How-to videos on loft conversions and structural home improvements by Chartered Civil Engineer, Robin de Jongh. Join the channel if you are a home owner, DIY enthusiast, builder or self builder, and check out my NEW loft conversion system at geni.us/loftbeam
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Make a ridge beam instead of board and make it load bearing directly under each end. Solid beam like a sawmilled tree. Dovetail the beam and rafters together.
You would have to have a solid ridge beam completely supported and notch it and the rafters to lock them together where they can not pull apart. Never stick frame that but never say never altogether though.
Stupid. It doesn't matter what the ridge beam is made of. It's the strength of the rafters at the point of the ridge that matters and/or whether the walls are buttressed where the rafters rest on them. This type of "ridge pole" construction is absolutely not the way to make a vaulted ceiling except where the walls are solidly buttressed against spreading. It's perfectly fine to have 2x12 rafters overlap each other to form the ridge and have glue and multiple screws attaching them with blocking in between them to finish the ridge, but best practice is to have the vaulted ceiling located where the walls the rafters attach to are solidly buttressed against the spreading of the rafters.
With so many (so obviously) opposed to the steel ridgebeam idea, and the meticulous well thought out and edited video regarding load transfers, you almost think that the creator is trying to teach the opposite point: that by removing the ceiling attachment and adding a laminated lvl or steel ridge beam can make the roof to wall connections weak and lead to wall-pushing
Boy a lot of people have got something to say. Engineers trying to show how cleaver they are, people concerned with terminology or whatever. The fact is, rafter deflection is what is being demonstrated. Try doing this with appropriate sized steel and weld it at the top. No deflection and no wall spreading. Do it with appropriate sized timber and fixings of the collar tie and again, little wall spreading. There are very good truss rafter designs that lend veey nicely to vaulted roofs, look at most churches and many have stood for hundreds of years.
If the ridge is adequate to carry the load there will be no spreading. The rafters also need to be adequate because if they flex it will pull in on the walls unless the plumb cut and seat cut start to gap then there will be spreading. Straps over the top rafter to rafter and also a positive connection on the exterior of wall to the seat cut will also work.
Steel beam as you described will not transfer the load to the gable ends unless it is supported at the gable end, but a ridge beam with gable end support should do the same but cheaper. A structural engineer would need to determine that though. I have wondered if installing a, let's say 12" wide wall cap might counter the side load and flex. That could work by transferring the side load to the gable end walls. I am not the structural engineer though.
Engineered scissors truss from a certified factory will push out the walls also. Mine were a 24' span and did a nice 1.5" push out over time. To counter this I should have tilted the supporting walls in. Since the truss' are wood it may have exceeded the inward tilt anyway.
The worry with Victorian roofs is that the nails fastening the ceiling joists to the plates rust through. Happily the nails they used seem to be high carbon cut nails and don't rot much. I used to add extra nails.
Why not set the wall plate on a box section steel member that could interface between the plate and the wall itself. If the box section is sufficiently tied at each end and strong enough to prevent lateral deflection, that seems like an alternative to a steel ridge beam that would need a fairly tricky load transfer arrangement if for example you had openings under one or both gable ends. Just a thought.
may I ask which application/ software you use to draw ? very nice explanation! although in my (non professional) opinion, don't necessary has to be a steel beam but some "beam" to hold the load... thanks for the video 😉
The single screw fixing at each end of Robin's collar-ties allows for rotation around the fixings themselves. No sensible carpenter would use just a single bolt to hold this connection. If the rafters flex/sag in time a bigger, stiff, properly connected collar will do a great deal to hold the rafters straight - heftier collars can really improve economically lightish rafters.
The UK is very lenient on enforcement of building regulations. You can get a private company to inspect and pass the property. For my loft conversion they came twice and I had to send a few pictures. I'm pretty pure the regs were circumvented. When engineering companies are fighting for business it's a race to the bottom.
And there in lies the problem. Steel and timber move differently, thus adding extra stress somewhere else. One would require a complete steel structure or one of timber, not these hybrid bastardised structures proposed here.
@4:20 The reason you are getting the rotation is because the rafter members are undersized and aren't resisting bending moment at the midspan of the rafter. With the appropriate collar tie and proper rafter dimensions calculated it won't push out on the walls. To the extreme you could even have just a steel ridge plate that is bolted to steel flitch plates that the rafters are bolted to just at the very top connection of the rafter ends. This will also work as long as you calculate the bending moment for the midspan of each rafter as part of your entire roof assembly and its live and dead loads and size the rafters accordingly. Obviously this solution will require more expensive hardware and more expensive and larger rafters to accomplish what you could achieve with a ridge beam. But sometimes a ridge beam isn't always practical or possible. The point is there are many engineering solutions to a situation. In this video this gentleman starts with an undersized rafter and is working his way to inventing a truss which is made up of many smaller cross-sectioned members. That's one way to do it.
I can see needing a beam for a long vaulted room but for a short area like an attic, not so much. My old house (pre-1900?) has a square/rectangular box in the vaulted ceiling attic (i.e., all four walls lean in to the peak area). Apparently this distributes the load effectively evenly in all directions so that the load is carried by all rafters out to the wall plate (-walls are lathe and plaster).
This does not belong on you tube....anyone who has to learn about roofs, rafters and trussed structures should not be trying to build them from a half baked you tube video....if you don't 'just know' what this video shows, then chances are you won't get in to a facility that would teach you how to design this type of structure....
Interesting. I'm guessing the 'stem wall moment' is what you use to calculate 'how to construct the stem wall'? So sponge cake would be different from concrete block+rebar, but I haven't found a video on how to use this figure to say spec this using brick as a material
