Controlling heat gain on western-facing glazing?
Hi GBA,
Trying to prevent solar heat gain from cooking interior spaces through a large amount of west-facing glazing and hoping to pick the collective brain here for suggestions.
Notes:
* Two gable forms facing west, one the great room and one the primary bedroom, both connected by a glass breezeway with lift and slide doors opening on to a stone patio – diagram attached.
*All views are due west.
* CZ6, western Montana. Cold winters, hot(ish) summers, lots of sunny days, very dry, ±4,000′ elevation.
* 1′-6″ overhangs currently. I ran some daylight simulations, and you don’t really start getting appreciable shading till the overhang gets beyond 6′ – so simply blocking the light before it’s a problem doesn’t seem like an option.
* Recessed, pocketed, automated shades throughout. Obviously this is problematic/not possible at the triangular gable glazing.
* Not opposed to losing that upper glazing at the gables.
* Pushing hard for triple pane windows. I have a good local rep for guidance on coatings, etc but any suggestions welcome. Seems like triple pane + a good glass spec might be the only options for really controlling heat gain here?
* There will be a mechanical engineer designing all the systems.
* Still in design, plenty of time to pivot.
(As an aside: this is a lot of glazing, and it’s a vacation home. Not exactly “green” but I am trying to make decisions about assemblies and materials that will meet the client’s goals while doing the least harm)
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Replies
Shades aren't going to help with the heat gain. Once the light has crossed the glass the heat is trapped in the room.
There are really only two solutions. Have less light get through the glass -- less transmission, lower SHGC. Or have less of the glass exposed to the sunlight.
Big walls of glass like that create a lot of problems. Where do you put things like outlets? It may not be what the clients think they want, but I would argue you can get a lot of the same effect with less glass.
I know you don't want to hear 'less glass' but
Less glass
There are ways to get the look you want with a lot less glass.
Part of the problem is the though process
WE need these gable ends to put a bunch of glass in to get the view
then we need to have glass to the floor for dramatic effect
Baloney
You will spend little time in the room admiring the view because it will not be comfortable
Glass below the outside deck rail is useless, you are just looking at the deck rail
Full width of the room, what you need to look at the fence and the garden shed?
A more direct version of what I was hinting at in my response.
The designer's challenge is to get that "all glass" feel with a reasonable amount of glass.
DC,
It's so site and climate dependent. I can get away with huge amounts of south facing glass close to the ocean here in the PNW. This one never overheats, and I can't think of what I'd remove to lower the amount of glazing.
I'd say a 1-1/2 foot up and a foot off each side and the view is unchanged. House looks different, but the view is still the same. ~30 percent less glass.
If you are trying to reduce glass, which is not the issue on this house, climate, shade trees and all.
But hey, glass is sexy....
That would make the views similar to the ones on the windows to the left in the photo, and they are not similar at all.
I kinda don't get what you are saying. I pretty much think everything below waist level is not really looking at anything. It is kind of an architect thing, if you will forgive me, that one must see every facet of a view from every spot in a room.
Again, in your application it is not a problem, but in the OPs they not only have to heat the place, but have the sun screaming in in the afternoon.
gusfhb,
It's a very site and climate specific exercise, and I agree: In general less is more.
That house has very few windows on the other three faces, but on the south side it has what in other climates would be too much glazing. It sits on high bank water front with a few trees interrupting the view. The low sill height lets you see some of the landscaping near the house when sitting down, so the water views don't appear disconnected. The high ones allow views into the nearby trees, one of which regularly hosts an eagles nest. Standing in that room when we get one of our rare snow falls is magical.
Wow that’s beautiful Malcolm!! The windows are definitely incredible in this example. I guess it would still be stunning with big windows minus to top part but I love it with those tall trees.
I feel like the tall windows don’t offer so much benefit though when it’s just the sky in view. Like with long view if the horizon is not up so high and the extra glass isn’t essential.
Izzza,
Yes, it's a rare situation where they make sense. As you can see from this photo, the ones on each side, where there are no trees in front do not extend upwards. I disagree about views of the sky. The views out over the strait are an ever changing panorama of squalls, stars, and flocks of birds. It brings to mind one of my favorite lines from James Joyce "A day of dappled sea-born clouds".
I'd be thinking of replacing the clerestories with reflective panels. Same look from the outside, not really noticeable on the inside.
