We are replacing an aged and leaking conservatory with a new more substantial and efficient orangery style build. I had a flooring chap come last night to price up the cost of running similar wood floor that’s in our living room into the new build bit. He’s doing that quote but it turns out he’s a building enthusiast in terms of energy efficiency etc. He suggested:

1. Instead of double glazing the orangery we should triple glaze it. The specified double glazing has a U of 0.9 at the moment (24mm units with argon).

2. Consider not pouring a traditional flooring slab but make the orangery build on a suspended timber floor with insulation between deep joists and an air gap underneath. We will have to lay a new base/subfloor anyway as the current foundations are only 27cm deep!

Do any of you with experience here have any advice re either of the options? The orangery is on the south facing part of the house and we will not be able to extend our radiators into it and are planning to put underfloor heating (electrical sadly) and make it all one room with the living room. Energy efficiency in both cold and hot is very important to us as the current conservatory has thin glass and is an icebox in winter and an oven in summer!

I’ve done google-fu and there are theories/is advice to support both sides of each argument it would appear!

Thanks team!

Build an extension with a proper roof that you can insulate and big windows that you can fit with blinds or curtains.
No matter how clever you try to be, glass is a poor insulator. Only have it where you want to look at things.

That’s sort of what we are trying to achieve Perchy – the living room is cut into a bank so is dark and the idea is the orangery style will let light in and let us see our garden so we are having a predominantly solid roof with a small lantern for light and the windows are on dwarf walls not floor to ceiling. I just want to maximise the thermal efficiency of what we are doing and was unsure if triple glazing and/or a suspended floor would make much difference in that respect.

If it’s an orangery with a solid/mainly solid roof it’s going to need a Building Regs application and will be classed as a highly glazed extension, which will need to comply with Part L. It will also need to comply in all other respects. A good (brief) guide for Part L HERE

I know the trend is to remove doors and have on open space, but seriously consider keeping doors in, or having new doors that work more flexibly. Generally, if you retain or install external grade doors between the dwelling and extension, and zone control the heating in it, you need not demonstrate compliance by any of the long winded methods above, just elementally with respective ‘U’ values. Regs aside, conservatories and highly glazed extensions with no effective thermal separation DO act as huge heat sinks, DO get cold and could make the rest of the house cold or dramatically increase your fuel usage.

Triple glazing is expensive, and suspended timber floors are outdated/rarely seen these days, for some good reasons, though they’re not terrible. Get the design and complete approach sorted before you focus on specifics.