How to defy gravity

I heard a wonderful interview with engineer Bill Lawson on a podcast the other day (Richard Fidler’s Conversations) where he talked about how engineering is really the art of defying gravity. I thought this was such a wonderful way to describe a science that’s all about working out how to keep heavy things from collapsing. Which is something that builders are pretty interested in too.


Lots of the work that JD does is replacing doors and windows – it’s a fabulous way of changing the feel and purpose of various rooms in a house. One of the things he most often gets asked about is knocking out a wall and putting in bi-fold doors – a change that really opens up a room. We did it to our old house that previously had no connection to the backyard at all and it was awesome.


However, before you pick up a sledgehammer and start swinging you need to talk to a builder, and probably a structural engineer, about what’s going to support those doors. Most bi-fold doors are top-hung – that means that they “hang” from the top, which must be strong enough to support their weight. A five-leaf bi-fold door weighs approximately 140kg and bricks alone will not be able to support that weight.


To defy gravity and have top-hung doors, you’ll need to install a beam, which is where your structural engineer comes in and also where additional – and necessary costs – come in. A structural engineer will be able to advise your builder on the size and type of beam that will be needed to support the weight of the doors. The builder will then be able to safely knock out the wall, support it with acro props, install the beam, install the doors and finish the job neatly.


Another alternative is to install bottom-hung doors which, as the name implies, have all the weight loaded to the bottom track. Not as many door companies manufacture bottom-hung doors, but your builder should be able to recommend a supplier.


Have you had a wall knocked down and replaced it with doors or windows? Was structural work required? Do you dream of defying gravity – I know I do!


  • Kit@lifethroughthehaze

    We knocked out a wall that had windows in it and actually built half a wall and put a glass door in its place. We actually did need work down because it was the back wall of our house but our amazing builder did something fancy where he moved the load bearing weight from one wall to another, I think it helped that he was replacing the roof over that section of the house at the time too.

  • Michelle - Jarrah Jungle

    We cut out a window and installed french doors in our dining room, we were lucky there was already a big solid metal beam there and once it was bricked up, rendered and painted, you would never know it was once a window – the french doors look amazing!


      French doors are awesome! And you struck gold by already having a beam in there. #winning

  • Nicole @ The Builder's Wife

    Happen to be a HUGE conversation hour fan!! Great advice, thank you 🙂

  • Bec Senyard

    When we’d have to core holes in slabs, we’d have to get an engineer to check that where we would be drilling would be ok and we couldn’t go through any support beams. I need to get onto Conversation hour by the sounds of things! I really like how Bill Lawson described engineering.


      Yes, I thought it was a great description! My dad was a civil engineer who worked on a lot of bridges – definitely gravity defying!

  • Clare

    I love the natural light and connection with nature that bifold doors bring. I really admire engineers and builders who have the know-how to make these dreams into a reality for people. One of the things I love about our current house is that there are a lot of floor to ceiling windows and doors from our two living areas looking out to the back yard. When we first moved in I thought I would need to install more blinds of some sort for privacy. But 5 years later we still don’t have the blinds and strangely I don’t mind it. It gives the house such a lovely open fresh feel during the day ( and really helps me keep an eye on the kids playing outside while I potter inside).


      Hi Clare – thanks for visiting. Oh you lucky thing having lots of full height windows! I love that you don’t have blinds on them – so much nicer to just have all the light coming in. Cheers.

  • Maxabella

    I’m very happy to have found your blog, Alix. We are just about to start a renovation (meaning, we have engaged the architect) and I’ll be looking for all the ‘hands-on’ learning that I can. x


      Thank you for your kind words Maxabella and thanks for visiting. I hope your renovation goes well – if you’re sydney based, we’d be happy to help. Cheers

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