vaulted ceiling ideas 1

[xxpegasus11]

Looking at a 3 storey terrace house with a hipped stick roof. Rafters are 4x2 at 400 crs with 4x2 collars. Roof on plan is 5.5m wide (front) and 7.7m long (sides). Perimeter walls are full brick 225mm.
Client wants rafter ties removed to form a vaulted ceiling with open plan.

Ridge board in the middle is only about 1.9m so putting a ridge beam/steel frame to support ends plus picking up the hip rafters seems impractical.
The new ceiling would be lined (could be with plywood) so some plate action would come into play, but very reluctant to rely on this alone.
Any ideas/suggestions from people more familiar with this are welcome.

Did not mention roof pitch near enough 45deg , ceiling height about 2.1 m, hence the need to increase ceiling height.

 

[KootK]

This may be the thread for you: Link

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[xxpegasus11]

Thank you kootk
Had a look at the link and some of the other threads here on vaulted ceilings.
The issue I guess is that with this being a terrace house, side walls are shared by neighbours so looking for options to minimise thrust and therefore movement of the walls.
It's an existing roof, rafters on a 4x2 wall plate on the perimeter brick walls, so no ring beams.
Introducing a beam over 7.7m span to act as ring beam isn't viable really. A ply diaphragm say 600mm wide around the perimeter could pick up thrust? but not keen to just have this supported on the rafters at one end and have any deflection show on what would be a perimeter ceiling?
I read the concensus in the link to finally be a steel ridge beam with steel hip rafters to take care of the moment connection (rigid moment connection between ridge beam and 2 hip rafters at either end - 5 beams/columns in total)?

 

[KootK]

I don't know if it was a consensus per se but the steel ridge beam with moment connections is what I was thinking for your scenario. Given your constraints, I'm not sure that it's possible to avoid some degree of perimeter thrust. Making a stiff rige beam frame would reduce thrust but certainly not eliminate it.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[xxpegasus11]

Many thanks - settled on a steel frame solution