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What size beam would be required to span 4.2m?

I'm planning a kitchen renovation where there are two pillars/posts in the middle of the area, which limit the use of space. The pillars support the ceiling and the flat roof above, which is clad with galvanised iron. The ideal situation would be to remove the pillars and support the roof with a single beam, fitted as much as possible into the limited ceiling space to mimimize how far it protrudes under the ceiling. The existing pillars already support timberwork protruding around 100mm below the ceiling level. There is around 150mm between the ceiling and the bottom of the iron roof.

For the beam to be fitted into the ceiling space the existing rafters would have to be attached to it with hanger brackets. If that is acceptable then if a beam of around 200mm depth would not protrude below the ceiling any more than the existing setup.

I estimate the weight of the roofing, roof timberwork and gyprock ceiling to be around 350Kg, evenly distributed across the width. (The only other loading might be someone working on the roof if necessary).

Before engaging an engineer to properly appraise the situation, I'm seeking some general advice to see whether the above solution is feasible. If the beam required would need to be greater than say 250mm in depth, then I think that would protrude too far beneath the existing ceiling to be workable. If it would need to be installed as an underpurlin then definitely unacceptable.

I have attached a photo showing the existing posts.

Any advice or suggestions would be most appreciated. Thanks in advance.

Bill

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EricL

Hello @Tadmore (Bill)

Welcome to the Bunnings Workshop community. It's sensational to have you join us and thanks for sharing your question about what beam size to use for a span of 4.2 meters.

In this instance, I can only recommend engaging the services of an engineer. Not only would they be familiar with the rules and regulations of the council, but they would also be familiar with the general structure of your roof.

In regards to this this matter, some of the factors that need to be taken into consideration are:

Type of Load: Whether the beam is carrying live load (people, furniture, etc.), dead load (the weight of the structure itself), or both or if the load is spread or is concentrated in a single spot.
Timber Species and Grade: Different types of timber have different strength properties.
Existing Joist Size and Spacing: The dimensions of the existing joists and their spacing can affect the load that the replacement beam needs to support.
Building Codes and Regulations: Local building codes in Australia, like the Australian Standards AS 1684 for timber framing, will have specific requirements based on these factors.

When you invite your engineer to assess the area, I suggest asking them about the possibility of using steel. If for example, the timber beam suggested is too large or will be protruding too far past the ceiling space, perhaps using steel will not occupy too much space. This will of course have its own set of factors, but I suspect that a steel beam will not need to be as large. The best way to find out of course is to speak to your engineer.

Other than that, my only other thoughts are to have this section of your roof reframed in such a way that there will be no need for a beam or at least a less obtrusive build that will not be seen from under the ceiling. My apologies for not being able to give you more ideas regarding this matter.

Let me call on our experienced members @Dave-1, @Nailbag, @diy_hausdesigns and @TedBear for their recommendations.

If you need further assistance, please let us know.

Eric

Dave-1

Good Evening @Tadmore

Welcome to The Bunnings Community page 🙂 And you have definently stared off with a decent project! 🙂

Looking the picture already makes me tend to think that its carrying a load. (just the way the pillars and the corners run)

I would be talking to an Engineer/registed builder for sure. A 4.2m span plus carrying the load through the walls ect will come under a few building rules for sure.

I like trying to figure workarounds to situations and with your ceiling space being minimal it makes it harder to work it.

Everything from one pillar to an off center pillar popped in my head 🙂 But it dosnt give you that clear space with no unsightly beam. I do like @EricL's suggesting of a steel beam as being less intrusive tho. You could always clad the part thatwill show with timber even if it shows the steel underneath (think of a black edged frame around the mounted timber to the beam)

Maybe start with a builders quote before engaging an engineer, that way you will have a $$$$ amount to ballance what you want against a price and the higher the price the more id want to be sure it was nicely designed.

Dave

Nailbag

Hi @Tadmore 100% agree with @EricL with your first job in contacting a local draftsperson or engineer to measure up the project and specify not only the beam, but the supporting structure at each end. When it comes to removing load bearing posts, there is no room for estimating weights as there will always be several other contributing factors involved. It won't be a costly exercise but a worthwhile investment in your project.

Regards, Nailbag

Tadmore

Thanks, appreciate all the advice so far. For now, project is on hold.

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