Why not do 6 or 7' roof extension? look at nordic designs. Idk how much an overhang will help on a western aspect as you get the setting sun but if your model shows gains, covered outdoor space is always a plus and a wall of glass protected by 6' of roof can only benefit.
Paul,
Along the same lines freyr_design suggested, what about a Brise soleil over the lower windows?
I have a largish 8x10 patio door that I was initially looking at putting a transom over. Cost and complexity nixed the idea and a lot of years down the road, I don't regret it. The extra windows up top would not have added anything but cost, the view is still great and I don't have to get on ladders to clean it.
As others have said above. Figure out how to get the most out of smaller windows. A bedroom with a wall of west facing glass (even low SHGC) will be an oven unless on its own HVAC, that is not cheap.
I do also have some larger west facing windows and get a lot of evening glare when the sun angle is wrong. I have seriously considered exterior slats to reduce it but can't figure out how to get the look right.
The one benefit of the west facing glass is a fair bit of sensible heat gain even with triple pane low E. This bit extra load really increases the runtime on my cooling which is great for humidity control, I can keep the house at 76F and RH never goes above 50% even in our hot and humid summers.
Agree with akos here
What benefit are the gable windows offering?
They *might increase the visibility of the mountains from the back of the room, but come to think of it, if you were that close, you wouldn't have a solar gain problem.
They will technically increase daylighting, but that often is practically neutralized by glare.
I just don't know what those windows are doing for the space. They do make the house look nice from the outside, but practically they're a problem that creates more problems. Lose lose
What am I missing?
As others have said… the solution is reducing the glazing. Your design looks nice, I would explore different window layouts though. If you absolutely must have all that glass, then I guess just get the best windows you can possibly afford.
Don’t mind the massive pile of rocks but here is a recent photo of my build, the view is nice all around but we put some big windows on the east side and as you can see it’s not all glass. The windows are 30” AFF so they don’t need to be tempered and honestly with like 7-8ft of glass, a window still feels huge IMO. I don’t wish we had more glass because it’s already so bright inside and the view is great. If anything I wish we had a tiny bit less glass.
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All, apologies for my lack of replies and thanks for chiming in - this community is fantastic. Some great project examples posted above.
Quick update:
After talking through some options with the client, we are reducing the glazing (somewhat). I attached a few images: one is the original design, the other (option A) eliminates the triangle gable glazing altogether, the third replaces it with rectangular transoms. We're going with no gable glass, no transoms - so hopefully that helps a bit.
Malcolm, thanks for posting that example: you're right, in that case, that gable glazing with the forest view is friggin' sweet.
Malcolm & Freyr, I still need to look at some exterior shading / Brise soleil options - without the gable glass above it'll be easier to incorporate, if I can make it look half decent.
To others points above about the gable glass not bringing much to the table:
Sure enough, I checked in 3D, and you can walk clear back to the kitchen 50' away and the mountains just baaaarely start to get clipped by the 9' head height of the lower windows. Screenshot attached.
Michael, thanks for the comments about glass specs. We're probably going with an Italian steel window company with great support for spec'ing glass, and I'll ask about your suggestions. The last project I did with them, our specs were: Triple pane, VT: 65, SHGC: 0.34 (I'll ask about getting this lower). Screenshot of the full spec is attached. I can't speak to those windows in the middle of summer, but I know that standing 6" from them on a -20°F day was perfectly comfortable.
"To others points above about the gable glass not bringing much to the table:
Sure enough, I checked in 3D, and you can walk clear back to the kitchen 50' away and the mountains just baaaarely start to get clipped by the 9' head height of the lower windows."
This agrees with my experience. I know you're already sold, but two other points: those high windows are a pain to clean. And while they don't admit much view, they let in direct sunlight when the sun is high which results in annoying glare.
The biggest selling point for ditching them was interior shading actually - the client wants recessed automated pocketing shades for all windows, and doing that on diagonal glass is insanely hard and I haven't seen a good solution to it yet.
Sounds like you have convinced the client already, but here are a couple more ideas:
If you keep the glass a couple feet up off the floor, you can design in a nice window seat for enjoying the view.
Replace the full triangle gable windows with a smaller accent window that still offers a view of the sky. I personally like the look of a small round window in a gable.