Support for ceiling lining cathedral ceiling

[flynnsart]

We were planning on using 12mm t&g lining boards (cypress or hardwood) for our cathedral ceiling. We were going to lay them over top of the exposed rafters, then place 3 x 2 battens on edge with silverbatts in between.

Now I look at it, the spacings of the rafters (900mm) is too big a span for 12mm and I would have to go up to 20mm which I do not want to do. Is it allowable to put noggins running parallel to the rafters in between the battens?, and use that as additional support for the lining boards so they have support every 450mm?

...and while I am on the subject. We were going to fix the battens with 100mm batten screws, which would mean that they would go through the batten, then through the lining board, and only about 10 or 15mm would go into the rafter, would this be alright? How else would you do it?

Donna

[OBBob]

Are you planning to paint the lining baords of have them as clear coated natural timber? There are plywood options that may span better?

[billbeee]

Donna,

For a none structural lining, over 900 span, especially if you are spanning more than two spans per board, and you are staggering your joints, you should get very little sag . I've used 12mm WR Cedar like this and we didn't use noggins.

I have no idea if you are working off a drawing, or what your roof material is, but in my experience 75 x 50 battens are usually laid on the flat, (of course we only use HW timbers for structural stuff), so you would be going through say 45 +12, giving you 37 penetration into your rafter with your 100 batten screw.

A better way might be using top hat batten straps, then you can fix down with 2/50 x14g type 17 hex head screws.

Again probably a better and cheaper way all round is to use metal roofing battens.

You could still drop say 50 x 50 timber noggins between them (notched to suit batten) with a few blobs of stud glue to the ceiling t&g if you like. No other fastening would be needed.

Always used to get a good coat of sealer on them before fixing though. Mainly to save work later, but also a bit of wet weather could leave water stains that are almost unshiftable otherwise.

Cheers
Bill

[flynnsart]

The reason for putting the battens on edge was to make room for the insulation. Loft roof spaces get quite hot.

I was planning on coating the lining boards with a clear finish........She wanders off to find out what a top hat batten strap is.......

Donna

[ausdesign]

The batten tie down [ screw, nail or strap] requirement will depend upon the wind catagory for your particular site, but you will probably need to use a 30*0.8mm gal strap looped over the batten & fixed to the rafter with at least 3/2.8mm*65 nails each end.
The exact fixing requirement will need to be designed & documented on the plans by your building designer.

[seriph1]

hi - I a wondering why you think 900 is too large a gap to put lining boards between .... they will never sag as they don't do anything other than sit there as far as I can make out. Of course, I may be understanding the project completely, which would be a surprise to no one!

This is a top hat - http://www.bluescopesteel.com.au/go/...ht-topspan-120 - I believe they come in 7 metre lengths, are easier to handle than wood and lighter/stronger. The certainly use smaller screws!

Finally - make sure to paint/coat your boards prior to installation..... your back, shoulders and eyes will thank you every day AND (note the BIG and) coat the tongues as well ..... this stops the million white stripes you may get if/when the boards shrink, revealing the unpainted tongues.

[ausdesign]

AS1684 has min. span sizes for t&g boards on a non trafficable roof with 12mm softwood only spanning 450.

[flynnsart]

AS1684 has min. span sizes for t&g boards on a non trafficable roof with 12mm softwood only spanning 450.

This is what I had read, and was not 100% sure whether this was meant for ceilings, as it calls it non trafficable roofs. ie you dont usually walk on your ceiling do you?

I definitely will be coating the boards before they go up, not a job I would like to do once they are up there! By the time they need recoating, my eyes will be too weak to see that far clearly, and the job will be left to the next generation

Donna