Home  5  Books  5  Magazines  5  News  5  GreenPro  5  HelpDesk  5  Your Cart  5  Register  5  Green Living Forum
Not signed in (Sign In)

Categories



 



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.




General: Window detail - light steel frame

Bottom of Page

1 to 24 of 24

  1.  
    • CommentAuthorborpin
    • CommentTimeSep 5th 2012
     
    Looking for some advice on window detail. This has been gone over before but please bear with me :bigsmile:

    Structure is a Light Steel Frame (filled with Icynene) with 120mm PIR on the outside, 50mm cavity then block and render outer. Built in Scotland so we need fire stops and I will rebate the window. Plan is to fit an 18mm ply window box to the LS frame and seal that to the frame before insulating the outside. Then fit the window using straps back to the main steel frame. The key question is where to place the window. I have sketched out 2 possible alternatives. The windows are 90mm 3G max size 1200x1200 so quite heavy I suspect!

    Concerns are thermal bridging and supported weight.

    I have considered insulating the internal reveal with Aerogel.

    Of the 2 alternatives I actually favour the one with the returned blockwork. I have looked at insulated cavity closers, but if I used them it would be outside the ply so would not improve on option 1. There is also a question of the Cill detail for option 1.

    Thoughts?
    •  
      CommentAuthorfostertom
    • CommentTimeSep 5th 2012
     
    From insul POV, the deep-set version - at least the ply box and the end face of the window frame aren't exposed to outside (or cold cavity) air. In the shallower-set version, the inside frame face is no distance at all away from cold air, and only a tiny 'run' of the ply box's and the frame's material acts as a heat-resisting insulator. In both cases, the ply acts as a well-cooled radiator to inside - should be covered on the reveal with hi-grade insulation/plasterboard laminate.

    Even the deep-set version wd be improved if some insulation could separate the ply box's edge and the frame's outer face, from the block & render/outside air.

    Why need straps? - the ply box is ample to mount the window frame unaided.
  3.  
    In general, the best place for the window is the centre of the insulation zone with no cold bridges around it.

    The left hand sketch shows plywood bridging the frame & frame/plywood connected to outer leaf blockwork. The right hand sketch shows plywood/fire stop bridging the frame & frame/plywood/fire stop connected to outer leaf blockwork. So neither is ideal.

    If you're using straps to fix the frames then the plywood box can stop flush with the inner face of the frame; i.e. so it provides a solid air barrier for fixing the straps, insulating plasterboard, etc without causing the cold bridge around the frame.

    If you're using straps to fix the frames all the way back to the steel frame then I'm not sure the plywood box is earning its keep. A sheet of polyethylene can perform the air barrier function with negligilbe cold bridging. A fire resistant cavity closer or cavity sock can provide the insulation continuity.

    Your sketch seems to show a wooden fire stop; is this a fire stop to protect the wooden frame or a wooden fire stop?

    David
    • CommentAuthorborpin
    • CommentTimeSep 5th 2012 edited
     
    Thanks. Reinforced my opinion and thoughts that what I had was not good enough.

    Posted By: fostertomWhy need straps? - the ply box is ample to mount the window frame unaided.
    Concerned that the weight would be too great for just the ply box (1200x1200 window).

    So starting from the left sketch (outside of window level with outside of insulation), move window and ply box inward by say 20mm and affix PIR to the outside of the box and the window then use a stop bead to bridge that gap for the render? How about some Compriband TP600 fixed to the outer edge of the window as it goes in rather than PIR?

    On the question of Compriband TP600 and never seen this sort of tape in action, how quickly does it expand?

    The frame is already made so changing the size of that is not possible. I could reduce the depth of the ply so it just overlaps the window. Any residual gap can be filled when the fixing foam goes in. I think I probably should use a tape as well then.
  5.  
    I wouldn't bother with the blockwork return & instead fit 50mm of PUR/PIR between the front face of the frame & the rear face of the outer leaf. Fix the stop bead to the outer face of the frame & the blockwork reveal & render over.

    Also reduce the depth of ply so it only just overlaps with the window frame; fit PUR/PIR insulation to frame perimeter & foam & tape frame to plywood. If required by fire regulations then fit mineral wool to frame perimeter in place of PUR/PIR.

    David
  6.  
    You could use EPS for the outer reveals for a really good fitting detail and plaster over them.
    If you use rockwool strips as firestop material, they could also insulate the frames.
      Window detail Enniskerry.JPG
      Window Detail Enniskerry 1.JPG
      Insulated Reveals.JPG
    • CommentAuthorWMS
    • CommentTimeSep 6th 2012
     
    Who did you eventually buy your windows from
    • CommentAuthorborpin
    • CommentTimeSep 6th 2012 edited
     
    Still investigating this, but is it just me or is the industry standard method of mounting windows fundamentally flawed? Every type of cavity closer I can find assumes you want to push the window outside the insulated envelope.
    • CommentAuthorborpin
    • CommentTimeSep 6th 2012
     
    Posted By: davidfreeboroughFix the stop bead to the outer face of the frame & the blockwork reveal & render over.
    Any sources for a suitable stop bead. I assume it needs a good depth of mesh to cover the insulation.

