direction of ceiling joists

[wendyr]

x4 How can i change the direction of ceiling joist after i frame my plan?

[Curtis Johnson]

Edit and delete your ceiling framing then try the joist direction tool. Haven't tried it for ceiling framing ... I usually work with trusses ... but it shoudl work for you. Go to Build > Framing to find this tool.

[HumbleChief]

Also 'bearing line' can change the direction.

[HumbleChief]

I've got the same problem with roof joists/rafters. I can't seem to get the direction to change no matter which tool(s) I use. I'll post when I figure it out.

EDIT: I figured it out. It's important to drag the initial roof line along the wall you want the rafters to run perpendicular to. Never knew that. HTH someone else. ONLY for rafters not joists.

[perryh]

If joists are going different directions you have to use the bearing lines where the joists change directions and also use the joist directions to show which way they go. Make sure your bearing lines go just beyond the point where they change back. I make the bearing lines very large (150) to see them easily and turn off when done. If that makes any since to you. the joists/ rafters must go the direction up from the baseline. I always give a 1/4" slope min and use ceiling check in the roof dbx. Start at the lowest point at the baseline. Rafter size depends on insulation going in and structural.

[Sydney23]

Suspect I can guess the answer to this, but here's asking anyway...

I need a flat roof (1 in 40) which slopes front to back as usual, but whose rafters span side to side. (Reason: This on a terraced house with almost full width dormer. We can't go above ridge height due to planning law and ceiling height inside is v tight. So it'll have to be a cold deck roof, which means cross ventilation through the eaves side to side (i.e. avoiding the ridge). I didn't make the house, the u value regs, the planning law or the laws of physics, it's just the way it needs to be.)

The only way I can get rafters to span the other way is to rotate the baseline, as suggested above. But that means my slope is now going sideways too - no good. I could probably do this manually but that would be a pain and probably not with my time. In reality this might be done with level rafters and firrings, but sloped rafters is good enough for me to help show section ceiling heights.

This isn't the first time I've had this issue and no doubt won't be the last given the price of land/size of houses in the UK.

Thanks.

[johnnyprc]

Andy - can you diagram this? Trying to follow...

[Dave Pitman]

Andy, If your slope is perpendicular to your rafters, then how are you going to achieve the slope?
Progressively thicker rafters....furring....siting on raked walls?

[Sydney23]

Dave,
Normally furrings (firrings?) are used to keep the ceiling flat below, but the joists can also be set out of level if need be. I could have the roof joists running down the slope, but the cross venting requirement would then necessitate counter-battens to allow the cross flow of air and cross battens = 2" of lost height. Cold deck roofs are not 1st choice due to moisture issues but sometimes they're the only way to make a project happen.

It's not only done for cross venting purposes (the ridge area can get too restricted for air flow if the 'height challenged' dormer has to have a steel right up at ridge height), it can also be to reduce span if the roof is longer than it is wide, or if there are suitable bearing walls below to split the span.

Johnny,
The diagrams I'd love to show you are in a book 'Loft Conversions' by John Coutts 2013, pages 177 and 187, showing some of the ridge beam/vent issues but I'm not Google so guess I'd be clapped in irons if I uploaded scans (it is a fantastic book - no idea if suitable outside of UK). I could diagram it but I have about 10 projects all needing work, yesterday! Sorry.