Gravenhill Solar Gain Factor 0.5-0.7 in Design Code

[Ferdinand]

Just for interest, a brief extract i came across from the Design Code at Gravenhill:

 

Quote

Energy performance criteria

Most self builders want to attain a good level of energy efficiency to ensure long-term low running costs.

At Graven Hill, there are some specific – but eminently achievable – performance requirements over and above what’s laid out in the Building Regulations. These include:

 

• Structural envelope Walls, ground floors and roofs must have a U-value of 0.15 W/m2K or less.
• Windows Must achieve a U-value of 1.4 W/m2K or less, and a solar gain factor (g-value) of 0.50-0.70.
• Airtightness Maximum air leakage of 3m3/hr/m2 at 50 Pascals (to be pressure-tested on site).
• Ventilation Good-quality mechanical ventilation and heat recovery (MVHR) is required, with an efficiency of at least 70% as well as a power consumption of below 1.5 W/L/s.
•  

The Design Code also recommends the inclusion of solar photovoltaic panels if the planned house’s roof orientation is suitable, but this is not a requirement.

https://www.self-build.co.uk/graven-hill-plot-passport-explained/

 

That line highlighted in red seems to me to be encouraging solar gain, rather than limiting it - as is more the need in well insulated houses.

 

AIUI the solar gain factor (ie amount of energy from sunlight that gets through to the inside) should be below 0.5 in a highly insulated house.

 

eg from Wikipedia

Quote

A g-value of 1.0 represents full transmittance of all solar radiation while 0.0 represents a window with no solar energy transmittance. In practice though, most g-values will range between 0.2 and 0.7, with solar control glazing having a g-valueof less than 0.5.

https://en.wikipedia.org/wiki/Solar_gain

 

However, this is not my specialism and the difference may be marginal.

Ferdinand

 

Edited April 6, 2019 by Ferdinand

[Jeremy Harris]

That is indeed a contradictory rule, and one that will probably lead to some houses overheating, unless additional measures are taken to reduce the solar gain in some way, I suspect. 

 

I dearly wish that I'd opted to fit glazing with a lower g value, as that would have probably removed the need to retrofit (expensive) reflective film.

 

 

[Ferdinand]

Email sent to sales@gravenhill.co.uk, which is their only obvious email.

 

Quote

Please pass on to whoever is your Design Authority for your buildings.

 

Your Design Code seems to demand a specification of windows, which in highly energy efficient houses will cause overheating through excess solar gain.

 

That is:
"Windows Must achieve a U-value of 1.4 W/m2K or less, and a solar gain factor (g-value) of 0.50-0.70."

 

Low energy houses should be in a range more like 0.2-0.5 as I understand it.

 

Example of a reference:

https://www.self-build.co.uk/graven-hill-plot-passport-explained/

 

and on page 5 of the Design Code itself.

https://www.gravenhill.co.uk/wp-content/uploads/graven-hill-design-code.pdf

 

This is being discussed on a thread at the Buildhub self-build forum, if anyone wishes to drop over.
https://forum.buildhub.org.uk/topic/9261-gravenhill-solar-gain-factor-05-07-in-design-code/

 

Given that overheating is becoming a key issue, this needs to be changed urgently.

 

Rgds etc.

 

 

F

 

(In case anyone is despairing, I am not THAT much of a nerd to know this off the top of my head.

 

I think it came up in consecutive search results in the Google snippets, while I was tracing up the spec of the chappie's Thermal Roof product from The Street programme, and then checking that against the required Specifications for Gravenhill.)

Edited April 6, 2019 by Ferdinand

[quintain]

Has Graven Hill people/person answered your email about Windows solar gain.

Regards

Richard

[SteamyTea]

Are those building codes really any better than basic building regs?

 

[Ferdinand]

Depends whetehr "better" means quality of build or ease of understanding.

 

The Gravenhill one is about 5% of the size of the Building Regs, for example, and for the layperson probably does not seem to be written in Chinese.

[Ferdinand]

19 hours ago, quintain said:

Has Graven Hill people/person answered your email about Windows solar gain.

Regards

Richard

 

No.

 

I have not checked whether the update has been made.