The devil is in the detail... of hidden rainwater drainage

[DKR]

Hello community

 

I am a construction professional looking to perfect detailing and have the opportunity to discuss pros and cons of solutions with knowledgeable and experienced builders / designers, based on lessons learnt from experience or simply best practice. My most pressing question tags on to a thread that went on back 2017, initiative by Visti (respect). I am after achieving the seamless facade / roof cladding with vertical charred timber board (T&G or open joint yet undecided, may be technically swayed to use one of the other). Image courtesy www.designmakeinstall.com. 

My understanding having searched widely is that there appears to be two options:

Option 1 (image courtesy Rodic Davidson Architects for a project in Dungeness): gutter concealed below the roof cladding, I've seen numerous details but this left me wondering how one accesses it to clean it / etc, it didn't seem good practice

Option 2 (image courtesy Guy Hollaway Architects, also in Dungeness)  : wrap the whole building with EPDM (roof) lapped onto good water resistant breather membrane (roof) and drain rainwater as eaves drop system with a drip at the base of the cavity behind the cladding (if open joint). 

 

I would welcome thoughts.

 

Thanks

DKR

[Trw144]

Nothing to add I'm afraid but following this as it's a look I would like

to achieve, but not sure I have the balls to go through with (water ingress does concern me).

Edited April 12, 2021 by Trw144

[tonyshouse]

The cladding join, roof to wall will suck I water and rot! 
 

the whole thing is mad! Glass roof over the wood for me with overhang 

[markocosic]

She she must be obeyed also liked that style. Monopoly house / plain barn in burned wood is very much in season at the moment I'm told.

 

 

If you're prepared to do it in standing seam metal (e.g. Rukki roof) it's pretty easy. Water proof / air proof but vapour open membrane. Vertical then horizontal battens. Metal roof that turns into metal wall. No gutter. Lift the bottom of the house >0.5 metres off the floor to avoid backsplash.

 

Ditto in slate or other doesn't really rot type material.

 

 

In wood...

 

You can have a decorative wooden cover over a metal roof. Use trapezoidal metal panels with horizontal battens fixed to the ridges. Attach your "open facade" to those. Expect the tops of your boards to rot quickly.

 

You can have a decorative wooden cover on top of an EPDM roof. Drape the EPDM over the "vertical" battens so that you have the equivalent of trapezoidal metal panels but in EPDM. Attach horizontal battens to these ridges. Attach your "open facade" to those. Expect the tops of your boards to rot quickly.

 

"Open facade" approach not ideal. Leaves and other debris will fill that drainage cavity over time (it isn't getting huge water flow or wind to clear it) then your battens start to rot...never mind the hidden gutter detail. Make the "vertical" battens enormous to avoid this.

 

Vertical tongue and groove is closed...and great for trapping water and reducing your drying area / airflow.

 

Putting a metal ridge on top helps. Sliding a metal strip in the roof-eaves jointline to deflect water off the top of the wall boards would help. An overhang helps. Closing the roof deck / facade helps.

 

It's a disposable aesthetic cover on a building. Make the wood as resilient as possible and it'll take longer to fail.

 

Less disposable is your timber frame. The EPDM should not enclose your wall/roof structure. (don't put a hard vapour barrier on the outside of your wall/roof and expect the wood not to rot - in a heating climate the hard vapour barrier is on the inside and the outside needs to be less vapour open; else you're doing the equivalent of putting a sheet of glass over grass in the sun and being surprised at all the warm condensation under it) Use breather membrane to close your wall/roof, then vertical battens as breathing (for the wall), then OSB and your EPDM. The second wall/roof detail is madness I think.

 

 

After some research we're going to try this...

 

 

 

Overlap boards. Very traditional with pine tar an 3-yearly re-treatment. Less traditional with alkyd/acrylate paints and 10-yearly re-treatment. But if detailed right / maintained is supposedly good for 30+ years. (the limit being how well it is maintained)

 

- Timber frame w/mineral wool (fibreglass falls down cavities; rigid foams between studs hard to fit/detail)

- Water and windproof but vapour open membrane that can be laid hard against insulation (not all can be)

- 50x25 mm vertical battens / 50x50 mm horizontals (to give nail purchase) every 600 mm

- Make from dried 150 x 25 mm boards

- Impregnate the boards (rough cut stuff is usually just dipped rather than pressure treated)

- Overlap by 25 mm (creates vertical ventilation grooves)

- Rebate (10 x 8 mm) the centre of the overlap to create a drainage groove / ventilation groove for the overlap

- Paint with good alkyd or acrylate paint...

- ...and paint the tops and the areas of the boards that overlap...

- ...but leave the backs that are exposed to the cavity and those 10x8 grooves unpainted to aid drying

- 5+ cm overhang

- Seal the walls to the eaves

- Vent from the ground floor to the ridge

- Cut the bottom of the wall boards at an angle to crate a drip edge

- Make provision to avoid splashback UNDER the house

 

 

No metal. No EPDM. Wind proof membrane underneath doesn't need to be UV stable. Can replace with metal or slate when you get bored with maintenance. Can decide that in 50 years time you'll be dead and not care.

