Why use a flitch beam for your garden room roof?

Find out how to use a simple flitch beam to create a thin garden room roof.
👍 Get my timber roof span tables here: geni.us/timbercalculation
Flitch beams are a superb way to reduce the thickness of a timber flat roof. They're simple to design, easy to fabricate, and sit within the rafter space. As such flitch beams are ideal for a garden room roof where planning regulations require the roof to be no more than 2.5m from ground level.
🎯 The second part: How to calculate a flitch beam • How to do a flitch bea...
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!*

[@RobindeJongh]

💥Get the timber roof span tables used in the video here: geni.us/timbercalculation

[@omugz9444]

Superb video and exceptionally explained. Simple and Concise. Thank you.

[@malagafarlopa]

Absolutely amazing, very informative, my building happens to be the same size and I’m designing the roof, this has helped me immensely, subscribed

[@kevinhowes3803]

Excellent video and perfect for a couple of projects I am planning at present.

[@jakebillington6817]

Great video, will definitely be applying this in my mark ups on my next project.

[@georgeomalley6066]

Brilliant Explanation

[@stuffoflardohfortheloveof]

Well I never….I’d never heard of these beams before this and wish I’d known before building my large workshop. Thanks very much for sharing the info. 👍🙂

[@RobindeJongh]

They definitely make sense for a workshop - maybe next time!

[@bloggs692413]

this is very helpfull for a garage build too

[@MatLampitt]

Iv got a garage that I’m considering the flat roof for. Max 2.5m height for PD. My roof span will be 4.6 from block wall to block wall. Iv been racking my brains trying to think of a solution around using 8x2s and this seems like a great idea. Hopefully using steel sheets on the roof and with the reduced joist depth it means the 150mm flashing will work too 👍. 🤞

[@stevet2603]

Informative, thanks. I’ve heard of flitch beams, wish I’d thought of using them when I built my garden room last year!

[@RobindeJongh]

Thanks Steve. How did your build go?

[@stevet2603]

@@RobindeJongh Went well and looks great but it was a one man build in my spare time so took a few months but I wasn’t in a hurry! I’m pretty handy at most things DIY/general building and started it prior to getting into KZbin but then came across Ali Dymock’s build and Oakwood Garden Rooms which both gave me ideas then came across your channel when designing my roof, had to go for cold roof due to height limitations but followed your guidance and as it’s a very low occupancy I don’t envisage having any issues! Keep up the informative vid’s

[@netchoivanov8533]

Hi Robin, I am impressed! Do you recommend flitch beams for Loft Conversion? Or can we use universal metal beam with adding two timbers inside to reduce the size of it? Could you help us with calculations? Thank you!

[@chineduufoeze4716]

Nice video. However why do you say it’s for a garden room. Can it not be used anywhere you want to reduced size or increase the capacity of a beam? Thank you.

[@CrimeVid]

Garden rooms etc, I tend to pick up joists arranged the short way with a cased ( vertically) beam in the centre, half inch ply glued and screwed to the 6”x2”. Takes out all the bounce out of the deck. This is a pragmatic,easy way out of a springy roof, using what you almost certainly have lying about !

[@RobindeJongh]

That's a great solution 👍

[@utensil999]

Great video. If those flitch beams are above the bi-folds. What kind of steel would you need above the bifolds, and would it be better to build the wall that contains the bifolds and supports the steel out of 5x3 studwork and have two ply studs either side of bifolds? Also what would be the spec of the steel?

[@unionse7en]

Other, possibly more efficient assemblies other than a plate, are Angle iron with one leg horizontal (bottom), or a flat stip along the bottom, or a flat tension strip with a significant spacer at the lower midpoint. These strip require robust anchoring at each end support.

[@armaandy3846]

Thank you for this video, I am looking to cover a span on an outdoor room that is 5m x 5m, to keep the height below PD of 2.5m these flitch beams seem to be the way to go. when it comes to installing the shorter span beams/joists to the Flitch, would these be attached to the flitch by using Hangers? Also for the Flitch would this rest (and attached) on top of the framed front and rear wall or hung onto the wall with hangers? Thank you.

[@jeremyvivian2180]

My garden room will have either bifold or sliding doors that traverse the centre point on the front elevation beneath where you indicate the flitch beam should go. Can the flitch beam bear upon upon this point as long as steps are taken to reinforce the bearer below - eg by using a steel box section next to it across the opening?

