Demo - Does a vaulted roof push out at the wall-plate?
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- Опубліковано 22 чер 2021
- Does a vaulted ceiling cause the supporting walls to spread?
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If you want a cathedral or vaulted ceiling, you will need to look carefully at the roof structure your builder is proposing to achieve the vaulted roof space. In this video you will see the various options in action using a timber model of a vaulted roof. You will see the effect on the supporting walls for an unsupported vaulted roof, collar tied roof, and what effect it has if you have the collar tie at 1/3 or 2/3 height to stop roof spread.
✅To analyse a roof like this to avoid roof spread see • How to stop roof spread
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I saw a video by a millennial couple who bought an older house. They were bragging about how they converted their old attic into extra, finished rentable space by removing all the collar ties, and were teaching others how to do the same. As if they were some stupid thing that older people did that didn't need to be done. The comment section wasn't kind.
I live in Portugal and many people buy a ruin of which only the walls are still standing, They are made out of limestone about 50 cm's thick. What they usually do nowadays is pour a thick concrete ring on top of the walls all around on which they build the roof.
The ties will work, if the roof members are rigid, which depends on their depth, if they are 50mm thick. Those little 2x1s have a lot of flex. The moment of inertia increases in cubic proportion of the matters distance from the centre line. So a member that is double the height if 8 times as rigid. Now compare a 2x1 to a 2x10 and you will get something like 125 x the rigidity for the same about of cross section at the top and bottom ie. 25mm of timber...but you still have to add the other 225mm of timber that the 2x10 is made up of.
Im a structural Carpenter since 1985. First of all, framing is about load transfer. If you want a open rafter or vaulted ceiling. You must transfer the load to a ridge pole that can handle the weights of the roof and snow load if applicable. 2 you can use vaulted ceiling trusses. I have built 12/12 pitch roofs with 2x12 dimensional lumber. with no ridge pole.
It's not a vaulted ceiling if you fill it up with rafter ties. You might as well just put in a regular truss roof. I just built a 10x10 addition with a vaulted ceiling that I *know* is fine, but I still had to have a lengthy discussion with the inspector about whether or not that doubled 2x10 will be strong enough to hold up three packs of shingles.
12 pitch is getting near the point of almost being self supporting. At least the collar beam could be installed closer to the ridge IF there wasn't a floor joist. We built an 18 pitch A frame but it was attached to a 2 X 8 knee wall only 30" tall AND we had a lotta intersecting, perpendicular walls as well so spread load was not an issue. This was out of 2 X 10 with no ridge beam. those beams were still pricey because they were special order 28' long back in the early 70's. We were actually considering plank & beam but it was even pricier. This was in Saint Lucie County. Yep that building is still there and in fact it now sports metal roof cover. I knocked on their door and said guess who? The female owner started crying because I asked them if the bed was still supported on chains and that blew her away. They were the 2nd owner but I knew that from checking county property records out of curiosity. Yep the bed was still supported by black chain!
The same problem of wall spreading due to roof weight resulted in some spectacular collapses in early European churches until the invention of the external flying buttresses. Even with these, eventually iron tie rods spanning the open interiors were added to reinforce deteriorating buttresses.
I have seen this happen in older, and even newer, car garages.
The real problem is that wood is excellent under compression, and lousy under tension.
I have “saved” a few of those garages with some relatively easy fixes.
Depending on the length, several tensioning cables are run between the tops of the walls, parallel to the bottom runner, or “ceiling joists,” to stabilize the sag and outward pressure.
Turnbuckles were placed, and standard cable clamps were employed.
After placement of the cable/turnbuckle combination was assembled, the turnbuckles are tightened.
Just an inch, they are tightened.
Then they are left for a few weeks, maybe a month or so.
Go back and tighten again, and another period of time, adjusted to the observation of the effect on the structure.
When the turnbuckle has no more to give, the cables, in steps, are loosened, and the cable clamps are loosened, slack taken out of the cables, and the process repeats.
This is done until the walls are true vertical again.
The cables and turnbuckles are left in place to keep the sagging from happening again.
Proper eye bolts and plates to spread the force out on the existing structure would be employed when the cables are first set.
Any novice engineer knows of the tensioning vs compression formulas, as old wooden bridges were designed and constructed with this in mind.
A cursory glance at some of the old exposed truss bridges that are still around can teach volumes with a little imagination and vision of what the engineer was doing to design the structure.
Good luck!
I am not sure that churches can be compared to regular homes people live in. When you compare these buildings they are so very different, it just doesn't work.
1. Windows in homes were small to make heating easier and big glass was expensive. In contrast, most churches tried to have big windows.
2. The Ceiling in homes was low to make heating easier and save building costs. Churches have high ceilings and are higher buildings in general.
3. More than 2 Floors was uncommon for homes. Churches commonly have no upper floor in the middle. This makes church wood frame very unstable and much harder to construct. And any mistake in the lower structure will affect the roof.
Also: are you referring to Roman or Gothic style churches?
Always keep in mind: medieval wood frame usually combined oak for the wall structure with lighter wood for the roof and EVERYTHING was connected with wood nails. Steel is a modern invention and iron was only used for emergency fixes and would rarely have the same stability.
Complete load of nonsense, a steel ridge member isn't going to solve the issue of flexing rafters.
There are two solutions, joists or tie beams. Also purlin and cross members over a limited length or roof or commensurate with the size of purlins used.
