Is a skillion roof with high windows less effective due to high ceiling heat loss?

I do house plans and am just wondering whether these high ceiling skillion roofs with high north facing windows is really better, since it is more difficult to heat a room with a high ceiling. I understand the high windows could be double glazed with internal blinds, and you have the benefit of heating up an internal thermal mass wall, but are the benefits really worth it? Say compared to a flat ceiling say 2700 mm high with north facing windows on the north wall, heating perhaps just a slab on ground.
Does anyone know any way to prove which is better in keeping the place warm in winter? Especially if the solar gain is not sufficient at times and one would need to add their own heating.

High ceilings can be a bonus in Summer to keep the place cool, so perhaps someone knows how to include this in their calc's too?

I'm assuming North windows being in the south hemisphere.
Also, with a skillion roof, if the higher wall is on the north side and the roof slopes towards the south, it would be more difficult to install solar panels on the roof and get adequate sunlight in winter, correct?

One more thing to consider in the calculations... if the majority of the radiant sun heat comes from the north, a south sloping roof would perhaps reflect heat easier than say a north sloping roof (if the south wall was the highest wall)

Hello Dieter,

dieter aschenbrenner wrote:just wondering whether these high ceiling skillion roofs with high north facing windows is really better...

I am not sure how to address "really better."

Perhaps to some degree for heat gain in winter if you are in a southern hemisphere (otherwise to the south in northern hemisphere) yet there are other challenges to these window, even though they add architectural interest and detail. Any fenestration (i.e. located in the upper ridge of a roof, or wall section like skillion, monitor, clearstory, pent, etc.) up high is going to lose heat faster than if lower down, as well as be more difficult to service.

dieter aschenbrenner wrote: but are the benefits really worth it? Say compared to a flat ceiling say 2700 mm high with north facing windows on the north wall, heating perhaps just a slab on ground.

First, unless the build is in a low rainfall area, I would never design or recommend to a client that they employ a flat roof design for most builds. Some form of slop, such as in any shed/pent roof system is always going to be more durable over time and less costly to maintain. I like living roofs, yet know of none either contemporary or traditional that last for long. Those that do...like traditional stone...can last a very long time, yet are not for the novice to design or build...plus they are majorly $$$$$$.

Second, I have never really been sold on the entire "passive solar" shtick. In some applications it is great, but over the years I have seen way more issues than gains with them over time. I do like solariums, atriums, and attached greenhouses, as long as they can be shut off completely for the rest of the architecture when need be due to heat, humidity, or other mitigating conditions.

Typically I look to the vernacular designs for a region and/or similar biome type to it and those regions styles.

dieter aschenbrenner wrote:Does anyone know any way to prove which is better in keeping the place warm in winter? Especially if the solar gain is not sufficient at times and one would need to add their own heating.

There are all kinds of positive research that can be found to "prove" that passive solar works. Yet...this "research" seem to always come from folks selling it, or the research is funded/supported by proponents of passive solar. There is some I have read over the years that lean more in my direction of..."it really depends...and most times...NO, not worth the long term effort." Unless it is in a proximal space to the structure, yet can still be isolated from it.

dieter aschenbrenner wrote:I do house plans...

I don't mean to sound questioning but this leads me to believe you "design architecture" for a living? What is your credentialing and/or background for this?

Regards,

j

I'm a builder, not a registered architect.
When I mentioned flat ceiling, I was referring only to the ceiling, not the roof. The roof could be pitched, sloped, or whatever.
I agree that high windows would lose more heat, which is why I think perhaps there is a way of determining just how much. Perhaps there's some software that could tell you how much heat is gained by the high windows onto a thermal mass wall, how much would be radiated from that wall, for how long, and how much heat would be lost with high windows and high ceiling, versus low windows and low ceiling.
Or maybe two neighbouring houses comparing the difference

Um, I think maybe Jay's point was that software and calculations and projections sometimes lead us astray with best-case scenarios. Perhaps better would be to look at some buildings with the kind of windows your talking about, and talk to the owners, especially as winter is coming on there in the southern hemisphere.

Where in the southern hemisphere are you, and do buildings in your area tend to spend more energy, money, and or discomfort on summer cooling or winter heating?

And finally, whoa Jay! I've been living in passive solar houses for almost 20 years, with no backup heat except a rubber water bottle in the bed at night. In a climate that makes Vermonters feel at home! But yes, we mainly heat with attached greenhouses, and we remove them for summer to avoid overheating.

Hey Dieter,

dieter aschenbrenner wrote:I'm a builder, not a registered architect.

Awesomeness...I was actually hoping for that!! Me too...

I have these often long drawn out discussion with my architect friend/acquaintances and too often (usually very soon in the conversation) it is very apparent they have a great "design sense," yet not a lick of actual applicable building knowledge (or common sense) when it comes to "thinking, creating and working around" the actual means, methods, and materials that will realize the true world form of their thoughts. They also spend an exorbitant amount of time trying to reinvent what somebody already did 2000 years ago...and usually better!

dieter aschenbrenner wrote:When I mentioned flat ceiling, I was referring only to the ceiling, not the roof. The roof could be pitched, sloped, or whatever would lose more heat, which is why I think perhaps there is a way of determining just how much...

