Hi All
Following on from my window suppliers thread I am a little further along the road of sourcing windows having visited a few supplier/manufacturers.

I am now at the stage of having whittled the choice down to a couple of options:

Option 1 - Alu clad passive spec single sash top hung outward opening window employing Spilka's Opus hinge.
This option looks good. In theory the opus hinge is designed specifically for alu clad windows and is concealed allowing for an un broken aluminium profile. The manufacturers have said the hinge will take the weight of the single sash units (1600 x 1400) of around 70kg's (in my enquiry letter with dimensions I stated I ideally wanted single sash providing the weight was within hardware limitations) they are however a trade supplier and I'm a little concerned if the hinge failed over time it's a case of "tough luck!" I should state that 3 other manufacturers were happy to supply single sash units including a domestic supply and install provider.

Option 2 Same spec window as above but using Spilka's classic hinge and with 2 equal sash's.
This supplier was concerned enough by the sash weight that they wouldn't supply single sash. Also when the classic hinge is employed, the cladding is effectively 4 pieces clipped to the frame and there is an opening in the vertical cladding through which the hinge protrudes. No issue for a timber window but my concern is the ingress of insects and air born contamination which will over time create the potential for decay ie a build up of muck in what is a hidden void.

Unfortunately, we visited option which uses the opus hinge first and had nothing to compare the window too however on visiting other suppliers using the classic hinge, the sash felt much lighter to open and turn.
In reality, I'm not sure if this is really much of an issue as we have managed without having to fully reverse windows to clean them (easy enough from outside) and we will probably only ever crack them for ventilation.
I've contacted spilka to query both design loads (max 80 kg's) and whether this takes into account wind load (if so then our 70 - 75kg sash's should be ok probably not if it doesn't) and whether the opus and classic hinges have different leverage ratio's whether that would account for the difference in perceived weight. They haven't come back to me.

Also, I was under the impression that outward opening doors and windows were a more weather tight option as they get pushed against the seals in harsh weather but further investigation has revealed a number of high end manufacturers using inward opening systems with more seals eg internorm. Internorm are out due to to cost but I wondered if one system had meaningful advantages over the other???

Any input or thoughts on the above would be greatly appreciated as it's frying my little brain!

+1 for what PiH said. What matters is the certified airtightness values at high Pa (100 or 75 Pa maybe). The window shouldn't be designed so that external wind pressure matters for its sealing.

Posted By: WillInAberdeenInward opening is common in Scotland where windows legally have to be safe to clean from the inside.

One of the features of the Spilka hinges being discussed is that they allow the window to be reversed so the outside can be cleaned, specifically without removing any plants that happen to be on the windowsill