@@dangeary2134 I can’t see the wood breaking under tension unless it is flimsy but I can see the join giving way if it is just a screw.
@@jimdavis8391can you explain why you think flexing rafters are involved? I can't work out what comment you are responding to.
A traditional solution to this problem is to build a "fake" vaulted ceiling inside the rafters, resulting in a truss of sorts.
One end of the truss component attaches to the base of the rafter at the wall. The other end about 1/3 of the way down the opposite rafter, and the same both sides. This forms the framework for the "vaulted" ceiling. You would now basically have an "X" inside your rafters. Where the two "cross members" intersect, should be connected by a horizontal member running the full length of the roof. In short, cross bracing the rafters to the opposite wall. Or you could probably use 2X2s and fiberboard.
That's called a scissor truss and it works great.
@@madmat990absolutely correct.
I've built massive A frames and you must use a massive beam that is supported at two ends all the way thru to foundation and the steeper the pitch the less deflection of load live and dead on the eave walls.
@@madmat990 I thought that was what they were called, the whole time watching this I figured that is where they would go with it...
The other option is the Flying Buttress. Not used a lot in residential housing, but it has been extensively used in gothic churches.
Or pinnacles, or a hammer-beam roof (I'd love a dining room with one in my modest house!) - which is the equivalent of pinnacles along the length of the roof - the spreading force being applied part way down the wall.
The other design that solves the problem of rafters is the A-Frame, with the rafters extending all the way to the ground. Although, perhaps that would be a special case of the truss with the bottom cord being the floor of the building.
We had an extremely heavy snowfall one year and buildings were collapsing all over town. My duplex was doing just that, tearing in two as the roof pushed the outer walls outward. The center ceiling beam slid a good 2" from the wall threatening to just fall off the wall. Yikes! Scary to look up from your bed a see the beam holding up the ceiling pulling out of the wall. After the snow was cleared the building mostly pulled back together. But we found there was ZERO cross bracing to the roof! Strong chains/cables across the flat roof had to be added tying the two roof sides together into a stable triangle.
Bearing in mind with that arrangement the rafters are under tension ie hanging from not supporting the ridge so make sure the attachment screws don’t rip out of the wood or bend once its loaded up with half a ton of slates or whatever, and supports for the ridge beam can support whole weight of roof but yes that would solve that problem. If anything I’d say resultant force on wall plate would be inward (pivot around ridge) max force at 45’ pitch. (diy designer/builder)
Collar ties are there to stop the roof being lifted by windloading as much as they are to reduce flex from other loads, especially if ceiling joists are absent. Lapped dovetails were one of the old methods of connecting them to sufficiently sized rafters with some aesthetic as well as structural value.
Yes, and if no ceiling joists are present. Such as in old Garages and I owned one built in 1953. There were at least wall ties every six feet. And these ties are still required on new garages that are built with conventional cut and stack methods. Now instead of wood collar ties Simpson strapping tying rafters and ridge together are used prior to installing roofing. After all this time There is still confusion about Ridge Board, Ridge Beam, what collar ties are actually used for. And it is important depending on the where you live and build. I live in earthquake country. Lol. And of course learning the buildings codes of the land is never a bad idea.
I've read it very clearly stated in numerous places that collar ties are NOT there to reduce wall spread but to prevent wind lift, even lower down. I am glad he pointed that out.
This video has been really helpful to me.
I've got a full comprehension of the physics going on the rafters, now.
Thank you !
Greetings from Buenos Aires
The Collar tie will absolutely help....! he's using a flimsy 2x2.... Try it with a 2x6...
This "test" is completely pointless with 2x2's.
It’s not rocket science it’s just basic common sense
Hi Robin: The Full height A-Frame without the tie is one option but you didn't explain the loading implications if the A frame is steel and mounted on top of the brick returns. I see a lot of extension builds made in this way and it would have been instructive to hear your assessment of the two construction approaches
Collar ties are supposed to prevent rafter separation during wind uplift, not to prevent wall spread.
The other obvious method is to use scissor trusses.
The part that wasn't touched upon is that the loads from the ridge beam (steel, LVL, Glulam, etc) have to be followed down to the foundation system. That means opening up the walls at both gable ends to add additional supports.
Collar ties can do both functions, if rafters and ties are sized properly, and then you don't need a ridge beam supported on the gable ends.
It seems like rafter engineering is pretty important. I wish he switched from 2x2 boards to 2x4 boards to show the difference in flex a different board dimension offers. What he's doing only exaggerates the wall flex because he's using such small boards that have a high degree of flex. You also can't forget that attached walls add to the flex resistance as well.
Collar ties by definition are located within top 3rd of rafter. Rafter ties must be within lower 3rd of the rafter to be sufficiently effective.
Ridge beams can be, and typically are, wood. Doesn't have to be metal.
If the ridge beam is supported at the gable ends, then you don't need the collar .ties@@RobindeJongh
Correct 👍
One could also use rods (maybe threaded rods with turnbuckles) to keep the top-plates or bond beams from spreading. These would disrupt the "open roof" look a little , but just a little, and the bigger the top-plates or bond beams, the fewer rods would be needed. Another approach would be to add ties that went from each top-plate or bond-beam, to maybe the 1/3 mark from the peak on the other side; making each triangle into a "cathedral truss", with a bolt at the intersection of the X. The interior drywall could be applied to these ties, and the ceiling would still have an open view of the peak, but if would be a lower peak than that of the roof itself, and all of the framing members would have to be larger. Then again, with big enough framing members, the horizontal ties at 3:08 could probably have been made to work. Of course, if cost and size is no object, you could always consider boomerang-shaped "gluelams" ....
