Simple detail to prevent water ingress above door?

[Tony K]

Evening all. 

In the garden of my SB I have built a home office. It's single skin block, which I will wrap in breathable membrane before cladding.

 

I have built a feature brickwork projection around the doors. There is a gap at the top between the brick and the block, as you can see.

 

To protect this I planned to get a bit of arris rail, wrap it in either lead flashing or roofing rubber, and fix it over the top of the bricks. I would then dress the membrane down over that. 

 

Thing is, that wouldn't give me a drip bead. I'm not sure if that matters. I might be overthinking it!

 

I have thought about using a pvc windowsill over the top, but I'm not sure how I'd address the junction between the sill and the block wall. In any event, I'd want a grey or black one and for the size I need I'd be paying more than seems sensible.

 

How would you treat this area?!

 

Thanks 

[torre]

I'd think in terms of building the world's smallest flat roof and I'd build it on the ground then drop it into place, bonded to the bricks with a decent adhesive.

 

Get a piece of OSB that will overhang 50-75 on three sides, put something like your arris rail around the underside edges to create a drip, then dress the whole thing with your roofing membrane, making sure to leave an extra strip that you can lap up the wall once it's in place, normally you'd have a cover flashing over but your main roof membrane may over lap to do that job

[torre]

(You could probably do the same from a single piece of lead, working it around the outside edges if you're careful)

[-rick-]

Or aluminium flashing either could try and bend it yourself or get a fabricator to do it (this opens up option to have welded edges and custom powder coat, for a price that is likely higher than the other options but not as high as you think).

 

Depends on the look you are after.

[Nickfromwales]

Is the cladding going behind the membrane?

 

It seems you need this ‘drip’ detail 360° around the building, so how far off the blackwork will your battens / cladding be?

[Tony K]

1 minute ago, Nickfromwales said:

Is the cladding going behind the membrane?

 

It seems you need this ‘drip’ detail 360° around the building, so how far off the blackwork will your battens / cladding be?

A couple of references made above to'membrane' seem, I think, to refer to the overhanging black roof rubber you can see in the photos? 

 

My plan is to wrap the walls in a breathable membrane similar to 'Housewrap'. I will start at the bottom of the walls, adding layers that overlap by the manufacturers specified amount, until I get to the top. I will put the housewrap membrane underneath the overhanging rubber sheet. 

 

Then I'll fix vertical timber battens over the walls. Then I pin cladding sheets to the battens. The battens serve to provide a ventilation gap behind the cladding.

 

My understanding is that the cladding does little to protect the walls from rain etc, it mainly protects the housewrap from perishing over time. 

 

All of which means I can't rely on the cladding to prevent water getting in above my black bricks.

 

It sounds like everyone else has similar instincts to me in terms of how to address it. 

[Nickfromwales]

11 minutes ago, Tony K said:

A couple of references made above to'membrane' seem, I think, to refer to the overhanging black roof rubber you can see in the photos? 

 

My plan is to wrap the walls in a breathable membrane similar to 'Housewrap'. I will start at the bottom of the walls, adding layers that overlap by the manufacturers specified amount, until I get to the top. I will put the housewrap membrane underneath the overhanging rubber sheet. 

 

Then I'll fix vertical timber battens over the walls. Then I pin cladding sheets to the battens. The battens serve to provide a ventilation gap behind the cladding.

 

My understanding is that the cladding does little to protect the walls from rain etc, it mainly protects the housewrap from perishing over time. 

 

All of which means I can't rely on the cladding to prevent water getting in above my black bricks.

 

It sounds like everyone else has similar instincts to me in terms of how to address it. 

Sorry, I meant will your roofing membrane become an umbrella for the cladding; I’m not seeing here how the rain won’t get down the gap at the top of the ventilation void.

 

You have 2 shelves to deal with here, one of the cladding, and another of the brick detail? 

[Tony K]

The end result, by the way, is intended to be something like this. I will clad the building in simple corrugated sheets, then attach mesh panels to the outside, then grow ivy on them. The corrugated sheets should prevent the ivy reaching the housewrap and block work. 

 

I think I'll make a little flat roof and wrap it up in rubber or something, as suggested above, fix it in place and dress the rubber up so it goes under the overhanging roof rubber, then proceed with the housewrap, battens etc. The end result would be the mini flat roof over the black bricks would project beyond the cladding and mesh.

[Tony K]

6 minutes ago, Nickfromwales said:

Sorry, I meant will your roofing membrane become an umbrella for the cladding; I’m not seeing here how the rain won’t get down the gap at the top of the ventilation void.

 

You have 2 shelves to deal with here, one of the cladding, and another of the brick detail? 

My understanding was that the housewrap keeps the rain from the block work, and that I'm not supposed to block off the gap at the top of the cladding as that, whilst it would prevent rain getting in behind the cladding, would also block ventilation?

