My Garden Room Build - 9m x 4m

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Molynoox

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Interesting. I had seen this in Mike’s design as well as others online. But like you say, hard to adjust when the majority of framing you see online places OSB on the exterior. I was probably thinking of doubling up and using osb on outside and inside of the frame. However, concern with that would be trapping moisture within the frame.

Ok - back to the drawing board with an internal wall height of 2.4m and just the breathable membrane, battens and wood cladding on outside.

I’m not yet sure about size of floor joists. We have incredibly rocky ground and the least amount of excavation the better for my wrists! I’m thinking concrete piers and the least possible, so it helps me to push spans and go for studier timber sizes eg. 6x2. I’m getting a local architectural tech to draw up my sketches so hoping he’ll assist. If not, we can get some structural calcs done. Anyway... my 100mm osb overlap was simply there to cover the join between bottom plate, floor sheets and joists. It doesn’t need to extend all the way to the bottom of joists, just enough to cover the above. I suppose with this new design (no external osb) it’s just a case of extending the breather membrane and battens below the bottom plate (sole).

Thanks for the correction on terminology... there does seem to be quite a bit of variation out there! I guess some of it is UK/US variations? Top and bottom makes sense to me anyway!!!

How big is the building?
Could you not just use span tables to get the right size joists rather than get structural calcs done? That's what I did for my floor and also my roof.

I've been thinking about this OSB on inside thing and I can't think of any reason not to do it other than a few minor things.
1. electrical second fix might be more hassle because there is OSB and plasterboard to cut through to fit the sockets. Not exactly a deal breaker.
2. No service void behind plasterboard to put the electrical wiring, assuming the PIR is tight up against the OSB on inside.
3. The PIR isn't 'sandwiched' unlike with traditional method, unless you count the breather membrane, but not sure if that is going to be as robust.
4. You might not be able to build the wall flat, including sheathing, breather membrane, battens, which is more efficient than doing it when it's upright. I'm again thinking of sequencing of the electrical first fix and how that works with this method.
Martin
 
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Humf

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Same size as yours about ideal for the plot. Although I can fine tune now to make the whole build more straightforward.

Span tables... yes, although I have to hold my hands up at this point and say calculating the dead loads is completely out of my current level of understanding.

I think (1) and (2) on your list are solved by battening vertically on top of wall studs before plasterboarding to create a service void and avoid disturbing PIR for any electrics.

Not sure what you mean by (3)?

(4) most certainly is an issue. Might be a workaround though so I’ll have a little dig around...

thanks for your replies on this Martin. Really helpful. If mine can be even half as impressive as your build I’ll be happy.
 

Jameshow

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An old chippie told me a ratio of 1.5 X joist depth in inches = span in feet.... That was on 16" centres. So 6" spanned 9ft.

Which works according to this...

 

Molynoox

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Same size as yours about ideal for the plot. Although I can fine tune now to make the whole build more straightforward.

Span tables... yes, although I have to hold my hands up at this point and say calculating the dead loads is completely out of my current level of understanding.

I think (1) and (2) on your list are solved by battening vertically on top of wall studs before plasterboarding to create a service void and avoid disturbing PIR for any electrics.

Not sure what you mean by (3)?

(4) most certainly is an issue. Might be a workaround though so I’ll have a little dig around...

thanks for your replies on this Martin. Really helpful. If mine can be even half as impressive as your build I’ll be happy.
With #3 I just meant that on a 'normal' build you would have OSB on outside and plasterboard on inside, hence the sandwich. With the alternative wall design option the only thing stopping the PIR falling out of the external side is friction and the breather membrane. Probably not an issue, but when I did my build I pushed the PIR, from the inside, tight against the OSB, which was sitting on the outside. So then I start thinking, no problem, just fit the PIR from the other side and push it tight against OSB on inside, but then you don't want it tight on that side because you want a service void, and in addition it would be a monumental ball ache fitting PIR via the external side as I only left 400mm space around the sides and back of my building. It's all just frazzling my brain thinking about it, seems like a simple change but it changes quite a lot about how you put everything together.
Probably over thinking it as usual, one of my skills / habits :rolleyes:

I'm glad the discussion is helping anyway, I spent 100's of hours researching this stuff and it seems like a bit of a waste not to share it. Thanks for the feedback on my build too, appreciate it, I am sure yours will be every bit as good as you want it to be (y)
Martin
 

Molynoox

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An old chippie told me a ratio of 1.5 X joist depth in inches = span in feet.... That was on 16" centres. So 6" spanned 9ft.

