How to do a flitch beam calculation the EASY way
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- Опубликовано: 1 июн 2024
- Here is a simple way to do a flitch beam calculation for a flat roof.
🚀Get my flat roof span tables here: geni.us/timbercalculation
Follow this tutorial to work out the size and strength of a flitch beam, used to reduce the depth of your timber rafters and create a thinner roof for your garden room or garden office. You may have seen a flitch beam used in Oakwood Garden Rooms videos - so here is how to do the calculations for it 👍
See the first video in this series:
Why use a flitch beam? • Why use a flitch beam ...
Here's the kit you will need to create a flitch beam:
Hangers for the rafters to the flitch beam: geni.us/NQkt0o
Correct bolts for the flitch beam: geni.us/o3l5uo
Oversize washers to clamp the timber: geni.us/akDtY
Get a decent drill bit for steel: geni.us/EfFO
What people don't tell you is that drilling into steel is VERY DIFFICULT with a hand drill. The professionals all use something called a "Mag Drill", which you can get for less than the price of the steel. Do yourself a favour and get one of these if you're drilling more than a few holes in 10mm thick steel: geni.us/iXATG
*These are affiliate links. If you appreciated the video, please use these if you're going to make a purchase. Many thanks!* 
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⚠ Remember to check deflection also. See my video here: ruclips.net/video/brC9JEKqV7M/видео.html
Many thanks for your generosity Robin
Bro, I love how you make things so simple!
Brilliant......Well explained,,,simplicity in itself
Fantastic mate thank you for a great video keep it simple 👍
Great way to simplify the design of a flitch beam.
Hi Robin, thanks for your easy to follow and informative videos. It would be interesting to see how the bending stress was distributed if the timber and fixings were also considered. Cheers Vaughan.
Best Flitch beam lecture on RUclips! Thanks.
Could you do a demonstration on determining bolt stresses and spacing on such a beam as this? Or perhaps just mention any other reference for this question?
Hi Robin. New subscriber... thanks for the great, clear explanations & calculations. Cheers... Clark
Your videos are awesome. Thank you for this video. Very info5
Informative😊
Thank you. This video is very helpful. As a globally out of step California contractor it is difficult for me to wrap my head around metric measurements, but I am working on it. I have a project that could benefit from angled flitch plates supporting opposing rafters. I understand that they require what here in the states we call "certified welders" to created the connection of the plates. I am wondering if they are calculated the same as a straight flitch plate or is there more to it. It would be very helpful if you could point me in the right direction. thank you.
Thanks Robin. Another great video. Could you at some point show design of a post, either as a single or in balustrade scenario please. Especially including baseplate and fixings. Thanks!
wow great video with great explanations. Love the channel. You got a subscriber from me. Exciting to see more of your videos soon! Thank you
Hello Robin thanks for the videos. They are very useful. I am currently trying to assess whether my loft is suitable for conversion. I like the sound of flitch beams rather than rsj for floor support as the individual components could be easily assembled in the loft space. Flitch beams would be installed just outside of existing purlins which would be retained. What do you think and what loading would I use to calculate flitch dimension? Thanks Jon
Hi Robin, great vid and very informative. Id like to use a flitch beam as a lintel for a current job. Im doing a small first floor extension above an existing ground floor extension.
I have a span of 3.8m which will support counter balanced floor joists, a 2m high wooden wall c/w windows and a flat roof constructed on top. The extension will only come out 1.6m from the house. Space is limited so hoping to use 2 No. 195x44 c16 spruce joists with a metal flat plate of 150x10mm bolted in between and restrained into brick with mortar. Is this possible or is a RSJ still best?
Many thanks
Amazing
Thanks Robin, great video. Could you not use steel for the top/bottom faces and timber as the sandwich filling in between to carry the shear? Would be a much stiffer beam with the same weight wouldn't it?
Hi, thanks for the informative video. How do you determine how much wood needs to be on each side of the steel flat to ensure that it doesn't buckle?
Excellent thanks
You are welcome!
