Russell griffiths Posted August 5, 2019 Share Posted August 5, 2019 Evening all. So fitting windows in a icf wall. My cill area is made up using the cavity closer system from the icf manufacturer (nudura) so I end up with a concrete core and 50mm of eps on top which closes the cavity and forms a no cold bridge type of design, super dooper however im concerned over the weight of the windows sitting down onto this eps insulation, will they sink over time?? im thinking I need something to spread the load over the eps, something like a cement board, or even a sheet of upvc or something, I have considered removing the closer and replacing it with a higher density xps type insulation. Please see pic. 1 Link to comment Share on other sites More sharing options...
jack Posted August 5, 2019 Share Posted August 5, 2019 What about cutting out a narrow strip along the line of the window and replacing it with something denser and more stable sitting straight onto the concrete? Something like a GRP box section or I-beam, or some laminated strips of concrete board? That'd minimise thermal bridging, although as you say, XPS might be a better shout on this point. What does the manufacturer say about long term compression? 1 Link to comment Share on other sites More sharing options...
Stones Posted August 5, 2019 Share Posted August 5, 2019 Our window openings / cavity closers were formed with timber. Yes, a cold bridge, but in the grand scheme of things didn't seem a detail worth obsessing about - provided an easy means for fixing windows. I'm sure it has a bit of an impact on our heating requirement, but at £200 a year for heating in our windswept location, I'm not really that worried. 1 Link to comment Share on other sites More sharing options...
ToughButterCup Posted August 5, 2019 Share Posted August 5, 2019 Dont worry man, yer overthinking it. You have no idea how much I enjoyed writing that. No idea. 1 Link to comment Share on other sites More sharing options...
willbish Posted August 5, 2019 Share Posted August 5, 2019 I've got same ICF cavity closer set up as you although in a different colour. I plan to install windows in an 18mm ply box, primarily to set the windows a bit closer to the outside as I've got 200mm outer EPS. If fixed on 4 sides through to concrete core I don't see the windows dropping. 2 Link to comment Share on other sites More sharing options...
Conor Posted August 6, 2019 Share Posted August 6, 2019 Won't the windows be installed with straps attached to the core that will take the majority of the load? What are you planning for sills? I'll be doing the same in about 6months time. Link to comment Share on other sites More sharing options...
Russell griffiths Posted August 6, 2019 Author Share Posted August 6, 2019 1 hour ago, Conor said: Won't the windows be installed with straps attached to the core that will take the majority of the load? What are you planning for sills? I'll be doing the same in about 6months time. They will be attached to straps, but I cannot see how a strap attached at 90 degrees to the load stops the load going downwards, yes the straps hold the windows in place, but a couple of hundred kilos of glass must need support from underneath ???? meeting with a couple of window suppliers this week, I will ask them. Link to comment Share on other sites More sharing options...
Jeremy Harris Posted August 6, 2019 Share Posted August 6, 2019 15 minutes ago, Russell griffiths said: They will be attached to straps, but I cannot see how a strap attached at 90 degrees to the load stops the load going downwards, yes the straps hold the windows in place, but a couple of hundred kilos of glass must need support from underneath ???? meeting with a couple of window suppliers this week, I will ask them. Just work out the compressive load on the insulation by dividing the weight of the window with the supported area under the cill. For example, if the window weighs 100kg and has a support area under the cill of 2m x 0.1m, then the compressive load is 500kgf/m² (100kg / (2m x 0.1m)). Converting that to units of force (Newtons) gives a force per unit area of about 4.9kN/m². EPS 300 (at 1% compression) is rated for 100 kN/m², so would be overkill. Even EPS 100 (rated at 45 kN/m² at 1%) is massively stronger than needed. Check what Nudara use (I doubt it's going to be less than EPS100) and then do a quick calculation to see how things look. (To convert from kg/m² to kN/m² just multiply by 0.00981) 2 Link to comment Share on other sites More sharing options...
