What is a Structural Engineer (for Timber Floor Joists)?

A Structural Engineer is a qualified professional who designs load-bearing structural elements for your build — in this case, the timber floor joists that support your flooring system. They’ll determine the correct timber sizes, spacing, span limits, and connection details to ensure your floor meets all Australian Standards for safety, stiffness, and long-term durability.



This work is required before floor framing begins, typically just after your main architectural or DA drawings are complete.

What does a Structural Engineer do?

Your Structural Engineer will complete works according to your agreed scope of works.


Typically, they will:

  • Review your architectural plans and site conditions
  • Specify the size, span, spacing and layout of floor joists
  • Nominate bearer and beam sizes (if applicable)
  • Confirm fixing and bracing details for floor structure
  • Provide a signed structural certificate or detailed joist layout
  • Liaise with your builder or frame manufacturer if needed


They may also review any custom loads (e.g. heavy kitchen islands, spa baths) to ensure your floor is appropriately reinforced.

Barry's Toolbox

If you’re using a prefabricated frame supplier, send them the engineer’s joist design early — it’ll avoid costly rework.


And if your floor covers both internal and external areas (like a balcony), ask for drainage and waterproofing allowances too — not all joist systems are created equal.

What to look for in a Structural Engineer

When reviewing quotes, look for:

  • Current registration with your state’s engineering board (e.g. RPEQ, CPEng, NER)
  • Fixed fee or hourly estimate with clear inclusions
  • Timeline for delivery and ability to coordinate with your builder
  • Floor layout or sketch provided as part of deliverables
  • Experience with suspended timber floors (especially if sloping or multilevel)


It's ideal if the engineer has worked with your builder, designer or certifier previously.

Before You Begin: What You’ll Need Ready

To get quotes from Structural Engineers for timber floor joist design, you’ll need:

  • A floor plan and site layout
  • Site classification (soil type, slope)
  • Span and support information (or architectural drawings)
  • Any special loads or non-standard finishes (stone tiles, in-floor heating, etc.)
  • Whether it’s part of a new build, addition or renovation

Average Timeframe

For this task, Pros typically provide quotes within 7-10 business days.

When Can I Expect Quotes?

Timeframes often vary based on demand and the type of Pro you're engaging (e.g. a plumber). If additional communication or clarification is needed is needed, the quoting process may take longer.

 

Don't be alarmed if you don't receive quotes or communication from any Build Buddy Pros straight away. Some work is more complex and the Pro may need time to comprehend your documents or scope of work. Depending on the job, there may even be some work required by the Pro before they are able to quote (e.g. a site visit might be required).

 

If the average timeframe indicated here has passed, and you have not received any messages or quotes, please feel free to contact the Build Buddy Expert Guidance and Support team for an update on quoting for this task.

Frequently Asked Questions

  • Can my builder or carpenter design the floor joists?

    Not if certification is required. For council approval or structural sign-off, a registered engineer must prepare and endorse the design.

  • What kind of timber is used for floor joists?

    That depends on span and loads. Engineers may specify LVL, treated pine, hardwood, or engineered I-joists.

How to Complete this Task?

STEP 1

Review and Adjust the Scope of Works

Timeframes may vary based on demand and the type of Pro you're engaging (e.g., a plumber). If additional communication or clarification is needed, the quoting process may take longer.

STEP 2

Confirm Required Documents Are Uploaded

Check that the following required document(s) are uploaded for this task. These are essential to proceed:

STEP 3

Update the Quality Assurance Checklist

Go to the Quality Assurance tab in this task and review the checklist. Edit any details to suit your project requirements. Being clear and upfront helps set expectations with the Pro. Updating the checklist before requesting quotes ensures everyone is aligned.

STEP 4

Request Quotes

Click the orange ‘Request Quotes’ button to start the quoting process.

STEP 5

Review the Quotes

Once you receive quotes:

  • Review each one carefully, including the payment schedule and any special terms
  • Download attached quote documents for detailed review
  • Check each Pro’s profile and read past client reviews

STEP 6

Communicate with the Pro

If needed, message or call the Pro to clarify details or negotiate terms.

STEP 7

Accept a Quote

Choose the quote that best suits your needs. Once you accept a quote, any other pending quotes will be automatically declined. An agreement will automatically be generated.

STEP 8

Complete the Tasks In Your App

New tasks will appear to guide you through this job — follow each step carefully. Make sure to use the Quality Assurance Checklist, and refer to your contract and final Scope of Works whenever needed.

NEED HELP?

Reach Out to Your Build Buddy Pro

If you have any questions or need a hand, your Build Buddy Pro is your best first contact. They’re a licensed expert in their field and can understand the ins and outs of your project. You can message them via the platform, or you can call them directly.


If you have already contacted your Build Buddy Pro and still need further assistance, the Build Buddy Expert Guidance and Support team are here to help. They will be able to guide you on your next steps or help you find answers to any questions you may have.