Which works according to this...

That's cool James (y) I'm going to remember that, could be handy when you need something quick and dirty and don't have access or motivation to look at span tables.
Martin
 

Humf

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Hi Martin

Looking around, 2700mm osb seems to be less common. As you’d expect. Given current pricing and availability of materials this just feels like I’m not going to get the best price.

What do you think about this idea....

3.6m top/bottom plates, using 450mm centres gives 8 equal studs with 400mm spacing. So the 1200mm PIR is cut into 3 equal strips. So far, so good.

Then OSB sheathing (if using 2400x1200 sheets) can have 2 horizontal pieces and 1 vertical ie. 2400 + 1200 = 3600.

That seems good. I’m only seeing 9mm metric OSB at the moment but will enquire at other yards.

I haven’t yet got my head around sheathing on the inside. I do get it but all residential framing does it on the exterior, so Mike G is bucking the trend on that.

Using 3.6m wide panels does make the overall size a bit tricky. 3 panels would give 10.8m which is a bit big. 2 panels gives 7.2m which is smaller than I would prefer. So I’m thinking maybe using 2 x 3.6 with a 2.4 on the end. This gives 9.6 which is perfect. One 3.6 for the shorter walls is fine.
 

Molynoox

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if you are having exactly 2.4m height, I seem to remember that was your plan, then your theoretical plan you describe gives near 100% utilisation on the sheathing and PIR, so it looks pretty good to me.

On the inside, you are going to have different wall dimensions to the outside due to the thickness of the walls and how they meet at the corners, so cuts will be needed on the plasterboard, but that is much cheaper than OSB and PIR, so you are doing it the right way round :)

you will need to cut your 2400mm x 400mm PIR strips twice again to account for the noggins in middle and whatever is left in top section of wall up to top plate (it will not be exactly right if you have made wall exactly 2400mm for the OSB)

I haven't gone 'all in' on the internal sheathing yet either

Martin
 

Humf

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Thanks all understood.

I was really trying to figure out the horizontal dimensions before thinking in much detail about the verticals. Having worked a little bit with plasterboard in the past, i’d much rather be making cuts to that. So if I keep the OSB on the exterior, it would make sense to include 100/150mm of overlap to cover floor joists and take a bit of a hit on internal headroom. Will look at that next!

One thing I’m not understanding, is wall insulation. With a cold roof, I understand that a void is left above the PIR and air is allowed to circulate preventing any buildup of moisture on the roof covering. Moisture is further limited by using a vapour barrier underneath the finished surface. But with walls, if osb is used externally, is the same principle followed? If so, the PIR is kept flush with internal finished surface and a air gap left between the insulation and sheathing, there would be no circulation because of top and bottom plates?
 

Molynoox

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One thing I’m not understanding, is wall insulation. With a cold roof, I understand that a void is left above the PIR and air is allowed to circulate preventing any buildup of moisture on the roof covering. Moisture is further limited by using a vapour barrier underneath the finished surface. But with walls, if osb is used externally, is the same principle followed? If so, the PIR is kept flush with internal finished surface and a air gap left between the insulation and sheathing, there would be no circulation because of top and bottom plates?

I went through that thought process too - nobody is venting the walls as far as I have seen.
If you look around at garden room companies, nobody is venting the roofs either :)

The problem with condensate is biggest in the roof due to the way that warm air rises upwards and tends to find the roof space and then condense on cold surfaces, hence why moisture barrier on walls seems to be less common / critical in garden outbuildings. I think its a case of drawing the line somewhere but I like your thought process of questioning everything before making the decisions.

Interstitial condensate can in some (possibly most?) instances safely happen inside walls / and roofs because apparantely it dries out again in summer months. But... and its a big but... that really depends how much you use the building and how you use it (with how many people for example)....

Martin
 

Inspector

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Primary reason for venting a roof is to keep it from getting hot and cooking the shingles. Air traveling from the soffits to the vents along the ridge carry the heat away and is self powered by convection. 😉

Pete
 

Humf

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Re. walls. I guess this is the thinking behind internal osb? Any moist air hits the ‘warm’ osb, minimising condensation, and any moisture that does make it through, is able to escape through the breathable membrane?

So the question is really for all those residential buildings and loft conversions that I see the likes of Robin C doing. I think you’ve answered it though Martin with your point about warm air rising and the roof being most susceptible...
 

