Airtightness detailing

[Stones]

Critical as such detailing is, with various other build issues, and all the time spent getting the forum up and running, I've overlooked one critical junction Thankfully I am still at the stage where I can do something about it. 

Our house is single storey, 2/3 of which has vaulted ceilings, the remaining 1/3 being standard height (2.4m) ceilings.

Vaulted ceiling current spec, Roof tiles, tile battens proctor roofshield breather membrane, OSB, 200mm PU between rafters, 25mm across rafters.  PU joints to be taped and sealed to ICF block at wall plate junction. Under the ridge beam we have a service void for lights, cables and ductwork.  Service void to external walls created by battens fixed to interior face of ICF block.  I am debating whether to swap out the PU between the rafters with earthwool batts and increase the across rafter PU depth, but regardless we would still have the continuous layer of PU taped and sealed. So far so good.

Normal ceiling current spec, Roof tiles, tile battens, OSB, ventilated roof space, 450mm earthwool between and over trusses, plasterboard.   I'm happy enough that the total roof build up will be okay in terms of condensation risk, and with the level of insulation it will be warm house, but even paying attention to ceiling light penetrations, I can see the glaring omission in terms of the junction between ceiling plasterboard and ICF block walls.  As there is no VCL or airtightness membrane on the ICF walls, there is nothing to fold/lap behind the ceiling plasterboard to close the service void.

In my last house, the reflective VCL from the timber frame was folded and fixed to the underside of the trusses and ceiling battens, a bead of silicone used to form a gasket and plasterboard fixed thereon, the ceiling subsequently taped and filled.    

Three options.  

Do nothing and hope for the best.  

Run a strip of of membrane around the perimeter of the ceiling in question, tape one edge to the ICF block walls and fold / clamp it under the ceiling plasterboard as per the detail in my last house.

Run a continuous AVCL membrane on the underside of the roof trusses to meet the walls, fold down and tape to ICF block.

I'm not that keen on option 1, option 2 seems like a faff but would leave the roof design otherwise unchanged.  Option 3 seems to be the most straightforward in terms of ease of installation and being able to get properly sealed up.  Not sure whether I can just fit the plasterboard directly on top of the AVCL or whether I would need to form a ceiling service void with battens to the underside of the trusses.

For any penetrations through the ceiling I'm planning to use offcuts of EPDM that I have to form 'grommits' which I can tape down to the plasterboard (if option 2) or the AVCL (if option 3)

Any thoughts or suggestions?

Edited June 12, 2016 by Stones
A few typos

[Stones]

Nobody? I feel so alone...

[Nickfromwales]

18 hours ago, Stones said:

Run a strip of of membrane around the perimeter of the ceiling in question, tape one edge to the ICF block walls and fold / clamp it under the ceiling plasterboard as per the detail in my last house.

As long as the tape / sealing issue is addressed properly during this method I'd say go with this. Overlapping or adjoining the airtight layer isn't a problem as long as the 'connection' is sound. The airtight tapes are damn good at their job as your probably aware, as you don't get a second chance to stick that stuff on, a real pita to work with on fussy junctions I found. 

[PeterW]

What are the surfaces of the ICF block like..? Can you tape to them or would it leave a hit and miss gap..?

 

[Stones]

Good point - Not the best of pictures, but the block has grooves on the surface.  0.5mm for the thinner grooves, 1.5mm for the wider groove.  How forgiving are the airtightness tapes - they obviously cope with OSB ?

[ProDave]

Before you stick the tape to the face of the blocks, go round with a good filler, and fill in the grooves along where you are expecting to stick the tape, and leave to dry.

[PeterW]

Another option is to use a Hotwire to cut a flush trough parallel to the ceiling and then stick the tape into this..?? 

What is the internal wall finish ..? Board or plaster ..?

[Stones]

Walls to be finished with taped and filled plasterboard on battens to form service void.

Useful suggestion re filling the grooves.  I'll be speaking to the builder in the next couple of days and report back on what he suggests.

[DeeJunFan]

you could try this.

http://www.ecomerchant.co.uk/liquid-blowerproof-brush-paint-on-airtight-sealing-membrane-5kg.html

 

[PeterW]

1 hour ago, Stones said:

Walls to be finished with taped and filled plasterboard on battens to form service void.

Useful suggestion re filling the grooves.  I'll be speaking to the builder in the next couple of days and report back on what he suggests.

One of the benefits I always saw with ICF was the ability to easily form channels in the EPS and then do a bonding/top coat plaster finish. Is that not an option..?

[PeterW]

2 hours ago, DeeJunFan said:

you could try this.

http://www.ecomerchant.co.uk/liquid-blowerproof-brush-paint-on-airtight-sealing-membrane-5kg.html

 

That looks remarkably like SBR Latex with some filler/binder and fibres in it.

You can do something similar with SBR and cement or an SBR floor levelling compound such as this http://www.builderdepot.co.uk/latexplan-25kg-trade-2-part-floor-leveller-1-to-10mm-powder-liquid-5kg.html?gclid=Cj0KEQjws_m6BRCv37WbtNmJs-IBEiQAWKKt0MUqR_mNJsoZLcUVt4n9JYYSkjqrMZEpG2htEI2CLKYaApA28P8HAQ