Purlin Position

[Louis1104]

Im in a chalet bungalow, there’s currently two bedrooms upstairs but on the side of the bedrooms there’s a fairly large loft space which I’m looking to put in an en-suite bathroom.
My only issue is I’m currently facing is the purlin and the supports coming off it. Could the rafters be doubled up so it could be removed or could the purlin be moved above what will be the ceiling height.
I’m going to be putting in a couple of velux windows so will need to double some of the rafters anyway.
I’m a plumber by trade and despite carrying out substantial building work downstairs on my property I’m not familiar with what could be done when it comes To purlins.
Thanks for any help

 

[Deleted member 174758]

Really only an SE could give you the answer as it requires structural calcs. Doubling the rafters next to the window opening and installing doubled up (at least) trimmers above and below the opening will also be required

 

[tony1851]

Assume the purlin is roughly halfway up the slope?

If you moved the purlin to - say - ¾ up the slope, the potential deflection of the lower part of the rafters would increase approximately 5-fold, other things being equal.
This would not be compensated for by doubling the rafters. The additional deflection itself may or may not be significant, except that it can cause the wall plate to be pushed outwards slightly.

Much depends on how the rafters are fixed at the ridge. If the tops of the rafters can be firmly secured to any opposing rafters eg by stout gussets of plywood, or collar braces, that would help to reduce the bend in the rafters below the purlin. In that case, doubling them up should allow you to move the purlin up; the less you need to raise the purlin, the better.

 

[cdbe]

Can't you put a couple of small velux above the purlin (if you have to have any windows at all, it's a bit of a marmite thing for an ensuite), consider a sun tube. Will the bathroom fit between the two props? Can't really tell. By the time you have the required depth of insulation in the roof slope the purlin will barely project into the room.