Just to add.. to this newbie at least, the units are confusing, N/mm2 and kNm and kN/m2 etc etc, took a bit of figuring out
@@JohnMullee Thanks for the feedback John 👍
Just out of interest, if this is based on a load factor of 2kn/m2, if we said the load was more of 1kn/M2 (no regular access and not likely to have deep snow) would that mean overall you would have managed with just the 1 beam instead of the 2 to keep you in spec? My thinking being if load is halved, strength can be reduced? Thank you 👍
Thanks for video Robin. When we calculate flitch beam capacity, do we have to put timber also in account or we just check steel plate capacity?
Hi Kenan. For a more complicated version of this calculation you can use the timber too, and take their combined effect in relation to the stiffness. Good question!
Your videos are saving me a lot of money! Thank you very much. One question tho< is there a simple way to find an exact number for Factored Load? 2 kn/m is around 203 kilograms of force on any given 1 meter. it seem to be a little more on most times on a residential project. if one to find out the exact or near enough number would probably be very helpful. is there a calculation or a formula for this? Thank you
HI. The 2kN is per square metre. Yes there is a lot of literature on loadings. I suggest starting with "design of structural elements" by chanakya arya. It has a good chapter on this. Also I cover it in my steel beam calculations course: geni.us/beamcalculations
Great video Robin, really what I needed and also looking to reduce my flat roof height by way of a flitch beam. Quick question, what is the significance of the load factor in your example here at 2kn - this seems like a magic number, are there environmental factors that would raise or lower this?
Hi Paul. Usually a roof would attract 0.75kN/m2 of snow in the UK, and then a dead load for the materials used. A load factor of 1.5x is an amalgamation of the 1.4x dead load and 1.6x live load that UK BS codes require. Confused yet? 😊
Is there a way to calculate the required breadth of the timber to restrain it? Im assuming because its restrained by the roof timbers, just enough to spread the load?
If I wish to increase door way height under a timber beam madeof 4 x 2x8 can I cut out lower 4 inches and add steel plate to eitjher side above the cutaway acroos door way ? Sort of an out side flitch beam ! I would run bolts through at side and middle ..
So total run for the wood cutout is 28 inches and steel plate would be 36 inches x 4 inches x 1 cm ..( would 1 cm thick steel suffice ?? )
Hi Robin, very informative content. I do have a question, would it be possible to increase unsupported spans by doubling up beams? For example, C16 2x6 doubled to make bolted 4x6s. How does this affect span maximums? And, in theory could this same logic be applied to flooring? I am researching building a flat room timber frame building on pier foundations, trying to avoid piers every 4ft for the floor and supports every 8ft for the roof joists.
If you double them up you halve the load on each. Deflection is a function if the depth cubed, so the most bang for your buck is achieved by deepening joists, not doubling them (I.e. widening)
@@RobindeJongh Thanks. Lost me a bit on the "Deflection is a function if the depth cubed". Im a layman :)
That said, from your span tables, it looks like C16 2x8 would tick my box for piers every 8 ft as they have a 3m span. However, in the flat roof with the same wood, it seems to give me an extra 1m on the span. I have seen firms alternate between doubling and flitch joists across a roof build. Just wondered, how much extra span they could get by doing this?
Hi Robin, thank you for these videos, to the untrained eye they are a great help 🙂 i have a question regarding the thickness of the steel, i know you said the depth is more important. I can get 5x120 steels at a good price but just wondering if they can be too thin? Obviously i would brace them either side. I have a project where i need to span 5m but cant go deeper than a 150 rafter... Any idea please? Thank you 👍
Hi Luke. I can potentially design that flitch beam for you, if it is just flat roof loading, if you provide some more details here (the 47 option) : geni.us/askrobin
Hi Robin, thank you for your video! Very insightful!
How would loadings be effected if I was only adding load to one side of a flitch beam? I am looking to use a flitch beam as a solution to a 3m wide lintel with the flat roof hung directly to it.
