ICF window details - Be VERY careful

[magnethead]

Hi There,

I just wanted to share my experiences with one of the biggest stressors for me on the self build, leaking windows - I had 3 of them  and it drove me mad. I'm here to share the experience and ask opinions on potential fixes...First of all I didn't want moustaches on my windows like this:

 

 

I can moan about the detail but in fairness......At least it's watertight

 

 

Here are my leaking windows, the Stone window/Doors have a different detail which is working perfect(thank God, don't fancy ripping off stonework)

You can see I jumped to the conclusion that something was wrong with the window because the only leaking windows were the windows with a fixed glass panel below an opening window..there is a more complex drainage system in these windows (Aluclad-PVC) ... Anyway after so many tests, it turns out it was the sill after all and you can see there is no DPC on the sills either below(It was cut short to allow the sills be stuck in place).

 

 

 

 

you can see the window on the right was ripped out last Month in an effort to address these leaks. (DPC sill in at the moment)

 

This is the install effort unfortunately I trusted the window installers who said once the DPC was past the concrete core, Everything was good (sweet Jesus) and I didn't know any better

 

 

Sill was CT1 to the window support....That actually was fine and watertight as I later found out.

 

 

Here is the final install:

 

 

 

I extended the window side drip edge because the window company did not manufacture the sills the way I had asked...I guess they were going for the mustache look?

Also they didn't know anything about drip edges under the main sill either? So I bent little strips of zinc and powder coated them and stuck them to the Sill.

 

 

 

Here's a really bad front profile of the sill, the edge of the sill is actually bent around in a C shape up until my little zinc add on above.

The leak is coming in on the seam where the render comes down onto the narrow little bit of aluminum. It was maybe 6mm-8mm  wide. All of the other windows seem to be unaffected

 

 

here's some of the water leaking in under the concrete cold joint the floor makes before the second Floor walls.

 

 

 

 

 

and here's some lovely salt lines on the head of the opening below the leaky windows  (about 1.5 years of leaking)

 

 

 

 

 

I never respected that ICF was like a sponge for water, I should have sealed up the foam before the sill was put in

 

That product mentioned by @Russell griffiths  Illbruck 295 is absolutely great stuff, super sticky and seem quite durable too.

 

 

 

[jack]

That sounds hideous. Thank very much for sharing - this will really help others.

[ToughButterCup]

Thank you for the time and effort to write this post , @magnethead.

It makes a huge difference when, without prompting, members post proactively about issues that they face. It gives others courage to do the same. It adds significantly to the value of this site , too. 

 

Now, would ya' come and fix mine please? ?

PS, nice looking house.

Edited March 29, 2021 by ToughButterCup

[Chanmenie]

The sill overhang looks short, are they same on the stone clad windows.

Probably has no affect on the leaking but it’s possibly what’s causing the moustache 

[magnethead]

Cheers @ToughButterCup,

sorry about the delay, fitting all my door handles the last few days. I'm in awe at this site,  It's provided with me so much useful information, from when I was back throwing drawings together for the council,  most of my first floors are poured concrete but a good section is rafters, and a guy suggested dropping them by 40cm which I did, gave me a lot more room on the lower end the Monopitch Roof. 

 

Just to spell it out about the Above, in case someone like me comes along here, the DPC should absolutely come out under your sill, then the render guys render up to it, and it's cut clean with the sill after that!! definitely  not cut back inside the insulation.

 

I was trying everything to stop this, leak, firing sealant into every little space. I wasted so much time on this.

 

 

 

 

 

and in the end, this big dirty blob of silicone is what proved the leak was coming in the side of the reveal where it meets the sill

 

 

 

[magnethead]

On ‎29‎/‎03‎/‎2021 at 16:59, Chanmenie said:

The sill overhang looks short, are they same on the stone clad windows.

Probably has no affect on the leaking but it’s possibly what’s causing the moustache 

 

The sill at the start is not my house, it was just an example of what happened after 6 years of life without the right detail. you are right it has next to no overhang, about 1c0mm, mine overhang a little about 40mm but not much

Edited March 31, 2021 by magnethead

[Moonshine]

21 minutes ago, magnethead said:

in case someone like me comes along here, the DPC should absolutely come out under your sill, then the render guys render up to it, and it's cut clean with the sill after that!! definitely  not cut back inside the insulation.

 

is this unique to ICF or all masonry builds?

[Bramco]

On 29/03/2021 at 11:12, magnethead said:

First of all I didn't want moustaches on my windows like this:

 

Looks awful - and I know it's not yours but anyone that does suffer from algae like this on render then try MMC-pro, it works a treat.  Obvs make sure if you can that you get the cill design right in the first place so it doesn't happen

 

Simon

[FM2015]

Problems befall all builds but water ingress is potentially the most damaging and difficult to solve.

