Low transmittance glass for skylight

[Bancroft]

Part of our house design has two areas - a porch and an outside kitchen - with a roof covering over them as they are incorporated into the house design.  

 

To allow light into these areas we have included skylights above each one on our submitted plans.

 

However, we live in a National Park and they have a 'Dark Skies' policy.  So, one of the planning requirements is that these skylights should have "...integral blackout blinds or low transmittance glass..."

 

I'm not keen on integral blackout blinds so I'm looking for skylights that have low transmittance glass.

 

I presume this type of glass lets more light in than it allows out (thus dimming any light going upwards from the covered areas at night) but I can't find anyone who provides this sort of glass (at least under this description).  They all seem to work the other way and are focused more on reducing heat than stopping light.

 

I suppose I could mount a skylight 'upside down' or ask a supplier to put the glass in back to front but that seems clumsy.

 

Has anyone any experience of low transmittance glass skylights or know of suppliers who have them?

[Alan Ambrose]

I think that’s really a misunderstanding by your LPA. In practice, will you light those areas at night in an objectionable way? Send them a detail spec of a unit (maybe with a drawing showing the lighting) and ask them whether that will meet their requirement? Otherwise external blinds are fairly easy, but since the LPA can’t insist you use them, a bit of a waste of time.

[SteamyTea]

5 hours ago, Bancroft said:

low transmittance glass.

Copied from here.

 

https://www.swiftglass.com/blog/key-differences-transmission-transmittance-apply-application

• Transmittance refers to the amount of light energy that the glass absorbs, scatters, or reflects. It’s measured using the formula T = I/I₀, with T denoting the transmission intensity, I indicating intensity, and I₀ indicating intensity at the start. This calculation allows you to determine the ratio of transmitted radiant power to incident radiant power, giving a greater idea of a glass’s ability to block photons.

[Mr Punter]

Unless they condition that the blackout blinds are drawn at night the planning condition is nonsensical.

[Bancroft]

Alan - no-one will see the light and we will use them only occasionally at night but the national park has a specific policy about maintaining dark skies.  Somewhat ironic considering we see a massive glow from two neighbouring cities and also our present house has 7 (yes, seven) security lights around it - put in by the previous owners.

 

Mr Punter - the planning approval document does state that the blackout blinds are to be kept closed during night-time hours.  That in itself is stupid because these aren't habitable areas and the most likely times we'll be using them is during long, warm summer evenings when there is still light in the sky.  But these are hoops we have to jump through.

[JohnMo]

9 hours ago, Bancroft said:

integral blackout blinds or low transmittance glass..."

The likelihood of the building inspector getting down to this level of detail is zero. Include whatever they want on the plans as long as you can retrofit, if they push it at the final inspection, all good you can retrofit.

[Adsibob]

2 hours ago, JohnMo said:

The likelihood of the building inspector getting down to this level of detail is zero. Include whatever they want on the plans as long as you can retrofit, if they push it at the final inspection, all good you can retrofit.

I’m not sure I agree. My inspector required me to evidence all manner of things before issuing my certificate. I had to supply documentary proof that I had installed toughened glass for one window and was made to replace a couple of doors because the glass within them was not fire rated. I can’t remember the full list, but it had at least 10 items on it requiring 10 different bits of paper. E.g. they wanted to see the commissioning certificate for the MVHR unit, another one for the sprinkler system.

Edited June 6 by Adsibob

[Kelvin]

That’s all standard stuff. The MVHR commissioning certificate is on my list too. 

[JohnMo]

7 hours ago, Adsibob said:

I’m not sure I agree. My inspector required me to evidence all manner of things before issuing my certificate. I had to supply documentary proof that I had installed toughened glass for one window and was made to replace a couple of doors because the glass within them was not fire rated. I can’t remember the full list, but it had at least 10 items on it requiring 10 different bits of paper. E.g. they wanted to see the commissioning certificate for the MVHR unit, another one for the sprinkler system.

Your talking safety and standard stuff, this is about a blind in a skylight

[Mr Punter]

The condition is a matter for planning, not building regs so it will not affect signoff.  It is very unlikely to have any repercussions if you ignore it, as long as you submit details of what you intend to do and have those details approved in writing.

[Adsibob]

Ok, fair enough. I thought it was a bReg thing. But yeah, if it is planning, I would ignore it.

[Bancroft]

The condition is a matter for planning, not building regs so it will not affect signoff.  It is very unlikely to have any repercussions if you ignore it, as long as you submit details of what you intend to do and have those details approved in writing.

 

 

Ah, interesting nuance and another wonder of our great planing system!