Bending Battens to Curved Bay

[mattu27]

Bit late to the party but wondering how you got on with this?
My situation is exactly the same and I've tried kerfing, soaking for a week and steaming the 19mm and 25mm battens. I could have basically wrote your exact post.

It seems impossible to get standard roof battens to curve that much without them snapping.

I'm using Marley plain tiles hopefully.

 

[wingit]

Bit late to the party but wondering how you got on with this?
My situation is exactly the same and I've tried kerfing, soaking for a week and steaming the 19mm and 25mm battens. I could have basically wrote your exact post.

It seems impossible to get standard roof battens to curve that much without them snapping.

I'm using Marley plain tiles hopefully.

I'm going to do a full post on the process next weekend, with photos.

I used 25mm battens, better to buy fully graded, a bit more expensive though. I kerfed the battens at 35mm, at 12mm depth.

I then poured boiling water on them, which helped a little bit, then I bent them around the brick part of my bay window at ground level, holding them in place with concrete blocks.

Still, the bending part needs patience, go slowly. as soon as you hear the slightest crack, find out where it's failing. At that point, for the weak points, I used a curved template with G clamps, and glued a thin strip of wood support on the back of the batten, and clamped in the curved position.

I had also stripped the plasterboard on the inside of the bay, and if I'd thought a bit harder, I would have bent the battens in-situ and clamped to the uprights, as both sides of the uprights were open.

I also started pilot drilling the nail holes because I found that the kerfed wood would split out at the back when nailed.

I used Lumberjack polyurethane wood glue.

Even with all of that, I found that only half of the battens would bend without breaking somewhere.

you might try 13mm kerfs, and not sure if it's a good idea, but once curved you might glue thin strips into the kerfs to strengthen the wood. I'd be interested in other people's opinions on that in particular.

I'll post more if it comes to mind.

Also, get the batten ends close to the walls on either side, just makes it easier when a tile lug is right up to the edge of the batten, seems obvious, but it tripped me up a bit.

 

[wingit]

I'm using Marley plain tiles hopefully.

Double cambered?

I'm interested in others knowledge on tiling a curved bay, are double cambered tiles better for fitting to convex curves? Seems to me they should be.

before posting I had a quick look and found this:

"· Creating curves – I get asked a lot about how we created the curved roof on Quintain House. We used a double camber tile as it lends itself more to the curved roof because of its latitudinal camber. I would say though that it takes many years of roofing expertise and craftsmanship to be able to create a curved roof of this nature!" from https://www.marley.co.uk/support/installation/how-do-you-create-a-curved-roof-like-quintain-house

 

[mattu27]

Would really appreciate if you get time to do a bit of a show and tell as yours is exactly the same as mine.

I initially tried with 25 X 38mm graded battens and kerfed the back to about 14mm depth. Left these to soak for a week in a bit of a jig and then tried to get them in position. Wasn't having any of it so then got some 18mm slate battens but not graded. I've tried soaking these for a week but they're exactly the same as when they were dry and just splinter upon the slightest tension.

I then had the idea to steam them but all I ended up with was a floppy bit of 68mm downpipe that I've since made into a snake for the kids!

Sounds like you kerfed the front facing part of the battens, when I tried that with mine they just snapped straight away. Unless I'm not understanding the glueing strips bit that you mentioned.

I've found that any slight imperfections in the batten cause a massive weak spot if they're bear the middle of the bend and also to cut the kerfs on the side of the battens where the saw marks are visible as this seems to be the propagation point of the splits when they happen.

Good call with the pilot holes, was thinking of using decking screws as they aren't affected by the tanalised timber.

Did you try and use ply at all? I'm considering two layers of 9mm to get the right thickness.

Any chance you could post a few quick photos before your write up?

I didn't even know that they did double cambered tiles. I've got about 200 dark grey plain tiles ready to go on!

 

[wingit]

Any chance you could post a few quick photos before your write up?

I'll try and post some photos tomorrow.

I tried a few different suppliers for the battens, they do vary have a look at this link https://www.marley.co.uk/blog/guide-to-specifying-roofing-battens

Where a batten had an obvious weak point, I kerfed it, then clamped on the weak point and glued a supporting strip of wood on the back (kerfed side), and curved to a plywood template I made

So the kerfed side is on the inside of the bend, the inner face.

Not sure at all, but soaking the wood that long might weaken it, anyone else know about this? I think the heat is effective, the boiling water seemed to help for me. A few rounds of that.

I didn't try ply wood, and I probably wouldn't, if I had to do a similar job again

I used stainless steel screws in a few tiles, I think they are recommended for pressure treated wood, not sure though. I just couldn't hammer the nails in on a few centre points between uprights, the battens bounced too much in places, must be a trick to that, but I couldn't figure it out.

 

[wingit]

The blue battens were from Wickes, and the others from my local roofing company. If you look at the third batten from the top, on the left of the image, you can see what I meant about reinforcing the wood on the kerfed side, at a weak point, time will tell if it's robust enough to last as long as the old tiles and battens I tore down (85 years).