Oooh...I like that part. I tend to have flat ceiling in most spaces that are "air conditioned" outside the external ambient. I love helping facilitate space that has as much "outside" living space as inside, and also some of the old elements of traditional architecture like "cold attics" and "living/sleeping space" outside the thermal envelope of the rest of the building. Here in Vermont (i.e. places) for example, having bedrooms or other spaces upstairs or in a portion of the house that isn't insulated (as was often the way of the past) the tax assessment on such spaces is much much lower...

I find cathedral ceiling to be a wee bit tedious and excessive in many modern builds, and try to confine their beauty to a space that is outside the thermal envelope, or only in a limited location within the conditioned space. Too much of a good thing lessons it impact and charm...

Perhaps there's some software that could tell you how much heat is gained by the high windows onto a thermal mass wall, how much would be radiated from that wall, for how long, and how much heat would be lost with high windows and high ceiling, versus low windows and low ceiling. Or maybe two neighbouring houses comparing the difference

There are calculations for factoring temperature loss through windows, walls, etc, yet the math is a bit "squishy" in my view...so use it only as a rough guide, if at all. Now comparative analysis and direct testing and monitoring is something of interest yet too often is not prophylactic in nature but after the structure is already built. Reading so many different studies over the years, I realized that I had to not only had..."read the data,".... but consider who "funded" the research to get the data, and if there was other mitigating forces (agendas) behind the research. Part of the reason I left the "sciences" was the amount of "politics, and agendas" present in the work...not just good research...it was actually surprising and overwhelming...

Instead, I would suggest that windows in wall that are well thickened (a common element of traditional/natural builds) be treated like small rooms onto themselves wherever possible. Think about designing and incorporating insulating textiles for periods that are cold/hot, and utilize the light drawing effect of mullin grills and embrasures to the deeper walls.

Really taking a close examination of vernacular systems, their logical seasonal functions, and related wonders is probably of more value that playing with statistical analysis. There is a discussion here about Christopher Alexander's book, "The Timeless Way of Building," that speaks to some of this rather empirical knowledge and logic. Most of Christopher's writing and lectures are very insightful when addressing the love and logic of vernacular systems.

Regards,

j

Hello Rebecca,

Rebecca Norman wrote:Perhaps better would be to look at some buildings with the kind of windows your talking about, and talk to the owners, especially as winter is coming on there in the southern hemisphere.

I completely agree that direct comparison of "long term builds"...NOT NEW ones is a wonderful form of empirical knowledge and example to emulate. This often has way more value than trying to project and extrapolate information from one design matrix into another...or...statistical analysis...

And finally, whoa Jay! I've been living in passive solar houses for almost 20 years, with no backup heat except a rubber water bottle in the bed at night. In a climate that makes Vermonters feel at home! But yes, we mainly heat with attached greenhouses, and we remove them for summer to avoid overheating.

You just made my case for me...thanks for that..., as I was hoping you would speak to this issue of windows and..."HOW"....passive solar is facilitated...attached or detached!! Yours, unfortunately is the exception after twenty years, and I would add, is not a full time "attached" system like a bank of large windows or "full frontal" attached greenhouse, which is what we find in so many of these modern passive solar structures.

Lets be really clear in exactly what I said, "In some applications it is great..." and I stand by that sentiment as well as the methods of designing passive solar that is the most effective, and enduring over time. I think your examples is absolutely worth noting (and I presume without seeing it) one of the better ones. Again, this is the exception as most after twenty years are looking to replace windows, deal with interstitial moisture issues in walls and ceilings, decaying wood elements, seasonal overheating challenges, etc, etc.....

I love it when someone gets the architecture they wanted and it performs as they need it to. As a designer, facilitator and student of architecture I see way more that doesn't meet the intended goals as "planned." In the comparative, and I tend to follow the understanding of the Architect Frank Gehry...most architecture isn't that well designed or built...nor does it meet the intended projected scope of how many "think" they will operate.

I would love to see photos of your place sometime, or perhaps a posting the profiles it and how you built it...

Regards,

j

dieter, I have a passive solar house with 14-foot ceilings, but the windows are not tall. I have spans of 11 feet of windows on the sunny side of the house, and another on the sunset side of the house only in the rooms that are used most, family room, living room, dining room. The height of the windows is just below the standard wall height of 8 feet. What has made the most difference is very thick insulation in the floors and ceiling, in addition to the walls, and having the siding tied to the ground, i.e., not up on piers, so the constant unfrozen earth temperature, which ought to be about 50 F/ 10 C, acts as insulation under the house as well. There's plenty of light inside without tall windows, even when it's overcast. They do cut down on wall space, but I'd much rather have the light than the stuff on the walls. I use thermal blinds and thermal curtains to block heat in the summer and keep heat in at night in the winter.

The exterior is very dark flat green, the roof is black. The windows allow heat through them, so they are not the latest to-code windows because those block out too much heat in winter. Low E is what they call them here. The kitchen is on the unsunny side, since it often puts out heat and doesn't need any heat in the winter. But a window over the sink makes it a lot more interesting to be there.

Ceiling fans make a huge difference in rooms with tall ceilings in the winter.