Really? R6.6? How?
Damien McGill
Engineering Happy Healthy Homes for People and Planet. Certified Passive House Consultant
The Big Bold Change
As you are probably aware MBIE put out the Outcome of Consultation document a week ago. The major change was the doubling in roof insulation to R6.6.
That is actually quite an upgrade in a New Zealand context!
Just think of it as putting a beanie on your home’s head.
As this is now a requirement, (all be it with a transition period through to 2nd November 2022), what might R6.6 actually look like on site?
I’ve come up with 5 options of what R6.6 may look like in your new ceiling. It’s just to give some ideas as a starter for 10 as a simple educational tool with some pros and cons, rather than being the definitive guide.
1. Simple Ceiling
2. Layered Ceiling
3. Insulated Services Cavity
4. PUR SIPs panel
5. PUR Warm Roof
This could be a standard truss or a skillion ceiling. It shows that the bottom chord of the truss or the rafter will need to be 290mm deep to achieve sufficient insulation.
There may be a few issues around vapour condensing and mould growth with this option.
This is a trussed roof arrangement that is quite common now. Installing insulation over the bottom chord reduces its size significantly for the same insulation benefit.
The issue here is how is this achieved at the eaves. But a more cost-effective system, timber wise.
Most ceilings are fixed to battens. I’ve shown timber ones as they are easier to model. Install an airtightness & vapour barrier, to address the potential condensation issues and provide an all-around better product, while insulating your services cavity.
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Just make sure the downlights are rated to have insulation around them. The volume of service ducts will affect the insulation rating too. A 90mm services cavity may be a better option, especially when running ventilation ducts within the thermal envelope.
This is where SIP panels come into their own. Especially SIPs panels made with PUR foam, which is more insulating that polystyrene. They only need to be 215mm deep, so super for skillion ceilings.
No real downsides, as SIP panels are inherently more airtight to begin with. (You’ll need 315mm using EPS in the same format.) A super scallion roof option.
Maybe we will finally see some warm roofs being specified and constructed? There are many different options for rigid insulation in warm roofs. I just went with PUR as a comparison with the SIPs example. No real downsides here either as far as I’m aware?
Conclusions
So, there you have it, five potential options and I’m sure there are many more variations on the themes above. It will be super to see what gets designed over the next year as the beenie beds in.
It will be interesting to see whether more SIPS and warm roofs are specified going forward and how layered ceilings continue the same volume of insulation up to the eaves.
PLEASE remember that the roof is part of a whole system and a healthy home is a system that should be looked at holistically rather than as isolated individual elements. Check out the Health Home Design Guide for more information.
Healthy Home Design Guide
Roofs
Healthy Homes as a Whole System
*Assumptions
Others may get different figures, this is an indication only, not a scientific paper!
Owner at Hawke’s Bay Install, Insulation Experts.
1yCompanies have not started producing products that meet these new standards so purchasing double the insulation means another increased cost to customers and an increased installation time. It’s great to have these standards but where do you draw the line?
Giving your facades a break
3yWouldn't it be easier to offset the insulation requirements in the ceiling with just slightly better wall and window performance? Many houses being built today have a very small roof area anyway (town houses) so R6.6 just seems dumb.
Experienced Development Director & Project Leader I Qiddiya Investment Company 🇸🇦| Chartered Surveyor I Professional Member, Royal Institution of Chartered Surveyors. Any opinions expressed are entirely my own 🙏🏼
3yI hope you don’t mind I shared? I credited you as author. Great article - thanks
Beautiful Superhomes 🦸🏻♂️and buildings🏡, healthy for people and the planet🌎 super energy efficient⚡️, superior comfort 😻with a tiny power bill 🔋the best internal air quality 💨 environment 🌱 linktr.ee/bobbburnett
3ywell done SuperDamo! Its super great to put a beanie on our homes but still a massive disappointment no puffer jacket and no socks and shoes!
Energy and Carbon Consultant | Net Zero Eco | 5 more years of global carbon budget to get to absolute Zero
3yModeling and use of PHPP included...so perhaps easier to get Passive House, Low Energy Buildings through local councils...would be great to see Airtightness, MVHR, Thermal Bridging included sometime...Scots are looking at legislation to make Passive House mandatory for all buildings...so why does New Zealand move so, so, so slowly on these things, less population than most major cities overseas and a single minor city in China...