Home  5  Books  5  GBEzine  5  News  5  HelpDesk  5  Register  5  GreenBuilding.co.uk
Not signed in (Sign In)


Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
These two books are the perfect starting place to help you get to grips with one of the most vitally important aspects of our society - our homes and living environment.

PLEASE NOTE: A download link for Volume 1 will be sent to you by email and Volume 2 will be sent to you by post as a book.

Buy individually or both books together. Delivery is free!

powered by Surfing Waves

Vanilla 1.0.3 is a product of Lussumo. More Information: Documentation, Community Support.

Welcome to new Forum Visitors
Join the forum now and benefit from discussions with thousands of other green building fans and discounts on Green Building Press publications: Apply now.

    • CommentAuthorGreenfish
    • CommentTimeMay 25th 2013 edited
    Having plasterboard ceilings and masonry walls with wet plaster finish. Plasterboard in ceiling will be fixed to the bottom chord of roof trusses, noggins positioned for the edge of each board, taped and skimmed, no downlights. Plaster and plasterboard generally forming the air tightness layer. How is it best to avoid air leaks through the inevitable crack that will form between the wall and ceiling junction?

    I am thinking that we just need to tape that junction, but with what kind of tape? Over or under the plasterboard or plaster? Does it need to be extra flexible? Going to have coving, properly fixed will help too or just hide the problem.

    Or should I be covering the ceiling with a VCL under the plasterboard, plastered into the wall at the edges. I have read that suggestion here, but it seems a lot of extra work (on stilts with a 9ft ceiling). Just empty roof space above, unventilated roof, 500mm of insulation (loft roll or warmcel). Surly the taped and skimmed plasterboard and taping any penetrations will be air tight, just the edge is the issue. Do ceilings need a VCL?

    Also read that not nailing too near the edge of the pbd will avoid edge cracks, but I'm not sure I would want to rely on that.
    • CommentAuthortony
    • CommentTimeMay 25th 2013
    I use a vcl/air barrier, eml over it and wet plaster this into the walls, airtight cheap and easy
    • CommentTimeMay 25th 2013
    Plasterboard can be airtight, but it isn't a vapour barrier. So the question is whether you need one.
    • CommentAuthorGotanewlife
    • CommentTimeMay 25th 2013 edited
    Posted By: djhPlasterboard can be airtight, but it isn't a vapour barrier
    unless you paint it with something airtight....
    Posted By: djhSo the question is whether you need one.

    So another question is whether you want to make sure you don't have one; after all, another escape route for higher internal humidity is always good, isn't it?
    • CommentAuthortony
    • CommentTimeMay 26th 2013
    No not if it causes damp/condensation to the structure.
    Posted By: Greenfish
    I am thinking that we just need to tape that junction, but with what kind of tape? Over or under the plasterboard or plaster? Does it need to be extra flexible? Going to have coving, properly fixed will help too or just hide the problem.

    I've used a metal corner bead at such a junction - it's metal on the inside and has paper, that you skim over, on the outside. No chance of that cracking!

    [ edit ] Another good trick is to caulk any change of plane with decorator's caulk - this also smooths out the junction and makes for a cleaner line if you're painting two different colours.

    Paul in Montreal.
    Another vote for metal & paper tape bedded in joint filler/compound. I tired of looking at cracks on ceiling-wall junctions so did most of my house this way.

    On the subject of airtightness, I wish I had the opportunity to gut my truss-roofed house during its renovation instead of doing it piecemeal. I would have done a few things in the "wrong" order. For one I would have pulled down the stud walls & ceiling upstairs and then put up the entire new ceiling and taped & jointed it before putting stud walls back up.
    • CommentAuthorPaul_B
    • CommentTimeMay 27th 2013 edited

    Any detail you decide on is going to be better than 90% of the homes in the UK, as I discovered after removing plasterboard in one of my rooms (circa 1998 build)




    • CommentAuthorGreenfish
    • CommentTimeMay 30th 2013
    Posted By: djhvapour barrier.. the question is whether you need one
    And I am still unsure. Unventialted roof space, so I would guess that I don't want and damp going up there. Then again won't the MVHR suck that away?