[@wolfy8391]

Thanks for this - brilliant video and really helped me, thanks for breaking it all down. I’ve got a 4m span and decided on three flitch beams like you’ve mentioned with two end beams which are fixed to the end walls fully (no chance of sagging), so a total of 5 beams across the 4m span (along a 7.2m long building, you’ve got a 6m length in your example), with joists in between them all. About to attach the joists which I think are around 1700mm each roughly, I’ve planned on using truss clips, so I have a flat surface across joists to fix the 22mm OSB T&G to. Rather than joist hangers. Does this sound ok to you?

[@tlangdon12]

A true truss clip would not work because they only have a single vertical edge to support the truss and this isn't designed to take the load directly on it. I suspect that what you are calling a 'truss clip' is actually a small face-fixed joist hanger (sometimes called a mini hanger) that would properly support the joist.. Used with the correct number and type of fixings, such mini hangers should be fine for the 1.7m joists and 22mm OSB roof covering.

[@peterkwameosei-bonsu6135]

What strength does doubling up a 5x2 offer in terms of span

[@douglaslopes1987]

Hi Robin, thank you for this video. But considering the cold roof here, when you change the direction of your smaller beams, how do you ventilate above the insulation? I mean, if all the beams go front to back, you'd have ventilation through the sofits passing above the pir insulation and below the roof deck as it should for a cold roof. But when you make the flitch beams and rotate the other beams, how will they ventilate and still compensate for the difference between the 145mm flitch beam and the 90mm of the normal ones?

[@BDB888]

You would have to cross batten the top the joists before fitting the firrings to vent the roof

[@johnybee8261]

I am doing diy calculations for exact same type and shape build flat warm deck roof only 2m longer and wider (6m by 8m). adding 2 flitch beams to cut the joist spans to 2.66m. Considering 47×145 or 63 145 C16 joists. How do I calculate what size joist and steel plate for flitch beam of 6m span?

[@davidreid2301]

Thank you for taking the time to make this video, it's very interesting, and much needed currently. I don't have a project in need of this, but I am curious: would you not need joist hangers for what would effectively be dwangs/noggins? They too would push the cost up a little if required. Or are you suggesting a traditional nailing method? Most people don't realise just how much of a finite source timber is, and how long it takes for a usable tree to grow! Up here, in Scotland, I'm seeing huge areas of fast-growing pine trees being cut down that were planted about 40 years ago, when I was a boy. In fact, in the '70s my own primary school had a day trip to a local forestry so all of the kids could plant a sapling, and take one home to plant. 40 + years on and that now has all been logged. It looks awful, and I'll most likely be pushing up the daisies by the time the next lot is ready for logging. I doubt there will be a whole lot of use for these logged trees either as they only have an average diameter of about 10'! And it's just knotty pine! We really do need an alternative. Thanks again, Robin, you're doing your bit! Cheers!

[@RobindeJongh]

Hi David.Joist hangers would do it. They cost about 60p each I think. I share your sadness at seeing forests cut down. Steel is 100% recyclable.

[@davidreid2301]

@@RobindeJongh Indeed! And infinity recyclable. Thanks again for a great tutorial!

[@malcolmswallow7226]

Hi Robin, I have been looking for a solution to the roof for a project I'm about to start, 5m x 5.5m garden room. My span is 5m front to back. I have one question what support would I need for the flitch beams on the front and back walls, great explanation by the way.

[@RobindeJongh]

Hi Malcolm. You will need to work out the end reactions at the support (i.e. the shear at the end of the beam) and then design timber studwork to support it. I have just the video for you😉 kzbin.info/www/bejne/laHVgGWjar2sp7M

[@stevering5255]

Hi Robin - Great video. My one question is, how do you factor in a slight slope to the flat roof on a garden room. I'm working on a garden room 7m long by 4.8m wide - but I need the slope to run along the 7m length from back to front (I could do it along the 4.8m width but then face on when looking at the build the roof will slope from left to right (or vice versa) - but if I used 2x flitch beams like your example above, they will obviously be true and flat - I was then considering placing SIP panels (100mm thick) on top of the flat roof joists - so should I lay them flat along the flat beams and add in a slope on top to get that run for water?

[@RobindeJongh]

Hi Steve. SIP panels can span a fair length structurally by themselves so you may not need any joists at all.

[@brendanclarke2813]

Can the structural resistance of the timber elements of the beam be used in the design calculations? Something tells me it can but I'm not sure how.

