Dormer cladding

[russellsmiler]

Are currently building a dormer as part of a larger extension to my property, its a bit hard to explain but on the face of the dormer I decided on a square bay window for which I have a small firreglass roof, below the dormer with is constructed as the dormer generally 4x2 frame faced with 18mm (it was surplus of another project) plyboard, breather membrane and 2x1 vertical batten 450mm c/c. I originally had this to weatherboard complete with 200mm featheredge timber, now whilst this is fine on the sides and the main face of the dormer, I cannot get it right on the rectangular projection beneath the bay window. I have scratched my head and considered all things.

I have decided to use a 9mm plyboard that is faced with oak, with some vertical oak plant ons to give the desired effect.

My question is quite simple, how does a veneered ply board cope with the weather, am reading on boating forums that it gets used a lot in boatbuilding so assume I could cut the front and 2 side panels, fix to the in place battens, add plant ons to give effect and hide panel fixing points, coat in 2 coats of Osma UV plus, and that should be good for year or 2 applying more osma bi annually or whenever. ( don't worry about the weather tightness or the corners, I will fix a Plastic dpc around perimeter and on battens) he corners are dealt with by an oak 2 x 2 that's on a bracket system I devised and the proposed faced ply would sit snugly just inside.

any comments grateful
russell

 

[tony1851]

Any wood-based product will require maintenance - why not clad in plain tiles?

 

[^woody^]

I'd not trust any sort of ply in an exposed location.

But I can't visualise what you are trying to do at all

 

[theprinceofdarkness]

The ply that is used extensively in boat building is marine ply. Its very expensive but very good. I built a shed out of 3/4" marine ply off cuts (11" x8') and it has not degraded over the 30 years its been up. And its only been "painted" twice, some wax based wood stain. For a shed its OK but I would not want it on the roof of my house, seeing as its rather plain and texture free.
There's the white plastic cladding, trouble is cos' its white your eye is drawn to it and they smack of 1970s jerry built houses and the whiteness goes grey with dirt.
There are plastic planking materials available in different colours and cedar shingles and, again nailed on mesh with painted render on it then back to tiles. If you can get matching tiles and sort out the external corner details , I reckon it the way to go.
Frank

 

[russellsmiler]

Ok have made decisions on this, but not going to complicate the issue.
Timber frame dormer constrruction 4 x 2 CLS, faced externally with 18mm Ply, breather membrane on this and horizontal treated 2 x 1 battens.
Proposing to clad this in match board (v groove) tongue and groove. My question is that i am tempted to put a DPC on face of battens as added protection, but voices are telling me this is wrong to do.

Any help please

 

[^woody^]

You'll trap moisture in with that idea. It has no purpose

 

[russellsmiler]

not sure if there is an image of said dormer attached to this thread.... but tought i would post one to give clarity to my crap description in initial post.

 

[^woody^]

You need to work on the basis that the cladding is not a waterproof layer, but a rain screen. Some water will always get behind it.

So you need to ensure that the breather membrane provides the waterproofing to the structure. This means good detailing at junctions and above/below openings, and drainage at the bottom where it joins the pitched roof.

 

[russellsmiler]

cheers woody
behind the scenes i am paying a lot of attention to waterproofing, the vertical corner junctions have been formed with a 2 x 2 oak floating on brackets with a hi build vertical DPC with a welted edge to channel any ingress back and down to the double lead upstand at the pitched roof, have used an arbo sealant as a continuous seal in many areas, the window sides have a metal L shaped flashing tucking into a small vertical rebate of the window profile, this again arboed in..in all quite pleased with the way its shaping, Glad i went of the oak veneer idea for below the window, and if you look you may now imagine how hideous horizontal cladding the same as the main dormer looked on this section.

 

[^woody^]

It's certainly a non-standard dormer! But that seems like a good choice and contrast for that bay cladding

You obviously don't mind the regular re-coating of the timber then? I was looking at that front bargeboard and it looks really high off the roof, and looks like it wont be accessible off a ladder, but will need scaffolding whenever it needs painting

 

[russellsmiler]

Thanks Woody, the dormer itself was an afterthought when i got to 1st floor level of my 2 storey extension that is on side of house, (plannners approved) the dormer itself is to create a en-suite in the new bedroom, the bay window idea is for two reasons, 1. the view from the window is fantastic and wanted to make it panoramic. the ensuite, although plenty of room will now have the washbasin sat on a marble or otherwise shelf that sits in the bay... a lovely place to brush your teeth in the morning, and frees up so much more floor area in the en suite.
Regarding maintainence.. I realise the access will be of scaffold, (I have my own tower plus youngmans etc.) but its lower than the picture shows, the main roof comes right down to 1st floor.. Osma uv oil is good for 2 years, and are giving it 2 coats at this stage.

will post the finished job soon...if this bloody rain will let me back at it...soaked last night!!

 

[russellsmiler]

Just about finished my dormer!! said i would post when done, quite happy with result..in paticular the way i dealt with the corners... I wanted to have an equal dimension so resorted to what i can only call floating vertical timbers..its a good detail that i would use again, happy to explain to anyone who gives a S**it