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Community and Q&A

Adding connected sun room and greenhouse, suggested plans?

ylekyote | Posted in Green Building Techniques on

I’m thinking of taking this concept and adapting to my situation.

Mine can be 15′ wide, connected to the house by addition’s north wall. Needs to be at least 25′ long, up to max 35′.

North wall of addition would join the house, and the long dimension will go south. The sides face east-west.

I plan to add the wall so I can pack it with insulation and make it sturdy for heavy snow years.

Unlike pic, I’ll have a complete or partial clear roof, and large windows on the south and west walls for max sunlight. That I can close with shiney ceiling and and window blackout curtains or partly obscure with lighter ones.

I’ll have light portal holes in ceiling (between clear roof and work area) over the south end greenhouse, and place triple layer clear thin plastic trays over them as needed to control heat and topward plant sun that way. I’ll cover rest of ceiling (not the roof) with 2 to 3″ rigid foam, and have foam inserts for the plastic removable windows as well.

I’ll slope the north end roof westward, and the south end southward, and use water barrels on both to collect or water lawn.

The north end is a multipurpose/fitness/spare sleeping room, and south end the greenhouse. They’ll share a wall, window and door between them which will also be highly insulated to keep summer heat out and my winter heat in.

I’m pouring a mono slab. But not sure of pro/con vs footer type. I could use the passive earth pipes idea for more air control I think. Would be best to install under the slab to feed in/out so not exposed at all. That’s my idea anyways, if slab foundation.

I may use hay bales between the house, and the two new rooms, and exterior walls, as insulation at those locations. I need to read if those bales can be treated with bug and fire deterrent. I’d like to use hemp stalk bales if possible. I think it’s hypo allergenic. Not sure if these help or make the walls more sturdy or what?

Exterior portions that aren’t windows will be stucco I think. Some wood trim to match house. Roofing will be windows and steel. Should I use steel support in roof, or wood? Wouldn’t lightly painted steel reflect the heat?

I’m pondering if I should make the addition on a short platform, like 24-30″ off ground like a big deck, or dig in with foundation. The addition yard area is level with existing house floor, so either is doable. One concern we have is heat in the summer…it can get hot and we don’t have or want A/C. So what’s best for coolness in summer? And I suppose 15×30′ deck more expensive than slab. So also a barrier perhaps.

Does anyone have any suggestions I should consider on this addition? This is my first green wing build. Would like to use best concepts with my area to maximize passive climate control in summer and retain heat for winter to help heat rest of home and provide clean garden air all winter long.

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  1. ylekyote | | #1

    The air vent could be a 4" chimney for propane or kerosine plant heater in winter and regular hot air release in summer by disconnecting pipe near interior roof. If ever needed in the freak weather seasons we have.

  2. GBA Editor
    Martin Holladay | | #2

    You raise a lot of questions. I'll address some of them.

    1. I assume that you are planning to put the greenhouse on your addition's south wall, not its north wall (unless you live in Australia, New Zealand, or South Africa).

    2. You wrote that you want the wall to be strong for heavy snow years. But you need to worry about the strength of the roof, not the strength of the wall.

    3. I don't recommend that you include large west-facing windows on your greenhouse unless you only intend to grow plants in the winter and spring. West-facing windows will lead to overheating.

    4. You wrote that you are planning "a complete or partial clear roof." If you mean a glazed roof, be careful. A sunspace with a glazed roof is cold in the winter and hot in the summer. I urge you to visit homeowners in your area who have sloped south-facing glazing -- ask them if they would ever include sloped south-facing glazing if they had a chance to build their house or sunspace again. Most will say "no."

    5. You wrote, "I may use hay bales between the house, and the two new rooms, and exterior walls, as insulation at those locations. I need to read if those bales can be treated with bug and fire deterrent. I'd like to use hemp stalk bales if possible. I think it's hypo allergenic. Not sure if these help or make the walls more sturdy or what?"

    Good luck finding a supplier of "hemp stalk bales." If you can find such a material, it will be extremely expensive. Hay bales don't make a wall "more sturdy." If you want a sturdy wall, use conventional frame construction or insulated concrete forms.

