ROOFING EAVES DETAIL

[rhrwilliams]

I am re-roofing my house. Well to be technical roofers are doing that bit and I am doing the carpentry.

The roof is going to be insulated between the rafters (as there is a loft room and no insulation currently) and so the roof is to be counter battoned to provide an air gap between the felt and tiles.

Im struggling with the eaves detail on the front and sides due to the counter baton and was wondering if someone could offer me some wisdom.

Before the counter baton went on, there was no felt, and just a fillet / wedge / sprocket (whatever the name for it is) which the tiles laid over. Ive machined up a new one as per pics.

Now the Counter baton is on - does the wedge go on top of the counter baton ? If so you will have a weird gap that won't look very good.
Or do you make a bigger sprocket / wedge to hide the counter baton behind it
Does the felt go over the sprocket ?

If there is a standard way of dealing with this I would be all ears

 

[Beau]

It's tricky. I put wedges on top of the counter batten but the snag with this was the felt then did not drape into the gutter and comes out behind it. No real problem as I see it but not how the pros do it. Would think the ideal is a wedge underneath and cutting the counter batten where it meets the beginning of the wedge. Hope that makes sense

Edit. This any help? https://www.google.co.uk/search?newwind ... afuizoRJ5M:

 

[rhrwilliams]

Thanks for the reply. Yes that makes sense, basically you would need to make a bigger wedge and then the felt goes under the wedge or lapped over.

How do the pro's do it ? .

 

[MikeG.]

When the membrane manufacturers still had counterbattening as a requirement, this detail was an absolute nightmare. It could only really ever work properly on steeply pitched rooves. However, it is no longer a requirement so long as the insulation doesn't come to the top of the rafters, so I am puzzled as to why you are counterbattening.

........ a fillet / wedge / sprocket (whatever the name for it is).......

It's a tilting fillet, and it's a wonderful detail which is sadly neglected these days. Other than for slate, I don't think I have drawn a roof without one for a few years now.

 

[rhrwilliams]

The rafter depth is 4" which I am insulating with Sheep's Wool as its a warm roof. There is no room to put any more insulation on underside as head height is tight.

Historic England in their guidance for insulting at pitched roof rafter level recommend counter battening to reduce condensation risk in warm roofs.

https://content.historicengland.org.uk/ ... roofs.pdf/

I thought it would be relatively straightforward to do it and minimise risk of condensation.

 

[MikeG.]

Ah, right, so you are fully filling the rafter. What tile are you using?

 

[rhrwilliams]

Sorry I should have said - its a peg tile roof.

Tilting Fillet ! I will call it the right name now.

 

[MikeG.]

Peg tiles? Literally, with holes and a wooden peg holding each tile? Or a handmade clay plain tile?

The big problem you face is that the tile is so short that the bottom batten is very close to the eaves, not leaving enough room to get the membrane up to where it needs to be at the underside of the tile before draping into the gutter. I've seen it where this would actually slope backwards, retaining water on the roof. What pitch is your roof?

 

[rhrwilliams]

Yes they are proper old peg tiles and I am re-pegging with aluminium pegs rather than wooden ones.

The pitch is about 50 degrees

To be honest Im thinking of not bothering counter battening now - there are so many little detail issues to deal with. I have another problem with a dormer window that will need to be re-made as the counter battening will mean the cill is too low.

 

[MikeG.]

I think this is probably the right course of action. The thing with peg tiles is that they have a double camber (ie along their length, and across their width). This means lots of airflow through the roof covering, and with it, the chances of condensation are much reduced. Slates are an altogether different kettle of fish.

 

[rhrwilliams]

Agreed thanks for the input.

 

[Beau]

The rafter depth is 4" which I am insulating with Sheep's Wool as its a warm roof. There is no room to put any more insulation on underside as head height is tight.

Historic England in their guidance for insulting at pitched roof rafter level recommend counter battening to reduce condensation risk in warm roofs.

https://content.historicengland.org.uk/ ... roofs.pdf/

I thought it would be relatively straightforward to do it and minimise risk of condensation.