Thanks, that's a great video.
I'll have to show it to the builders next time I'm on site and they're telling me ceiling ties aren't needed!
Under-ridge beam spanning between the gable ends. Supporting the ends of the beam is a post or stud pack at each end. Special attention is applied to the connection between the upper rafter-to-beam. If the ridge line no longer moves, the bottom of the rafter cannot move outwards. The beam, rafters and fasteners must be revisited to ensure they can perform their new roles properly of course. Unless a hurricane blows in the windows and exerts an uplift on the underside of the roof, the walls will not bow outwards. Kidding aside, this is the only practical solution to converting an attic floor joist roofing structure to an open cathedral ceiling to the room below.
Would this also be the solution to dropping the ceiling height to allow for a loft conversion without compromising the roof?
Great vid! I have seen two US vids where they were nailing the rafters to the side of the structural ridge beam rather than on top as at the end of this video. They were using 10 inch rafters though. It was a Bob Vila video.
Great video. However, it doesnt need to be only a steel ridge beam. Today we have a lot of great wood products that can achieve this, and even in the past we could have done a long truss ridge. As long as the stiffness provided can restrain the top of the rafters movement downwards, then no substantial lateral forces can be carried out to the supports. In your first example, if you would add two columns to the start and end of your short ridge, there would have been no lateral movement at the base.
Can I just clarify Benjamin, (diyer only) are you saying that if a post is put from a load bearing wall up to each end of the ridge (on a four way hip), that would be sufficient to reinforce/strenthen the whole roof? Do hope you see this and reply, on a 'I need to know" basis :). Thanks hopefully?
Hi@@jesshothersall, it wont provide stiffness to the ridge unless the posts you mention are continuously being extended all the way from the bearing wall to the ridge. Like another bearing wall in the attic so to speak.
@@jesshothersall do you have ceiling timbers running from plate to plate or a vaulted roof with sloping ceilings? If the former then a traditional roof configuration may be possible with ceiling joists tying the rafters feet together to prevent spread, and binders running perpendicular to the ceiling joists to tie that direction. If vaulted then yes, provided your ridge beam is strong enough, and often overlooked, the hip beams are strong enough to carry the load from all the rafters fixed to them, then yes posts at the end of the ridge at the intersection of the hips could support that but hip and ridge beam sizes need to be designed by a structural engineer and are usually huge compared to what you might expect
@@jesshothersall -- You cannot put your post just anywhere on top of a bearing wall. Any such post is almost certainly carrying 1000s of pounds of weight. So if your post sits on a bearing wall and the nearest studs are 7 or so inches away, then this post, which is bearing 1000s of pounds, will severely compromise your top plates. Even if you have a stud in your bearing wall directly underneath the added post, the building code will tell you that you need a double or triple stud to support that post. You absolutely must have a post built into the bearing wall directly below the post you are adding, a double or triple stud. But it doesn't stop there. You need to verify that the bottom end of the this post in the bearing wall is also being strongly supported from below. Most houses are built in a platform style, where there are floor joists covered with plywood or USB, and then you build the walls on top of the floor. So if you have a post carrying 1000s of pounds of roof weight, it could easily punch a hole through your OSB floor unless you put support underneath the post. So if this post is directly above the foundation, you can simply stick a block the height of your floor joists on top of the mudsill and under the flooring to support this post fully. Otherwise in your basement or crawl space you should have doubled or tripled joists under where that post comes down, or equivalent. Every structure is different so you really need to understand and analyze what is the right approach for your situation. Structural engineers refer to this subject as the "load path." You need to think about every load in your structure and make sure that every load is transferred all the way down to the foundation and thus supported.
Here's another quick example. Why do they put headers over windows and doors and sometimes the framing around those openings have multiple studs? Well, the rafters bearing a heavy roof sit on the wall and also ceiling joists that bear the weight of drywall etc. Over an opening your going to need some kind of beam to support all this weight so that it doesn't crush your opening. So you put in a header, which is really a small beam, and that header may need 1 to 3 jack studs. So ALL the weight of the roof and ceiling over that window is carried by the header beam. And since the beam is supported by jack studs, all that weight on the header is now transferred to the jack studs and downward onto the floor. So now you need to determine if those jack studs have adequate support underneath. It all depends. A lot of times a bearing wall is spanning joists but also rests on the rim joist which gives it a huge amount of support and there are no issues. But you have to look at every case individually to verify.
@@dennmillsch Those are great points. In retrospect, I think it is best to avoid giving general ideas about the physics and legal issues behind structural work as they may give a false feeling of security to the DIYer. You are best to hire a local engineer ma'am.
In America, anytime there’s a vaulted ceiling, the gable ends have a post that sits under the wood ridge beam. The weight is transferred to the sole plate which will have a ganged stud to transfer the weight to the ground.
