Ridge Beam Enough?

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Hi, looking for general opinions and options for my roof on my self build extension.

It was last year I did the plans and cant remember how I calculated the ridge beam size, and now I have installed it I am doubting myself.

Quick facts:-
Beam is 75mm x 225mm C24
Rafters are 47mm x 175mm C24 at 400 centres
Distance from from wall to beam is 2.8m each side
Pitch is a low 20 degrees.
Wanting a vaulted ceiling.

The extension is an 'L' shape, the beam runs 4m across from current building to new gable. The first two metres will actually act as a ridge plate as a lean to roof, it will be bolted even though the beam is supported BOTH ends on blocks to the foundations. This leaves the remaining 2m of ridge beam to hold the rest of the roof with rafters both sides.

Looking at forums the ridge beams seem much bigger, although this is quite a small extension. I could easily run a block pillar up the edge of the current build where the 'L' bends(centre of the ridge beam) from the foundations, thus supporting the ridge beam in the middle, so effectively the beam is spanning just 2m from new pillar to gable.

Worst case scenario, and SE decides its not enough, would it just be a matter of adding ceiling joists and doing away with the vaulted ceiling?

Many thanks in advance.

Sam
 
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My Georgian cottage has a 4" X 4" ridge beam, in the Victorian barn next to it , the ridge beam is 6" X 1". The only valid "fixing" to them is the friction of the cut ends of the rafters, there is not enough wood at the cut end of the rafters to hold in a couple of toshed in nails. For the ridge beam to be truly load supporting either it has to be lower then the apex and cross pieces from rafter to rafter rest on it or steel straps from rafter to rafter run over the top of it. I saw a very prestigeous penthouse being constructed on the top of some flats. They were 14" X 6" X 20' rafters that were half lap jointed at the top and bolted. Top grade timber too.
The biggest problem is the roof spreading at wall plate level. So a couple of clear timber collars could be enough to restrain the wall plates. The other problems with vaulted ceilings is the insulation as it will tend to occupy the depth of the rafters, especially adding in the 1" air space above it for venting damp air beneath the sarking cloth.
Frank
 
Haven't you posted this before and not answered the replies as to what type of roof you have, and whether it is actually a ridge beam that you are talking about?
 
@priceofdarkness - Not against collar ties but such a low pitch it doesnt seem worthwhile. I thought a ridge beam got rid of the need of ties as the weight is on the beam and wall going down, provided the beam doesn't sag/bend there should be no outward force on wall, right?

@woody - Not sure if you are confusing with another post. It is a ridge beam but half of it will run across a wall that will have the rest of the roof as a lean to. (I did do a post weather rafters abut or go over ridge beam, going with above for my piece of mind)

Thanks
 
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@woody - Not sure if you are confusing with another post. It is a ridge beam but half of it will run across a wall that will have the rest of the roof as a lean to. (I did do a post weather rafters abut or go over ridge beam, going with above for my piece of mind)[/QUOTE]
Yes this //www.diynot.com/diy/threads/ridge-beam-to-rafters-connection.440933/ was the thread you started but couldn't be arsed to reply to.
 
Apologies for last thread, last time I looked there were no replies and for some reason I dont get notifications on that thread. Thank you for the replies, I forget how hard it is to imagine a project without images. I am stuck at work at the moment, so snapped up a quick drawing (not to scale, no ruler can be found).

In attached image it maybe clearer on how the ridge beam sits, with half acting as ridge plate. I know it probably is a weird way but I have a very small area to play with to get extension in. The beam sits in old external wall and new external gable, point z is where I can add a column to support ridge beam in the middle, leaving a 2 metre span from new column to new gable.
 

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