Green Building Forum - breather over or under counter batten Sat, 30 May 2026 03:27:34 +0100 https://www.greenbuildingforum.co.uk/newforum/ Lussumo Vanilla 1.0.3 breather over or under counter batten https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14440&Focus=244986#Comment_244986 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14440&Focus=244986#Comment_244986 Tue, 02 Aug 2016 11:18:20 +0100 MarkyP
80mm PIR under rafter
170mm 0.032 rafter roll wool full depth between rafter
OSB3 15mm sarking over rafter
counter batten
breather
batten
slate

Now, we have not got a tin roof over this so I want to avoid getting the OSB wet and I am planning for the worst case which will be a period of time where the joiners are done but the roofers not ready to start. I'd be happy to DIY fit the breather membrane but to do that I'd need to fix it under the counter battens. My drawings indicate it over counter battens and draped. But I cant see any reason not to put it under, allowing me to get water tight and not worry too much if I have to wait a few weeks for my roofers. Any thoughts?

edit: just to add the OSB is both for an air tightness layer and to provide structural/racking strength in allowing me to remove some large under rafter internal cross braces as we convert the loft space. There is no ventiliation gap under the OSB in this design.]]> breather over or under counter batten https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14440&Focus=244993#Comment_244993 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14440&Focus=244993#Comment_244993 Tue, 02 Aug 2016 13:22:36 +0100 JC48
Tyvek - it is under the counter batten see
http://www.dupont.co.uk/content/dam/assets/products-and-services/construction-materials/tyvek-building-envelope/Documentation/Literature/DuPont-Tyvek-Technical-Guide-for-Roofs.pdf]]> breather over or under counter batten https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14440&Focus=244997#Comment_244997 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14440&Focus=244997#Comment_244997 Tue, 02 Aug 2016 13:56:55 +0100 MarkyP breather over or under counter batten https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14440&Focus=245448#Comment_245448 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14440&Focus=245448#Comment_245448 Tue, 09 Aug 2016 09:58:33 +0100 CWatters breather over or under counter batten https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14440&Focus=268814#Comment_268814 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14440&Focus=268814#Comment_268814 Wed, 06 Jun 2018 09:16:29 +0100 Sprocket
Roofer has put breather membrane (TIL-R) over the counter battens.
He has also pulled it tight so it is pulled up against the battens.
So we have an air gap above the membrane and below it. He says this is better because it's all ventilated.

Manufacturer installation instructions say "must not be pulled tight against the underside of the battens" and "When installed as a fully supported system, the Underlay is laid over the support and secured using counter battens".

So, it's clearly not installed how the manufacturer says, but now that it's done what should I do?
If I make roofer pull it up re-do it then I make myself unpopular and potentially mess up the underlay and counter battens by removing and replacing it all.

Is this a significant issue? Should I just let it go?]]> breather over or under counter batten https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14440&Focus=268817#Comment_268817 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14440&Focus=268817#Comment_268817 Wed, 06 Jun 2018 10:47:32 +0100 gyrogear Posted By: SprocketHe says this is better because it's all ventilated.

Well, I fail to see how the gap between the sarking and the counter-battens is "ventilated" ?

Geometrically, it should consist of a series of partitioned enclosures...
In any event, per literature,
http://www.til-r.co.uk/products/pitched-roof-underlay/breathable-pitched-roof-underlay/
TIL-R is precisely made for use in "non-ventilated cold pitched roof systems"

therefore the "ventilated" argument looks spurious.

Add spuriousness to non-compliance with mfr's instructions, and in my view you could be heading for trouble in the short or long term...

Sounds like the membrane should be over the OSB, nailed down by the counter-battens.
Vapour permeating from within should then condense on the membrane, and run down to eaves, gutter etc.
Idem, precipitation getting in to the roof through a broken tile etc. will run down the topside of the membrane.

However, if the membrane is drum-tight across the tops of the counter-battens, said precipitation, and vapour permeating, condensing then running down the topside of the membrane will, in places, be intercepted by the tile battens, which will effectively be "sitting in wet".
The tile battens, being horizontal, will prevent or impede water runoff - that is presumably why the mfr says it must not be pulled tight under the battens - latter could ROT...