Finally!!! I can’t believe no one else mentioned this. Most barns use this concept. Bravo to you👍
@@richardsilva-spokane3436 thank you, good sir. I just thought it odd that no one considered that. I looked through some of the comments, and thought something should be said😬
Interesting video once again fella. It clearly shows what is happening within the frame under load. In the real world the connection of the collar tie is critical. This should have at least two bolts and a timber connector to ensure all the forces are being passed through the joint. Also, correctly sized rafters and collar tie will reduce the spread as there would be less bending and deflection in the rafters. A cavity wall will also provide a little bit of lateral resistance. I’ve designed lots of vaulted roofs with collars tie at about one third down from the ridge without a ridge beam and none have failed. I agree that a ridge beam would be a design option, albeit the fixing of the rafters to it is important to ensure the all load goes on to the beam. I think the span of the roof is key as to whether a ridge beam is adopted or not. Keep the vids coming 😃
Those are great points, Paul. No reason why any collar tied roof can't work as long as it's well designed to control the deflection.
@@RobindeJongh I have a possible roof to put on an old 20x25’ stone building. We want a vaulted ceiling ideally if possible. I would love some thoughts on this.
Exactly Paul.I work from India for clients in UK - since 2004.On one refurbishment job,an existing roof had a collar tie and some dummy posts to support ceiling lights.The new owner wanted the dummy posts removed and I explained that no additional structure was required based in collar tie and cavity wall + deflection check.The builder did not listen and energy ahead with loads.of steel purlins !
General common sense until you get to the I beam then no explanation vid ends….
and no clues as to how to attach it to the wooden beam overhead either @@diogenes1815
I had the exact issue with a detached garage. The walls started to flare out in the middle of their length at the top. The design had been alright with a flat roof, but I replaced with a pitched one, also was alright, but then I put about 2 tonnes of tiles on top! I corrected the issue by affixing cross-beams that screwed into the wood that ran atop the walls, placing some kind of platform/vertical wood beam, that I had a car jack applying lifting force to the apex of the roof, the single long beam that went the length of the roof. I jacked the dip of the roof that had developed in the middle, until it was gone, and then cut cross-beams, and as they screwed in, the ‘dip’ in the roof central apex had disappeared. Then, still jacked in the middle, I fitted every second or third ‘A’ frame with, er, the cross-plank that makes it into an ‘A’, as you did here. The roof is still straight and the walls still are no longer buckled/flared out at the top. Of course, I didn’t know when I bought the property, the walls were single-brick…ah well, next job. Take care all, thanks for the insight.
Be aware thst dynamic loads, wind and snow, are very different for a flat roof vs a pitched roof. Make sure that you have sufficiently reinforced it for high winds and that you have strapped the roof down to the walls and not just the wall plate, and that the walls weren't damaged too much by the movement.
I like this, its all about translation.
If you have a solid lateral cross section, tying both wall together together. The pressure from above cannot push the walls apart. The two other parts of the triangle, need depth to make them riged, but dont need to be very thick. And like you show, the ridge suport beam needs to be strong, steel is great, but you could use wood with a metal chanal screwed to the underside of the ridge. This will prevent any sagging over time.
By keeping the full triangle on each spex, you have an extra space or room. All the apexs, spaced at 1-1.5 metres apart.
Thank you for your explination.
My 130 year old home has no problems, still, without any of the recommended solutions, my (brick) walls are still pointing straight up 👍
Hi Robert. I quote the author of the book "Structures, or why things don't fall down": Naturally, the buildings we see and admire are those which have survived.
@@RobindeJonghgreat book👍
We have to think about what can happen not what has happened. For example, how long does it take a building to collapse in a fire? And how does it collapse when it is damaged?
Good illustration of the forces at work. But no mention of the effect of adding vertically orientated purlins set into the gable/partition walls, with the rafters birdsmouthed over them.
great demonstration here!. I'll be recommending this one as required viewing for the grads!
Thanks Tony - glad you liked it!
I've seen a few of your videos now, I thought i'd take the time to quickly say thankyou so much for the info you put out there! This has been hugely helpful for me in tackling an attic conversion with lots of rotten timbers! I was pretty confident of the physics of it and this has confirmed the theory :) Thanks again
I am looking to raise the ceiling height in my garage: the pitched roof has a conventional ridge board but also has pretty robust timber purlins and collar ties every fourth rafter. Would increasing the number of collar ties be a viable method of removing a section of ceiling joists to allow use of my car lift, do you think.
in our country, Croatia, on Dalamatian cost we traditioanly build wooden roofs like this. when we raplace roof, we do "serklaž" basicly reinforced concrete ring on the end of the wall in thicknes of wall 50 cm height. that element provide stiffnes and hold house together, we dont do any cross beams in attick
Thanks Nenad. That's a great solution. I think in countries where earthquake is an issue they also use concrete ring-beams.
Thanks alot mare. Been looking for videos about this issue.
I am constructing a garage with this setup. However down the middle under the top beam I will build a very sturdy and strong wall to support the top beam. I am guessing this will also eliminate any movement of the walls ?
I would suggest that you put a tie from the bottom of the rafter to 1/3 of the way down the opposite rafter, Do this on both sides and you still get a pitched ceiling without the spread of the walls
Your channel is amazing, thank you
I don’t see how just adding a steel ridge beam solves the problem. The problem of the walls spreading didn’t seem to be that your ridge beam was flexing, but instead that the rafters were flexing.
That’s a weird place to cut off. I see the algorithm is pushing this video hard the past few days. Basically you can use an I beam or engineer spec’ed wood beam and support it with a load bearing wall or post on each end (imagine at the siding and in front of the camera) so all loads are simply transferred out to those 2 points.