Churchy00

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Apr 2021 - Beam Calculations (for above the doors)

I spent way too long looking into different options for door headers. I was a little paranoid about deflection as I didn't want to have any problems with the doors working properly over time. I have heard of a few people that have had issues with bifold doors and the root cause seems to come back to a combination of:
1. the door header not being suitable for the door span + roof loads
2. the sensitivity of the door to vertical deflection (but reason 1 seems to be the big one)

In addition to this, changes in the weather through the seasons can (I have heard) cause flex and movement which can lead to issues. My doors are alu so that means theoretically more stability versus PVC, and hopefully less issues, but the main reason I selected alu was for the sharper looks (if I'm honest). So... operating from the assumption that vertical deflection is the true nemesis of bifolds this became the factor which I needed to focus on and my mind was set on giving my lovely new doors a stress free life via a suitably deluxe door header experience. This meant doing a bit of research into what my best options were.

Results from my research
Unfortunately, most of the good guidance I found was for multi storey buildings and hence they were often coming up with solutions that would be not be suitable for a garden room. For my particular application, these recommendations would be either:
1. overengineered in terms of strength and cost
2. cause me issues on overall building height
3. or both

Mildly relevant distraction #1:
Regarding the height thing, when working within permitted development you need to keep everything under 2.5m (when building within 2m of the boundary) and for that reason you really need to think about what you are doing every step of the way. For example, assuming 2000mm for your door height, that leaves only half a metre for the base, the headers and the roof (not to mention the air gap under the building, and possibly even your floor boards depending on how you build it).

Anyway, I'm getting distracted, the point is the only other guidance I found for header selection / header design was pretty anecdotal and didn't seem to have any theory behind it. That isn't necessarily a problem, but on this occasion it wasn't giving me enough confidence to make a decision, considering the potential impact of getting it wrong (fiddly / sticky doors of annoyance).

The cunning plan
So... logically, I decided that I would leverage my complete lack of structural engineering knowledge to manually calculate the beam deflections for all of the options available. So here are the options I considered:

1. Doubled up 6 x 2, C24 timber
2. Flitch beam (C24 timber and steel 'flitch plate' sandwiched together)
3. I beam (sometimes known as a H beam or a 'universal beam')
4. RHS (rectangular hollow section)

Note: I did not include concrete lintel or glulam beam, for reasons which I honestly cannot remember, and there may be other options which I dont even know about, that I am hoping people will point out to me.

My plan was to use the below formula to calculate the maximum deflection on the beam. I would still of course have the problem of not knowing how much deflection was acceptable for my particular bifold door, hmmmm... HOWEVER I would be able to COMPARE them all

View attachment 117771

Mildly relevant distraction #2:
I did contact some of the door manufactures to find out what sort of deflection they think their products could handle, or even what headers they recommended for different spans - but alas, nobody wanted to commit to anything specific, other than to say "computer says no" or "zero deflection required" which is of course theoretically impossible, even if I made it from diamond.
Note: making it from diamond would represent a significant cost save for the build, considering how much I'm planning to spend on materials and 'essential' tools so far)

Mildly relevant distraction #3:
Note that there are lots of different formulas for this sort of thing, but the one above should represent worst case for my door header because it assumes the beam is simply supported at either end (in reality it has lots of engineering screws holding it in place along some of its length and also has the roof load partially distributed either side of the 'fulcrum' too, which I imagine restricts the movement - not that I know what I am talking about). Oh yeah, please note that I am absolutely NOT qualified in this topic, and everything I say should be considered as science fiction, even the science part is pushing it a bit.
I will point out though that I am lucky enough to know somebody that does know what he is talking about, and he checked this over for me and helped me with some of the calcs, so it isn't completely worthless. As a minimum I think it gives a good indication of how the options stack up against one another. Worst case its a bit of fun, and a good opportunity for everybody to laugh at my mistakes.

Variables

View attachment 117772

The legend in the pictures explains what the variables are, so I wont double explain those, but it is worth noting that the values for youngs modulus for each material can be found online in the so called 'blue book', as can the values for moment of inertia (which is specific to each shape / cross section) - you can calculate this if you want to, but its easier to look it up. I vaguely remember us covering how to do this in my mech eng degree, but that was 20 years ago and I was rubbish at it then and suspect even crapper now so much prefer standing on the shoulders of giants. Oh yeah, 'w' or roof load is the other funny one. I think for that one I calculated the weight of my entire roof (timber, insulation, EPDM, chipboard) and then added some for static snow load, and finally I think some for dynamic load for people / person (me) walking on there. I also divided the numbers by two because (approx.) half the load is on the front wall and the other half is on the back wall (my side walls do not support any load) Honestly can't remember exactly how I got that number, but as I say all my assumptions are clearly shown in the workings so as not to mislead anybody into how I got the overall deflection results. Looking at these numbers now, we have 14 N/cm which is 1.4kg per cm, which is 140kg per metre - so that 'feels' in the right ball park for the amount of load along that beam.
Finally, regarding variables, you will notice the slightly hilarious use of 'cm' as a unit. I am advised that the golden rule with SE calcs is to pick one unit and stick with it, and because a lot of the numbers provided for free in the blue book are in 'cm' it makes sense to use cm throughout.

