing and implementing the structural aspects of a Passive House project. Engaging with an engineer as early in your self-build journey as possible makes the combination of structural integrity and energy efficiency easier to achieve.

AC Structures have completed over 70 projects, many of which are low-energy or passive houses. If you’re looking for low-energy engineers for your project, contact us now!