The ridge can’t flex with a steel
If the ridge Doesn’t defect.
The wall-plate can’t move
A steel ridge beam stops all roof spread because there is no horizontal component to the forces any more. See the next video here for an explanation: ua-cam.com/video/BtsZk0UR2EI/v-deo.html
Imagine a solid post or pillar going from the beam all the way down to the foundation.
The model in the video has a "ridge pole" and NOT a "ridge beam." A ridge BEAM absolutely WILL solve the problem. It will need to be designed to handle the load and for many buildings can be wood and not steel. Do not confuse a "ridge beam" with a "ridge pole". A ridge pole is what is shown in the video, typically a plank running on edge at the roof ridge and mostly serves as a nailer for rafters. It does not intended to carry the roof load and can simply be a single 2x plank. A RIDGE BEAM is different. A RIDGE BEAM is designed to carry a load which is why they are ALWAYS supported by posts, usually at the ends.
So for example, imagine a shed 12 feet wide and 16 feet long. If you do the ridge pole approach, you might use a single 2x8. It may be supported on the ends, but only to hold it in place but not to carry any significant weight. The weight of the roof is carried by the rafters which transmits the weight diagonally to the walls, thus pushing down on them but also pushing outward. The ridge pole method needs ceiling joists at the bottom of the rafters, or else collar ties no more than 1/3 of the way to the ridge. HOWEVER, if you use a ridge BEAM, it WILL be supported at the ends and is much heftier than a mere ridge pole, hefty enough to bear up to 1/2 the roof load. So for this shed instead of one 2x8, a ridge BEAM might be three 2x10s sistered together. A ridge beam carries some of the roof load and eliminates the sideways push on the walls. A ridge pole doesn't carry any load to speak of and thus the rafters end up pushing out the walls. Big difference.
I worked on a single storey extension project a few years ago which incorporated a vaulted ceiling and the engineer designed a welded box steel wall plate to prevent wall spread
Yes that's a great solution.
We had plans which used flitch plate beam on supporting posts supporting top collar tie's with new bolted floor joists to rafters as tie's creating a triangle. Engineer said by bolting it would be far superior to nailing.
Right at the end you talked about a steel ridge beam. Could you make a video detailing that approach?
Yeah it’s unclear to me how that solves the problem - at least with the scale model he is using here.
@@Pseudify The beam is supported at both ends so the peak of the roof is resting on a beam that is transferring all the load down to the foundation. If the peak can't move down, the rafters can't push the walls out.
@@bradley3549 Yep I figured that out soon after I posted this. Thanks.
Thank you for your videos. How is steel ridge beam supported in case there a hipped roof to one side and a chimney breast is in the way on the gable end side?
The scissors type roof construction also works well, creating a clear span with a reduced internal apex height.
It also provides more/better insulation options as well as providing room for utilities.
You simply use larger trusses and perlins, depending on the span of the rafters will determine the number of perlins, size of trusses etc.
Large truss and perlins look beautiful with vaulted ceilings inbetween
Another option is if doing an attic conversion, the new floor becomes the tie, tieing the walls together.
Simple stuff, but always best to get a structural engineer to calculate timber dimensions that are needed
Totally agree with you. Trusses with purlins don't give you a fully vaulted ceiling, but definitely an option.
You can also use a steel ridge, or large glue lam ridge beam. Depends on the size of the room, but with glue lam beams I think they can span something stupid like 35 meters, so no restriction really, you just have massive looking timbers the longer the span, standard limits are timber length basically (length of trees) larger you need glue lam or steel. Weight is then transfered to the gable ends....
for a 8 foot span or so I use 2x12 full birdmouths every 16 inches. I use solid metal rod with threaded ends as bottom cord. I paint them black and I do pullups from them. Only 3 in 8 feet. its snows here. just an entrance mudroom. bottom cords make a small area smaller,the idea is to open up the ceiling while keeping integrity of structure.
Excellent analysis. Thanks
Proper construction is steel ridge beam with support purlin 1/3 down and collar tie to complete roof triangulation, strapping at wall plate, should be wall plate strapped to wall, and also rafters strapped to wall, using 40 x 5mm Galv ms straps.
Debating this with my architect right now. Initial plan was heavy ridge beam. Current plan is collar tie/ceiling no further than 1/3 up the rafters, using engineered plywood I-beams.
Hi Michael. Are the I-Beam manufacturers ok with their product being used for this application?
One could always use 2X6 ripped at the end so the entire top plate is being utilized for stability . I did that on the front of my shed for my stability for my 25” extended front eave
Concealed heavy duty L-brackets at the bottom of the wall bolted to floor system or a foundation in addition to a collar tie would solve the problem.
Steel reinforced concrete ring beam. You can make it as strong as you like depending on what kind of forces you're expecting to encounter. You can even turn it into an achitectural feature.
Fantastic, thank you. The simple demos were really helpful
My roof had vertical lengths of timber in the centre to shift load onto the centreline of the ceiling. I removed them as the bolts holding them in place were lifting the ceiling slightly. Instead I placed 10 X 6" beams from one end of the gable to the opposite side placing them into the block/brick wall half way down the riser on both ends, then using hex bolts with wooden thread I pre-drilled the holes and screwed through the beam and into each roof spar/truss.
