Rafter ties/ceiling joists

[pilsbury]

If my dormer roof was a 45 degree pitch, instead of adding rafter ties sitting directly on the wall plate, can I add these ties 1/3 of the way up? Trying to maximise ceiling height.

Dormer will be 3600mm wide, 45 degree pitch and have a ridge beam (as opposed to board). Total height of pitched roof 1800mm.

 

[^woody^]

Why not!

You may also call them collar ties if you like

 

[pilsbury]

Not to question your knowledge, but on my reading, I thought collar ties were in the upper third of the roof and didn’t offer much in the way of preventing spread.

My thought was that ceiling ties were up to the lower third of the roof and still acted to prevent spread. I was wondering if my assumption was correct to avoid a pancake plop of my roof.

Note that all my knowledge is read off the internet and could be written by a spotty 13 year old who plays Fortnite.

 

[^woody^]

I've always known these as raised collars

IIRC, the approved docs allow for these ties to be raised up to 1/3 of the height, and after that you'll need to justify by calculation

From LABC warranty

 

[pilsbury]

Thanks for your clarification.

By the way, do you play Fortnite? Are you over 13?

 

[jks7492]

have a ridge beam (as opposed to board).

If you have a ridge beam then the ties become redundant in preventing the roof from spreading and you can put your ceiling joists in at whatever level you want to

 

[pilsbury]

If you have a ridge beam then the ties become redundant in preventing the roof from spreading and you can put your ceiling joists in at whatever level you want to

Seeing as I need ceiling joists they can be belt and braces ties too.

 

[^woody^]

If you have a ridge beam then the ties become redundant in preventing the roof from spreading and you can put your ceiling joists in at whatever level you want to

They may still need to brace the walls