FWIW, I am not a roofer

gg]]> breather over or under counter batten https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14440&Focus=268819#Comment_268819 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14440&Focus=268819#Comment_268819 Wed, 06 Jun 2018 11:44:18 +0100 djh Posted By: gyrogearHowever, if the membrane is drum-tight across the tops of the counter-battens, said precipitation, and vapour permeating, condensing then running down the topside of the membrane will, in places, be intercepted by the tile battens, which will effectively be "sitting in wet".
The tile battens, being horizontal, will prevent or impede water runoff - that is presumably why the mfr says it must not be pulled tight under the battens - latter could ROT...
Plus the standing water will eventually find its way through the membrane, initially at nail holes. Thus potentially rotting whatever's below.

I'd say the issue is significant and the roofer needs to make it good, which will be a pain. It's a pity it couldn't have been spotted and discussed when the first piece went up.]]> breather over or under counter batten https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14440&Focus=268825#Comment_268825 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14440&Focus=268825#Comment_268825 Wed, 06 Jun 2018 18:26:32 +0100 mark_s breather over or under counter batten https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14440&Focus=268827#Comment_268827 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14440&Focus=268827#Comment_268827 Wed, 06 Jun 2018 20:08:14 +0100 djh Posted By: mark_sBut then again if the membrane is sitting in contact with the osb will some moisture pass through the membrane ?
In that position there's no standing water, and thus no static head of pressure. So the membrane is more likely to remain waterproof. And if it's draped, as opposed to laid flat on the OSB, the nail holes won't see much water at all.]]> breather over or under counter batten https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14440&Focus=268828#Comment_268828 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14440&Focus=268828#Comment_268828 Wed, 06 Jun 2018 21:28:25 +0100 gyrogear Posted By: mark_swill some moisture pass through the membrane

well, per mfr's info, *NO*...
(assuming that nobody tore, ripped or cut it during installation etc.).

The purpose of the membrane is to let moisture *out*, and not let water *through*. Period.

gg]]> breather over or under counter batten https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14440&Focus=268830#Comment_268830 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14440&Focus=268830#Comment_268830 Wed, 06 Jun 2018 22:13:09 +0100 gyrogear Posted By: SprocketIs this a significant issue? Should I just let it go?


I'd contact the membrane mfr's help line...

http://www.til-r.co.uk/keeping-in-touch/

gg]]> breather over or under counter batten https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14440&Focus=268837#Comment_268837 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14440&Focus=268837#Comment_268837 Thu, 07 Jun 2018 15:51:24 +0100 Sprocket On closer inspection (partly because of this) it seems there are other "issues" so I have added "roof underlay incorrectly installed" to the list :-/
I did not expect to have to get this closely involved in the details of our roofing but I have no choice now.
:-/]]> breather over or under counter batten https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14440&Focus=268838#Comment_268838 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14440&Focus=268838#Comment_268838 Thu, 07 Jun 2018 16:03:03 +0100 Sprocket breather over or under counter batten https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14440&Focus=268839#Comment_268839 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14440&Focus=268839#Comment_268839 Thu, 07 Jun 2018 16:21:28 +0100 gyrogear :shamed:
and in any case there is quite a large gap in the sarking board along there... Why ?
(The eaves protector is not intended to replace the roof structure...)

Don't know how much ice-damming is likely in your part of the world but I'd try reading this:

https://www.aviva.co.uk/risksolutions/help/faq/answer/1769/

"Snow and ice on a roof exerts vertical loads that can cause a roof to deflect or bow downwards. Also these extremes in weight load can transfer horizontal forces through the structure that can cause walls to deflect outward at either the top of or base of the wall. Where snow loads imposed on a roof are within the design limits for the roof then generally any minor sagging or deflection that may occur will usually be temporary and simply disappear after the load is removed".


best of luck,

gg]]> breather over or under counter batten https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14440&Focus=268840#Comment_268840 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14440&Focus=268840#Comment_268840 Thu, 07 Jun 2018 19:11:34 +0100 fostertom
Certainly not tightened under the tiling battens, for reasons given by gyrogear and djh above - must be draped.
Reflective insulation doesn't work unless it can 'see' free air i.e. between its shiny under-face and top of OSB - so mustn't touch the OSB. Shiny side down because less liable to coating with dust and muck - half a chance of staying shiny.

