moisture a problem when attaching greenhouse to house? Solar gain for home?

I have a south-facing exterior wall of my house (insulated) that the living room patio . If I build a greenhouse against it, will I have trouble with humidity down the road?

What can I do to prevent overheating the house in the summer (we get several days of 30 dec C) - Do I need to pull down the house roof so that the room is shaded in summer, but not in winter? We currently use a roll down blind.

I have not heard of any issues regarding humidity . I would look at blinds for the green house and good ventilation .

David

Ben Falk talks about potential moisture issues when attaching a greenhouse to an insulated building.  He recommends attaching it to an uninsulated building like a barn....  I haven't really heard anything else against the idea.  We built our attached small (7ftx14ft) greenhouse last year on the SE side of our house.  We only use it for starting seeds though so we haven't really used it at all past our frost date.  We use a separate hoophouse for growing tomatoes in the summer.  I put vents up at the peak of the greenhouse to allow moisture and heat to easily escape.  The vents aren't big enough though and we had to often keep the door open during the spring when we had seedlings.  As I mentioned we've only had it for a year, and I can't very easily see inside my walls, but everything seems fine so far.  We also were able to keep kale alive in there all winter last year without heating it.  We experienced outdoor temperatures of at least negative 25 degrees F last winter but I don't think it got below zero in the attached greenhouse simply because it was absorbing heat from the house.  The outside walls of our house are covered with tar paper and plywood siding.  So I would say if you have tar paper or house wrap under your siding, you'll probably be fine, but I suppose only time will really tell!

Oh yes and I would recommend doors on both sides for cross ventilation..... and larger vents at the peak.

maybe if you call it a conservatory you wont have these problems :-)

My experience says in summer when heat and moisture are highest, ventilation is not only possible, but desired, so no real problem.

In winter when house is closed, things are naturally dryer, so  moisture is welcome, and not a problem.

Depending on house and vent design, a greenhouse can create a solar stack effect that can actually assist ventilation from the rest of the house through the greenhouse if desired.

If there is a source of cool air- under the house, a shade house on the north wall, or an earth tube-- the greenhouse stack effect could actually help cool and dehumidify the house

I live in the same cold wet climate at Ben Falk.  Moisture is a problem in attached greenhouses here in New England.  My husband and I are considering adding an attached greenhouse to the front of our house or a free standing barn and greenhouse combination.   We want to put in a climate banking system to pull the hot air and humidity below ground to reduce the temperature swings inside the greenhouse.  

I also took a tour of Steve Whitman's greenhouse which is also northern New England and his greenhouse uses a climate banking system and it didn't have a musty smell or signs of too much moisture effecting the wood framing.    I was really impressed with his design and how it functioned.  It struck me as a better solution to a grid tied house than Ben's greenhouse for reducing moisture damage to the main building.  

Here is a video tour of his property and he starts talking about the greenhouse at the 15: 20 minute mark.  
https://www.youtube.com/watch?v=yP_grF8dvyg

If you decide on getting an exhaust fan, either now or down the road. There are humidistat thermostat combinations available to regulate both heat and humidity conditions in your greenhouse. The heat gain in summer made a house I had owned in Boulder Co. unbearable, though in winter I had a common door to direct the solar gain into the house and made winter heating costs very reasonable and a great place for morning coffee. Opening windows just did not do the job for the summer heat gain. I did not have exterior shades but had interior shades which was a mistake.

You can also, more passively design a solar chimney from a thermal mass inside the greenhouse that creates a convection current to exhaust unwanted heat, but does little for humidity control.

Isn't it possible to minimize moisture loading by mulching everything. I also thought that it wouldn't be too difficult to drain all the catch pans into a container and recycle the water.  I tend to think about the ideal of living with your garden. We give them love; nutrients; water and CO2. They give us Oxygen; psychological warm-n-fuzzy feelings and food.

House exterior walls are not waterproof. If you have super high humidity air on the outside, it will make its way into your house's walls and feed mold, rot wood, etc. cement is not waterproof. stucco is not waterproof. wood is not waterproof. tar paper may be pretty waterproof, but usually when the side of a house is layered with tar paper, kraft paper, or house wrap, it's layered, much like shingles. it's designed so that gravity will pull water droplets (i.e. from rain) away and out from the building. If you build a greenhouse, humidity is air, not water droplets, and will happily go upwards into your house.