Loadings would be calculated as being from one half of the roof span. The flitch beam would need to be well laterally restrained by the roof, and the roof would need to have sheathing to allow it to act as a diaphragm.
thanks Robin, appreciate your reply!
I assume your comment on lateral restraint and sheathing would be to avoid any twisting in the beam?
I am looking having a warm roof construction so I would imagine this will give plenty of rigidity to the structure.
How would you work out the size required for a clear span beam above a large doorway with just the roof above?
Same as this method, but you only have one side of the roof acting on the beam.
Helpful Video. Just constructing a garden room under pd's and need a very shallow roof beam/joist, to allow us to keep the internal height as best possible. My room is external measured 8.2Mx4.2M. Any chance I can get a calc? I would like to use 47x120 timber or smaller. Timber is supported on double skin of block work so the span is 3800mm. Is load factor always 2 KN/M2 on flat roof with rubber epdm. I think I need a line value 16KN/M and using the 47x120 plus 10mm steel plate = 6.6. So does that mean I need at least 3 of those and then I just use standard 47x120 to infill the rest? I do have an engineer on the project but he seems lost.....! I'm just following you video but with no other background. Any help appreciated?
Hi! Yes I can do the flitch beam calculation for you. Send your enquiry here, and any drawings or sketches: geni.us/structural
Hi Robin! What is the minimum thickness of the steel plate that can be used and what it depends on (if does at all)? The price would be affected as well. TIA
Hi Petru. Thickness of plate affects buckling, so the important thing is to have the beam restrained from buckling, by a roof or floor diaphragm as shown in this video. Depth of steel makes much more difference to the strength of the beam than thickness does.
I understand the steel depth is crucial. But still, how important is the thickness? I could argue that buckling is not an issue, as the joists in between them won't allow much movement (they're like noggins). Both top and bottom sheeting play a stabilizing role as well. So there's a constraint from all 4 sides of both beams. This is where your expertise is needed. 8mm thick is considerably cheaper than, say, 12mm, that's why I'm wondering how thin it can reasonably be. Regards
Can you do concrete as well and rebar selection?? Please!!
One day I'll get around to doing some more reinforced concrete - thanks for the suggestion! 👍
Or would I be better off replacing the complete 10 foot x 4 pcs 2x8 beam with a 4 inch I - beam ? There are 3 places in the basement wher the 2x8 beams reduce ceiling height too much
Robin can you please show the correct way to retrofit Roof to gable wall lateral support on a 9” solid brick wall can’t find it anywhere on RUclips or even the internet the house has stood 100 year without any.A yank said your roof will be flying down the road with a 9x4inch brick attached to it pitched roof. Cheers if you can do one on it prove it if possible
Hi Robin. I just heard of 'Flitch Beams' for the first time tonight. So I did a search and your name came up on top of the search result, and I thought to myself, 'thats interesting'. It was also interesting to note at the end of your video, that to double the strength of the 'flitch beam', all that was needing done, was to double the 'steel plate'. Which brought home the point you made in that other video, how much stronger steel is over timber. And in this situation, the timber is really only the 'white bread' in the sandwich of the 'Flitch Beam' holding it all together. But the real meat in the sandwich is the 'steel'. So to double the strength of the 'Flitch beam', all you need to do is add another layer of the steel plate. I'm sure its much more complicated than this in the real world , where much more complex calculations have to be thought through. What would you say are the applications for Flitch beams. Would it be about the ease of getting these seperate parts of a Beam into an awkward spot, compared to one big heavy Beam. These videos are great Robin. Thanks so much.
Hi Jude. Flitch beams are great where steel needs to be hidden away in a timber building. The flitch beam itself is not as efficient or lightweight as a steel "H" shaped beam would be, so for any other task the normal steel UB or UC sections would be preferable.