Some say the space between tiles and breather should be through-ventilated, to allow evaporation, whether condensation from below or water from above. But any space between breather and OSB should not be ventilated.]]> breather over or under counter batten https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14440&Focus=268852#Comment_268852 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14440&Focus=268852#Comment_268852 Fri, 08 Jun 2018 12:52:26 +0100 borpin Posted By: SprocketI did not expect to have to get this closely involved in the details of our roofing but I have no choice now.LOL If you don't the buggers will just do what they want, how they want - one of the most frustrating things about the building industry. It is almost a pathological desire to bodge things.

I'm glad that isn't my roof.

Posted By: fostertomI wd put ordinary breather felt flat and tight on the OSB, held down by the counterbattens
+1]]> breather over or under counter batten https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14440&Focus=268857#Comment_268857 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14440&Focus=268857#Comment_268857 Fri, 08 Jun 2018 18:47:29 +0100 Sprocket They have nailed it to the OSB with clout nails. Is that OK?
I was expecting the only nails to penetrate the membrane to be at the counter batterns?
(Counter battens are not fitted yet so I presume they mean to add those after the weekend).]]> breather over or under counter batten https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14440&Focus=268858#Comment_268858 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14440&Focus=268858#Comment_268858 Fri, 08 Jun 2018 22:12:20 +0100 gyrogear They have nailed it to the OSB with clout nails. Is that OK?.

Not really - the mfr's procedure states:

"When installed as a fully supported system, the Underlay is laid over the support and secured
using counter battens of at least 12mm thickness fixed through to the support or rafters with
appropriate corrosion resistant staples or galvanised clout nails".

The membrane is not nailed to the OSB.

They seem to be making it up as they go along, and it is *your* roof (TG it is not mine...).

Your 15-year warranty is probably not going to work...

gg]]> breather over or under counter batten https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14440&Focus=268859#Comment_268859 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14440&Focus=268859#Comment_268859 Sat, 09 Jun 2018 08:21:13 +0100 Beau Only a self builder so dont take my word for it but it looks a complete mess to these eyes.

Sorry Mark but I would want to cut my losses sooner rather than later.]]> breather over or under counter batten https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14440&Focus=268863#Comment_268863 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14440&Focus=268863#Comment_268863 Sat, 09 Jun 2018 11:49:09 +0100 Doubting_Thomas
We've got the same thing, membrane onto OSB with counterbattens as fixing points. When we got to the eaves the gutter guy wanted to fix onto the horizontal battens directly below the slates to be as close as possible to surface. However, this would leave our secondary drainage plane (i.e. membrane) with nowhere to drain to, so we've insisted on mounting the gutter lower, below the vertical counterbattens instead, so that the membrane can lap straight down into the gutter.

What this means is we'll have a ~75mm gap (50mm counterbattens + 25mm tiling battens) between the slate surface and the gutter below...I'm thinking this is fine (and necessary to allow ventilation) but feels a bit like a gap in the weathering surface which is odd.