Adam2 Posted August 6, 2019 Share Posted August 6, 2019 Does your Nudura supplier have a recommendation? Beyond selling EPS closures :-) I'm thinking to go with wood framework in place of EPS for anything > [a loading TBD]. Certainly would be concerned about my 2.8m high 3G sliding doors on EPS given the calcs in the earlier post so very interested. I think I remember an earlier thread where the recommendation was to mount the windows over the outer edge of EPS (on a support) to reduce thermal bridge, that feels like a lot of work for potentially not much incremental gain - for me at least, am sure is appropriate for some people/situations. Link to comment Share on other sites More sharing options...
Adam2 Posted August 6, 2019 Share Posted August 6, 2019 Ahh thanks @JSHarris most helpful for me also. Link to comment Share on other sites More sharing options...
Russell griffiths Posted August 6, 2019 Author Share Posted August 6, 2019 @Adam2 I plan to support my doors on marmox blocks, I would not even consider using wood under your doors. I was just a bit concerned when a window quote came in and it included weight of the windows, I have 2 that are around 400kg a piece. Link to comment Share on other sites More sharing options...
Jeremy Harris Posted August 6, 2019 Share Posted August 6, 2019 3 minutes ago, Russell griffiths said: @Adam2 I plan to support my doors on marmox blocks, I would not even consider using wood under your doors. I was just a bit concerned when a window quote came in and it included weight of the windows, I have 2 that are around 400kg a piece. What size are the 400kg windows? The weight isn't the real concern, it's the pressure exerted on the support area that determines what's needed. If the pressure's too high for the normal max working stress of the material then the area that's loaded needs to be increased to reduce that pressure. A bit of timber can do that, if need be, but best to work out the pressure to see if that's really needed. Our whole house rests on EPS - there's nothing else supporting it at all. 1 Link to comment Share on other sites More sharing options...
Russell griffiths Posted August 6, 2019 Author Share Posted August 6, 2019 Frame width is 4200mm @JSHarris i was going to do the sums to tonight, and ask the window company on Friday. Link to comment Share on other sites More sharing options...
Jeremy Harris Posted August 6, 2019 Share Posted August 6, 2019 5 minutes ago, Russell griffiths said: Frame width is 4200mm @JSHarris i was going to do the sums to tonight, and ask the window company on Friday. OK, assuming that the window bears on a strip that's 100mm wide at the base, then the pressure exerted by that weight and width will be ~9.35 kN/m². A bit of EPS100, for 1% compression, will take about 45 kN/m², And I doubt very much if Nudara is less than EPS100. Doesn't look as if there's any problem in just resting the window directly on the EPS to me. 1 Link to comment Share on other sites More sharing options...
Russell griffiths Posted August 6, 2019 Author Share Posted August 6, 2019 You really are top shelf @JSHarris a proper legend. ???? Link to comment Share on other sites More sharing options...
andyscotland Posted August 6, 2019 Share Posted August 6, 2019 1 hour ago, Russell griffiths said: You really are top shelf @JSHarris a proper legend. ???? Seconded. I've been trying to work out something similar and my school physics kept getting me almost there but not quite... Really helpful to see your worked example! Link to comment Share on other sites More sharing options...
SteamyTea Posted August 6, 2019 Share Posted August 6, 2019 (edited) Mass [kg] is the amount of stuff in a material, it is not the weight that is affected by gravity. Force is mass times acceleration. The unit is the newton [N] Area [m2] is what it is, the length times the width, or pi.r2 or the integral of a curve, which is just the area under a line on a chart. So taking a mass of 1 kg, and acted on by Earth gravity, 9.81 m.s-2 over an area of 1 m2 1 [kg] X 9.81 [m.s-2] / l [m2] = 9.81 N/m2 So the 400 kg window sitting on a strip 4.2 m long and 0.1 m wide: 400 [kg] X 9.81 [m.s-2] / (4.2 [m] X 0.1 [m]) = 8743 N/m2 8743 [N/m2] /1000 = 8.743 kN/m2 N/m2 is often written as N.m-2 and is a pressure, in derived SI units, pressure is also known as a pascal [Pa]. 1 N.m-2 = 1 Pa With a bit more arithmetic trickery, it can also be expressed as 1 J.m-3 which is energy density. For more about the pascal: https://en.wikipedia.org/wiki/Pascal_(unit) Usual disclaimer, it is late and I have had another record breaking night feeding people. 10 hours ago, JSHarris said: Doesn't look as if there's any problem in just resting the window directly on the EPS to me. Is EPS a true solid, or can it flow over time as the air inside it is compressible? Edited August 6, 2019 by SteamyTea 1 Link to comment Share on other sites More sharing options...