    Posted By: Andrew_DoranAnother vote for metal & paper tape bedded in joint filler/compound
    Are the metal bead/tape combinations mentioned by Andrew and Montreal Paul available as a product in the UK, or is it a DIY thing?
    • CommentAuthorJamesce
    • CommentTimeMay 30th 2013
    • CommentAuthorGreenfish
    • CommentTimeMay 30th 2013
    Thanks for the link Jamesce, I was imagining something completely different. Doh!
    • CommentAuthorGreenfish
    • CommentTimeJul 10th 2013
    Reviving this thread (I hope). I was veering towards getting air tightness the way Tony suggested - VCL plastered down into wall - because it sounded simple, and would keep water vapour out the unventilated loft. A bit more reading I discovered that with an unventilated roof construction BS5205 requires me to have a "well sealed ceiling", and a ceiling level VCL is the obvious way to do that. However I am currently reassessing the practicality of doing this.

    I have gone for masonry internal walls too. The obvious way to plasterboard the ceiling is to continue above these in the gap made by the wall plate, and fill the gap at the top of the walls after. Taking the VCL across the top of the internal walls in a similar way could be difficult, and by time I have stapled it up there, taped joins etc. just how air and vapour tight will it be anyway? Anyone done that job successfully, am I worrying about nothing?

    Are there other ways to create a "well sealed ceiling"? Taping, caulking and coving can make the edges and joins air tight, but what of a vapour barrier? Paint the ceiling with something?
    • CommentAuthortony
    • CommentTimeJul 10th 2013
    once the vb is taped, seal all penetrations, then the big problem is hermetically sealing it to the walls, I trap the vb/air barrier in my case poly behind eml on the wall plate join and plaster it all in.

    my air tightness was less than one.
    • CommentAuthorEd Davies
    • CommentTimeJul 10th 2013
    Posted By: GreenfishA bit more reading I discovered that with an unventilated roof construction BS5205 requires me to have a "well sealed ceiling",


    BS 5205:1990

    Specification for adjustable metal walking sticks

    Do your building regs or whatever other law actually applies reference whatever BS you actually have in mind? British Standards are entirely optional unless the law specifically references them (e.g., as I think BS 7671 is referenced for wiring regulations).
    • CommentAuthorGreenfish
    • CommentTimeJul 10th 2013
    Er walking sticks... This is what I meant - BS 5250: 2002 (Code of Practice for Control of Condensation in Buildings), sorry for typo :shamed:

    Will get back to the regs (unless someone can help me out), but the roofing underlay makers mention it with regard to unventilated roofs, my BC also mentioned using a VCL in a comment that I initially took to relate to the attic room only but possibly relates to all my unventilated roof spaces, and finally having a "well sealed ceiling" does make sense to me.

    Tony - ever taken such a VCL over the top of internal walls? That is the kind of air tightness I want to achieve.
    The ceiling VCL should always go over the top of internal partition walls as the cavities within partition walls and behind plasterboard in general are one of the biggest sources of air leakage into loft spaces. Wet plastered solid masonry internal walls do not have this problem, so the ceiling VCL can either go over the top or be sealed to the wet plaster on both sides.

    • CommentAuthorwookey
    • CommentTimeSep 7th 2016
    What sort of VCL do people use for this job? Just plain polythene sheet, or something fancier?

    I have an existing plasterboard ceiling (some in poor condition due to old water leaks), and there are cracks in some places, so I propose to cover it all in vcl (does one tack it up or glue it?), then put up a new plasterboard ceiling, so it' ends up sandwiched between the old and new plasterboard. I assume that screwed fixings will clamp it well enough not to induce much leakage.

    I'll tape the edges to internal plaster/insulation on walls.
    • CommentAuthortony
    • CommentTimeSep 7th 2016
    I always take vcl over the top of internal walls, purlins beams etc. By doing them first if necessary even with a wide strip of poly then joining later. I much prefer to do single sheets with welted joins of whole houses.

    And yes wookey poly will do it, it does not need to be thick.
    • CommentTimeSep 7th 2016
    Posted By: wookeydoes one tack it up or glue it?