 

With ICFs as well, it is a perfect storm of poor detailing and poor quality installation.  And the solutions tabled by some brands are incredible.  One would say don't use a check reveal and use illbruk's tapes adding up to £200 per window, plus ICF installer labour (wasn't aware we fit windows) plus your window and their fitting.  And it still isn't bomb proof.

 

I'd guess you are fairly exposed where you are, with driven rain?  Leaks worse in certain direction?

 

I'm in a similar position with next to nothing between me and Brazil.  We might be SW England but that just means it's warmer when the rain is horizontal.  

We live in an ICF with uPVC windows and slate sills, a combination that often results in leadwork, illbruk's million pound tapes or leaks.  

 

Totally not necessary. Don't have anything other than physical doglegs and silicone.  No leaks either.

 

Well formed check reveals, cills which extend left and right and a sealant applied to frame before fitting.  Cement board on the reveals has become a given down here because the renderers got fed up with people not being able to make a nice opening.  The advantage is another physical dog leg for the weather to circumvent.  Otherwise, render to a stopbead, silicone the stopbead/window join and happy days.

 

Low cost extras: DPM under cill, forming concrete to shed water outwards, over width cills.

 

It might sound like you're doing a fair portion of the window fitters job but down here they're on £50/window and really don't care that much.  Understandably.

 

In your case, would it be possible to remove the cills and replace with wider ones?  They shouldn't be fixed to the window.

Coincidentally, that's often the number one cause of leaky windows in my ICF experience: low cost windows, fitted averagely, then screwed down through cill.  Window leaks then funnels water straight into the wall.

 

Find an old house with wooden windows, chances are, if the frame is sound, the window doesn't leak.  No tapes, no lead, no silicone.  Just decent geometry and quality workmanship.  More than one way to skin a cat too!

 

 

[SteamyTea]

I saw on here (or on the predecessor) that some well insulated places are attracting mould onto the exterior because the wall is now colder.  I have never seen any real research into it, but like the idea.

There is a set of relatively new buildings down here that after 2 years looked dreadful because of exterior mould on the East and North sides.

[FM2015]

12 hours ago, SteamyTea said:

I saw on here (or on the predecessor) that some well insulated places are attracting mould onto the exterior because the wall is now colder.  I have never seen any real research into it, but like the idea.

There is a set of relatively new buildings down here that after 2 years looked dreadful because of exterior mould on the East and North sides.

It could be that actually it's warmer.  Doesn't moss grow on the south side of trees?

[SteamyTea]

44 minutes ago, FM2015 said:

Doesn't moss grow on the south side of trees

https://www.woodlandtrust.org.uk/blog/2020/01/moss-and-trees/

[FM2015]

57 minutes ago, SteamyTea said:

https://www.woodlandtrust.org.uk/blog/2020/01/moss-and-trees/

Ha, been a while since I was a boy scout? and was better at tying knots!

 

I've seen reports on some builds that show thermal inefficiency, ie the outside warming up or being warmed from the inside, allowing some moulds to grow.  On all sorts of builds.  I've seen it on ICF where expanding foam has been poorly applied to make good a surface prior to render.  The EPS and spray foam have different thermal properties and you can see where the foam is due to the darkening of the render due to mould/lichen type things.

 

 

[Nick Laslett]

@magnethead Thank you for making this post. It will prove very helpful when I come to fit my windows.

[Babak]

Hi I recognise those ICF blocks from TH! I have also used TH on mine. The roofers are almost done (tiling the roof panels installed by the same company) and renderers will come afterwards and then the windows.

 

I know the TH technical manual states you must have the dpc all the way to below the cill and into the EPS at the sides and render and then cut, but my window suppliers have their own ideas and say that is not necessary with (aluminium) cills. But they do insist that rendering must be done first, so they can seal the window frames against the render (I am using aluclad wood by Rationel).

 

 

Thank you for sharing - looks like I have only a few weeks to do research and make any necessary changes. 

Edited June 27, 2022 by Babak

[Russell griffiths]

i did this to all windows and doors. 

[Nick Laslett]

11 hours ago, Babak said:

Hi I recognise those ICF blocks from TH! I have also used TH on mine. The roofers are almost done (tiling the roof panels installed by the same company) and renderers will come afterwards and then the windows.

 

I know the TH technical manual states you must have the dpc all the way to below the cill and into the EPS at the sides and render and then cut, but my window suppliers have their own ideas and say that is not necessary with (aluminium) cills. But they do insist that rendering must be done first, so they can seal the window frames against the render (I am using aluclad wood by Rationel).

