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With spectacular timing, our window order went in too late to beat the summer factory close down, resulting in a 4 week delay on top of the normal 6 - 8 week delivery time. Better late than never, our windows arrived a fortnight ago, all the way from Poland. Having a passionate hatred of UPVC windows, we specified 3G aluminium clad timber windows. I obtained a few quotes from different manufacturers / suppliers, but in the end, after pushing hard on price, we went with Rationel, (supplied in Scotland via ADW Ltd). Without seeing them in person, it is difficult to appreciate the quality of the windows, but we are absolutely delighted. They appear very well made, so much so that all of the joiners working on our build have so commented, and my builder has switched to Rationel as his supplier of choice. Performance wise, we have a combination of 4-20-4-20-4 and 4-20-4-18-6 triple glazed windows, with U values ranging between 0.7 and 0.9 depending on the size of window and an overall project U value of 0.8. Price wise, including the extra delivery costs relating to our location, we've paid £290 per sq metre for our windows and doors. Fitting the windows took a couple of days. Whilst the majority of the openings in the ICF blockwork had remained true, one or two were slightly out which meant the odd packer here and there to ensure the windows were level and plumb. The windows have all been positioned such that they protrude 20mm beyond the outer face of the ICF block: : and are secured in place internally be metal straps fixed to the window frame and the timber openings: The standard Rationel installation detail is a little odd (as has been experienced by ProDave) in that they want a gap left between the edge of the alu cladding and the window reveal / ingo, so as not to block the drainage channel that forms part of the alu cladding. We deviated from this detail, primarily because neither I nor my builder had any confidence in it. We were both of the view that if left exposed, such a seal was bound to fail within a relatively short period. In fairness, Rationel do say that it is up to the installer to fit the window to suit local conditions. http://www.rationel.co.uk/media/1614084/Installation-Drawings-ALDUS.pdf Rather than using expanding mastic tape (compriband) we are using a Soudal sealant to seal the timber window frame to the timber opening. External insulation is then brought hard up to to the aluminium window cladding. This keeps the drainage channel on the alu cladding open but completely conceals the main line of sealant behind. The window reveals / ingos will be finished with render or timber clad hard up to the alu cladding. In the case of render, a stop bead will be used at the alu cladding junction to ensure a good finish and an effective seal. The window cill which you can see pictured above was sourced independently of Rationel / ADW Ltd. For reasons I cannot quite fathom, Rationel do not supply cills. This is the responsibility of their agents who in the case of ADW Ltd source them and have them painted to match the windows here in the UK. Unfortunately, they were unable to supply me with cills deep enough for me needs, so I had them fabricated and painted by a company in Glasgow - MSP Scotland Ltd. I paid just under £250 for all my cills. Again, we are delighted with the quality - 2mm folded cills, which fit snugly into the preformed cill groove on the underside of the Rationel windows. Two depths of wall insulation have been fitted to our house, 100mm to the section to be timber clad, and 140mm to the section to be rendered. The main reason for restricting extra insulation on the timber clad section to 100mm, was to facilitate the subsequent fixing of battens to carry the timber cladding. To facilitate precision cutting of insulation, a hot wire cutter was used: The external insulation was fixed using a combination of expanding foam and mechanical fixings. Foam was applied to the back of the insulation sheets which were then positioned on the wall. Mechanical fixings (pictured below) were then used to firmly secure the sheets, in the case of the timber clad section (100mm insulation), the long screw and black washer which fixes into the plastic ICF block formers in the core of the block, and in the case of the rendered section (140mm insulation) a plastic type plug drilled into the concrete core of the block. The insulation itself came in different sizes. The 100mm insulation was supplied in interlocking 1200 x 600 mm sheets. The 140mm insulation came in 2400 x 1200mm sheets. Opinion on site was split between the pros and cons of each size with advantages and disadvantages to both. Fewer joins when using bigger sheets, but smaller interlocking sheets were easier to work with. A couple of pictures of how it now looks: All being well, the scaffolding should be removed shortly, ready for the render system to be applied. The joiners have started fitting battens to the section to be timber clad so it's all systems go.