How I will contextualise the results
Seeing as I don't know how much deflection is tolerable by the doors, due to the fact it is a secret (not disclosed by the door manufacturers), I need a way to contextualise any numbers that pop out of the calculations. I am clutching at straws a little here, but I did find some rough guidelines that I think could help put the deflection values into context: I understand that some people work the following rule:
• <2m span = doubled up 2 x 6 timber is ok
• >2m span = metal beam required (or you could use thicker timber, but you can't simply add in 9x2 headers when you only have 2.5m overall building height to play with - so we end up in metal beam territory once a 6 x 2 isn't strong enough)

So, I will use a doubled up 6 x 2 timber as a sort of baseline solution that is 'probably' acceptable for a 2 metre span. Considering my span is 2.4m, I know that any alternative designs only need to be say 20% stronger, for the same constrained / max 150mm header thickness. (I think I mentioned this already, but I cannot just simply add thicker timbers and be done with it, due to the 2.5m building height restriction. That in itself is the ONLY reason for doing all this faffing around - I am fixed with 150mm max for my header)

The results
I will include some extracts below from my summaries for each of the 4 options so that you can see my assumptions (mistakes) in all their glory. As you can see, the timber option (for my 2.4m wide bifold) gives 3.4mm deflection (in the middle), and the metal options are far stiffer ranging from 0.71mm to 0.34mm deflection.

View attachment 117773

View attachment 117774

View attachment 117775

View attachment 117776

Below are the full workings in excel.
View attachment 117777

The decision
So to cut a long story short (oops too late for that) I have decided to use doubled up 6 x 2 timber for above the french doors which have only a 1.6m span, and a flitch beam for above the bifold door which has a 2.4m span.

Factors influencing the decision:
COST
From a cost perspective timber is cheapest (about £50), and all the metal options work out in a similar same ball park, although flitch was cheaper than the other two metal options by about 30 or 40%
STRENGTH
Again, all the metal options are basically the same - as a minimum they are 4 times stiffer than timber, and if we work from the assumption that the timber option is good enough for a 2m span, then we can conclude from the numbers that the metal options are all way stronger than needed for my 2.4m. So, for my span, strength is not really a factor when choosing between the metal options.
WORKABILITY
the primary reason for choosing flitch beam over i beam or RHS was the fact that the flitch beam gave me a timber surface on both sides, which is nicer to work with (attaching cladding on outside or plasterboard on inside). I dare say flitch beam is slightly more hassle to erect than RHS or I beam because you have to drill holes in the timber and bolt it all together, which takes time, but its probably 2 hours of work to construct and install a flitch beam versus 1 hour to install RHS or I beam so probably not significant in the grand scheme of things.

Mildly relevant distraction #4: I just checked with future self, and I / he has confirmed that the flitch beam did take about 2 hours, not including the 30 minutes spent staring at it proudly afterwards, or the 15 minutes spent explaining it to my (completely uninterested) wife

Summary
Overall I believe flitch beam to be the best option for this application, but I reserve the right to change my mind later, probably when its too late. See below for some top secret pictures which I took from the future.

View attachment 117778

View attachment 117780

Cost wise we are looking at about £100 for the flitch plate, which then gets sandwiched between two timbers to create a flitch beam. Note that the delivery costs for these things are huge (prohibitively so), so I picked mine up in my A-team van as the place was only about 40 minutes away. You will also need some bolts too. And wood. Under £200 'all in' I guess, which feels like good value if it keeps the doors working properly.

I am sorry for the length of that post, I find it hard to filter and I also find it hard and distinguish between useful and useless information. But, one man's trash is another man's treasure. Maybe that means my garden room could actually be worth something in the future.... :-D

Martin
Hi Martin,
Fantastic post!! I've been trying to figure out what beam to use in the garden room I'm planning. I've trawled the internet and this is the first time I've seen anything like an explanation that tries to lay out the basic calculations required....So many thanks for that!!

