hey all! i have a workshop to which i have fitted a car lift...but i now
need to remove the ceiling ties(to which there never was a ceiling fitted),
and the purlins which are half way up the 45degree rafters, in order to be
able to lift the car into the roof space suficently enough to allow standing
room underneath. i know the only way is to suficently strengthen the
rafters so that they dont sag and install collars higher up. but i want them
as high as possible..not just the third of the way up that is recomended.
so my thinking is to strenthen the rafters with u chanel 3 or 4 mm steel
cupping and screwed or bolted to the raters. then using steel strips as the
collars but higher up...say in the top third. has any one any experience of
this method or any comments? all very welcome! (arcitect due to advise
later next week..but would like some feedback on my ideas)
A couple of better forums are alt.home.repair and alt.building.construction.
That said, if you have a stickframed roof with rafters on 16" or 24" centers
(etc..) with ceiling joists (your 'ties'?) and collar ties (your 'purlins'?)
above you can:
1. double or triple the rafters outside the space needed for the lift;
install fullspan ceiling joist members to these rafters with sufficient
mechanical connection to resist the outward forces; install 2X horizontal
framing members (purlins) between the reinforced rafters (keep the o.c. span
to within the limits of the existing roof deck); reattach the roof deck to
the new purlins.
2. alternately install a ridge beam that spans the area you want to open and
hang the intruding rafters from it.
A lot of this is dependant on the spans and loads of your particular
building. Your architect will have a better take on it than I.
the collar ties main function is to keep the building from spreading....that
said, anything you can do to stop that from happenning, and you can remove all
the collar ties you want....have you considered flying buttresses?
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