The weight load is now trying to push on the ends of the gable in the direction of the angle downwards. Think of two triangles and on the two top edges A long beam joins the triangle directly opposite, this keeps the roof line straight and any forces applied are acted upon by the gables in a downward, not outward force. It's a solid roof and has had tons of snow on it, never budged.
good demo. thanks
Nice video! How the structure can be look like if we need lowering a ceiling?
The collar tie would have worked considerably better if you were using 6 x 2 for the common rafters and collar tie, with bolts. Although i understand this is a basic mock up, the bendy tile spline wasn't very reflective of normal rafter characterists.
This is pretty much a scale model.
I agree, the rafters are to skinny (not really to scale) 6”, 8” and or course 10” rafters would be much preferred with way less deflection and collar ties would work better .( But load bearing understood for this demo… )
no, it's a good representation of the physics. What you describe would add unnecessary resistance to the model which would make the results erroneous.
We want to look at the lateral effects at the base when gravity loads are applied and this video achieved it perfectly. If the thicker rafters with multiple bolts were used in this small model, the distance between the bolts would be significant enough to add moment resistance basically creating a rigid frame. If you were to build a house with 24 inch rafters and ties (±your proposed scale), the same effect could develop in the connections, but that in turn would be unrealistic because nobody builds with these dimensions. I recommend you find a real interest in the physics because once you get a good grasp, it is truly a mindblowing experience. I've never quite seen anything like it.
As others have said, sure it would work better but at a real roof scale and load, it would require very large timber and connections.
It is Not a "steel" ridge beam. It IS "Structural" ridge beam. Depending on the span, to can easily be made of wood, or engineered wood (LVL) . A scissor truss is also a popular solution.
Hi Robin this video has been an eye opener however what I am aiming to do is remove the 11 3" by 2" ceiling joists and replace them with 4 oak beams approx 8" x 2" would this enough to stop roof spread ? or should I still put in a ridge beam?
you have to cross your ceiling joist to the opposite side of the ridge you go from the top of the right side rafter down to the left side plate and opposite the other side and fasten the rafters to the ceiling joist top and bottom and the roof and walls are locked out with no steel needed. It is like a scissor truss.
Hi Robin, many thanks for all your videos, I'm certainly learning a huge amount from them.
One thing I'd like to know related to this video is could the "wall spread" be avoided by having a horizontal member from wall to wall below the wall plate level? I appreciate that I would lose triangulation, but I'd like to attach a ledger board to each wall using appropriate fixings and then use joist hangers to attach much more substantial joists from wall to wall. The rafters are supported by a fairly substantial purlin on each side, and there are also collar ties approximately a third of the way down from the ridge. I would ensure that a new dwarf wall, from the new joists up to the purlin on each side, were also connected to the existing joists at that point (they'd be cut for the central section) to try to tie everything in. I'd also consider using a 3-4" timber sandwiched between the old joists and the new ones up until the dwarf wall so that effectively there would be a 15-16" joist, partly resting on the wall plate and also attached to the ledger board for the eaves section on each side, with just the bottom 8" continuing across the attic for the usable space.
The reason I'm asking is that I have a Victorian terrace with an original attic room. The existing joists, although they've been there for about 140 years and have supported the floor of the attic room for that long so far, really aren't great (barely 4" by 2") and so I'd like to upgrade them, but there's only 2m of headheight as it is. Ideally I'd like to lower the floor by a total of 150-200mm, whilst fitting 8" by 2" joists (there's a spine wall in the middle-ish of the house so the maximum span is only 3.8m). It's early days and I will seek paid professional help in due course (do you cover SW England?) but I'd be interested to know if what I'm suggesting is remotely feasible as it would avoid the need for steels into the party walls and, with the spine wall, the required spans really aren't that long.
Hi John. Thanks for your question. If you would like to send an email and include some photos and sketches I may be able to take a look for you.
@@RobindeJongh Many thanks for the reply, when I realised how long ago you made the video I wasn't really expecting one tbh, so it's much appreciated. I'll email something over in the next couple of days when I've got together as much accurate information as I can.
Another great vid, thanks
Great vid. We have just had a report from a RICS homebuyer surveyor and indicated some roof spread. We are looking at purchasing a property with a vaulted roof... now I know what he is taking about ;-(
Good practical demo. That's why it's important to use a P.C. software design licensed and endorsed by Building and Regulatory Governing Bodies to determine roof truss design. A wooden lam. Beam to stressed designed parameters would be more aesthetically pleasing and also adds l a decor/designer detail feature and conversational point. Plus side also, it appreciates the value of the building.Done plenty of these for this type of roofing configuration.
If anyone is struggling to see what a ridge beam is actually “doing” that you can have no rafter ties, try this:
Take scissors, with the tips of the blades on a table, holding the pivot pin between forefinger and thumb so the scissors can’t collapse flat. The ridge beam is your finger providing vertical support. if you lift the pin the rafter ends get closer, if you lower it, the tips of the blade slide out (obviously you need loose scissors for this, but you can still visualise what’s trying to happen). You could have a long prop going from this point to the floor which would do the job of the ridge beam, or if you don’t want a series of props in the middle of your building, you build 2 big props (your gable walls) and run a bridge between them (your ridge beam) to pick up the rafters. Now the total weight that all those props would have had to support, plus the weight of the beam itself is resting on the gable walls (half each side). And the bottoms of the rafters are sitting on the wall plates, which see no sideways force, just the balance of the weight of the roof system which is not sitting on the ridge beam and transferred to the gable ends (I’m curious if it’s 50-50 between ridge and wall, or some other ratio? It feels like it should be evenly split)
My pre WW1 era house rafters were built with a near 90° peak with collar ties, knee braces for a half wall 2×8s for the flooring...many old houses were built that way and are still in use...26 feet square with a load bearing wall down the center...it sat on large rocks for piers...the unusual thing about the house were the walls...three 1x12s vertical; 2 on the outside overlapped with one on the inside held together by horizontal 2x4 stringers...I also have a small barn built much the same as your demonstration, only with poles to keep the walls speeding....due to snow all the standing old buildings have steep roofs...
