Any engineers in the house?

[RossJarvis]

...or better still a roofer. I've mentioned elsewhere that I'm putting up a "timber frame" building (I.e a "balloon frame" or stud wall building).

The engineer has specified a ridge beam which is about a foot wide and two foot deep glue-lam, which is b****y well mahoosive and must weigh a ton. Surely that can't be right, every other roof I've seen has no more than an 8"x2" board. We'll need a crane to put it up. Can anyone comment? By the way, we're roofing with 140mm thick wood "fibre-board" (Uditop) and tile on top.

I don't think we're parking a chieftain tank on it :roll:

 

[MMUK]

How big is this building going to be? Sounds a little over kill. Unless you're planning to rent it out to Tesco :lol:

 

[heimlaga]

I have a degree in structural engineering.....before I ended up unemployed and went back in to carpentry.

A tile roof is incredibly heavy. Even more loads are added if all the insulation follows the slope of the roof and is carried by the rafters. I don't know what the code says about snow load in Hampshire but let's guess a worst case scenario with something like 10 or 15 cm of very dense wet snow on a tile roof. If you have a ridge beam carrying the rafters without additional supports and the building is long with an open plan without load bearing partition walls to support the ridge beam between the gables you do inevitably end up with a very large beam.

However if something has gone wrong in the calculations I would think that has to do with the width of the beam. A height to width ratio of 2:1 would not utilize the wood very well. Both bending strenght and stiffness increase more with height than with width.
However there may be other factors (beam buckling or just shortage of headroom under the beam) that have forced the engineer to choose a not so efficient height to widt ratio. Anyways it seems a bit strange.

I think you should ask the engineer who designed the building!
Be polite and ask in the width of the beam was misswritten on the drawings. Such errors do happen. If the engineer is serious about his job he (or she) will double check that everything is correct and answer yes or no.

 

[RossJarvis]

Thanks guys.

Yes it's open plan, only supported at each end, with a span of 8.4m. 6m across the eaves. There are planning restraints on the total height, which influences headroom. The insulation is wood fibre, 140mm between rafters and 100mm on top, which I presume is notably heavier than foam, plus the tiles, Plus PV solar panels on top of the tiles (so yes it's a heavy roof).

The preliminary drawings had a beam of 100mm wide by 220mm tall, but this is getting on for 3 times that. I knew it was going to be big but it was only when it turned up that we realised how big it actually was :shock: My main concern is getting access for either a tele-lifter or crane to get it in...oh...and dropping it on something squishy like me

We'll get the engineer to double check I think.

Ross

 

[MMUK]

If you were to go down the Metrotile route that would decrease the tile weight by around 80%

 

[RossJarvis]

If you were to go down the Metrotile route that would decrease the tile weight by around 80%

I think we have restrictions on the tiles as we're extending a listed building (it's not mine so I don't know most of the details).

 

[MMUK]

If the existing is slate, you may get away with resin slate which is about 30% lighter

 

[RossJarvis]

If the existing is slate, you may get away with resin slate which is about 30% lighter

I'm thinking of buying a Zeppelin, lifting the beam with it and then tethering this to the roof, remember in Hampshire, hurricanes hardly ever happen so it shouldn't move around too much, I think this will solve all problems :lol:

 

[RobinBHM]

If the roof is vaulted then it could well be correct as it has to stop the rafters pushing outwards. Normally a ridge is only small as each pair of rafters is pushing inwards and the ceiling joists stop the spread.

The biggest glulam Ive used is 115mm x 630mm which weighed nearly 300kg. With an 8.0m span this section beam has a max load bearing of 8.0 tons.

 

[heimlaga]

8,4 metres is a gigantic single span for a ridge beam carrying a tiled roof 6 metres wide on a building withouit proper ceiling joists to keep the walls from spreading.
The only think that puzzles me is why the engineer has chosen such a low and wide beam...... though the overall size makes sence to me.... you'd better ask.
The limiting factor on a single span beam like that should be deflection. Not breakage.

8,5 by 0,6 by0,6 metres makes 3 cubic metres so if it is reasonably dry it will weigh roughly 1500 kilos.
Lifting a beam like that requires a mobile crane. Almost any mobile crane would do. We once used a mobile crane to lift an entire 6 by 6 metre log building weighing some 20 metric tons and that crane wasn't particularly big.
Some big lorries have cranes that can lift your beam even at maximum range. A large farm tractor with a front loader should be able to lift it anywhere of it wasn't for the limited lifting height.

If the building site is difficult to reach I am pretty confident that four men could manhandle it in place using tackles and gin poles or shear legs. This old method isn't legal any more but it is a very good last resort which has saved me from great trouble a few times.

Good luck!

 

[RossJarvis]

8,5 by 0,6 by0,6 metres makes 3 cubic metres so if it is reasonably dry it will weigh roughly 1500 kilos.
Lifting a beam like that requires a mobile crane. Almost any mobile crane would do. We once used a mobile crane to lift an entire 6 by 6 metre log building weighing some 20 metric tons and that crane wasn't particularly big.
Some big lorries have cranes that can lift your beam even at maximum range. A large farm tractor with a front loader should be able to lift it anywhere of it wasn't for the limited lifting height.

If the building site is difficult to reach I am pretty confident that four men could manhandle it in place using tackles and gin poles or shear legs. This old method isn't legal any more but it is a very good last resort which has saved me from great trouble a few times.

Good luck!

Thanks for all the help Heimlaga

I remember that the overall height and headroom were noticeable factors, which I think influenced the beam profile.

I'm going to check the lifting capacity at extension of a "Teleloader" which we have easy access to. The extension is behind a house away from the road, with narrow access. I'd thought of lifting tackle, but don't know enough about it to feel safe. Another limiting factor is the floor under the beam, there are dwarf walls for the frames and it'll be filled with a low density "foamed" recycled glass product, which is like pumice. So we probably won't be able to lift from inside the building eliminating a standard forklift.

