New-build recently completed. Fully plastered (skim on pl'bd). Now occupied but quite 'moist', still (humidity figures N/K). Householders noticed condensation on frame of (2G) alu sliding door/windows with thermal break. Stated Ug around 1.2.

They write:

'' internal air temp 22 deg C, GF lounge 2 pane slider, cill internal – 14.5 deg at same time as cill external was 10.4 deg C. The vertical in the middle of the window on the inside slider (ie no direct contact with the outside world except for its interlock with its outside mate) was 15.5 deg c midway up ie 1.5m above floor level, this gets warmer the higher one measures it.''

I am sure the (probably) high humidity has something to do with it, but the differential between room temp and window frame surface temp seems quite big.

Anyone got any experience of room/wall temp vs frame temp differentials for modern alu windows?

End of main Q

(Background comparison data):

By comparison, in my living room this afternoon:

Room temp is between 19 and 20, depending on which bit of the room you’re measuring.

Frame temp of timber-framed 3G Green Bldg Store windows: 17.9

Ext temp: 3.4

(All degrees C, of course)

My dining room, for contrast:

Room temp 11.9 (Brrrrrrrrrrr…….)

Frame temp of 30-year-old, definitely not thermal-break-equipped alu patio doors: 7.2

Frame temp of 30-year-old timber windows: 10.2

Ext temp: 3.4

Any thoughts gratefully received.

Even at Ug1.2, which ain't bad, the glass performance will be compensating highly for the Al's poor performance.

The super-value 3G windows I usually use, claim Uw1.1, but I bet their 3G glass isn't as high performance as your 2G glass - it needn't be because their solid (non thermal break) wood frames will be insulating better than your thermal-break Al.

So even with thermal break, it's prob right that your Al frames are relatively cold.

... ha ha .. I doubt that they achieve that when installed.
I had a complaint from a client years back; newly plastered refurb, alu-framed windows (c/w thermal break) but fitted with MVHR.
So much condensation running down the frames, it was staining and damaging the lovely oak window boards.
The temp differential across these frames was minimal despite the thermal-break, forming massive cold-bridges.

Good luck

Have you seen how the thermal break is achieved? It's a couple of strips of plastic embedded in grooves that hold together two alu extrusions. It's not as though the frame is a kingspan sandwich, or filled with any foam etc

I wouldn't have expected a lot of condensation on a surface that was 15 degrees.. RH must be quite high?

Just watch, it'll turn out that:
22 was the temp they'd set on the thermostat, the air wasn't there yet
They'd been drying washing all day on an adjacent rad, just made 3 cups of tea and were actively steaming some veg at the time the measure was done
They'd had them open for 10 mins immediately before
Their MVHR commissioning skipped a vent/is wonky/isn't done/unit doesn't exist and windows incorrectly have no trickle vents

Etc


Not that I expect alu windows to be great in any regard but the plastic strips should at least mean that the frame isn't hugely worse than the glazing. I do often think though that there should be some PIR in a frame somewhere, plenty of places to sneak it in, including a thin layer of it under a powder coated alu veneer that forms the aesthetic face of the profile. Such is the price we pay for wanting massive sliding expanses of glass that "connect the inside and outside spaces in a seamless torrent of archi-jargonal bullshit"

They didn't take a huge numbe of measurements, would have been nice to know the internal and external spot data for several point s on the frame. Your window frames in your house dropped nearly 50 percent of the temp, theirs dropped a third

I'd install some curtains (I'm going to.. My house has 6 sets of bi folding doors between 3 and 4 metres wide. I'm not so precious about looks that I'm prepared to have all my heat fly out of some fancy glazing), try and get the temp gradient to fall to dew point across them instead, at least they'll absorb it and release the next day.. But do check for a discrepancy between moisture generation by human activity plus fabric versus ventilation effectiveness?

Posted By: cjardHave you seen how the thermal break is achieved? It's a couple of strips of plastic embedded in grooves that hold together two alu extrusions. It's not as though the frame is a kingspan sandwich, or filled with any foam etc

Oh right, that explains it. A sandwich is exactly what I was expecting.

Posted By: cjardIs this sentence free from typos?

Yes - it's possible, but the 2G's extra measures like super-coatings may make it expensive compared to an easier 3G solution.

cjard: ''Have you seen how the thermal break is achieved? It's a couple of strips of plastic embedded in grooves that hold together two alu extrusions. It's not as though the frame is a kingspan sandwich, or filled with any foam etc''

I haven't actually seen a sample of the frame and extrusion in this case, but I have been sent the spec for the (fibre-reinforced polyamide) extrusion, and it seems to be as you suggest. A hollow, foam-filled section wold be nice, but you still need the 'break', and then effectively you are into semi-structural insulation.

I suspect that the frame and house generally was probably colder and more moist when the condensation was present, but that info must have been imparted in a phone-call, as I cannot find an e-mail ref to the condensation.

Seems odd to use aluminium (apart from it's poor enviro cred.) for windows unless well broken, due to it's conductive properties. Power sanding some aluminium trim today and with regular dousing in a mugful of water, had a nice hot cuppa in a few minutes...
Simon, how are you getting on with your GRP windows? Think you had some teething trouble- paint scratches, etc? Your frame temps. are very impressive but understandably low, given that pultruded GRP is used as the thermal break material by alu and timber frame manufacturers.