You can have a similar structure but with some mods.
Vertical link as a key on the top. Link from the top of the link to each wall, link from the bottom of the vertical link to each wall and then a horizontal link at 2/3rd of the hight.
This gives some complex structure and double the wood but lots of headroom.
French construction. You will find this in lots of old barns.
Great practical demonstration. The only thing that would make it better is to demonstrate (or mock up) the effect a steel ridge beam has on preventing spreading.
See my explanation here: ua-cam.com/video/BtsZk0UR2EI/v-deo.htmlfeature=shared
If the ridge beam is supported by gables at both ends, AND is of sufficient size to carry the load, then there will be no downward force.
Yes, no sideways force at the eaves.
Yes use a Ridge Beam not a Ridge Board. Entirely different Roof Dynamics.
When I worked in the roof truss industry, we would attach only one end of a vaulted truss to the top of the wall with a hurricane clip. The other end was free to move. The adjacent truss was attached to the wall at the opposite end. So, the trusses were attached at one end and the attachments alternated from one wall to the other.
hes not talking about a truss system
It’s all about the downward force producing vectors. The only solution is a triangle with its base at the wall plate and a strong enough joint there. Without the triangle base the walls will collapse outwards. With the base the joint will break before the joist will break in tension. The steel girder will only add to the problem unless it is otherwise supported by the gable ends. Then the gable end will need to be sufficient. Basically you can’t have a heavy vaulted roof without the base of the triangle unless you have flying buttresses of some sort.
The demonstration is great for showing how gable roofs exert force on outer walls. I think the demo could be improved by discussing truss design relative to load. After all the model adequately supported itself when no additional load was applied. When the model was over loaded it failed. All structures can fail so the conclusion that a steel beam is needed for support is to simplistic to provide value for real world application. The conclusion that a steel beam is needed would require an analysis of the entire system that supports a roof under a design load.
I love vaulted ceilings, but never thought of this problem, but makes sense.
I used an LVL to span 20 ft. One end falls over a 6 ft window. The load sits on top of a header above the window and is transferred to the posts under the header. Hasn't moved and hasn't cracked in 20 years.
I’m no builder but I’ve worked in construction all my life, there are other ways to design it using all timber and no steel ridge beam look at old church ceilings and how the building was built
Steel ridge beam is what we do. Steel columns at each wall end to support it. Rafters will be solid.
Brilliant video and thank you. Very simple principles explained concisely. I have a question, why is placing the cross beam at ceiling level not a good arrangement for a vaulted roof?
It is a great idea. That’s what the video starts with, and as you can see there is no roof spread.
Scissor truss is the go here. Basically another rafter below the main rafter but opening up from the birdsmouth and attaching about of 1/4 of the way down from the ridge on the opposite rafter, making an x that is wider at the bottom than the top.
The only way the steel beam works is if the beam is adequately supported on the ends all the way to the footing. If it is, there is very little load on the walls. If the steel ridge beam doesn't deflect, the rafter can't push horizontally. Half the roof load will be vertical and shouldn't worry the wall.
Thank you.
Thank you you're awesome
the flex of the wood is part of the reason those walls are pushing out. In a low load situation (Desert, never snows) I would go for more of a scissors truss, where the roof provides its own support like a pot lid. A bolt through the crossing joists to add rigidity. That would give a vaulted look with the right finish. In a high load situation, ridge beam and post is probably the only solution.
ua-cam.com/video/CmTOMBlMBVw/v-deo.html
Answer: supported ridge beam. I've done it many times, and it works like a charm.
Levels are good to use.
I am comparing this to our roof and other similar roofs. The solution are very diverse and all of them are entirely wood.
It is not just a collar tile, supported by columns and diagonal beams, it is also diagonal "Windrispen" that stabilize the roof further. Never try to save wood there, because the roof is the most exposed to wind and has to endure forces in all directions!
I am talking about roofs that are up to 500 years old. So, these are survivors. Most of them are from 1800.
Seeing a lot of ideas here about a lot of things EXCEPT making the ridge strong enough so it doesn't deflect. The top angle cuts of the rafters must TOTALLY bear on the ridge board which results in the ridge protruding down into the living space some amount. At that point you can scab some filler on the bottom edge of the rafters so drywall forms a perfect "V" on the inside of the ceiling. Use metal clips to reinforce that rafter-to-ridge connection if necessary.
I your ridge beam is sized properly no collar ties needed. They do connect the walls better. I'll see when the next quake hits here how well the vaulted does I did a while back without ties.
Great stuff from Great guy
Thank you!!
Good demonstration of what works and doesn't work.
The explanations as to why they do so is lacking, though.
Finally, no demo nor explanation offered as to your recommended solution.
In the old days they ran metal rods from side to side on the upper walls with cast iron plates on outside of wall. Also most homes incorporate shear walls to address some of this.
