Replacement window & Sill

Discussion in 'Builders' Talk' started by oops, Oct 4, 2013.

  1. Sean_ork

    Sean_ork Screwfix Select

    here's a pic showing the base of one of my own windows, which I haven't yet fitted ........ and the positioning of the stub cill, in the hope it might help the OP

    this is designed to sit on a stone cill, as shown in the previous detail dwgs

    the drain point can be seen as a oval shaped slice in the frame (to the right of the orange sticker)

    as the OPs new window DOESN'T have front facing vents, so WILL have a bottom drain, it needs to be sat on a stub cill, which allows any water passing the seals, or condensate that builds up with the extrusions, to drain out and be directed over the top of the stub cill, onto a stone/conc cill, or other suitable surface

    you could bodge the installation, without a stub cill, by trying to seal just at the back of the frame, or seal such that the drain isn't blocked, in the hope that you've sealed it well enough to stop driven rain - but that's not how windows without a front facing drain are intended to be fitted

    View attachment 4710

    Attached Files:

    Last edited: Oct 17, 2013
  2. Mr. Handyandy

    Mr. Handyandy Screwfix Select

    That is a good picture with good detail.

    Now let's see one similar with a concrete sill in place of the upvc one.

    Note the profile at the bottom of the window. Note how the drain holes would(on a concrete sill) fall onto the sloping part of the concrete sill.

    And yes, a simple line of sealant on the sill before fitting behind the drain area, AND a full seal at both ends is essential.

    Manufactuirers/archies/experts don't tell you that either.

    What would happen to any rain that does get blown under the window(plastic or concrete sill)?

    It would go between window and sill and where would it most likely escape? Run and over the ends of the sill into the cavity. FACT. Where is the experts advice on that?

    You seem to think they know everyting. They don't.

    Mr. HandyAndy - Really
  3. Sean_ork

    Sean_ork Screwfix Select

    did you ever wonder why window makers, architects or ''experts'' wouldn't advise anyone to do what you've recommended ?
  4. Mr. Handyandy

    Mr. Handyandy Screwfix Select

    No I never did wonder. But if I did, I would tell you it's because they are sh|te.

    Book readers. Same as you. Can't think outside the box and apply common sense.

    Mr. HandyAndy - Really
  5. Sean_ork

    Sean_ork Screwfix Select

    well that's your opinion, I think Norman would disagree (but what does he know)

    anyways, I hope the OP now has a little more understanding of how a window should be fitted, even if you don't :rolleyes:
  6. Mr. Handyandy

    Mr. Handyandy Screwfix Select

    All i will add is that if the OP leaves his window as YOU suggest, it will cause problems within months.
    Drain holes are there for a very good reason. Telling someone to leave them sealed up, is incompetent to say the least. Be off with your attitude. You are wrong
  7. Sean_ork

    Sean_ork Screwfix Select

    handyman .........
  8. Know this was couple of weeks back but only just flicking through forum, below photo of UPVC frame direct onto existing cill with front facing drainage (bottom right) and cover caps needed as there is no UPVC cill to drain onto (stub or otherwise), in my opinion this looks best and as Handyandy states the existing cill is a "cill" therefore works as a "cill"
    BUT ....

    if you have an existing cill more like this as per earlier post...
    . stub cill.PNG
    then having a stub cill will remove the need for horrible thick layer of sealant below frame that would be on show as the stub cill will conceal it ( I have seen this).

    Attached Files:

  9. Mr. Handyandy

    Mr. Handyandy Screwfix Select

    'horrible thick layer of sealant below frame'

    Agreed, but even then, there is no need for the big fat seal. All that is needed is a smaller seal where the frame meet the sill/tile up underneath, and if you work the illustration down, you will see that having the frame on the sill will leave less gap underneath than a stub sill would! :)

    Mr. HandyAndy - Really
  10. Agreed but would look a bit of a miss match if front of frame appeared to have gap under it, don't get me wrong I would rather no stub cill when existing concrete, tile or other cill is on situ but they can ease a potential problem and lets be honest most firms want to install UPVC casements the easiest possible way and not always the way that looks best.

    I have got some good images of frames on concrete cills, good and bad, will dig them out.
  11. phmode

    phmode New Member

    Sean, thank you for posting the pic of your frame and stub cill.

    I have exactly this arrangement with my existing windows sitting on an 85mm stub cill which in turn sits on a stone/cement cill. My drain holes are exactly the same as the ones in your photo.

    The house is 11 years old, faces South and is exposed to high winds and driven rain. I have had many instances of damp above the inner cills with the plasterwork showing signs of damp from water filling the frames and weeping out and wetting the inner cills and thence the plaster.

    I discovered that my frame drains were badly cut/whiskered/blocked by bugs etc. I have cleaned them out and drilled VERY large holes to ensure no recurrence of water filling the fixed light frame and weeping out onto the inner cill causing damp in the reveals. This has proved very effective.

