You could use higher density EPS, read pages 13 and 14 of this document http://www.viking-house.ie/downloads/BS%20EN%2013163%20-%202001.pdf

I think you're underestimating the peak forces - snow load likely to be e.g. 0.72kN/m2 = 73 kg/m2 in http://www.kingspanpanels.com/Resource_Centre/Technical-Information/Structural-Performance/Basic-Snow-Loads.aspx - try holding that up! - it far exceeds the dead weight of the materials.

EPS and the accessory items obtainable from specialist suppliers the likes of Chris Hirst http://thinjoint.com/, who also provides a bit of training and supervision in the package, so the warranties will apply.

If you're concerned about the loading, you can brace the end of downslope battens with timber "false rafter feet" connecting through the EWI to the "end of rafter board". With attention to detail, these can be made into a nice feature or used for fixing a soffit board.

David

Take a look at Mike Whitfield's AECB conference presentation half way down the following page:

http://www.aecb.net/conference2007.php

He's not using EWI, but I'm sure you can re-use many of the same ideas.

David

.

Wa wondering on the length the stub rafter should go up the roof pitch , the less the better , I'm guessing for a 500m over hang you'd need 750mm-1000mm ( total 1250-1500mm )
Nogging between hit nd miss stub rafters to fix to main rafters , could you use 50/50 to reduce thermal bridging in 2 layer ERI or would a full 100/50 be better
how about nogging from below and fixing stub rafter through OSB into this

Is the benefit worth the effort in reduced thermal bridging or would fixing stub rafters directly over main rafter be a structually sounder jobs

cheers Jim

Ok thanks , so the inboard nog , 50/50 along top of stubs could be Ok
Cant drop the blockwork , as 152/152 steel below plate for windows/doors at 2050mm from FFL
Pitch restricted due to other end needing to finish under first floor windows.
"and cantilevering both ways to provide all the support for the stubs where they hang in 'mid air'! "
bit confused by this bit ? what the "both ways" bit ?
how about stub length , could I get away with less than 750mm inboard for 500m over hang?
thanks

I still wonder if a decent baton running over the top of all the insulation wouldn't be strong enough to support the eave especially if both stuck on and screwed through the EWI. This would completely avoid thermal bridging.
Paddy

If custom made windows/doors, they needn't be nom 2000 high - drop the heads by 100, squeeze the pitch a bit flatter, push it a bit higher under the 1stFl cills. Must be all-window, no EWI'd wall, to need 152x152 steel! What a high-conductive bridge - how about a slim column to reduce span, subst a 100x150 timber lintol laid flat, needing no additional wall plate.

I agree this is an elegant solution & probably fixes all the issues. The load on the insulation could be spread by fitting plywood under the counter battens where they run over the junction of EWI & roof insulation. This plywood could be extended onto the overhang if you don't want to look at the underside of the tiles/tile battens. However, this approach is not compatible with draining the roofing membrane into the gutter & ventilation of the undertile void is fiddly.

As the membrane is under the counter battens, the gutter needs to be close to the toe of the first tile & the gutter needs to be fixed to the counter batten ends. If the counter battens taper to 100-125mm thick on the overhang then the membrane needs to come up through this thickness to drain into the gutter while maintaining a downwards slope. This can be done, but then there's nothing to fix the gutter to. Some solutions get around this by not draining the roofing membrane into the gutter. Instead it just drains over a flashing on top of the EWI.

It is best practice to ventilate the undertile void. If the roofing membrane drains over the EWI then you need to fit a ventilator to each of the rafter openings. A continuous ventilator is a lot easier.

These issues & the need to ventilate above a woodfibre sarking board led me to the "cantilevered eaves board" solution. Here a plywood eaves board is used to tie together the rafters, eaves batten & false rafter feet. This could be easily adapated for a EWI/warm roof junction & avoids all the thermal bridges.

David

a designer i know, has kindly had a go at a solution to this wall/roof detail for EWI
ones an improved version of my warm roof sketch more along the lines of what Toms suggesting i think .
the others a cold roof option, I've attach it below

Posted By: fostertomIf custom made windows/doors, they needn't be nom 2000 high - drop the heads by 100, squeeze the pitch a bit flatter, push it a bit higher under the 1stFl cills. Must be all-window, no EWI'd wall, to need 152x152 steel! What a high-conductive bridge - how about a slim column to reduce span, subst a 100x150 timber lintol laid flat, needing no additional wall plate.

Yes , 2400 doors and 1800 window , 1100 inbetween , hadn't really thought about the "high-conductive bridge" i presumed the EWI above heads would be my get out of jail free card.
I considered 2 140/140 box lintels but went for a steel to tie it all together.
I should have considered the wood option , though possibly wrongly I presumed wood lintels tricky to get accepted by BC . Not really up on that area. would be interested in more info.
Tile finishes just under 1st flr cills so no room for change there.
I cut and pitched it today so will look to insulate/felt and batton tomorrow and post some pics

david , i'm not to concerned re windtightness as i feel the foil faced PUR will achieve this
here's some pixs of what i did in the end , a bit of a mix of several methods
there are also 2 x 2/2 noggs below the OSB spaced equally down the stub rafter , towards the plate and a wooden wedge under each stub rafter where it hits the plate ( this is a point of insulation bridge)

So 150mm rafters with full fill rockwall in between / 110mm ( 60+50 staggered joins ) PUR above rafters / counter battons fixed with 200mm timber lock structural screws at recomended spacing to main rafters ( much easier to use than helixfix spiral fixing etc. ) / breather felt / battons /tiles

Was unable to follow previous warm roof drawing i attached due to plate height/pitch restrictions etc. but by perhaps looking into using wooden beam ( rather than steel) to reduce plate height and raising main rafter so a it hit the plate as shown in the designers diagram , would have been a better solution
Lining up counter battons with rafter under the ERI was simple and only missed once or twice out of 200+ fixings, it's a good idea to mark up the PUR so as you dont need to think about it.

Oops -- better not tell anyone this but there should be 150mm between the tiles and the window sill, that's if you can get them to fit but I've seen plenty without and without problems too.

Superb tidy site - like a photo-shoot!

After my posts on the EWI below ground insulation thread. I am now getting to the eaves details.

Again I have put together a sketch up file based on all the ideas above. if anyone wants a copy let me know.

Any comments/suggestions welcome, I havent shown the fascia/soffit on the diagram as it covers up the details, but I would fix the fascia to the false rafters.

I have a couple of questions:

1.Does the OSB need to be 18mm thick or would say 9mm do?

2. 'Bubble glue' has been suggested in the past for joining the osb, any trade names for this?

3. If using EPS/Fibre glass for insulation do we need a vapour barrier in board of the insulation?

4. Does the EPS sheets need joining with anything or is just pushing them togehter good enough?

Thanks