Are cupolas worth considering on a well insulated home for ventilation?
Are cupolas worth considering on a well insulated home for ventilation in the summer? In zone 5a there are some months where the day time requires some A/C and the night does not. A whole-house exchange of air would be nice around 8 o’clock at night, when the temps outside drop.
The idea would be to open up the cupola along with the first floor windows and allow the stack effect to exhaust the air. I guess it’s the same idea as the whole house fan that pulls all the air out of the house and into the attic. We had one in our old house and it never seemed to work as good as the theory.
My concerns about a cupola are, another hole in the roof, demanding more detailed flashing at the peak, potential for leaks, another hole in the insulation, possible bug haven, actual usage of 4 1/2 months at best in a year, and most importantly……….do they actually work?
Thanks for any advice given
Rusty
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Replies
Russell,
If the outdoor air is cooler than the indoor air during the summer, and you want to cool your house, it makes sense to open the windows. If you have a two-story house, you can open a few windows downstairs as inlets, and a few windows upstairs as outlets. This works, but the air exchange rate may be slow.
In theory, you can use an attic cupola (or attic gable vents, or attic ridge vents) instead of upstairs windows as outlets. The main problem with this approach is that someone has to get out a step ladder every evening to open the attic access hatch. You will quickly get tired of this routine.
The best approach is to install a whole-house fan in your upstairs ceiling. The fan will move a lot of air quickly, so your house will cool faster. The fan will use lot less electricity than an air conditioner. If you decide to install a whole-house fan, buy a Tamarack model. Tamarack fans are equipped with insulated motorized shutters.
For more information on whole-house fans, see Fans in the Attic: Do They Help or Do They Hurt?
In much of zone 5A if you air condition during the day then ventilate at night you end up raising the latent-load (humidity) for the AC to chew on the next day before any significant sensible cooling occurs.
For night-ventilation to not add to the latent-load the outdoor dew point has to be below 55F, which is more typical of climate zone 5B.
If you are NOT air conditioning or mechanically dehumidifying the place, go ahead. The outdoor dew point in the pre-dawn AM will usually be below the indoor dew point of a non-air conditioned house, and night ventilation would offer at least some latent cooling as well as sensible cooling.
Thanks for your help Martin and Dana.
This is such a valuable source of information. Thanks for taking the time to answer.
I think Martin answered most of my concerns about cupolas if I can get away other forms like windows.
Dana's point narrowed the window of usage even further when it comes to humidity. Another reason to avoid the added expense.
Since I won't have an attic ( insulated cathedral), the next plan would be to use windows. Now the challenge is, how to incorporate a whole house fan when you don't have an attic.
Thanks again
Rusty
Russell,
Several manufacturers make whole-house fans for homes without attics. Click here to see a website with many inexpensive models of whole-house exhaust fans for flat roofs.
A better option that one of those inexpensive fans would be the TC1000-H fan from Tamarack -- a model with an automatic insulated damper that prevents heat flow and air flow when the unit is not in use.
I'm not an expert like the other respondents but here's my anecdotal experience.
We rented a 1950s brick ranch (poorly insulated with vermiculite, single paned glazing but with lots of mature tree shading) for a bit over 3 years. It had a whole house fan centrally located in the house through the nearly flat roof and no a/c. It also had carpet on slab with no vapor barrier. This is in climate 5b (front range colorado). The whole house fan along with open windows addressed all of our cooling needs very satisfactorily and typically needed to run only from sunset to midnight. It didn't have a timer or thermostatic controllers but those would have been nice add-ons.
Caveats:
We really had to have all the bedroom doors and windows open while cooling. Depending on your family, having bedroom doors open from sunset to midnight could be problematic. Depending on your neighborhood, you might also be concerned about security.
We had plenty of operable windows in each room.
The layout of the house was single level and quite open.
We built a custom insulated, air sealed lid for the framed opening for the house fan. In the season prior to doing that, I think we lost a lot of heat to the whole house fan.
Alternative, our current residence has a multi-level layout and a swamp cooler which is ineffective at cooling the house and a maintenance pain compared to the the whole house fan. We've considered converting it but that has its own issues.
Anyways, if you can figure out how to add a whole house fan that can be sealed and insulated well in the fall and do not have a/c, I think you would it an energy efficient cooling solution.
https://www.greenbuildingadvisor.com/green-basics/fans-and-natural-cooling The lead page on this Web site regarding natural cooling techniques points to a design system leveraging a cupola and a fan pulling hot air up and out as the featured illustrated design. Just writin'.
If your bath exhaust fans (or kitchen range hood) aren't very noisy, you could leave them on overnight, with windows open elsewhere for supplying cooler dryer outdoor air. No extra installation expense.
During hotter summer weather (Rocky Mountain Front Range, Colorado, climate zone 5B), leaving one upstairs window open (at the top of the stairs on a two-story house) cooled the house well. There were no other open windows. Cool air would fall down the stairs, and warmer air rise out the window. The first floor happened to be a tiled concrete slab, so the thermal mass of the slab made the home felt air-conditioned cool until the following afternoon.
The solutions are probably very climate dependant. Here in the PNW the summer days can be quite hot, but each evening cool ocean air moves in. We have a chimney/cupola with operable windows on two sides. If we open this in the late afternoon, and one window on the lower level, the house cools very quickly.
I'm re-roofing and re-doing the roof structure, and because my house is a dome the most efficient design is a cupola, but I'm not building a cupola with windows or vertical louvers - I am building a low profile cupola, and the vents are under the soffits of the cupola. This design is to vent the exterior of the roof, and keep things cool and dry, and as a afterthought, I am cutting five 12 inch holes in the ceiling below - one hole in each triangle that makes up the top center pentagram and bringing short ductwork through the insulation and into the vent space, inside the cupola. There will be insulated plugs for the five holes for the cooler months. A slight breeze, should in theory at least move warm moist air from inside to the outside, and allow catching cooler air at night. Not sure a cupola like this would look good on all structures, but I could see it on a square hip roof.