    However, I still have damp in the reveals above the inner cills when there is wind driven rain like now. This is NOT from water coming in via the frames and sitting on the inner cill.

    Interestingly, my window frame has a 1-2mm gap between it and the stub cill and I can run a steel rule between the two for the whole width of the window apart from a packing piece in the centre and to a depth of 55mm.

    So, my question is, what stops wind-driven rain from wicking between the frame and the stub cill, being drawn along the cill to the ends and then soaking into the plasterwork? I have no idea what SHOULD stop this from happening and have no idea what my builders did to attempt to prevent it.

    Any and all advice received with gratitude,

  12. Mr. Handyandy

    Mr. Handyandy Screwfix Select

    You shouldn't have a gap like that. All you can do for that(apart from removing it all and refitting it properly) is thoroughly dry in the gap and fill it full(as if to create a whole new floor under the frame and not just seal the front) with silicone(in this case I'd recommend a low modulus) all the way along, but ensuring you don't come out as far as the ventholes(altghough I assume you now have large holes in the front of the frame).

    Really do see some errors in fitting like having screws through frames into sill and those letting water down, and sills not fixed at all. Really can't imagine why yours has a gap AND a packer between sill and frame. Never any need for this-NEVER. It's just not done. Sill should be tight to frame always.

    Mr. HandyAndy - Really
  13. phmode

    phmode New Member

    Many thanks for the rapid response Andy (I assume).

    I have seen reference to the packing pieces in other sites and have never understood the need nor the logic; if the stone cill is true (and it is, brand new concrete imitation stone cill) then the stub cill should sit true and level on it and the frame should sit true and level on the stub cill! The whole thing seems as logical as a chocolate fireguard to me.

    I was very careful when I drilled the holes down and so I merely enlarged the oval holes shown in the above photo from Sean, hence, no holes in the front face of the frame. I have tried to get a silicone gun nozzle in the gap to apply sealant to the gap but it is rather narrow, only about 9mm between the bottom of the front face of the frame and the sloping top surface of the stub cill.

    As an alternative I considered 'caulking' the gap with something like narrow bore silicon or neoprene tubing which I could 'push' into the gap with a putty knife. This might not fill the gap all the way back but would at least stop the ingress of the wind driven rain.

    Oh, and by the way, as soon as you mentioned 'screws down through the frame and into cill' I had a sudden 'deja vu' moment and a quick check revealed that, yup, I have that little feature also. Doncha just lerrrrrve contract builders?

    I'll go away and cogitate the next move but I guess nothing is happening until the tide goes out about April and the gap dries out. I have four windows facing the wind and all need doing. I am tempted to pull all the frames and do the job properly, it isn't like it is rocket science but something tells me I may find more critters under the rocks so maybe I'll let sleeping dogs lie and just 'mind the gap'!

    More anon and many thanks for the advice,

  14. The window frame and cill should be fitted directly to each other with a bead of silcone run on the internal edge when assembling, as mentioned NO spacers should be between frame and cill and if you look at photo posted by Sean the internal edge of cill has a lip on it therefore there should be no way of sliding a ruler in between cill and frame ?!
  15. phmode

    phmode New Member

    Thanks for the response. I agree that it should be fitted directly, but all the windows in my 12 year old house have the windows fitted with spacers between the frame and the stub cill. As such, from the outside, one CAN run a ruler all the way BACK to the upstand you mention, and all the way ACROSS from one side to the other apart from about 20mm in the middle of the frame where the spacer is placed.

    What I am looking for is a workable solution to stop wind-driven rain getting into this gap, hopefully without having to remove all my windows and refit them correctly.

  16. is it possible to work cill loose (remove any sealant, remove or cut screws etc...), remove the spacers and then screw from inside frame into the cill, pulling the cill back up tight to frame, then re seal underside of cilll

    Failing that the only real option is to seal from the internal edge, need to keep that front edge clear for frame draining.
  17. Sean_ork

    Sean_ork Screwfix Select


    confused - first you say there's a 1-2mm gap under the frame - and now there's a spacer ?

    the frame should sit flush on top of the stub cill - a bead of gloop on the rear, just in front of the internal upwards return will stop most wind driven - if it doesn't then perhaps it's time to consider fitting shutters or move to more sheltered lighthouse
    Last edited: Jan 4, 2014
  18. Sean_ork

    Sean_ork Screwfix Select

    can you post a few images
  19. Mr. Handyandy

    Mr. Handyandy Screwfix Select

    What do you mean ' ?', ?

    What don't you understand? Do you think a packer between a frame and sill should be used, leaving a couple of mm gap ?

    Mr. HandyAndy - Really
  20. Sean_ork

    Sean_ork Screwfix Select

    why would you ask that ?

    I've previously posted an image showing the fit between the frame and stub cill - and from my last post


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