Renovating a house into solar passivity?

Up until now I've only been considering building from scratch, which makes a passive design relatively easy. However, now we're seriously considering buying a house to renovate. How feasible is it to renovate a house so that it becomes passive? We don't have any particular house in mind yet, so I understand answering this question definitively is not really possible. I can sketch a probably scenario though: We buy a brick house in Belgium, don't change anything substantial to the bedrooms/bathroom. At the ground floor, we want 1 large space with a kitchen, living room and greenhouse. It might be easy to connect living room and kitchen, and extend the space with a greenhouse. It's reasonable to assume the house is pretty well insulated. Lots of windows around the greenhouse would bring in sun. But of course, this would probably not be enough to make it solar passive. Some uncertainties I have:
-can we introduce enough thermal mass for the entire house in just this 1 space?
-how to walk the line correctly between warm enough in winter, but not too hot in summer?
-what are the parameters that would make such a design (im)possible? How to properly vet a candidate house for this?

Philippe,

Anything is possible, however there are downsides to capturing the heat energy in a location that isn't where you need it, namely you have to use fans or other mechanisms to move the energy as it is used. It takes more airflow than you would think to move btus from place to place using air with a small delta in temperature, and fans take energy to run.

My personal experience is that if you design the solar capture to provide enough heat on your coldest nights you need a way to turn the system "off" when the weather is more mild, e.g. exterior shades and/or a heat dump (opening a door).

Moisture control would need well thought out if connecting a plant growing greenhouse to a normally constructed house or you risk mold.

Anyway hope some of this helps, best of luck.

To get ideal solar heating in winter and avoid any heating in summer, you have to have your main windows or glazing be only on a wall that faces exactly south, or within about 15 degrees of south. Any other direction of windows will lose heat in winter and gain unwanted heat in summer, especially early autumn when the house is already hot. That makes it hard to retrofit a random house to passive solar heating.

These are great tips I hadn't thought about! I'll ruminate a bit on these, and I'm sure I'll have lots of (more specific) questions

If you choose a house with a roof ridge that's orientated west/east as a basis, and ideally, already has the living areas facing south, you can, if needed, add bigger windows and shading to allow the sun to shine into the house in winter and keep it out in summer.

I'd recommend having a lean-to greenhouse on just part of the south-facing side with a way of sending the heat upstairs to an open loft area in summer and use climbing plants, trees etc. to shade the sun. I use plants a lot for wind breaks and for controlling the comfort around our house. They're cheap and beautiful and carefully chosen, can leaf and flower exactly when you need them.

We're in South West France and have temperatures that range from -15°c to 42°c. Our house is about 350m² and I've never seen it more than 25° in the summer and it's warm and comfortable where we need it in the winter. A few times a year we've more than twenty people here for PDCs and other courses, normally in October and January. We use less than 4m² of wood each year to heat the house, cook, for hot water, drying plants, clothes etc. We also buy two small bottles of propane a year for summer cooking and use a pocket rocket fuelled by corn husks and waste wood. We're off grid with a very modest array of photovoltaic panels.

I've posted some details of the house (including a video of the interior temperatures when it's more than 40° outside) plus a few more ideas to provide more comfort. The thread is here, I hope it helps you in your planning.

https://permies.com/t/90659/today-August-Southern-france#960988

-can we introduce enough thermal mass for the entire house in just this 1 space?

Probably not. But you don't need to. If you can introduce some thermal mass, that would help to increase the temperature when you need it, even if it's not comfortable, you will expend less in heating. Think of it as saving on your heating bills.

-how to walk the line correctly between warm enough in winter, but not too hot in summer?

By using manual elements, such as opening/closing windows, shutters, shaders, etc. Also using decidious plants. In summer, we have to operate the blinds twice a day. It's a work, but it's less expensive than running the AC the whole day.
Attics also help to regulate temperatures, by opening and closing their windows and doors, provided they are not inhabited (better used as storage room).

-what are the parameters that would make such a design (im)possible? How to properly vet a candidate house for this?

Being shaded by other buildings is a big no-no. Major windows facing North is another.
Having some planting space in the front door, and maybe the possibility for some temperature control pools are bonuses.
Then, there are specifics situations you should be aware of, like having a house in the sea shores, or where strong dry winds may happen.

Not sure if I understand what you mean by this:
'Having some planting space in the front door, and maybe the possibility for some temperature control pools are bonuses.'

One bioclimatic strategy is to have a decidious tree or vine in the sun facing facade. If the house you are going to renovate doesn't have a grape vine, but you have the possibility to plant it, then that's a bonus. Maybe you like mulberries more. This vegetation works by shading, evaporation (keep them watered) and also by the photosynthesis coolness effect. All combined, they make the air coming from your front door more liveable.

Another strategy is to use a small water pool inside a patio to regulate humidity. Do you remember these spanish houses with a small fountain inside the backyard? They were not just for the looks. In hot dry summers, the extra humidity works as thermal mass and also the evaporation cools the air. If your climate has wet summers, then it's of little help. In this case, plants will do better.
Also, large shallow pools on the sunny side help to capture sunlight in winter, like a mirror, if you have water to spare.

You don't have to do these things, but I would value the possibility just in case I needed more bioclimatic features to get the house comfortable.