Attached Greenhouse to a Hempcrete Home Thoughts?
Convergence
| Posted in General Questions on
I’m interested in building a hempcrete home with an attached greenhouse to the south wall of the home. Although moisture issues can be an issue, I would think this would be less of an issue due to the nature of hempcrete’s open vapor barrier and mold proof material. I love the idea of having the thermal mass of the hempcrete absorb the sun’s heat, while also having a door to the house to allow the home to take advantage of this additional heat sink of the greenhouse.
Thoughts on designing something like this and if it’s worth doing the attached greenhouse instead of a standalone?
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Replies
Convergence,
Attached greenhouses were very popular in the 1970s, but have largely disappeared due to the difficulties in integrating the varied demands put on the space. If you decide to go ahead, they have a much higher chance of success the more you drill down into exactly what you want them for and how they will be used.
If it is primarily for growing plants, then humidity can be a problem. Not perhaps as you say for the hempcrete, but for the ambient levels in the house if it is linked to the space.
If the thought is to also use the space as a sun-room, that's almost certainly not going to work. The humid, hot conditions conducive to growing will make the place uncomfortable. Around here the the popularity of sun-rooms was followed quite closely by the growth of an industry dedicated to removing them. There are several companies near me that specialize in just that.
The third use - as a solar collector - is perhaps the most problematic. The times when you want that extra heat coincide with when the other glazing in the house will also be generating gains. At night, when the house could most benefit from that heat are when the greenhouse will be losing it rapidly though the glazing.
All this is a long way round to saying it could work, but you would be in the minority of people who have tried it if it does.
I tend to think moisture would be a benefit to the house in the winter due to our dry climate in Colorado. The moisture in theory would migrate through the wall due to the open barrier and humidify the air. Acoustics in the 12in hempcrete are supposed to be great.
Regarding humidity levels and heat in terms of it being a sun room, this would be countered by proper ventilation through fans and openings. I've been in a few earthships with this type of design and still found the environment to be enjoyable to sit in. Obviously this will depend how well I insulate the space.
Regarding heat sink capabilities, I think having a nice slider or french doors could assist during the day, since we will be at 9,000 feet. The hempcrete walls are great with thermal mass so this would be stored in the connected south wall of the house. I'd imagine we'd still have to turn on a heat pump at night but likely a lot less due to stored energy.
Certainly want to think all these things through though, thanks for your input!
Convergence,
You are starting at a much better point than most due to your climate. Good luck with your build.
"I love the idea of having the thermal mass of the hempcrete absorb the sun’s heat."
I urge you to do some calculations before going too far down this road.
There are many, many passive solar houses that don't live up to the owner's expectations, and almost always it would have been totally predictable if some engineering had been done before the house was built.
I recommend starting out with an energy modeling program like BeOpt.
I will be working with an engineer who is familiar with hempcrete, so I think the performance should be good. We won't be overdoing the south facing windows like other designs, but intend to take advantage of solar gain with proper overhangs on windows when needed.
Is he a structural engineer or a mechanical engineer? A structural engineer will keep your house from falling down, but a mechanical engineer is the expert you need to do energy modeling.
The energy side of this is not something simple, it's certainly not the kind of thing where if you follow a few simple rules of thumb you'll be OK. There's a not-insignificant chance that your desired design is not in fact viable.
To my ear it sounds like you have been infected with the passive solar bug.
Sadly, there is no cure this infection it seems to prevent logical thinking.
No amount of evidence and history of failures can convince the infected to see the facts as they are. Passive solar is a quaint idea of the 1960, If it was at all workable in the real world if would have taken over the market and no home would be built without it today. The landscape is litter with costly failed attempts.
Walta
I was trying to lead him there gently.
-Hempcrete is mold-resistant, NOT mold-proof.
-Thermal mass is greatly over-rated in almost all situations.
-Controlling the amount of heat a sunroom provides is challenging but it can be helpful if you don't mind it being somewhat labor-intensive. I know of several people with attached greenhouses and I can't think of any that actually open and close doors and vents after the first few year or two, except on rare occasions.
In my experience nothing is mold-proof. Given the right circumstances, mold will grow on stone, concrete, glass, steel, plastic. Here in DC if you leave a car parked for a while a layer of mold will cover the exterior.
In my experience nothing is mold-proof except copper and zinc.
Walta
The idea of enjoying some time in a sunny greenhouse on a winter day sounds great. But for almost every hour of the year, your greenhouse will be either too hot or too cold.
Even if the main idea is growing plants (rather than providing a pleasant place for people to sit), adjusting the temperature of a greenhouse is a constant chore, as the temperature swings from too cold to too hot.
I speak from personal experience.
Things may be technically mold proof, but mold may still grow on them. :/ I'm sure with a proper smart vapor barrier, you could eliminate a lot of the condensation. That's in my plans for our home future add-on.