Originally, I had a 2.5m bi-fold chosen and was planning on a 160x80x5 RHS as I know they are widely used for that span, especially by Oakwood Garden Rooms (great videos on YouTube by the way!). Then the wife changed her mind and I'm re-planning for a larger room with a 4m bi-fold. I contacted Liam at Oakwood and asked him if the same RHS but longer would suffice and he advises that he's used it across the same span...but I wanted to check the math/deflection.

That's where I've come a cropper....because trying to figure out the equations is proving VERY confusing.
Your post here really helps...but I do have some questions...

I've tried to follow your calculations and referred to the Blue Book online (https://www.steelforlifebluebook.co.uk/cfrhs/ec3-ukna/section-properties-dimensions-properties/) but can't make the numbers right for your beam dimensions on the RHS option? Can you help? I'm assuming the second moment of area is through the Z-axis? What about the the elasticity variable?...the blue book refers to cm^3 not cm^2 and then your Excel has a N/cm^2 unit of measure?

Also, you don't make it clear in your explanation but presumably you are only using the section of roof supported by the beam as the 'w' variable? How did you account for your weight during a maintenance period....or a snowfall? These are temporary loads so presumably only a portion is used in the calculation?

Another one - I assume you measure the beam length as the "unsupported" span (i.e. not including the sections at each end that are supported by the stud walls)?

Sorry for all the questions - I'm not degree qualified but I like to think my maths is reasonable, so can you help me understand how all the calculations work? Perhaps send me the Excel sheet you worked to?

In simple terms...all I'm looking for is what the deflection would be over a 4m bifold span.

(Yes, I could just employ the services of a SE...but I do like to understand these things myself, if possible - and besides I'm tight as!!).

Many thanks!!
 

Molynoox

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Hi Martin,
Fantastic post!! I've been trying to figure out what beam to use in the garden room I'm planning. I've trawled the internet and this is the first time I've seen anything like an explanation that tries to lay out the basic calculations required....So many thanks for that!!

Originally, I had a 2.5m bi-fold chosen and was planning on a 160x80x5 RHS as I know they are widely used for that span, especially by Oakwood Garden Rooms (great videos on YouTube by the way!). Then the wife changed her mind and I'm re-planning for a larger room with a 4m bi-fold. I contacted Liam at Oakwood and asked him if the same RHS but longer would suffice and he advises that he's used it across the same span...but I wanted to check the math/deflection.

That's where I've come a cropper....because trying to figure out the equations is proving VERY confusing.
Your post here really helps...but I do have some questions...

I've tried to follow your calculations and referred to the Blue Book online (https://www.steelforlifebluebook.co.uk/cfrhs/ec3-ukna/section-properties-dimensions-properties/) but can't make the numbers right for your beam dimensions on the RHS option? Can you help? I'm assuming the second moment of area is through the Z-axis? What about the the elasticity variable?...the blue book refers to cm^3 not cm^2 and then your Excel has a N/cm^2 unit of measure?

Also, you don't make it clear in your explanation but presumably you are only using the section of roof supported by the beam as the 'w' variable? How did you account for your weight during a maintenance period....or a snowfall? These are temporary loads so presumably only a portion is used in the calculation?

Another one - I assume you measure the beam length as the "unsupported" span (i.e. not including the sections at each end that are supported by the stud walls)?

Sorry for all the questions - I'm not degree qualified but I like to think my maths is reasonable, so can you help me understand how all the calculations work? Perhaps send me the Excel sheet you worked to?

In simple terms...all I'm looking for is what the deflection would be over a 4m bifold span.

(Yes, I could just employ the services of a SE...but I do like to understand these things myself, if possible - and besides I'm tight as!!).

Many thanks!!

Blue Book
I don't know if this helps, but I made some notes when I got into all this thinking I would forget how it was done, below is the page on RHS beam. Elastic modulus is probably supposed to be volume not area, so typo in my excel I suspect. Its been a long while since I looked at this so honestly cant remember :)

notes 2.jpg

W variable
I calculated the weight of the roof by multiplying the volume of each component multiplied by the density for each material (EPDM, C24 etc), then I added some dynamic loads such as snow and people to get the total loading. In terms of which part of the roof weight to use, from memory the units were 'per metre', so it all cancelled out. If that makes sense.