    6. You wrote, "Roofing will be windows and steel." I think that you may be in over your head. You can't use windows for roofing. It is possible to purchase and install skylights, but these are different from windows.

    7. You asked, "Should I use steel support in roof, or wood?" Rafters and beams can be made of wood or steel; either will work. In either case, I strongly suspect that you need to consult an engineer.

    8. You wrote, "One concern we have is heat in the summer. It can get hot and we don't have or want A/C. So what's best for coolness in summer?"

    For starters, you should skip the sloped south-facing glazing and the west-facing windows.

    9. "Does anyone have any suggestions I should consider on this addition? This is my first green wing build."

    Sunspaces were popular in the 1970s and 1980s. They are less common now, because they tend to be cold during the winter and hot during the summer. If you need a commercial greenhouse to start plants, you probably know your needs. You'll need good ventilation during the summer and space heat during the winter -- and you probably realize that the needs of plants and the needs of humans are quite different. Commercial greenhouses tend to use a lot of energy.

    If this is your first building project, I strongly suggest that you invite an experienced friend or professional builder to join your team.

  3. ylekyote | | #3

    So do you think I should only make sun port holes in the garden area ceiling? The greenhouse will only be the south half end of the addition. Yes, I'll build from my south facing wall towards the south, about 15' x 25' (to 35' max).

    I have free double paned windows a carpenter friend of mine salvaged from an Aspen remodel. The windows are in good shape, steel framed.

    Do you have any design packages that you've seen that would work well for my needs?

    I could separate the addition by about 8' and keep it from effecting my household climate. Do you think that's a better idea than having it connected and trying to design it to keep my house cooler in Summer and hotter in winter? If that's even possible, the Summer cooling especially.

  4. ylekyote | | #4

    Maybe insulated reinforced concrete forms would be best too...

  5. GBA Editor
    Martin Holladay | | #5

    A sunspace has few energy benefits for a home. The cost of building a sunspace will be much higher than the value of any energy that the sunspace collects over its lifetime.

    If you want a sunspace badly, build a sunspace. It can have as many skylights or sun-tubes as you desire. As long as you realize that it won't help heat your house, you can let your imagination run wild.

    By the way, "earthtubes" (buried ventilation ducts) have been associated with mold growth and IAQ problems. They are also expensive to install. You should be aware of the risks before you install one.

  6. STEPHEN SHEEHY | | #6

    Andy- you haven't articulated why you want this space? Are you an avid gardener who wants to grow food? An orchid collector? What you want the space to do will help determine how to build it. A greenhouse being used to extend the seasons at both ends is much different from one that must be heated to 70 degrees all year. Sunrooms/sunspaces are completely different from greenhouses both in how they are built and how they are used.

    Sunspaces are great. I have one in my new house and had one in my old house. They certainly add heat when the sun is shining, but lose it when the sun isn't shining. As a nice place to sit and enjoy the view and the sun's warmth, you can't beat a sun room, but only if you want it as part of your everyday living space. Sticking one on the side of your house and expecting it to keep you warm is probably not a good idea. Putting glass on the ceiling will probably roast you in summer and bankrupt you in winter, unless you are in a very benign climate.

    Where are you located?

  7. ylekyote | | #7

    I'm just a regular gardener of many veggies and sometimes decorative plants/flowers. Just a hobby and for home grown groceries.

    Here in western central CO we don't have to even turn on heat or burn wood on days it's sunny and above 25 F. It's great. Our stucco house has more windows than typical facing south and west, and 3 small 2x3' skylights.

    I figured the addition would be half greenhouse and half multipurpose/sun room wouldn't be too hard to keep warm in winter. If too cold I'd just shut it off on those colder days we have scattered thru winter. It is the heat in Summer I'm more concerned about.

    I have a good existing 17 x 30' slab on grade the previous owner poured for a barn he never built. One long side faces south.

    It's large enough for the same type addition but only thing is its about 50 yards from the main house. No big deal but not ideal.

    I could build on it instead and likely make it an off-grid cottage, fitness center, greenhouse all in one. It's large enough to have a loft for small bedroom on one end. I thought about having half of it be a tall 2-story height green house (for growing larger and tall trees/plants and opposite that would be a first level all purpose room with loft above it. Maybe a composting toilet and primitive shower with passive solar and wood heat in winter.

