Dormer construction sheathing issue

[0Floz0]

Hi everyone

Currently refitting the facing of a dormer. It was a cowboy job 20 years ago but in fairness has just about lasted. I’ve ripped the previous sheathing off which was plasterboard…it’s being replaced with ply. The plan was as follows:
Ply
Breathable membrane (tyvek housewrap)
Battens
Upvc cladding.

However, I’ve just realised that the existing one didn’t have battens and so if I were to use them the facing would stick out past the fascia boards. I really don’t want to mess with those as it means redoing the roof, or at least the edges?

How essential is it to have the battens. Appreciate they allow the ply to breathe but if a breather membrane is on is that not enough? What are my options here?

Attached a pic of it helps.

Thanks all!

 

[DAZB]

You may find that any new or replacement cladding now has to be fireproof due to new Regs etc so these are a good alternative and can be nailed direct to the ply. Other styles and versions are available from other companies but it gives you an idea.

Fibre Cement Wall Cladding, Light Grey woodgrain 210mm x 8mm, 3.66m length

3.66m Fibre Cement Board Cladding, available in seven colours as well as unpainted. Cladco Fibre Cement Cladding is weather resilient with an embossed woodgrain effect surface. FREE Samples are available, with Excellent ratings on Trustpilot.

www.cladcodecking.co.uk

 

[0Floz0]

You may find that any new or replacement cladding now has to be fireproof due to new Regs etc so these are a good alternative and can be nailed direct to the ply. Other styles and versions are available from other companies but it gives you an idea.

Fibre Cement Wall Cladding, Light Grey woodgrain 210mm x 8mm, 3.66m length

3.66m Fibre Cement Board Cladding, available in seven colours as well as unpainted. Cladco Fibre Cement Cladding is weather resilient with an embossed woodgrain effect surface. FREE Samples are available, with Excellent ratings on Trustpilot.

www.cladcodecking.co.uk

Thanks. The issue I’ve got is I’ve already got the upvc cladding ready to go so would lose a fair bit of money going with something else.

It’d be cheaper to mess with the roof I think

 

[noseall]

Thanks. The issue I’ve got is I’ve already got the upvc cladding ready to go so would lose a fair bit of money going with something else.

It’d be cheaper to mess with the roof I think

The plastic cladding is ok. Battens (even the thinner 19mm thick ones) will help deal with any moisture build-up on the surface of the felt and allow it to run off. You should just be able to manage with 12mm ply and 19mm battens, without having to faff with the roof.

 

[0Floz0]

The plastic cladding is ok. Battens (even the thinner 19mm thick ones) will help deal with any moisture build-up on the surface of the felt and allow it to run off. You should just be able to manage with 12mm ply and 19mm battens, without having to faff with the roof.

Thanks. I think the issue I’ll have is that it’ll stick out past the fascia on the sides. So I’m not sure how to compensate for that. The fascia needs to overhang the cladding slightly doesn’t it?

 

[mrrusty]

Over that small area IMHO even a 5mm space between the membrane and the back of the cladding should be enough. As long as that space has a gap top and bottom any condensation will still evaporate.

 

[noseall]

The fascia needs to overhang the cladding slightly doesn’t it?

ALWAYS especially the gutter drip (50mm min).

 

[0Floz0]

ALWAYS especially the gutter drip (50mm min).

I don’t have gutter drips on the sides as it’s angled to drain on the front. Does that sound right? I’ve got gutter drips that will be 50mm min for the front. But what about just fascia on the sides. How much does that need to overhang?

 

[^woody^]

Just put it back together, how it was before but with the extra insulation and good vapour barrier detailing, and it will last at least another 20 years, probably much longer.

 

[0Floz0]

Progress update. Got the front face on. Will weather proof it tomorrow before the rain.

I was thinking about the battens and wondering if ply would be good? I’m going to have some spare so could run some 50mm wide strips off for it? It’s 12mm thick so would give enough of a gap I think? The picture from the side is with a 25mm batten under it. It’s got the old cladding on that part still so it would end roughly there under the fascia.

Also there’s a bit of a mould smell. Any tips for dealing with that. Think it’s lingering from some of the wood which I’ve sanded back and put some wet rot hardener on topped off with filler. There isn’t any mould that I can see now.

 

[0Floz0]

Hi all, any recommendation on if ply would work for the battens or is it likely to fall apart?

 

[^woody^]

One option for dealing with the projection is

It could also be designed with a ventilation strip.

Ply battens could work, but there is a risk of them delaminating over time due to exposure to potentially moist air. Long fixings through into the frame may counter this.

If you are not venting the cavity top and bottom, then you don't need to worry about the batten thickness as you are then just reliant on luck. In this case, internal vapour barrier detailing and quality of installing becomes much more important.

 

[0Floz0]

One option for dealing with the projection is

View attachment 310996

It could also be designed with a ventilation strip.

Ply battens could work, but there is a risk of them delaminating over time due to exposure to potentially moist air. Long fixings through into the frame may counter this.

If you are not venting the cavity top and bottom, then you don't need to worry about the batten thickness as you are then just reliant on luck. In this case, internal vapour barrier detailing and quality of installing becomes much more important.

Ah that’s a good point. On the front there is a vent in the soffit but that’s to vent the cold roof. So the front face will vent but do I want that going into the roof?

In your picture the cladding would still sit under the fascia. It’s just closer to the edge than before.

How would you usually vent the top of the cladding?

 

[^woody^]

So the front face will vent but do I want that going into the roof?

It's not a case of it venting into the roof, but one of through-ventilation with the roof.

If the roof has ventilation at the one end, and you vent at the bottom of the cladding then it's just one run of ventilation. Imagine it as just folding a roof 90° and the ventilation remaining continuous.

But yes, you don't want to vent into a roof that is not open at the other side of it.

The image demonstrates the principle of covering cladding that projects further then the fascia. The cladding could be another 50mm out, but the principle remains the same.

Venting top and bottom of cladding involves either fitting proprietary vent strips or fitting stainless steel mesh. The top needs to be covered to prevent rain ingress, and the bottom needs to be detailed along with some flashing to prevent ingress to the frame and to let any moisture drain out to the roof surface. It needs care to detail. Have a google, or I'll see if I have some details on the principle.