Warm roof, large fascia detail. Is there a reason why....

[2020c]

Forgive my sketch as you can see, not the greatest you'll see on here. But one thing I've been looking at with the warm roof that bothers me is the large fascia which could be 395mm where I am. One thing that has crossed my mind, why do roofers not do what I have in the diagram drawn below with notching out the joists where it meets the front skin of blocks to reduce it so one can get away with using the 225mm fascia board and with an overhang soffit (I forgot to draw in the soffit)

Is there a reason why this isn't finished this way.

 

[Celeronmanuk]

Reminds me of this video, see 12:37

 

[Swwils]

Wouldn't you just construct a parapet?

Or am I missing something!

 

[catlad]

No reason, I've done it.

 

[catlad]

You can loose more than that! if you haven't already built it I suggest using the 18mm osb t&g as your top deck.

 

[2020c]

You can loose more than that! if you haven't already built it I suggest using the 18mm osb t&g as your top deck.

When you say lose more, can I take it down to just the 170ish mm and not have any of the joist pretruding out.

Why 18mmosb at the top. I was of the thinking 11/12mm would do for the top osb board.

Have you any pics of work you've done with this detail cat.

 

[2020c]

Wouldn't you just construct a parapet?

Or am I missing something!

Just something I haven't done. Would this be cheaper and easier to do. I was always of the thinking the parapets more can go wrong.

 

[catlad]

If you finish your joists at the outer edge of the cavity you can then let the osb oversail to your finished fascia position, then I use a length of rough sawn timber 6x1" which you will probably have to rip down to match the depth your insulation boards, then stand it on the edge of the osb and fix it down. That then gives you an upstand to place your insulation against ( also helps to stop it being blown away) I then screw a piece of timber 2x2" to the top of the 6x1" once you have started fitting the top deck bring it to the edge of the 2x2" and that will give you your drip edge into the gutter.

 

[2020c]

If you finish your joists at the outer edge of the cavity you can then let the osb oversail to your finished fascia position, then I use a length of rough sawn timber 6x1" which you will probably have to rip down to match the depth your insulation boards, then stand it on the edge of the osb and fix it down. That then gives you an upstand to place your insulation against ( also helps to stop it being blown away) I then screw a piece of timber 2x2" to the top of the 6x1" once you have started fitting the top deck bring it to the edge of the 2x2" and that will give you your drip edge into the gutter.

Finding it difficult to visualize from your text. My insulation will be 140mm.

What I'm gathering from your txt above is, the joist will be on the wall plate sitting on the inner wall and continues over closing the cavity but stops behind the exterior block.

The osb that's on top of the joist will continue over on top of the exterior block and for the soffit to screw onto the underside.

The insulation will be on top of the osb. At the perimeter where I want the fascia to be, you say screw a rough 6x1 for the insulation to tuck in behind it, plus gives something for the fascia to be fixed too.

Then the osb on top of the insulation to be screwed through the insulation to the joists below, but at this detail at the front, the osb screwed on top of the 6x1 with a 2x2 screwed onto the face of the osb and 6x1.

If this is what your mean, what about uplift from the wind with the overhang. It isn't secured onto the outer face block or does this matter because the joists will be secured to the inner wall with straps.

 

[catlad]

Yes you have got it, the osb sort of cantilevers over the joists several inches depending on your soffit. As for wind uplift that will depend on the size of your soffit.

 

[2020c]

Yes you have got it, the osb sort of cantilevers over the joists several inches depending on your soffit. As for wind uplift that will depend on the size of your soffit.

Ty! If that is the detail, I will add an L strap somehow to the underside to stop uplifting. This is what I'd be very worried about! Maybe even keep the soffit to 4 inches or less.

 

[catlad]

Don't forget the top deck extends over the 2x2" to give you your drip edge.
I assume you will clad it all in pvc. to finish it off.

 

[2020c]

Don't forget the top deck extends over the 2x2" to give you your drip edge.
I assume you will clad it all in pvc. to finish it off.

Yes I know about the extra 2x2 for the drip edge.

There is already a slope in the existing roof which has a 4inch(or more) soffit over hang. I'll be stepping the extension I say 6 inch's but might throw the flat roof on out to meet the fascia on the excisting roof or have them separately. I am now considering a parapet instead aswell.