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Structural Engineering FAQ for New Homes and Renovations

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What is a structural engineer?

This FAQ kindly provided by Queensland based
Cornell Engineers

A structural engineer is a professional civil engineer that has a specialised understanding of the forces and loads in structures that include bridges, buildings and tunnels. Residential structural engineers specialise in the design of residential buildings including houses and units. 

Why should I hire a residential structural engineer?

Residential structural engineers have specialised knowledge and training to calculate forces in residential buildings. Structural engineers can make sure that the structural members in your house are the correct size (not too big and not too small) to resist and transmit forces in buildings. They do this by using Australian standards to calculate forces in members and member capacity manuals to check that the members are strong enough to avoid collapse or too much deflection.

You may not need a structural engineer if you are building a simple new home or extension. Simple projects can be designed by qualified building designers or drafters without the input from an engineer.

However sometimes houses and units are complicated or are built on poor ground. In these cases your building designer might recommend that some or all of the building be designed or checked by a structural engineer.

You might need a structural engineer if your building has one or more of these elements:

  • Reinforced concrete columns.
  • Earth retaining walls.
  • Roofs in cyclone affected areas.
  • Footings in clay soils or on soft or sloping sites.
  • Steel floor beams and roof girders; and
  • Suspended concrete slabs.

In some states, the builder’s statutory insurance policy requires that a structural engineer must design and certify house footings, steel floor beams and retaining walls. Check with your building designer to see if this is the case in your state.

How do I select a structural engineer?

It makes sense that if you are building or renovating a house that you select a structural engineer that specialises in residential buildings.

How do you find a structural engineer?

First, ask your builder, building designer or architect for a referral. They will probably have an existing relationship with one or more structural engineers that they have worked with before.

You can also try this link for a list of structural engineers for your area. Look for an engineer with recent experience in your type of project. If site inspections are required, limit your search to engineers that service your area from a local office.

Try to speak directly to the engineer that will work on your project. A good structural engineer will want to know about your project, what you hope to achieve and what services you are expecting. How the engineer responds to your questions will tell you a lot about the engineer.

Pertinent questions show that the engineer is interested in you and thinking about your project. A little bit of informal advice from the engineer means that the engineer wants your project to go well. Look for an engineer that is accessible and one that doesn’t hide behind secretaries, standard forms and junior staff.

Take note of how long it takes to respond to your request for a formal quotation. Big companies might have more paperwork and policies, better quality assurance but take longer to respond to simple requests. Smaller companies might be more personal, quicker to respond to questions and offer personal service. Try to match your requirements to an appropriate structural engineering firm.

Finally, don’t be afraid to ask your engineer for a copy of their professional indemnity insurance and public liability insurance certificates. This insurance is your protection in case of a design error or oversight. Check this article by Matthew Cornell for what to look for in an engineer’s insurance policy.

Note that in Queensland, structural engineers must be registered with the Board of Professional Engineers of Queensland or work under the direct supervision of a registered engineer. Note that professional indemnity insurance is not mandatory in Queensland. Search the BPEQ register to engineers registered in Queensland.

What does structural engineering cost?

Structural engineers charge by the hour or a fixed ‘lump sum’ fee. The fee will depend on the scale of your project and what the structural engineer has to provide. 

Hourly rates are determined based on the experience of the engineer working on your project. Hourly rates for graduate structural engineers start at $100 plus GST per hour. Expect to pay up to $250 plus GST per hour for very experienced and fully qualified structural engineers. 

You can negotiate a lump sum (fixed) fee for most projects. Lump sum fees for a simple beam design could be as low as $300 including GST. The lump sum fees for a complicated house design with footings, suspended concrete slabs and complicated roofs could be as much as $20,000 including GST.

Don’t forget to shop around. The time taken to ask for two or three quotations from different structural engineers is a great investment in your project.

Does the structural engineer need to inspect my renovation property?

If you are renovating or extending an existing property, it makes sense to arrange for your structural engineer to inspect and view your property. They will want to look at the floor framing, the location of wall framing and the type of roof framing. 

Some of the existing structure might be hidden by wall and floor cladding, but an inspection of the shape and layout of the building will still reveal clues on the existing structural framing. 

Another inspection might be required once your builder has started work and more of the structure has been exposed. Expect to pay more if more inspections are required.

Can a structural engineer determine if I can remove a wall?

If you’d like to remove an existing wall to create a larger space, a structural engineer can inspect your building to work out if the wall is loadbearing. You can use a builder or a building designer to do this inspection too, but if the wall is loadbearing you will need a structural engineer to design a new beam to replace the carrying capacity of the wall.

If the wall you want to remove is loadbearing, expect to receive some drawings showing where new beams are required, where replacement bracing walls are required or both.

What things doesn’t a structural engineer do?

  1. Structural engineers prepare drawings and specifications that document the required structural member sizes and how to connect them. These are some of the jobs structural engineers normally don’t do:
  2. Structural engineers rarely remove wall or ceiling linings to look for internal structural damage. If the damage is not evident on the surface of the building, a visual inspection by a structural engineer might miss it.
  3. Structural engineers do not submit your drawings to a certifier or to council. Application fees need to be paid when submitting plans and these costs are not included in the engineers quote. This service is normally performed by your builder or building designer.
  4. When doing damage assessments, structural engineers can’t see behind walls or in hidden spaces any better than you can. They look for indications of movement and damage, but unless the cladding is removed or the roof space is totally accessible, structural engineers cannot find every building defect or locate every problem.

Will an engineered house be guaranteed to be ‘crack-free’?

No. Even if your new house or renovation is designed by a structural engineer, you will not receive a guarantee that your building will never crack. Cracks might even occur in the first six months after construction. That’s because there are a myriad of reasons cracks appear in buildings – and not all of them indicate poor construction or design techniques. 

Cracks or concerns with new buildings should be taken up with the builder in the first instance. An inspection by the structural engineer that designed your property should be arranged if you aren’t satisfied with the explanation or rectification procedure proposed by the builder.