T&G width to select

[RickH]

I have a job to clad an outdoor ceiling with T&G - PTG&V, I posted a Q yesterday on what nails to fix with - a separate Q arose when I came to order.
I can get clear treated in 125 width (119 finished) or 100 width (95 finished)

Is there any benefit to using 100 mm wide, compared to 125 wide
I had assumed I'd be using 125 wide ..... but is wider plank more likely to warp ?

It's being run as panels, 2 are 750mm wide and 2 are 1.08 wide ..... all are about 3.5m long

 

[Deleted member 174758]

I have a job to clad an outdoor ceiling
Is there any benefit to using 100 mm wide, compared to 125 wide
I had assumed I'd be using 125 wide ..... but is wider plank more likely to warp ?

The answer is maybe... amongst other things it depends on the actual cut from the tree, the species of tree as well as how warm of humid you expect the room to get. Given identical species, processed in an identical way, and sawn on a flat cut, the wider planks will tend to warp more. If the timber is more or less a rift or quartersawn cut then the difference will be negligible. In reality the width is a matter of aesthetics (and thre ability to support kt) as much as anything - I feel narrower T&G looks better, more in scale, with smaller rooms

 

[RickH]

The answer is maybe... amongst other things it depends on the actual cut from the tree, the species of tree as well as how warm of humid you expect the room to get. Given identical species, processed in an identical way, and sawn on a flat cut, the wider planks will tend to warp more. If the timber is more or less a rift or quartersawn cut then the difference will be negligible. In reality the width is a matter of aesthetics (and thre ability to support kt) as much as anything - I feel narrower T&G looks better, more in scale, with smaller rooms

Thnx .... this is an open-sided 'roof' over a hot tub ,,,, situated on a raised deck.
I accept your comments .. and maybe 100mm maybe better option.

 

[Deleted member 174758]

In that case you really do need stainless fixings - and try to source timber which quartersawn or rift sawn if possible. This will be more expensive, but a lot less likely to move or warp as much in a fairly aggressive environment

 

[RickH]

I have bought stainless nails ,, so that is sorted.

Not sure what the timber will be, other than profile & its Redwood clear treated ..... or even if I can get a choice, I'll ask ....

 

[RickH]

I can't get 100mm wide clear treated locally, so it will be 125x25 ptgv. clear treated.
Looking at one source on fixing it states to "Leave a gap of approximately 2mm between each of the subsequent boards to allow for possible expansion."
Is this considered best practice ? ...
On a separate Q on fixing sizes, it was suggested adding "put a bead of polymer adhesive on the underside of the joists as well" will this up any expansion/contraction? Would it be good to have 2mm expansion gap and polymer glue ?

 

[big-all]

keep in mind the coverage is less 4" is around 88mm and 5" is around 112mm as the tongue is included in the width
also it used to be with txg ship lap the 6"extra inch would be double the 5" amount as in £12.50for 5"[2.50 per inch
£17.50 for 6"[5x2.50=12.50+£5]

not actual amounts but for ease off illistration

 

[Deleted member 174758]

Looking at one source on fixing it states to "Leave a gap of approximately 2mm between each of the subsequent boards to allow for possible expansion."
Is this considered best practice ? ...

Yes, but it tends to be a finger in the air exercise. If your timber comes in very dry and you install it in a warm, dry spell you'll really need that 2mm in the next wet winter when the timber will swell. If, on the other hand, your timber comed in pizz wet through having just come out of the pressure treatment chamber, and you are installing in the middle of a monsoon (like at present), the gap can become optional.

On a separate Q on fixing sizes, it was suggested adding "put a bead of polymer adhesive on the underside of the joists as well" will this up any expansion/contraction?

Polymer adhesive have a degree of elasticity.