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Community and Q&A

Light shelves

rpmgCTG9g2 | Posted in Energy Efficiency and Durability on

I am designing a 1,200 s.f. passive solar home in southern Utah with ideal southern exposure and a 10 ft. high ceiling in the open plan living / dining / kitchen room. I am looking for an affordable light shelf system that also projects outside the windows to provide shading of the midday summer sun but lets winter sun in. The south-facing 15 ft. long wall will have five 24 inch wide windows and a high gable allowing 24 inch high windows above the light shelf / sun baffle.

80 inch high windows and french doors on south-facing flank walls will require sun baffles but no light shelf or upper tier of windows.

Can anyone recommend a product and supplier. I could also fabricate a bracket system to support a suitable shelf and baffle.

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  1. user-869687 | | #1

    Tim, your best bet is probably a site fabricated canopy with a reflective top surface. It would be a good idea to prop the canopy out ahead of the wall rather than against the wall, so the clerestory window sills can start just above the reflective surface of the canopy, without running into issues with rainwater splash-up.

  2. user-659915 | | #2

    TJ's suggestion to separate the light shelf from the wall assembly for free drainage is an excellent one. Not sure what he means by a site fabricated canopy but it brings to mind a stretched fabric on steel frame assembly which could be made to order by your local commercial awning fabricator. These canopies are usually sloped for rain-shedding but if properly detailed for snow load etc. I see no reason they could not be horizontal. A variety of highly durable fabrics with excellent reflectance is available with the potential advantage of partial translucency and perhaps rain-permeability as in the popular Australian shade-sails. BTW good reflectance on the lower surface as well as the upper surface is important if you want to avoid contrast glare.

  3. user-659915 | | #3

    Oh, and if you prefer a non-fabric solution there are also aluminum louver systems made for exactly this purpose for commercial buildings. There's no reason you could not install this on a personal residence. Here's an example from Alcoa:

  4. Chad Huff | | #4

    Not sure if you are too far down the design path yet, as this is an older post, but we have introduced a new style light shelf to the market recently and it might be a fit for your project. Ours is interior mounted, but I can assure you you will be pleased with the light output. Our system only will require about 16" of daylighting window to function properly at your latitude, so you may have some bypass light with lower altitude sun. We have a time lapse video of our product posted on youtube as well. Good luck with the design. Call or write if I can help further.

  5. jbmoyer | | #5

    "I am looking for an affordable light shelf system that also projects outside the windows to provide shading of the midday summer sun but lets winter sun in."

    I would recommend that the light shelve is not continuous from inside to out. Make sure that there is a thermal break within the wall.

  6. rpmgCTG9g2 | | #6

    Many thanks for all your helpful replies. Here's my plan:

    - Interior light shelf will be a 2x4 framed and sheet rock-ed shelf projecting 2 ft. into the room and 7 ft. height to the underside, putting the top of it at sill height of the 24 in. high daylighting windows above. The upper surface will be finished with a reflective material or coating - not known yet. The shelf serves to reflect light back onto the 10 ft. ceiling, as the only other daylight source for the 33 ft. deep room is a 4 ft. x 4 ft. skylight towards the rear. The rear wall will have a mirror panel across the full 14 ft. width and from 7ft.6ins height up to the 10ft. ceiling - to bounce reflected light and create a 'trompe l'oeil' extension of the room.

    - The exterior device will be a louvered sun baffle to shade high sun off the lower windows and french doors. The louvers can then be adjusted or removed during winter months to let more sunlight in when required for passive solar gain. The louvers can be mounted on bolt-on brackets thus avoiding any drainage issues or thermal connection to the interior.

    I plan to see how it works, and may need to add blinds for the upper daylighting windows in summer. Glare was mentioned (by James) as an issue - specifically with regard to using a reflective surface below the light shelf also.

    Am I being realistic that this will work ?? By the way, I'm not able to run any calcs on light distribution back into the room, but wall colors are going to be another factor - curious about the glare issue !

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