Purlin removal

G

george765

I have structural plans for a loft conversion.
The plans seem to suggest that the purlin on the sloping roof is removed, and the rafters supported on a knee wall which rests on an RSJ embedded in the load-bearing end walls.

The knee wall will bear the weight of the roof vertically downwards onto the RSJ, and the rafter spans conform to the relevant building regs tables.

What is worrying me is that the purlin is currently supported by wooden struts that are at 45 degrees, giving support to the rafters vertically and horizontally. The knee wall will have little or no support in the horizontal plane. The engineers plans are sketchy to say the least, and the plans give no hint that horizontal support is required,
Does it need any?
 
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I would think that, properly designed, the beam would not need struts, as the load on it would be supported by the gable walls, not the intermediate wall that the struts currently (presumably) sit on, but I'm not an SE.

With struts in place you would not have much of a room, hence the solution.

Building control will have to approve the plans, if they have not already done so, and they will scrutinise them independently.

Blup
 
Don't confuse the function of a purlin on an angle and strut transferring load perpendicular to the roof, with a vertical purlin / wall and the load going vertically.
 
I should have pointed out that the purlins do not join to a wall at either end, One end meets the hip joist and the other end joins on to another purlin which goes through a stud wall to next door (the house has been split vertically prior).
It looks to me that the 45 degree struts stop the roof rafters bending, but would vertical short 2x4's bolted to each rafter resisted the horizontal movement ? I can't get hold of SE as I think he's retired. Do you think I need to get another SE to check things before taking out purlins ?
 
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You need to stop worrying. What you have there is in thousands of lofts all over the UK.
 
ok, thanks woody, being a poor diy'er I do worry about making a costly mistake.
 
Let us know if anything happens when you take the purlin out .
 
D

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