Jeremy Harris Posted August 7, 2019 Share Posted August 7, 2019 7 hours ago, SteamyTea said: 400 [kg] X 9.81 [m.s-2] / (4.2 [m] X 0.1 [m]) = 8743 N/m2 8743 [N/m2] /1000 = 8.743 kN/m2 I think there's an arithmetic error here: 400 x 9.81 = 3924 N 4.2 x 0.1 = 0.42m² 3924 / 0.42 = 9343 N/m² = 9.343 kN/m² (I rounded the result up to 9.35 kN to err on the side of caution previously) 7 hours ago, SteamyTea said: Is EPS a true solid, or can it flow over time as the air inside it is compressible? Given that the whole mass of our house is sitting on an EPS foundation, then I hope so! Seems well proven as a foundation material, as it's been used like this for a few decades. When I was looking into it I found examples of basements in Germany that had been built 30+ years ago with load-bearing EPS underneath them. Link to comment Share on other sites More sharing options...
SteamyTea Posted August 7, 2019 Share Posted August 7, 2019 (edited) 7 minutes ago, JSHarris said: 3924 / 0.42 = 9343 N/m² = 9.343 kN/m² Whoops, it was late. I got G wrong, had it as 9.18. 7 minutes ago, JSHarris said: Seems well proven as a foundation material, as it's been used like this for a few decades That should be OK then. I seem to remember putting something quite light onto some polystyrene and it sunk into it, pay have been EXP though. Edited August 7, 2019 by SteamyTea Link to comment Share on other sites More sharing options...
Adam2 Posted September 5, 2020 Share Posted September 5, 2020 On 06/08/2019 at 12:23, Russell griffiths said: @Adam2 I plan to support my doors on marmox blocks, I would not even consider using wood under your doors. I was just a bit concerned when a window quote came in and it included weight of the windows, I have 2 that are around 400kg a piece. Wondered what you ended up doing with your doors / heavy windows - just kept with Nudura eps closures or did you go with Marmox in the end? Link to comment Share on other sites More sharing options...
Russell griffiths Posted September 5, 2020 Author Share Posted September 5, 2020 under my sliders 460kg I used strips of xps500 cut to the width of the wall, the door sits directly on this, rock solid stuff £70 a pack has done one slider and two doors. Under the windows I just fitted them straight on top of the icf cavity closers, after Jeremy’s mathematics it looks like there is t that much load, my big windows are 240kg. 1 1 Link to comment Share on other sites More sharing options...
Adam2 Posted September 6, 2020 Share Posted September 6, 2020 (edited) Great, did you find out what type of eps Nudura ? I couldn't see it anywhere but well ask next week. I guess for the small amount needed xps500 is a low cost option. Am waiting for weight info on my sliders, could be a lot when 3 triple glazed units are all slid to one side! Edited September 6, 2020 by Adam2 Link to comment Share on other sites More sharing options...
Russell griffiths Posted September 6, 2020 Author Share Posted September 6, 2020 its All about force over area isn’t it. If you put your best high heels on and stand on that eps you will make a big hole in it, but if you stand on a chunk of 4x2 your weight will not have an impact. I also slid a 6mm cement board on top of the XPS, forgot to mention that, just to help with any point loads that the door might have. Link to comment Share on other sites More sharing options...
craig Posted September 6, 2020 Share Posted September 6, 2020 18mm marine ply all around, that’s all you’ll need. Link to comment Share on other sites More sharing options...
willbish Posted September 6, 2020 Share Posted September 6, 2020 7 minutes ago, craig said: 18mm marine ply all around, that’s all you’ll need. This is what I've used but if I was doing it again I think I'd use Storbord or similar plastic product. Very similar price to a decent ply board, machines nearly as well and will never rot. Link to comment Share on other sites More sharing options...
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