Roof Spread

[robinbanks]

Any other input please?

I think you're good to go; is there a particular concern?

 

[Notch7]

Where are you thinking the torque that would do this will come from?

I guess I was thinking if the other half of the roof is unrestrained there will be a horizontal and vertical force at top and bottom

we dont know any details of the ridge


I wasnt saying the roof could spread, I said "I wonder"

 

[Cocopop17]

It’s a ridge board we have

 

[catlad]

What's bothering you about it, @catlad?

Not sure exactly! but it looks very busy with additions.

 

[Cocopop17]

@catlad busy in what sense please?

 

[DAZB]

Probably relating to the number of steels and amount of bolts etc as it does look a bit congested, was there a reason that it was specified in shorter sections rather than a couple of longer pieces ?

 

[Cocopop17]

It was in shorter sections as the total length was 7.5m and we couldn’t get it into the building. So was sliced into 3. The original job was to support the rafters as we took out some internal walls that had a similar support system to break the rafter span.

The half vaulted ceiling was an after thought.

 

[robinbanks]

Think I'd have sooner bashed a hole in a wall than paid the extra for all that bolt work.. but I do like the industrial look. I'd be intumescent painting it so I could leave it on show

 

[Cocopop17]

We did consider that approach but the beam would have clashed with the neighbours property at the angle we had to bring it in.

Have you come across a roof like ours before, with purlins but no ridge beam or joists?

 

[robinbanks]

You're saying you have no ridge beam? Can you do a sketch of what you do have and the supporting structure of it?

 

[Cocopop17]

We don’t have a ridge beam - just a ridge board and the two structural walls.

See attached image from the loft view when work was underway. Hopefully that makes the structure clearer. Pictures are when work was being carried out. Basically, there used to be walls running from the ground floor up to the loft that acted as ’purlins’ to break the rafter span. We decided we wanted an open plan approach so had the rsj’s installed to support the roof structure Via the 8x2 stud walls.

This all worked out quite well as the walls in the loft had failed - blocks with poor motor mixture were basically loose!!

During the work we decided we wanted the downstairs ceiling vaulted.

Some original photos attached of the structure. Floorplan edited to show the RSJ positions and vaulted sections.

 

[freddiemercurystwin]

Have you not notched those rafters sitting on your new dwarf walls?

 

[Cocopop17]

@freddiemercurystwin no, the top plate is screwed to each rafter using two 5x80mm screws. i did think birds mouthing them would have been better.

 

[Cocopop17]

You're saying you have no ridge beam? Can you do a sketch of what you do have and the supporting structure of it?

See images above.

 

[robinbanks]

So, notionally your rafters are balanced at an angle on the new dwarf walls and cantilever out to the ridge, span down to the walls. If the span from ridge to dwarf wall is shorter than from dwarf wall to house walls then it's likely stable enough with the self weight of the roof but if they sag over time, either side of the dwarf wall you may well see some spread and rotation of the dwarfs. Interesting design but if an SE's signed off on it then no problems!

How did you fix the wall ends of the rafters?