Removing purlins and ties

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)
cheers!
steve
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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.
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Go with the architect's advice. Why bother getting it otherwise?
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-Mike-
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Drive-by gloat of having a car lift?
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render the site and give it to the engineer anyway.
Dave
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Depends. For something simple like this an architect can do the calcs and stamp the drawings. That is as long as they are not clueless.
-J
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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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Those generally ware not there to hang a ceiling. They hold the walls from spreading apart as the weight of the roof tries to spread them apart. They generally run perpendicular to the ridge row.
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