[@RobindeJongh]

Hi Brendan. Yes it can but it’s a very complicated calculation.

[@johnbosworth3663]

Great video! I'm building a 5x5 room and been advised to use 5x2 doubled up with steel at every joist, 400c. Seems alot to me and expensive. Do you think alternating flitch then doubled up 5x2 bolted would be adequate? Thank you.

[@RobindeJongh]

Hi John. Alternating isn't a good idea, because your roof will sag at every other joist. The OSB board isn't designed to span 800mm. For a 5x5 room, you can put a flitch beam in the middle and have 2.5m joists running perpendicular, or two flitch beams with 1.65m joists running perpendicular.

[@johnbosworth3663]

@@RobindeJongh many thanks for responding Robin. Sounds like a plan. So if I use one flitch beam along the middle, would the perpendicular ones need to be doubled and bolted? Would have to rethink how I'll do the front overhang.

[@coachgius]

why not using the original span but with all joists being flitch beams? Would the steel plate not help reducing the section required?

[@RobindeJongh]

Because that would increase steel costs and a lot of time spent drilling and bolting. Good question!

[@m215900]

Hi Robin, great video thank you!, I am looking to do something similar with 100mm Kingspan insulated roofing panels on a 6m x 4m Garden Room using a flitch beam as shallow ridge for 4 x 3m x 1m panels, my thoughts are that with the roofing panels being considerably lighter tham a traditional timber roof I shouldn't have any issues, walls will be SIP construction, would you have any concerns with my thinking?

[@stevering5255]

Hey Robin - how did this go? I too am building a garden room - but it is 4.8m but 7m - but was considering building the walls out of 100mm thick SIP panels and again on the roof the same 100mm tick SIP panels - did you complete your roof yet?

[@m215900]

@@stevering5255 Hi Steve, I did, using flitch beams with 10mm plate steel tied into 120mm x 47mm joists, I used Kingspan roofing panels, they are light and strong defo worth a look 👍

[@smallbatchbrewingco5675]

Can you just use flitch beams all the way across , front to back or just doubling up the 5”x2” joists ?

[@RobindeJongh]

You could use flitch all the way along but that would be expensive. However it would allow you to use a much smaller timber and thinner steel flat, so perhaps it's worth looking into.

[@nigelfreeman1]

Hello. can you use a flitch beam as a ridge beam for a pitched roof?

[@MG-nm9gt]

I shouldn’t see why not but it may require structural calculations by an engineer to ensure it can take the required load.

[@user-ix4ge6rr7u]

👍

[@simonh73]

Could you just use multiple fitch beams on 60 centres?

[@RobindeJongh]

Yes you could but that would be expensive.

[@startrack3744]

By watching your video, its implied the 2x6 flitch beam can span 6m without issue, is that correct? What would be the max span for 2x6 flitch?

[@RobindeJongh]

Hi. It is spanning the other way, a 4m distance. The depth and breadth of the beam, especially the steel flat, has to be ascertained by calculation.

[@tlangdon12]

@@RobindeJongh I think many would be interested in seeing a worked example of the calculation for a steel flat to go into a Flitch Beam.

[@tonyb83]

What about the extra cost of supporting the flitch beam?

[@RobindeJongh]

Minimal cost.

[@henryblicharz5556]

Why don’t you simply use ceiling joist trusses at 24 in center saves time and money !

[@gmail8483]

Is a flat roof actually flat?

[@martinsmith6049]

Won't those flitch beams be sat on top of the French window lintel?

[@RobindeJongh]

Hi Martin. The lintel would need to be designed for the point load.

[@martinsmith6049]

@@RobindeJongh Thanks Robin. I'm a bricky and thought it was a big no-no to do that. I bow to your expertise. You do good videos, mate. I'm subscribed.

[@threepennypirate8529]

Great info but grrrrr I’m so annoyed I’ve just bought 9” x6m timbers at not only great expense, 24 cost me about £1200 plus I’m building of my own so lifting them on to the walls was slow .. I’m a 62 year old woman. Built a block and table in the end. This would have made life so much easier . Thanks Robin, I love these tutorials, they are giving me a good insight into how buildings work and hold together. Thankyou for your time

[@RobindeJongh]

I'm so sorry to hear that! Thanks for sharing your insights - as you said, both the weight and expense are major factors here especially when doing the work yourself. I'm kicking myself now for not getting this info out their earlier. Glad you're liking the tutorials though!