I would not recommend an attached greenhouse, because of the humidity.

An attached/enclosed porch is different, because there is no moisture.

Kevin Wang wrote:House exterior walls are not waterproof. If you have super high humidity air on the outside, it will make its way into your house's walls and feed mold, rot wood, etc. cement is not waterproof. stucco is not waterproof. wood is not waterproof. tar paper may be pretty waterproof, but usually when the side of a house is layered with tar paper, kraft paper, or house wrap, it's layered, much like shingles. it's designed so that gravity will pull water droplets (i.e. from rain) away and out from the building. If you build a greenhouse, humidity is air, not water droplets, and will happily go upwards into your house.

I would not recommend an attached greenhouse, because of the humidity.

An attached/enclosed porch is different, because there is no moisture.

Kevin I think you exaggerate humidity's ability to pass through vapor barriers. If it were true then greenhouses would never accumulate humidity, they would just release it to the outside air.

But I think I'm the other way. I want to trivialize humidity.

One factor to consider is the temperature of the greenhouse. If we allow the temp to get very hot the greenhouse becomes a powerful evaporator. If the temps are kept low by heat-sinking to a thermal mass it becomes a poor evaporator.

I think with some carefulness I think plants can be house-trained. Incorporate these:

<> efficient heat transfer to a substantial thermal mass

<> keep all soil well mulched

<> drain all catch pans

<> avoid over-watering,  which I think people tend to do to help the plants survive the massive heat of the "hot house", which if you control becomes a non-issue.

<> good ventilation (and not just for the plants, we need ventilation also). Install a heat recovery system and exchange 4-500 CFM.

Hi Susan,

What type of construction is your house?

Your profile says that you're in Lake Geneva Switzerland, and I know that while Masonry is common in the cities, a lot of places are still built with a significant amount of wood, especially on upper stories.

From what I can look up online, it seems that Geneva averages 60%+ humidity most of the year. This is important because of the relationship between relative temperature and humidity. If there is a significant change in temperature from the outside-in or vice versa, you are likely to have condensed water on the glazing of the greenhouse. In a dryer climate, it's much less of an issue.

If you have a house that has a significant amount of wood in the south facing exterior wall, I would strongly suggest you deal with a local architect or building scientist on how to detail the attachment, of the greehouse. They might tell you that it's not a good idea, or will require a significant amount of additional ventilation to do without endangering your house to mold and rot issues in the future.

If you do have a house with a southfacing wall that is primarily/only masonry, you shouldn't have any major issues. You should still want to pay close attention to either side of the wall during the first few season, and that will allow you to see if anything develops before it is a health hazard. Make sure that furniture isn't touching that wall so you have a clear view of the entire surface when you're checking.

Best of luck on the new greenhouse!

Nicola

Kevin Wang wrote:House exterior walls are not waterproof. If you have super high humidity air on the outside, it will make its way into your house's walls and feed mold, rot wood, etc. cement is not waterproof. stucco is not waterproof. wood is not waterproof. tar paper may be pretty waterproof, but usually when the side of a house is layered with tar paper, kraft paper, or house wrap, it's layered, much like shingles. it's designed so that gravity will pull water droplets (i.e. from rain) away and out from the building. If you build a greenhouse, humidity is air, not water droplets, and will happily go upwards into your house.

I would not recommend an attached greenhouse, because of the humidity.

An attached/enclosed porch is different, because there is no moisture.

i see your point, siding is generally oriented in mind with water travelling towards earth and there is lots of air gap between each shingle or sideboard. with long enough exposure, high humidity will seep upwards through the gaps in the siding.

perhaps it would be a good idea to extensively caulk any air gaps and put a strong layer of paint on top of the wall which will get the attached greenhouse .

We are considering building a Walipini in a nook area of the south side of our home.  Part of why we picked the location is due to the cellar walkout.  (Image below to see the set back area for clarity)  I'm a bit concerned about the short end facing west instead of east, but for the walk out ease and the nook in general, it seems a rational placement despite that.

Thank you to everyone that contributed to this thread, as it gives me some more points of information to research and consider.