With just 4" of sheep's wool insulation how are you going to meet regs or do you not need to? I dont know anything about peg tiles as we had slates but my understanding for the counter batten was first to aid air circulation but secondly to stop any water that does find it's way in from pooling behind the roofing batten as when you insulate between the rafters the felt cant sag between them to allow any water to escape.

 

[Jacob]

Whatever else you do you must have your insulation tight up against the ceiling plasterboard with no air gap. If not you run the risk have having cold air getting in over the ceiling and completely bypassing the insulation. The insulated space above ceiling between joists needs to be draught sealed at the building edges all round. It only takes a small gap for there to be a steady cold air flow if it's at all windy outside.

 

[Woody2Shoes]

I think that you need the tilt fillet whether or not you have counterbattens - either on top of the rafter feet as before or in the same position but on top of the counterbattens (which actually are just providing the effect adding another inch of thickness to each rafter). Some roofers just use a length of batten (or a couple - you need about two inches of thickness, with a two inch overhang) instead of the nice wedge profile you've created - this often creates (as MikeG notes) an opportunity to create a little puddle unless you're careful with the detailing (e.g. extra boards between the rafters). The tilt fillet is necessary so that the last row of tiles sits at the same angle as its brothers further uphill. Will your roofers be using special eaves tiles at the eaves/ridge?

http://www.roofconsult.co.uk/articles/tiling/tips83.htm

If you do choose to go ahead with the counterbattens - I so no real reason not to - you'll have a (larger) gap at the eaves - you could fill this with insect-proof (esp. important to keep moths out!!) mesh and/or fascia/soffit boards - depending on the existing roof design.

Cheers, W2S

 

[Beau]

If you do choose to go ahead with the counterbattens - I so no real reason not to - you'll have a (larger) gap at the eaves - you could fill this with insect-proof (esp. important to keep moths out!!) mesh and/or fascia/soffit boards - depending on the existing roof design.

Cheers, W2S

It also keeps rodents out

I did not initially fit a mesh and got woken to the sound of gnawing. Mice had gone up above the Tyvec and were chewing at god knows what. I had to remove all the guttering and barge boarding to fit a mesh.

 

[rhrwilliams]

Jacob, i'm using sheeps wool and lathing out between the oak rafters, then plastering that - basically going back with what was there previously. As I'm using sheep's wool which is on a roll there will be the odd gap etc as its very hard not to.

ON a side note Jacob - I made a set of saw horses following the notes on your website. My head spun for a while but I made them !

Incidentally I do lots of surveys of historic buildings in my day job and I can say from looking at literally 100's of old buildings using thermal imagaing when they have been plasterboard and celotexed between rafters (not compatible materials in my opinion) - it is never air tight - never. Its impossible. The celotex is a rigid material that does not flex. The timbers in old houses are not straight and there are always cold bridges.

I am not a big fan of celotex at all - its also bad for the environment and very flammable and does not achieve its stated u Value in breathable traditional construction.. but thats going off topic slightly.

I do not need to meet regs as its a 1700's house and meeting current regs would be unfeasible. There are actually quite a few clauses in part L of the building regs that indemnify certain properties of upgrades that would be very difficult to achieve or have a detrimental effect on the building fabric.

I did a mock up today of the counter baton as a couple of chaps from the other forum gave me a hand also -

From doing the mock up I've decided I am not going to counter baton. It will raise the roof too high and cause knock on issues. Such as the gable end walls will have to be built up a course. The dormer window cill will need raising. However. I will need to be careful about insulation inside to ensure no intersistual condensation.

 

[Harbo]

Be very careful using sheeps wool, it’s got a very bad press recently as it’s very prone to moth infestation!!

Rod

 

[rhrwilliams]

Yes there were batches and bathes of it a number of years ago from Thermafleece that were eaten by moths because it was not treated properly ! I thought the issue was one that was long in the past and isolated to certain batches of Thermafleece (e.g not BlackMountain or Sheepswool.ie) - have you heard of any recent cases ?

The way its made / treated was changed as a result (or so Thermafleece claim)....

 

[Harbo]

Recent story but insulation installed a few years ago:

https://www.google.co.uk/amp/www.telegr ... moths/amp/

Rod

 

[rhrwilliams]

Bloody Hell - not good !