Best choice is to do a single slope roof with shear walls, much stronger, much less expensive.
Close. First, your ridge beam needs to be an actual beam and not just a ridge board as is commonly used when it's tied by the ceiling joists. That could be a steel beam, LVL, PSL, glulam, or multiple dimensional boards together. But more importantly, that ridge beam needs rigid support at both ends, which wasn't mentioned.
This isn't the only solution though, a vaulted truss assembly could also be used if the conditions above cannot be met.
Is there any difference if you split the roof load on the front and rear walls, and your floor loads on the gable end walls? Which means the 2nd story floor joists are running parallel to the front and rear walls, not perpendicular. But, all the 2nd story floor joists are sheathed all the way across to the rim joist on the front and rear walls.
If you want a vaulted ceiling, use scissor truss and purlins. Strong, looks nice.
I have a vaulted ceiling 12/3 pitch with 2x12 for a ridge beam and 2x6 for rafters. The distance from the ridge beam to the wall is ten feet.
The building measures 16 by 20 feet with ten foot high walls. The top of the ridge beam is close to 13 feet up.
I used hurricane ties on the ridge beam and rafters at both ends.
Post and pier construction for the building wall supports. It's about a meter high off the ground.
Any constructive criticism is greatly appreciated. Thank you.
I shouldn't have watched this (very interesting) video! Through admitted ignorance, we've gone from slate to concrete tiles on a tyneside flat. Roofers said it would be fine. Ended up getting a structural engineer out who said that the beams looked fine and calcs showed minimal deflection with plenty of head room. I don't think we mentioned anything about roof spread, and I'm not sure we have any ceiling joists connected across either. Going to have to take a look, but I hope there's an easy fix because the floor boards have come up and some minor cracks starting to show! Does roof spread have a limit or does it keep moving until the roof slips? Thanks, really interesting videos!
You could've added scissor-style trusses, almost doubling the carrying capacity of the roof, and certainly increasing its strenght, while still getting the visual effects of the vaulted ceiling.
Edit: I suscribed to your channel. You're providing very interesting stuff in your channel.
Thanks for sharing.
That's a good suggestion - thank you! Scissor trusses wouldn't give a totally vaulted roof but perhaps good enough for some people.
Yeah i used scissor trusses on an addition that gets tons of snow. I didn't even get the stud spacing correct but it worked regardless. No movement in 15 years.
Robin, A vid on gable end ladders would be useful. They are always a compromise, Some options for different methods of construction would be useful. I have 'droopy gables' because of heavy tiles on a relatively large eaves overhang. I am going to start with a steel ridge beam or flitch plate, but what about the support on a cantilevered steel wall plate?
Great suggestion! Hope you're getting your droopy gables looked at?
@@RobindeJongh Robin, I will strip the gable end back in the Spring and then fix it myself. If you want to feature the problem in a 'Gable End Ladders' video then I can send you the video once stripped back. I want to keep the structure open with no A frame or cross-bracing. It is a bungalow near Totnes in Devon
A very basic but very effective demonstration. There are some incredibly ignorant people around judging by the comments section. It’s worrying to think they’re building things if they can’t understand the principles of this demonstration 😮
I would use the word "un-trained", because it is often because of a lack of education that people jump to these conclusions. It is a pity that in this country (UK) builders do not need any kind of training to call themselves builders. That's not the fault of the builder but of the industry and government who should insist on a minimum level of education. I am trying to do my bit to plug this gap 👍
Would putting purlings half way down either side help with spread. Im gonna build a 4m wide workshop from timber and want a vaulted ceiling.
They could, although they would need to be designed for minor axis bending because they would resist both vertical and horizontal forces
It's clear the force pushes outward. Why a simple beam across the base is in tension. Then the roof just "sits" on the walls w/o pushing them outward. You could use steel cables, for that matter. And the cross beams (or cables) can be set fairly high and provide that tension.
Do you think its best practice to butt the rafters against the ridge beam or to overlay them on top
plumb cut if tied roof
sat on top if structural ridge beam
the traditional rafters needs collar ties and that seel ridge beam won't do the job by itself. You will need to augment the steel beam with at least two (preferably steel) support columns at each end to stop any downward movement of the roof. Those beams will need to be bound to the walls they adjoin to take advantage of the anti wracking features of the sheathing.
The purpose of collar ties is not to prevent walls from spreading, it is solely to connect opposing rafters in order to resist the ridge uplift cased by wind loads.
@@wooddoug1 solely eh?
@@Raul28153Yes solely to unitize rafters and ridge to prevent uplift. Any resistance to wall blow out by collar ties is negligible and is not mentioned in US Buildings Codes for that purpose.
whats the steel ridge beam you recommend at the end do to keep the walls from pushing out?
its not connected to the walls or rafters in a way that would prevent wall rotation. if anything its just going to pre load the rafters and make the issue worse.
It’s a beam supported at each end.
Ridge beam carries the load to the end walls.
This is why 5/8 Probolts should be used properly on any wall with a vaulted ceiling.
This is a high school trigonometry issue. To make the vaulted ceiling you need a ridge beam that is capable of supporting half the roof. Snow loads and solar panels increase the load that must be supported. Engineered beams are the most commonly used material for this purpose. Steel and solid wood beams can also be used. An engineer should be consulted about sizing and columns to support them.
reinforced concrete ring beam? or would it still lack the nessesary strength?