Roof windows

Moggaman

Hi.
I have 9 roof windows in my self build.
I am looking at velux and fakro.
I have asked for prices on triple glazed roof windows .
I am keen to know opinions on whether this is over the top.
What standard of roof windows are going into A2 rated houses these days?.
I suppose I am wondering if going from double to triple is worth it?
Thanks

BryanF

Remind us,

what is the u-value if the triple v double?

And what does the BER require?

Moggaman

BryanF wrote: »

Remind us,

what is the u-value if the triple v double?

And what does the BER require?

BER calls for 1.0 or less for roof windows with thermal flashing. Double glazed would meet that. Just wondering about diminishing returns on going triple glazed .
Also, I note that fakro have an automatic controlled ventilation??.. surely that goes against airtightness theory ?.. although all veluxs have vents which you can open and close, so I suppose they are weak points in the velux

BryanF

Suggest you do a bit more reading into the ventilation add-on. It’s probably not something you want if your going with MvHr for example.

As regards the u-value, personally when I was doing my extension I went with triple 0.8w/m2k, and paid particular attention to thermal continuity. There are no vents or anything unless the unit is opened.

If we take it your walls are ~0.2w/m2k (or better) and your windows are 1w/m2k, you know where the heat loss is going to be and where surface condensation may occur.. At 0.8w/m2k (or better) the internal surface temperature will be better, ensuring avoidance of internal surface condensation. That’s one of the reasons 0.8w/m2k is the minimum acceptable passive house certified window u-value.

Moggaman

BryanF wrote: »

Suggest you do a bit more reading into the ventilation add-on. It’s probably not something you want if your going with MvHr for example.

As regards the u-value, personally when I was doing my extension I went with triple 0.8w/m2k, and paid particular attention to thermal continuity. There are no vents or anything unless the unit is opened.

If we take it your walls are ~0.2w/m2k (or better) and your windows are 1w/m2k, you know where the heat loss is going to be and where surface condensation may occur.. At 0.8w/m2k (or better) the internal surface temperature will be better, ensuring avoidance of internal surface condensation. That’s one of the reasons 0.8w/m2k is the minimum acceptable passive house certified window u-value.

Thanks Bryan . You said on yours there are ‘no vents or anything unless the unit is opened’...do u mean opening the actual window as opposed to cranking open the vent part of the window..?..is it velux can I ask because I was told all velux have vents .?

BryanF

Velux
There is mechanical handle the opens a vent, I do t use it as I have MEV, except in mid summer when the skylights are opened wide to create air flow through the house.

ec_pc

We built A2 rated last year with double glazed Fakro roof windows.