    So is the advice that if I build this onto my home, as attached wing, it may make climate control (of main home) more difficult, instead of better?

  8. StoneCircle | | #8

    Not to co-opt the question too much, but I am also interested in a greenhouse in the future. I'm in Massachusetts. It would keep house plants in the winter (cold intolerant plants like Boston fern, Wandering Jew, and Pothos), and we'd move many of the plants outdoors during the summer.

    Should we just use a south facing room inside the building envelope instead of trying to construct something outside the building envelope? Or, if we do have a "greenhouse" what should we be considering to make it worthwhile?

  9. GBA Editor
    Martin Holladay | | #9

    Keeping cold-intolerant plants happy during the winter always takes energy. You can provide them with artificial light, but that takes electricity. If you provide the plants with natural light, the glass -- either sloped south-facing glass or vertical south-facing glass -- will lose lots of heat on cloudy winter days and cold winter nights, so you will be using energy (space heat) to keep the greenhouse warm.

    The simplest solution, for one or two plants, is a south-facing window. A more elaborate approach is a bay window with a wide sill (stool) for plants. Still more elaborate is a greenhouse addition on the south side of your house. The greater the area of glazing that you include, the higher the energy penalty.

  10. STEPHEN SHEEHY | | #10

    Clara-Our pretty well insulated sunroom faces south. It has pretty good windows. Here in Maine the lowest temperature we've seen so far this winter is -8 F and the coldest it has gotten in the sunroom is about 40 F. So you can use such a room for plants that are cold-tolerant, keeping in mind that there is always the risk that an extended period of cold and cloudy weather may cause the inside temperature to drop below freezing. Not much growth happens, but in any northern climate, not much growth occurs in winter anyway. A south facing window wall will provide enough light. You really just want to keep plants alive until spring. You can always install a supplemental heat source and only use it if necessary.

    In our previous house, we had a similar room, but not as well insulated. We still managed to keep plants like rosemary through the winter, even though the room got below freezing.

    A free-standing greenhouse will require supplemental heat to keep temps above freezing. The typical greenhouse has minimal insulation and loses a lot of heat through all that glass. You also need ventilation to avoid cooking your plants. I think in our climate, greenhouses are great for extending the seasons, but too expensive to build and heat unless you are growing a very-high value crop.

  11. StoneCircle | | #11

    Thanks. Looks like it'll be better to incorporate spots to put plants by southern windows that are already in the design rather than creating a room with more glazing or a greenhouse.

  12. Rob_Shearer | | #12

    If you are interested in building science and greenhouses, check out this study by ACEEE. It may make you rethink what a greenhouse is or should be.

  13. wisjim | | #13

    About 25 years ago we added a sunroom on the south side of our 100+ year old farm house to replace an old porch that was rotting away. We used patio door type of insulated (tempered) glass panels and 4x4 framing between the glass. Roof is 2x12 rafters with fiberglass insulation between them. There are 2 skylights in the roof. Walls below the glass are 8" concrete block with 1" styrofoam outside of them. Floor is ceramic tile on 4" slab with 1" (maybe 2", don't recall for sure) foam under it. Most of the East and West walls are 2x6 frame with modest casement windows in both end walls for ventilation. All the glazing is vertical. The roof overhang was designed to give total shade of the south glass on June 21, but allows sun to reach the back wall by Dec. 21. The room is 24x12 feet, long dimension runs E-W. One exterior door to the east, and one door into the house.

    First thing we noticed is that the sunroom made the living area immediately adjacent to it warmer in the winter since that area didn't have the south wall exposed to the outside anymore. Without any auxiliary heat the sun room can get down to the low thirties/maybe high 20s if the outside temp is minus 20 or colder and it is cloudy. I often lose the pepper plants that I am attempting to overwinter in the sunroom, but my figs and other perennials survive with occasional nipped leaves.

    If I were to do it over, I would omit the skylights as they lose heat and let in excessive summer sun-and they leaked rain badly for many years until we completely replaced the original shingles and improved the flashing and sealing around the skylights. I would also do a better job of insulating the outside walls and under the floor--but I thought we did pretty good for the early 1990s.

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