[Nickfromwales]

10 minutes ago, Tony K said:

My understanding was that the housewrap keeps the rain from the block work, and that I'm not supposed to block off the gap at the top of the cladding as that, whilst it would prevent rain getting in behind the cladding, would also block ventilation?

Not at all.
 

The cladding is classed as a rain-screen, and you should have a drip detail that closes off the ventilation gap, by being slightly higher and protruding beyond it; rain strikes this and runs off down in front of the cladding. It’ll also need an up-stand to disappear up behind the roofing membrane. 

 

Back to the drawing board I’m afraid. 

[Nickfromwales]

@Tony K
 

[Tony K]

8 minutes ago, Nickfromwales said:

@Tony K
 

I was just about to do a similar drawing, but I don't have the same access to colouring in pens!

[Nickfromwales]

3 minutes ago, Tony K said:

I was just about to do a similar drawing, but I don't have the same access to colouring in pens!

CAD here; Welsh version = Crayon Aided Design   

[Nickfromwales]

3 minutes ago, Tony K said:

I was just about to do a similar drawing, but I don't have the same access to colouring in pens!

You'll need to add all these layers together so you don't go and feck yourself up by detailing something for the brickwork that doesn't marry up to the cladded sections.

[Tony K]

12 minutes ago, Nickfromwales said:

You'll need to add all these layers together so you don't go and feck yourself up by detailing something for the brickwork that doesn't marry up to the cladded sections.

Yes, hence asking on here at this early stage!

 

Mind you, I've read a good few things on line suggesting that rain can and will get behind cladding, and that it's fine. I mean, surely hit and miss cladding proves that cladding isn't intended to act as a proper waterproof screen for the building?

 

This is AI but has good references...

 

Because water gets behind the boards, professional installation relies on a specific design to manage it safely:

 

Vented Cavity: Installers use battens to leave an open air gap (usually at least 25mm) behind the wood.

 

Breather Membrane: A water-resistant yet vapour-open membrane is wrapped over the main structural wall to block water from entering the building.

 

Drainage and Airflow: Gravity pulls water down the back of the cavity, while continuous airflow evaporates any remaining dampness.

 

 

Edited yesterday at 11:08 by Tony K

[Tony K]

Mind you, AI also says this, depending on what you ask it!

 

At the top of external cladding, you must install a head trim, flashing, or a vented closure profile. This seals the top edge, sheds rainwater away from the wall, and keeps an open gap for necessary cavity ventilation.

[Tony K]

Actually, why am I questioning it?! It won't do any harm to protect the top opening at all, even if it's belt and braces.

 

Ta.

[Nickfromwales]

2 hours ago, Tony K said:

Actually, why am I questioning it?! It won't do any harm to protect the top opening at all, even if it's belt and braces.

 

Ta.

It’s not belt & braces, it’s basic minimum detailing.

 

Anything less will simply fail long term, then you’ll have pull it all back off and do it properly at 3x the cost!

[saveasteading]

There is rainproof cladding, and there is decorative cladding. You might have both.

[Tony K]

1 hour ago, Nickfromwales said:

It’s not belt & braces, it’s basic minimum detailing.

 

Anything less will simply fail long term, then you’ll have pull it all back off and do it properly at 3x the cost!

I'm sure you're right. I'll use corrugated sheets as cladding, which will allow me to put the dedicated flashing trim they do over the top, albeit mounted on a batten to bring it further out from the sheets.

[Tony K]

14 minutes ago, saveasteading said:

There is rainproof cladding, and there is decorative cladding. You might have both.

The corrugated sheets should be rainproof, it's just that rain would have gotten behind them anyway via the gap at the top.

[saveasteading]

2 hours ago, Tony K said:

corrugated sheets should be rainproof

Could we see your version of the above sketch?

 

[Tony K]

1 hour ago, saveasteading said:

Could we see your version of the above sketch?

 

Something like this I think. The red is the housewrap stuff. The fascia is that which you can see in the photos,v so I will build outward from that.

Edited 22 hours ago by Tony K

[saveasteading]

Does this need an air gap?. The corrugations  provide air flow anyway, unless sealed with the relevant profile filler.

Beware ivy. The roots get in everywhere, so avoid gaps. Lovely for birds nests though.

[Tony K]

1 hour ago, saveasteading said:

Does this need an air gap?. The corrugations  provide air flow anyway, unless sealed with the relevant profile filler.

Beware ivy. The roots get in everywhere, so avoid gaps. Lovely for birds nests though.

 

No, I might not need to create an air gap as such. As you say, the shape of the corrugated sheets will do the job. I may end up doing it anyway, though, as I need to fix battens to the wall to attach the corrugated sheets onto, and they will create a (larger) gap.

In fact I will probably double layer the battens, as I need the first batten to run vertically so that water can escape, then the second batten to go horizontally for ease of fixing the sheets. I can't see a more efficient way.

 

Regarding Ivy, I think I would be able to get to the vulnerable bits in the case of this project and regularly rim any stray parts of the plant from going where it shouldn't!