Couple of simple q's about counterbattens, battens and nails

[S1llyB1lly]

Hello helpful folks

I'm looking into redoing my roof, here is how things stand at the minute (everyone likes a picture don't they!)

1. John Brash make proper treated red colour battens. I plan to use 25mm x 50mm for vertical counterbattens and same again for horizontal battens as I will be using natural slate about 8mm thick. Should counterbattens AND battens be same size ie. 25mm x 50mm or should the be different sizes?

2. In terms of best practice, what type of nail or screw should be used to fix the counterbattens to the rafters and then the horizaontal battens to the counterbattens?

Cheers.

SB

PS: I will upload a pic later today, not that it is anything extraordinary, it will simply give some colour to the post!

 

[noseall]

Why do you need to counter-batten?

 

[S1llyB1lly]

I'm no expert, but there was a thread I read (might even been on here), that stated the benefits of a vertical counterbatten are:

1. Increased airflow as they lift up the tiles slightly

2. It helps with water dissipation as water can simply run down under the main battens

3. Whenever I have seen pitched roofs being worked on, they appear to have counterbattens and battens

Happy to be advised otherwise if good reason?

EDIT: forgot to add, my picthed sides are very shallow, between 15 to 20 degrees, I will try and get a more accurate reading today when I go back down to site

 

[S1llyB1lly]

There is a good explanation here, which simpletons like me could understand quite well:

http://blog.kingspaninsulation.co.uk/why-are-counter-battens-used-in-pitched-roofs/

Summary of it is:

"Roof tiles are usually laid horizontally, attached to timber tiling battens.. Underneath these battens, you will find your counter battens, running vertically, and, beneath these, a breather membrane.

If your tiles are laid without counter battens, rainwater could pass between the tiles and get stuck behind the tiling batten, building up a pool of water over time. As you can imagine this is not what you want as it can then damage the structure of your roof – as well as the insulation that’s keeping your house all cosy and warm!

So you can understand the importance of counter battens, which create a clear path for rainwater to run and eliminate the chance of water pooling, or seeping down into your roof."

 

[JohnD]

In England, the roofing felt or membrane is laid somewhat loose, so it sags down between the rafters. Rain that penetrates the tiles runs down the channel formed by the sag.

In Scotland, sarking boards are normal, so there is (should be) no perceptible sag, so counterbattens are used to raise the tile battens and leave a gap down which water can run.

Occasionally rigid insulating slabs are used in the same way as sarking. In your Kingspan link, the diagram shows PU slabs between the rafters, hence in that example, counterbattens are needed.

Read further down your link, to where it says "Example of why you might not use counter battens"

Do you have sarking boards?

 

[^woody^]

You don't need 50mm battens unless you have 600mm centres of the rafters.

Normal 3.5mm flat head nails will do. 75mm long

Counter battens are only for when there is a rigid material on top of the rafters

 

[S1llyB1lly]

Morning all, thanks for the replies.

Couple of follow up q's:

1. My initial plan re: counterbatten + batten, is it simply plain wrong and could cause issues, or is it just overkill? I don't mind it being the latter as I often tend to overspec most things just to be on the safe side. I'm also friendly with my local timber merchant and I can have 25mm x 50mm batts for same price as 19mm x 38mm...

2. I have some stainless steel screws kicking about, any reason I should not use them? They are at least 75mm possibly even 80mm in length.

Pic as promised attached...flat warm deck with pitched sides.

EDIT: forgot to reply to John: no, no sarking boards being used, unless you tell me it is a better way to construct a roof in which case I can do so

 

[^woody^]

You'll be counter battening that roof because you will need to extend the flat roof deck and cover down that shallow pitch.

 

[S1llyB1lly]

You'll be counter battening that roof because you will need to extend the flat roof deck and cover down that shallow pitch.

Ok, counterbatten and batten it is then. 25mm x 50mm ok? It costs me same as the smaller stuff unless you tell me I specifically need the smaller stuff. Aiming to use natural slate, 8mm or so thick.

Pitch is something like 15 to 18 degrees. I will check and report back!

Any view on whether I can use stainless steel screws or should I stick with aluminium nails (copper ones are bloody expensive it seems).

 

[^woody^]

Pitch is something like 15 to 18 degrees

It looks more like 10

 

[S1llyB1lly]

Ok, now I'm panicking...I'm gonna go measure and report back. I hope it isn't as the Velux I will be putting in are only warranted to 15 degrees, anything below that and there is no guarantee they will not leak. Yikes!

 

[S1llyB1lly]

Woody, further to your post, I panicked and went to measure up.

To be double sure, I also installed an angle app on my mobile, put it on a spirit level to ensure it was calibrated and got 18 degrees on one beam and then 20 on the other, which I think makes sense as I measured about 4.5" inches rising (after marking 12" across the level, holding it plumb).

 

[S1llyB1lly]

You'll be counter battening that roof because you will need to extend the flat roof deck and cover down that shallow pitch.

I'm being a bit thick, but do you mean I should cover my side pitches with a sarking board (I have plenty of OSB3 T&G board 18mm on site), leaving a gap of about 5mm between each board and then counterbatten + batten on top of that? Or do you mean something else? Pitch is about 18 to 20, as per my post above.

 

[chappers]

get it right 20 degrees is really the limit for natural slate

 

[S1llyB1lly]

Would you advise I use something other than slate? What if I was to lap the slate more than necessary would that be ok?