Lots of details online suggesting I'm on the right track, but the gutterer was equally uncertain. Worried that a flash of rain would just sheet straight off the roof and over the top of the gutter!]]> breather over or under counter batten https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14440&Focus=268868#Comment_268868 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14440&Focus=268868#Comment_268868 Sat, 09 Jun 2018 17:01:15 +0100 Peter_in_Hungary Posted By: Doubting_Thomasbut the gutterer was equally uncertain. Worried that a flash of rain would just sheet straight off the roof and over the top of the gutter!
It shouldn't if the gutter is wide enough and stands out from the wall enough, positioned to catch the vert. drips and anything sheeting off the roof. It's about positioning the gutter properly.]]> breather over or under counter batten https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14440&Focus=268875#Comment_268875 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14440&Focus=268875#Comment_268875 Sat, 09 Jun 2018 20:03:09 +0100 djh Posted By: Doubting_ThomasWorried that a flash of rain would just sheet straight off the roof and over the top of the gutter!
As PiH says, it's about getting the gutter in the right position. But even if it isn't, it's not a disaster if rain blows over the top of the gutter. It will also be blown away from the house wall.]]> breather over or under counter batten https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14440&Focus=268893#Comment_268893 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14440&Focus=268893#Comment_268893 Sun, 10 Jun 2018 21:35:54 +0100 fostertom Posted By: Doubting_Thomaswe'll have a ~75mm gap (50mm counterbattens + 25mm tiling battens) between the slate surface and the gutter belowYou're eave-ventilating the airspace between breather and tiles underside? That's good - are you using something like http://www.glidevale.com/fascia-ventilators/p/3 RV250 (equiv to continuous 25mm vent opening) which is 35mm high, fixed to top edge of fascia board to support the tiles underside? Then bring the breather out under the RV250, supported on an eave tray ramped up through the counterbatten height (making sure it still falls outward).]]> breather over or under counter batten https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14440&Focus=268896#Comment_268896 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14440&Focus=268896#Comment_268896 Mon, 11 Jun 2018 12:32:10 +0100 Sprocket I have now stopped these roofers and will try to get someone else to take on the job. Stopping the job with rooflights still out is a bit of a last resort but I didn't feel I could trust them not to keep screwing up more and more.

The lastest messes are the hacking about of my nice straight-edged gable end (which was a lime-mortared limestone rubble wall) trying to fit timbers down to it (for their attempt to fill the 2" gap where sarking falls short of the wall);

and today they fitted new counter battens (now on top of membrane over OSB as it should have been) with the bottom end nailed over the eaves protectors which are propped up against a spare batten nailed to the top of my old facia (to kick out the bottom tile row). Of course this means the counter batten (now curved as nails try to hold it down) cannot sit flat because the end is lifted... leaving a gap under the batten to expose nail through membrane.

This was the last straw :-(]]> breather over or under counter batten https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14440&Focus=268897#Comment_268897 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14440&Focus=268897#Comment_268897 Mon, 11 Jun 2018 12:33:37 +0100 Sprocket breather over or under counter batten https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14440&Focus=268899#Comment_268899 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14440&Focus=268899#Comment_268899 Mon, 11 Jun 2018 15:13:40 +0100 gyrogear Posted By: SprocketI presume they were expecting to fill these new holes with cement...

an extremely concrete possibility...

Good riddance to them :shamed:

gg]]> breather over or under counter batten https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14440&Focus=268914#Comment_268914 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14440&Focus=268914#Comment_268914 Tue, 12 Jun 2018 12:37:59 +0100 borpin Posted By: Doubting_ThomasLots of details online suggesting I'm on the right track, but the gutterer was equally uncertain. Worried that a flash of rain would just sheet straight off the roof and over the top of the gutter!The advice I was given was to place a straight edge on the top of the final finish and position the gutter such that the outer edge touches the underside of the straight edge.]]> breather over or under counter batten https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14440&Focus=268915#Comment_268915 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14440&Focus=268915#Comment_268915 Tue, 12 Jun 2018 13:09:10 +0100 borpin
Plastic should be nailed to the facia (that is what the small flat profile is for). The batten shown is just temporary. the membrane then stops on top of the plastic, no need for it to be in the gutter (that is what the plastic does) - put a small piece of DPC where the plastic lengths joined. I actually did not kick my slates - they just follow the same angle all the way. If you do have a tilting fillet, put it under the membrane and let the tile weight hold it in place.]]> breather over or under counter batten https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14440&Focus=268918#Comment_268918 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14440&Focus=268918#Comment_268918 Tue, 12 Jun 2018 18:21:04 +0100 Sprocket breather over or under counter batten https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14440&Focus=268928#Comment_268928 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14440&Focus=268928#Comment_268928 Tue, 12 Jun 2018 22:22:17 +0100 borpin