    Posted By: davidfreeboroughIf required by fire regulations then fit mineral wool to frame perimeter in place of PUR/PIR.
    I think this may be the solution. Is there any suitable preformed mineral wool product?
  10.  
    There are a number of fire rated cavity closers:

    http://www.cavitytrays.co.uk/closers/view/3/53/1/cavi120-type-v-cavicloser-fire-rated-designation-

    http://www.ybsinsulation.com/products_cavity_typerfire.htm

    http://www.cavalok.com/fire_rated_cavity_closers.html

    Alternatively you can just use a fire rated cavity sock to fill the gap between partial fill insulation & outer leaf:

    http://www.polypipe.com/polypipe/controller?action=TDI-Cavitysock

    http://www.knaufinsulation.co.uk/products/cavity_barriers.aspx

    Most cavity closers are not designed to take window fixings, hence the use of plywood boxes in wide cavity applications where the designer wants to put the window in the insulation zone. There's one exception that I'm aware of, but this may not be well suited to your situation:

    http://www.cavalok.com/cavalok_structural_closer.html

    Hope this helps.

    David
    • CommentAuthordjh
    • CommentTimeSep 7th 2012
     
    Posted By: borpinis it just me or is the industry standard method of mounting windows fundamentally flawed? Every type of cavity closer I can find assumes you want to push the window outside the insulated envelope.

    I think traditionally the concern has been to push the windows out as far as possible to reduce the possibility of rain finding its way in. Industry hasn't yet caught up with changed priorities in some parts of the market.
    • CommentAuthorborpin
    • CommentTimeSep 7th 2012
     
    @davidfreeborough The Cavlok structural closer is the closest I have seen, but even that is really pushing the window out too far.

    I had considered the ybs closer for rebated windows but used in reverse i.e. the closer outside the window then render across it. It still does not feel right and I would be concerned as to how the render copes (traditional roughcast).
    • CommentAuthorborpin
    • CommentTimeSep 7th 2012
     
    @davidfreeborough - any suggestions for stop bead suppliers?
  14.  
    The Cavalok structural closer allows you to put the window where ever you want. Are you concerned about rendering over it?

    There shouldn't be any movement in the Compacfoam insulation, so why not fit the window 50mm back from the inner face of the outer leaf & fix standard render mesh / stop bead to the exposed sections of cavity closer?

    For rendering accessories try:

    http://www.expamet.co.uk/

    http://www.wemico.com/

    David
    • CommentAuthorborpin
    • CommentTimeSep 8th 2012
     
    Posted By: davidfreeboroughThe Cavalok structural closer allows you to put the window where ever you want. Are you concerned about rendering over it?
    Yes I am. There are several cavity closers out there (thermabate for instance) that I could fit in reverse but that would mean rendering over it and that does concern me. It is the differential expansion that I fear will cause cracking. I am using a traditional render (rough cast). The Thermabate type cavity closer has plenty of grooves etc for a reasonably good key but .....

    You added a bit about compacfoam. Are you suggesting that on its own or is it part of the Cavalok system?
    • CommentAuthorborpin
    • CommentTimeSep 8th 2012
     
    Ah Ok, I have found this but it is a bit light on detail and what can be achieved using this material. http://www.cavalok.com/compacfoam.html
    • CommentAuthorTimber
    • CommentTimeSep 8th 2012
     
    Run the details using Therm and see what you get.

    I have found time and time again, that things are not as simple as it might appear. In a previous thread looking at a similar detail but with EWI showed I ran some numbers and it transpired that the best place was almost as far out as possible. This seamed counter intuative, but looking at the heat flux you could see what was happening.

    Not sure where the best place for the window is, but start with it in the centre line of the insulation then move it in and out a bit and see what change that makes. Then improve and refine from there.
    • CommentAuthorborpin
    • CommentTimeSep 8th 2012 edited
     
    Posted By: TimberRun the details using Therm and see what you get.
    Tried Therm before and just could not get started with it at all.
    • CommentAuthorborpin
    • CommentTimeSep 8th 2012
     
    Neither Expamet or Wemico do a wide mesh stop bead. Renderpas do a PVC one with a 40mm wing but that is the largest I have found to date.
    • CommentAuthorborpin
    • CommentTimeSep 8th 2012
     
    Posted By: Viking HouseYou could use EPS for the outer reveals for a really good fitting detail and plaster over them.
    With a traditional render?
    • CommentAuthorTimber
    • CommentTimeSep 8th 2012
     
    Well try again :tongue:
    • CommentAuthorborpin
    • CommentTimeSep 8th 2012
     
    Posted By: TimberWell try againhttp:///newforum/extensions/Vanillacons/smilies/standard/tongue.gif" alt=":tongue:" title=":tongue:" >
    No time - I could not work out how to get started at all when I tried. Suspect I will end up returning the blockwork and using an insulated DPM. Not ideal but better than pushing the window outside the insulation I suspect.
  23.  
    Posted By: borpin With a traditional render?

    External Insulation cement type plaster on the EPS.
    External Insulation fibre glass mesh layer overlapping the blocks.
    More external Insulation cement type plaster applied in a heavy layer.
    Traditional Render over that.
    • CommentAuthorborpin
    • CommentTimeSep 9th 2012
     
    Posted By: Viking House
    Posted By: borpinWith a traditional render?

    External Insulation cement type plaster on the EPS.
    External Insulation fibre glass mesh layer overlapping the blocks.
    More external Insulation cement type plaster applied in a heavy layer.
    Traditional Render over that.
    Interesting idea. I'll have a think....

1 to 24 of 24

  1.  
Add your comments

    Username Password
  • Format comments as
 
Back to Discussions Top of Page
   
The Ecobuilding Buzz
Site Map    |   Home    |   View Cart    |   Pressroom   |   Business   |   Links   
Logout    

© Green Building Press