Expansion of uPVC fascia boards

[MLDams]

If I fit 18mm full replacement uPVC fascia boards I am required to allow a gap for expansion - 5mm for 5m length I believe. My question is, if I have fixed the board into the rafter ends every 600mm with polytop s/s nails how will the last set of nails be able to move to allow for the expansion. Will they not end up working loose. I dont see any statements anywhere on the web about being obliged to predrill oval shaped holes to allow for this.

 

[Mw Roofline]

The whole fascia expands not just the last bit. I don’t know how but it does. Just nail it normally on the last rafter. You’re actually supposed to nail one side of the fascia joiner and leave the other side to ‘move’

 

[MLDams]

But if the exxpansion gap is 5 mm and can be exxpected to close up when hot it implies that your closest nails have to move by that amount. So I presume the middle set of nails dont move but all the other rafters will have movement, more as you going out towards the end, with the end ones trying to move by 5mm.

 

[^woody^]

As MW says, its not just the last bit that expands but the whole length. So each mm of the board (5000mm) can expand by 0.001mm, and it might be 2.1mm each end, or 3mm one way and 2 the other or, it might be just expansion of the centre 1m of board and this it taken up by compression or slight deflection of the other section of board.

So it's not linear and it does not imply that any movement is restriced to any end or any nail.

BTW, nails will flex in the timber rafter ends anyway.

 

[MLDams]

Thanks. I was concerned about nails working loose but it seems like in prtactice that is just not an issue then.