 

[Billy Flitch]

Ross I could be a mile out but I`ll give it a go to explain whats going on. Heimlaga and RobinBHM both do a good job of explaining whats going on and you your self the reason why.
The first thing to note is there is a difference between a ridge plate and a ridge beam, so what is the purpose of a ridge plate.
Its to give you some where to fasten the spar too and also keep the spars the set distance away from each other.
The tops of the spars are cut plumb and set directly opposite each other fastened through the ridge plate.
So when the weight comes on the roof the spars press against each other and equal the stress on the roof, the ridge plate is not structural. There is a fault in this construction, if the weight becomes to much on the spars they are likely to slip down and transfer the load to the wall plate. you can see this when the ridge plate sags or hogs and the wall plate bulges out.
To stop this from happening collars and ties are used to directly tie opposing spars and stop them from moving.

You mention dwarf walls so this could stop the use of ties and may be the reason the structural engineer has uped the size of the construction and now gone with a ridge beam.

On a ridge beam the spars sit on the beam and are cut out with a birds mouth for the beam and the wall plate, this transfers any weight directly plumb down onto the ridge beam and the wall plate and therefore removes any danger of the roof slipping sideways. A ridge beam is structural Hence the size I have never worked with a glue lam beam 1`wide and the deepest that I`ve used is 1.200 cm. There is a way to reduce the size of the ridge beam but it involves introducing two fairly heavy perlins rather higher than what would be thought of as normal and this would allow you to reduce the size of the ridge beam but this is all part of a structural engineers brief and I'm not a structural engineer.
Hope this makes things just a little bit clearer.

 

[RossJarvis]

On a ridge beam the spars sit on the beam and are cut out with a birds mouth for the beam and the wall plate, this transfers any weight directly plumb down onto the ridge beam and the wall plate and therefore removes any danger of the roof slipping sideways. A ridge beam is structural Hence the size I have never worked with a glue lam beam 1`wide and the deepest that I`ve used is 1.200 cm. There is a way to reduce the size of the ridge beam but it involves introducing two fairly heavy perlins rather higher than what would be thought of as normal and this would allow you to reduce the size of the ridge beam but this is all part of a structural engineers brief and I'm not a structural engineer.
Hope this makes things just a little bit clearer.

Cheers Billy, thanks for the clear explanation.

I'll need a new chart with the architect, though, as the rafters are detailed coming to a plumb cut on the side of the beam, as with a ridge board, not birds mouthed on top. I think this is to do with the overall allowable height. Fillets are shown on top of the beam to bring the roof cladding to a point!!

Meanwhile we're back to discussing block and tackle to get it up :shock: We'd possibly need a crane to crane a crane into the back garden!!

 

[Billy Flitch]

Ross I understand its not your shout but when the architect asks you to form pieces to sit on top of the glue lam it sounds like he is misunderstanding what is going on, understandable when your not used to the system. The spars continue on after the top birds mouth so they form the ridge of the roof. if a batten needs to be added to fasten the ridge tile then it is just added across the top of the spars.If he drops the pitch of the roof by I`d say less than 1/2 a degree he would be back to his height. the whole thing may cost him about say25 cm of space inside the roof .
Any way I made a rough diagram to show you what I mean, it also shows the load being transferred plumb down.

 

[n0legs]

Ross check out Genie lifting rigs.
HSS Hire rent them out. We've used them loads over the years, a couple of times lifting over 300kg.
A pair of the biggest might get you sorted.

 

[Woody2Shoes]

One alternative, if it's the size of the glulam load-bearing ridge beam that's a concern, would be to use a steel beam instead (clad with suitable timber to disguise this if you want). The steel would still be heavy(!) but it would look less bulky when in situ. Cheers, W2S

 

[MMUK]

Ross check out Genie lifting rigs.
HSS Hire rent them out. We've used them loads over the years, a couple of times lifting over 300kg.
A pair of the biggest might get you sorted.

Or seeing as I work for A Plant I could sort you out a discount

 

[RossJarvis]

Ross I understand its not your shout but when the architect asks you to form pieces to sit on top of the glue lam it sounds like he is misunderstanding what is going on, understandable when your not used to the system. The spars continue on after the top birds mouth so they form the ridge of the roof. if a batten needs to be added to fasten the ridge tile then it is just added across the top of the spars.If he drops the pitch of the roof by I`d say less than 1/2 a degree he would be back to his height. the whole thing may cost him about say25 cm of space inside the roof .
Any way I made a rough diagram to show you what I mean, it also shows the load being transferred plumb down.

Thanks again Billy. I think the Architect (she) is relying on the engineer to help on the bits she isn't familiar with, however, the engineer seems to use the phrase "as per usual practice" quite a bit.

 

[RossJarvis]

Thanks for the comments guys. nOlegs I'd thought about the lifting rigs, it may be a goer, but I'm a bit wary of going up 5m with a very large and heavy beam.

Woody, there's a very large lump of stuck-together pine sitting on site. A bit late for steel unfortunately.

If still alive I'll probably show you how it all comes together :shock:

 

[Billy Flitch]

Ross I knew I had pic somewhere so I went looking for them,I had to resize them to get them on the forum. You can see that I practically finish one side before starting the other this is imposable with a ridge plate because the the spars would push the plate way over one way.With the beam the weight, as I`v said comes plumb down and every thing is steady.

I`v used genies in shop fitting and their good for what they do But as Heimlager has said the beam could weigh about 1.5 tonnes so putting it on the genies and wind it up 5mtrs in the air while standing underneath it Emmm just not for me thanks.