Oak frame direct glazing

[pudding]

Hey all, 

 

I'm thinking of adding an oak framed orangery type extension to our house, with a flat roof and a large skylight.

 

It would have a dwarf cavity wall, say 3ft high, stone clad to match our house with some form of cavity insulation (full fill PIR trying to keep wall thickness as low as possible?). Then atop this would be the oak frame. Insulating the dwarf wall to good standards wont be hard, but what about an oak framed glazing system. I'm thinking it would be fixed glazing, direct to the frame such as this:-

 

 

I know this isn't going to be the pinnacle in terms on insulation but we'd like oak on view inside and out. I was thinking about improving the above standard detail by replacing the softwood spacer with some form of insulation (PIR strip?) and going triple glazed which would match the rest of our house. Anybody seen this done before or have any better ideas?

 

[Jeremy Harris]

3G would make sense, and I suspect that even then the heat loss through the glazing in a room like this will massively exceed the thermal bridging through the oak posts, so overall I'd not worry about trying to add insulation where the softwood spacer sits.

 

That glass fixing detail seems to work well with oak framed buildings (that are always subject to a bit of movement), from what I've heard, and looks pretty easy to build, too.  An extension that's largely all glazing like this is unlikely to meet building regs in terms of heat loss, anyway, so presumably it's small enough not to need to.  Being able to close it off from the rest of the house with well-insulated doors, when not in use, would seem a wise move, both in winter when it's likely to lose a lot of heat and in summer when it may well tend to get a bit warm (depending on orientation).

[pudding]

Yes that's true about the heat loss through the glass vs through the oak posts, although every little helps, especially if it would add virtually no extra cost.

 

The building i dont imagine would be massively different from our main living area in terms of heat loss. At the mo we've got 2 large 3G sliding doors (2.2m and 3m wide), plus another two 2-2.5m wide windows., so lots of glazing. The new orangery extension wouldnt be vastly different in terms of % glazing i'd guess, but would have the extra heat loss through the roof/skylight. Quick crude sketch here, shaded areas would be oak posts/wall:-

 

 

It would be off the 2.2m wide sliding door from the kitchen which we'd leave in place so easily shut off from the rest of the house if needed, although ideally we like to make the new extension usable all year around.

Edited November 27, 2018 by pudding

[Jeremy Harris]

Good 3G might have a Ug of around 0.5 W/m².K, whereas a building regs minimum specification wall would be 0.18 W/m².K, so very good 3G has a heat loss that's not far off three times that of a minimum building regs specification wall.  If the oak posts were around 150mm square, then they would have U value of around 1 W/m².K.

[reddal]

I'd recommend these guys for adding glazing to an oak frame - http://www.blackpig.me/glazing-systems/ . 

 

Their website has some info on different techniques.

 

- reddal