I cut the kerfs with a circular saw.

 

[mattu27]

Really appreciate you taking the time to reply and put some photos up. When its light outside again I'll take a photo of current progress.

See what you mean now about the reinforcing strips. Can't see it being a problem as that wood glue is very decent stuff. I suppose the battens will ease over time and some of the tension will cease.

After the battens had soaked for a week they were pretty slimy and still not flexible. The closest I got was the kerfed 25 X 38 graded stuff to getting round the profile. I made a bit of a jig out of 4x2 studding to start the kerb but maybe I was missing the boiling water to get them closer.
I did notice that the graded stuff is a lot more resistant to splitting in the smooth cut side rather than the rough side.

Seems like the approach is the right way to go as yours looks ace now it's all battened out, any reason they you didn't go for membrane behind? I've got breathable stuff over the celotex and framework as a belt and braces.

Did you keep the lead flashing at the sides? I've rememoved mine and am just going to get the tiles as tight to the wall as possible, maybe put a small amount of silicone esk sealant between the tile and brickwork.

What tiles did you opt for then? Double cambered?

It looks good anyway mate. Well done for showing me it is possible.

 

[wingit]

What tiles did you opt for then? Double cambered?

I went with Rosemary Clay Plain tiles, not double cambered, the wife just insisted that she wanted those ones, I am happy with them. I'll post a picture of the end result in a few days when I get a chance to take a photo.

Seems like the approach is the right way to go as yours looks ace now it's all battened out, any reason they you didn't go for membrane behind? I've got breathable stuff over the celotex and framework as a belt and braces.

I did think about it, but the breathable membranes I looked into, need to be double battened, as they expand [edited after clarification from another member that this is false, and breathable membranes do not expand], and need room to do so, and my window sills were not deep enough to accommodate that. I spoke with the manufacturer and that was what I understood of it, I wouldn't want anyone taking my word on that though as I'm not an expert.

Did you keep the lead flashing at the sides?

I kept some of it, but replaced the ones at the bottom with new lead, I think silicone is not really up to decades of weather on it, lead was on there originally for a reason. What's the reason that you don't want lead on?

Are you rendering over the tiles at the sides or leaving the tile to brick edge exposed?

On the subject of lead, the lead beating into shape for the top row flashing was a bit tricky, I made a form out of ply, and beat it into shape on that first, maybe an unnecessary step, but it worked for me.

 

[datarebal]

Top flashing should have been a tray .
You don't have to counter batten provided there can be a drape.

Expanding membrane ? Which ones ?

 

[wingit]

You don't have to counter batten provided there can be a drape.

Expanding membrane ? Which ones ?

I spoke with tech support for one of the leading manufacturers of breathable membranes for roofing, and he said counter battening was necessary, and to my memory said something about them expanding, I can't really remember now as it was a while ago. It's very possible that I misunderstood what he said. I'll try and remember which brand it was.

Draping the membrane makes sense, but I wonder how effective that would be in a vertical hanging scenario? Would it sag and move closer to the tiles?

I'm interested to know why counter-battening is needed, is it purely to make enough space between the membrane and the tiles? Looking at the thickness of breathable membranes, they are very thin.

 

[mattu27]

I kept some of it, but replaced the ones at the bottom with new lead, I think silicone is not really up to decades of weather on it, lead was on there originally for a reason. What's the reason that you don't want lead on?

Are you rendering over the tiles at the sides or leaving the tile to brick edge exposed?.

I don't like the look of lead new or old. I know that it's a necessity for the top row of tiles but couldn't really see it being a problem at the sides. I've repointed mine after removing the flashings and accompanied by the membrane beneath the tiles I can't see it being a problem if it's not there. I may just mitre the tiles nice and tight to the wall and leave it as is.

I've done my membrane with a little slack in it but not alot, hopefully this won't turn out to be a problem.

Did you end up mitering the tiles at the edges to get them sitting nice?

Possibly going to be tackling mine tomorrow, might go down the booking water route.

 

[mattu27]

Top flashing should have been a tray .
You don't have to counter batten provided there can be a drape.

Expanding membrane ? Which ones ?

Datarebal, could you elaborate on the top flashing a bit? I was thinking of doing mine in three 1.2m sections with the middle section being the top layer, and forming an inch deep lip, cut in finger like sections so it'll fold around the curve of the bay, then lead clipping it into the gap between the top tile and the cill above. Or am I being daft?

 

[datarebal]

I spoke with tech support for one of the leading manufacturers of breathable membranes for roofing, and he said counter battening was necessary,

Nope
There are circumstances where its not necessary .

Which brand?

to my memory said something about them expanding

Nope

 

[wingit]

Did you end up mitering the tiles at the edges to get them sitting nice?

I did, I used a sliding mitre saw with a diamond blade on it

 

[wingit]

Nope
There are circumstances where its not necessary .

Which brand?


Nope

I can't remember the brand.

Good to know, thanks for the clarification