Removing ceiling ties and purlins

[r.p.mcmurphy]

hey up! 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

[Rob Morley]

I can't help thinking it would be less hassle to dig a shallow pit than mess around with the roof structure.

[BigWallop]

Could you remove the rafters from the above the area you need, and then build them back square with the wall and roof height. Like a big L but upside down to match the roof height and the distance out to the wall.

Create a big dormer is what I'm trying to say. :-))

[Capitol]

There appears to be nothing to stop you from doing this. If you look at church roofs from the late 19th century, many of these used straining rods at high level to prevent the rafters from spreading. I'm sure that a bit of old style O level maths would let you calculate the forces involved and let you determine the sizes etc required.

Regards Capitol

[Rob Morley]

I expect the rafters and walls were rather more substantial than those in the OPS garage though. If he's going to follow church architecture he should build some nice buttresses to support the roof.

[Dave Plowman (News)]

I had similar in my attic conversion, and the existing purlin was replaced by two steels - postions determined by the size of the exposed sloping ceiling. Obviously, calculations were done to support this. They are tied to the rafters.

I'm surprised you're so tight for space that a purlin position matters? In my case, it was for cosmetic reasons.