 

Maybe not the look that they're after. Depends how much fot eh future work they're going to do.

[Trw144]

8 hours ago, markocosic said:

Ditto in slate or other doesn't really rot type material.

Yes, to be honest I wouldn't opt for wood. Will look great in year one but I think could quickly go downhill in the aesthetics department. I have lots of samples of cement board which I like and could be used instead of the wood in your detail a above, but again isn't at all common. Failing that zinc is probably my fall back option, but I m concerned the standing seams could be too busy on a 15m length, double story (plus pitched roof)  part of the house.

Edited April 13, 2021 by Trw144

[gc100]

We initially wanted a wooden 'wet roof' setup. We decided against it after discussing with a cladding supply company owner, who knew of 2 projects that had done this, as the roof was a complete mess after 5 years and all wood needed replacing. We went with zinc in the end. Happy with it now and the hidden gutter, drainage is easy to clean and I sleep soundly knowing it is unlikely to fail.

[markocosic]

Cement boards are definitely a classic ?

https://lemora.lt/stogo-danga-priedai/stogo-danga/siferis/3189-eternit-agrol

 

Hardie plank is a safe option for a decorative open rain screen. It's heavy though. Not as pretty (looks plastic to my eye) but long lasting. The comments EPDM and not trapping moisture within the wall structure would still apply though.

 

 

Standing seam - I suspect the first image that you attached looks messy because nothing lines up (roof vs walls) and the walls are covered in unnecessary seams. (that length can be made in one piece) Standing seam roofing can be premade zinc plated / powder coated steel too rather than made off the roll. Max off the shelf length on Rukki is 10 metres. It's ~€15/m2 in the baltics but how much it would be to import to the UK though. 

https://www.ruukki.com/roofing/products/roofing-sheets

https://nordicroofing.co.uk/

 

 

"Architectural" panels have wider (~1m) spacing between seams if you want fewer of them:

https://www.kingspan.com/gb/en-gb/products/insulated-panel-systems/insulated-wall-panels/quadcore-architectural-wall-panels-ks600-1000

 

You might want the opposite with MORE seams (or ridges) to make them less prominent rather than a hard seam every 500 / 1000 mm though? I think this looks clean because the seams between panels are much less visible, they're the same on the roof and the walls, and the gutter breaks any mismatch between roof and the wall:

[markocosic]

What were the 5-year failure boards and how were they treated gc100? 

 

That's a short life even for noddy basic Wickes decking boards. Were they untreated softwood? "No treatment needed" larch panels?

[gc100]

11 hours ago, markocosic said:

What were the 5-year failure boards and how were they treated gc100? 

 

That's a short life even for noddy basic Wickes decking boards. Were they untreated softwood? "No treatment needed" larch panels?

 

I'm not sure. But at a guess they where not treated and left to 'silver'.

[Trw144]

20 hours ago, markocosic said:

 

Standing seam - I suspect the first image that you attached looks messy because nothing lines up (roof vs walls) and the walls are covered in unnecessary seams. (that length can be made in one piece) Standing seam roofing can be premade zinc plated / powder coated steel too rather than made off the roll. Max off the shelf length on Rukki is 10 metres. It's ~€15/m2 in the baltics but how much it would be to import to the UK though. 

https://www.ruukki.com/roofing/products/roofing-sheets

https://nordicroofing.co.uk/

Could be a trick of the camera but to me, there doesn't seem to be much of a seem on that build which is what draws me to liking it (I agree the roof and walls need lining up though). I also like the width on the roof, but appears much wider than what I have been told is possible with zinc (circa 500mm Max).

 

The bottom grand designs image I would need to see in the flesh, it appears clean and contemporary but I'd be concerned it looks too barn like close up for what I am trying to achieve (fine for them as it's on a small holding). Fortunately it's local to me so I might see if I can take a peek. For reference, this is what I am cladding (there is a bit to be worked on still - gable to be recessed and the flat roof part to be tweaked to be more interesting, ground floor won't be white render)....

 

 

Edited April 15, 2021 by Trw144

[markocosic]

That first one looks like ~500 mm standing seam on a 9-10m long "1.5 storey" building (left side full height) to my eye - scale it from the velux windows?

 

 

Slate example attached:

 

[Trw144]

4 hours ago, markocosic said:

That first one looks like ~500 mm standing seam on a 9-10m long "1.5 storey" building (left side full height) to my eye - scale it from the velux windows?

 

 

Slate example attached:

 

I thought the roof on the first one looked wider than 500mm seams but could be wrong (I was looking at what appears to be the doors at the front and rear which appear to be similar to the roof width, and guessing these doors are 850mm or so). Other detail I do like is the walls sides have no seam, and the roof is hard to tell but at the very least a low seam. Not so keen on the tiles (slate or zinc)  as I find them a bit busy for the walls. Thanks for the help  - keep the suggestions coming!