@@RobindeJongh Hi Robin. that is interesting. The reason I ask is because I have to get a 300x75 LVL 'ridge beam' up to a 6.0m height, to support 200 x 45, 6.5m rafters, supporting a sheet metal roof, of less than 40kg/m2, for a Gable roof. The 'RWL' is 5.8m. The 'ridge beam' needs to span 6.4m, but is itself 10.0m in length, being a continuous member. The issue is that there is no access for a crane, so getting such a heavy beam up 6 metres up off the floor is going to be very difficult. This is a remodel of my roof, and the only way I can do it is by doing it as a self build. Are you familiar with such a predicament. Is there anything you can suggest to help me figure this out. Thanks Robin.
I'm a structural engineer based in UK and this calculation is not only too simple the timber and steel stresses correctly calculated are too high and the deflection is also too great. What are your qualifications Robin? are you in the USA?
Hi John. This calculation is perfect for people who don't have a degree in structural engineering. I've checked it and the calculation is correct. By all means please watch it again and let me know what specifically you have an issue with. Regarding deflection, I don't show that in this video, and viewers can check my other videos on deflection if they wish to learn how to do that. Please do get back to me if you have any concerns 👍
@@RobindeJongh The calculation is too simple in that it makes no reference to the part played by the timber. Load will be taken by the steel and timbers in relation to their stiffness values, ie the EI for the steel and timber. A flitch beam is really for too complex for someone with struc eng degree to be doing. And as I say if you do the calculation with a 20 mm plate you find the deflection is too great (even accounting for the part played by the timber, and at 0.005 times the span the deflection is big). I've sent you an email with a calculation done using a timber/steel software package that I use a lot called Superbeam by Tony Byers/Greentram.
@@johncranna Hi John. Thanks for sending the Superbeam calculations. They agree that the beam passes, although they give a higher deflection. Superbeam uses the old BS449 code whereas I have used the newer BS5950. The newer code uses imposed only load for deflection. I've just checked the beam to BS5950 and the deflection is span/322, which is well within acceptable limits for a garden roof structure. However, I totally understand and appreciate your over-arching comment, and I will pin a comment to this video encouraging viewers to check deflection 👍
Why do you not take into account the bending strength of the timbers in the flitch? Also is the deflection already assumed to be within allowables? What yield is the steel? 235 , 275 or 355. Thanks.
Hi Kevin. Taking into account the timber strength is much more complicated and not something a general audience would want to contemplate, so this way is easier though a little conservative. You would need to also check deflection. The yield I've used in the video is S275.
the maths are a bit over my head but love the attention to detail.
What if the beam is not fully restrained, load on one side only?
If unrestrained you would need to do a complex buckling calculation, taking into account the two different material stiffnesses
The equation for calculating the moment in 5:20 ignores the bearing capacity of the wooden beams. For example, if you were to reduce the width of the steel to 0 (variable d->0 flitch->ridge beam ), the Moment resistance would decrease until 0, which makes no sense.
Moment resistance of the flitch beam is calculated here using only the breadth and depth of the steel plate.
There was no check on the deflection of the flitch beam which should be limited to .003L where L is the span. Furthermore it is unsafe to consider the beam to be restrained as the timbers forming the resptraint are liable to shrinkage over time thus reducing effect of the restraint
Hi Richard. Absolutely correct, the deflection needs to be checked. See my video here: ruclips.net/video/brC9JEKqV7M/видео.html Not sure I agree with your point about the beam being restrained. It's about as well restrained as physically possible 👍
8:18 Sorry, Robin - putting your beams in at 1/3 points only reduces your load by 33%. You would need to put them at 1/4 points to reduce the load by the 50% you need.
Bad advice!
So much for thinking on the fly! You're right, I'll see if I can remove that bit. Well spotted 👍
Pfft, somebody just needs to create an app where you just put in the distance and dimensions of the supporting beam or joist and it tells you what size flitch you need. Anyone who isn’t a structural engineer isn’t going to do all this nerd stuff.
How much would you pay for such an app if I created it?
It would take 15 minutes to create that spreadsheet - including your deflection check: Roof loading > span > loaded width > wL2/8 > 0.013wL4/(IE) > sorted