 

 

Thank you for sharing - looks like I have only a few weeks to do research and make any necessary changes. 

We had the rendering done after the windows were fitted. Our door fitters had the exact opposite view that the render would provide the weather tight seal and be done after the door fitting. They also felt that aluminium cills did not need the same dpc detail as the TH manual. 
 

Having the render done first may have a lot of advantages. My inexperience might be showing here, but I actually thought the windows had to be in before you could render, I never even considered that it could be done first. We did the same as Russell with the windows and put down the liquid dpc. 
 

We fitted all our windows. We used window straps, Illbruck tape. Drilling holes in TH ICF is tricky due to the depth and because you are drilling blind into 75mm of EPS first and then there is the issue with the embedded rebar. I managed to snap one masonry drill bit as it fused on the rebar. 
 

Do you have the check reveal detail on the window openings? The door fitters cut this off for the door install. But I kept them for the windows. 
 

The window, cill and check reveal detail is very tricky as indicated by the original posts in this thread. 
 

 

[Babak]

On 28/06/2022 at 09:34, Nick Laslett said:

We had the rendering done after the windows were fitted. Our door fitters had the exact opposite view that the render would provide the weather tight seal and be done after the door fitting. They also felt that aluminium cills did not need the same dpc detail as the TH manual. 
 

Having the render done first may have a lot of advantages. My inexperience might be showing here, but I actually thought the windows had to be in before you could render, I never even considered that it could be done first. We did the same as Russell with the windows and put down the liquid dpc. 
 

We fitted all our windows. We used window straps, Illbruck tape. Drilling holes in TH ICF is tricky due to the depth and because you are drilling blind into 75mm of EPS first and then there is the issue with the embedded rebar. I managed to snap one masonry drill bit as it fused on the rebar. 
 

Do you have the check reveal detail on the window openings? The door fitters cut this off for the door install. But I kept them for the windows. 
 

The window, cill and check reveal detail is very tricky as indicated by the original posts in this thread. 
 

 

 

Yes its odd how different installers (and manufacturers) have such differing ideas about what should be best practice. My Windows and doors (Rationel) are also designed to rest against check reveals which I guess is why they insist on having the render done first - so they can pressure seal against those extra lips on installation. But in my case I had to remove the check reveals that come with TH. At 2.5cm plus the 8mm of render they would have been too wide for the frame to sit against and still have enough frame left between the sash and the external opening. Plus my frames would sit a little further forward so the TH lips would have been in the wrong place.

 

I am a little worried about the DPC. I think the order of things as they will happen in my case will be 1- Render all the way up to the opening maybe slightly lower, 2- put DPC/DPM on reveal base and use CT-1 or similar to seal against the render 3-Fix cill  4 - Install windows. Just keeping my fingers crossed that following Rationel requirements will at provide an installation assurance.

 

The cill will be cut to go round the reveal (like normal installations) rather than into the polystyrene as suggested by TH. But if I am right, the cill was not the problem above, it was the lack of full DPC/DPM all the way below the cill?

 

Not sure if it helps anyone else, but below is a hand drawn detail of how it should work in my case, except for the DPM and cill detail which will be slightly different (credit to my XXX for sharing properly drawn originals from elsewhere!). The cill will not turn back onto the render to close the air gap.

 

What is Illbrook 295? I can find Illbrook, but not the 295. Is it tape or silicone type?

 

 

 

 

[Firsttimer]

On 28/06/2022 at 08:57, Russell griffiths said:

i did this to all windows and doors. 

What product did you use @Russell griffiths ?

[Russell griffiths]

40 minutes ago, Firsttimer said:

What product did you use @Russell griffiths ?

Triton TT gas and water liquid membrane. 

[Firsttimer]

I'm half tempted to paint all of our walls with a liquid membrane. 

 

I do wonder about cracks in concrete and water getting into the core through the joins in the EPS blocks.

 

We will be going with a black cladding rainscreen and if the cladding ever split etc then we would see black, rather than the grey EPS.

 

 

 

 

 

 

[Russell griffiths]

On 05/09/2024 at 22:07, Firsttimer said:

I'm half tempted to paint all of our walls with a liquid membrane. 

 

I do wonder about cracks in concrete and water getting into the core through the joins in the EPS blocks.

 

We will be going with a black cladding rainscreen and if the cladding ever split etc then we would see black, rather than the grey EPS.

 

 

 

 

 

 

If I was to build mine again I would use a thin render base coat on the entire house, under the cladding and on all the window reveals before fitting windows and cladding.