Beam length
yes its the unsupported part, the building edges act as two fulcrums at either end, thus defining the span

4m beam
Using my crazy excel sheet the deflection for your 4m beam comes out at 2.6mm (quite a bit different to a 2.4m span surprisingly)

hope that helps anyway.
and by the way I understand your position having done similar research myself, its not so easy to get the answers and I only started doing all this faffing around because I couldn't find a nice off the shelf answer online.

disclaimer again: I know nothing.

Martin
 

Churchy00

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Blue Book
I don't know if this helps, but I made some notes when I got into all this thinking I would forget how it was done, below is the page on RHS beam. Elastic modulus is probably supposed to be volume not area, so typo in my excel I suspect. Its been a long while since I looked at this so honestly cant remember :)

View attachment 136130
W variable
I calculated the weight of the roof by multiplying the volume of each component multiplied by the density for each material (EPDM, C24 etc), then I added some dynamic loads such as snow and people to get the total loading. In terms of which part of the roof weight to use, from memory the units were 'per metre', so it all cancelled out. If that makes sense.

Beam length
yes its the unsupported part, the building edges act as two fulcrums at either end, thus defining the span

4m beam
Using my crazy excel sheet the deflection for your 4m beam comes out at 2.6mm (quite a bit different to a 2.4m span surprisingly)

hope that helps anyway.
and by the way I understand your position having done similar research myself, its not so easy to get the answers and I only started doing all this faffing around because I couldn't find a nice off the shelf answer online.

disclaimer again: I know nothing.

Martin
Hi Martin,

Thanks again for your reply....it does help...a lot!! Appreciate "you know nothing"!! :)

Couple more questions....the Blue Book I found online doesn't have the graduations on beam size that yours appears to....can you send me the link to the Blue Book you are using?

Also, can I ask a favour...I'm kind of OK with with the 2.6mm deflection you have calculated.....at the end of the day the roof will already be constructed before the bi-folds get fitted....so most of the deflection will already be apparent.....and I'm already allowing a 10mm gap for the bifold fitment....so should be OK!! (the bi-folds should still run smoothly...."he says, hoping with everything crossed"!) but....

What would be the deflection on a beam of the same dimensions (160mmx80mm at 4m span - overall beam length 4600mm) but at 6mm thick, not 5mm? I'm hoping the deflection would be less and thus may be a better option.....(please note I'm using 150x47 joists at 400 centres).

Would appreciate your comments....even though you're no expert!!! :D
 
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Molynoox

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The 2.6 was for 6.3mm thick, it is 3.1mm deflection with 5mm thick steel @ 4m span

blue book link here

note: I have used the roof weight from my building design, which was a 3.7m building depth - your building may be different size and hence roof weight. my joists are same as your though, 150 @ 400 centres.

Martin
 

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The 2.6 was for 6.3mm thick, it is 3.1mm deflection with 5mm thick steel @ 4m span

blue book link here

note: I have used the roof weight from my building design, which was a 3.7m building depth - your building may be different size and hence roof weight. my joists are same as your though, 150 @ 400 centres.

Martin
That's great mate...thanks. Actually my roof is about the same size. Will take a look at the blue book but think my mind's made up.

Very many thanks for your help. I'm gonna study your follow on posts on the other build elements so expect to be quizzed some more!!

Thanks again!!
 

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That's great mate...thanks. Actually my roof is about the same size. Will take a look at the blue book but think my mind's made up.

Very many thanks for your help. I'm gonna study your follow on posts on the other build elements so expect to be quizzed some more!!

Thanks again!!
Haha, no problem, feel free to ask if there are other parts of your build you are not sure about, I might have been through the exact same dilemma... I had plenty of those.

Martin
 

OldGreyDog

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When I was involved in engineering calculations the simple formula for bending moment of a beam carrying a uniformly distributed load was WL/8 (others include point loads at mid-span PL/4 etc.).
Deflection of a beam was calculated to not exceed 1/360th of its span, the formula for simple beams being 5WL³/384EI (where ‘E’ is the modulus of elasticity and ‘I’ the gross moment of inertia of the steel section being tested). I can’t find my steelwork manual now - think I gave it to a mate many moons ago, but its all online now. The linky’ below has tables of available steel sections, most being rolled in different weights to handle different loads. I think there should still be ’safe load charts/tables’ in there for the commonly rolled beam sections - there used to be in my paper version!
 
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BucksDad

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@Molynoox enjoyed reading through this thread again last night as I've now decided to switch from SIPs to timber frame after costing it up this week.

What size nails did you use for the framing and what size for the cladding? Did you use the 1st fix Hikoki for the cladding or did you have to get the 2nd fix gun as well?
 

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