    If you're using polythene, it's quite difficult to glue. It is possible to use sticky tape to hold it up until the plasterboard goes over the top though, so no need for extra holes in the VCL.
    • CommentAuthorwookey
    • CommentTimeSep 12th 2016
    OK. One other issue. Part of the existing plasterboard ceiling has sagged due to previous overflow-tank disaster. Is there any way to make it flatish again before I put up the new ceiling?

    Screwing a chunky batten up works, but it springs back again when I take it off. If I leave it long enough will it get the message and reshape? Or not unless I soak it again (not an ideal plan at this time of year). Might just a mild damping do the trick?

    I could batten up the whole ceiling to let the new one go in flat. Or I could bite the 'serious mess' bullet and replace the warped boards (which involves removing the loft fluff).
    • CommentAuthorgyrogear
    • CommentTimeSep 12th 2016
    Posted By: wookeyIs there any way to make it flatish again before I put up the new ceiling?

    Maybe consult YearTubs for a video or two called
    "Repairing a Plaster Ceiling"

    • CommentAuthortony
    • CommentTimeSep 12th 2016
    Bonding plaster or I would take it down and redo it with new.
    Can you lose any height? I would put money on not being able to 'fix' the warped boards. I can't see any other choice but to remove and redo or counter-batten so as to straighten the board and put new PB up. There is also the risky proposition of glueing (well!!) new PB to the old ceiling and bracing the new bits where the old isn't straight until the glue is dry. Then you'll have made a laminate and 'theoretically' it should retain it's shape. Nothing to be lost but 12mm of height and 3£/m2 (I guess cost) plus your time - but it is a quick job to see if it works; if it doesn't work you can still rip it all off and start again or batten and make a new ceiling.

    If it were me I would go straight to batten and new PB but that's because 1/I would hate to make that much mess 2/I would hate to make that much mess 3/I would hate to make that much mess 4/I have tons of height in my house
    • CommentAuthorDave_07968
    • CommentTimeSep 15th 2016
    Do you have access from above? You could just put a noggin between the joists and use that to hold up the sagging area from the other side, then proceed as planned.

    I'm guessing your ceiling generally looks OK for overboarding, in which case I'd be loath to take the hassle of battening under the whole job, but if it's not great anyway and you have the headroom, maybe just bite the bullet?
    • CommentAuthorGotanewlife
    • CommentTimeSep 15th 2016 edited
    Posted By: Dave_07968Do you have access from above?
    I had assumed he didn't otherwise the solution would be obvious, I thought, but clearly if there is access a solution is simple. In short:anything is better than ripping it all down:cry::cry::cry:
    • CommentAuthorwookey
    • CommentTimeSep 17th 2016
    I can get in the loft, although there is a lot of fluff to shift. I guess some noggining up there is actually rather a good idea, especially now it's not summer anymore. I'll give that a go.
    • CommentAuthorwookey
    • CommentTimeSep 21st 2016
    So, it turns out that you can more-or-less flatten sagged plasterboard, but you have to shove _really_ hard. And put an awful lot of screws in. With two large T-props I was able to shove the plasterboard back up and put in screws every 100mm or so to get it to stay there without the screws pulling through. I came close to getting my car jack out for applying the necessary force, but it wasn't _quite_ necessary.

    You end up with a slightly wavy ceiling (10mm?) and I put a couple of noggins in too to help with that.

    So, a pain, but easier then pulling it down, making a hell of mess and starting again.

    I can now add a taped membrane and new plasterboard below to make it a) airtight (I've made a lot of holes in the existing ceiling now) and b) smoother and flatter, and not covered in artex(!).

    And I see that long plasterboard screws are easy to come by (screwfix).
    • CommentAuthorthe souter
    • CommentTimeSep 22nd 2016
    Wallpaper steamer does a fair job of making p/b malleable, dependent on paint sheen. I like the Piher board props- they can take up to 450kg, allegedly. Broken a couple of the cheapy one-handed jobs, cranking up 12.5mm board...
Add your comments

    Username Password
  • Format comments as
The Ecobuilding Buzz
Site Map    |   Home    |   View Cart    |   Pressroom   |   Business   |   Links   

© Green Building Press