Front Porch Sunspace/Greenhouse Conversion

Plotting on converting my south facing porch into a sunspace and figure it’s always good to reach out to the community for feedback. So if you care to follow along I’m open to suggestions!

General plan: glaze the south (front) and east (right) sides of this portion of my front porch.
Goals: greenhouse to start plants for the permaculture garden, utilize excess heat to warm the house by opening the house windows (and vice versa to keep the greenhouse from freezing when cloudy), nice place to enjoy some winter sun.
Design considerations: minimal disturbance to current structure. Build essentially a bubble out from the house wall but still using the structure for stability. Adding an insulated floor on top of the decking. Insulating the ceiling between the joists and adding sheeting underneath. Glazing inside the porch rails. Creating an air-lock double door entrance on the west side.
Reasoning: Thinking “bubble” on the existing decking for ease since it would be difficult to take this to the ground. Missouri has hot summers so I see little benefit to angling out glazing beyond the porch roof. I’d rather just take advantage of the low angle of winter sun. Airlock door to open porch would be easier than cutting a door into the house itself.  Thanks!

I love having an attached greenhouse on the south side of my house! It heats the house in winter.

I think your plan sounds great, very reasonable. A vertical glass wall is much easier to build, and yes, will collect less sun in summer than a sloping south-facing wall. Even better would be if you can remove the glass panels in summer (and maybe replace them with screened panels to make a screened in porch) to reduce overheating.

In the shoulder season (spring and autumn) it might get roasting hot in the daytime and kill those beloved little seedlings, so I strongly recommend you keep a way to completely open the east and west ends in daytimes and close them at night when needed. Large doors or windows. In early spring you'll still need to close up at night and open in the day.

I also like the idea of opening it up fully in the summer.  Pests and disease seem to thrive when they're in a more protected area.

Condensation in the winter on the glazing is worth thinking about before it happens.  The interior can get pretty humid as well so making sure your house siding and other wood doesn't start to rot is worth some planning as well.

Mike Haasl wrote:I also like the idea of opening it up fully in the summer.  Pests and disease seem to thrive when they're in a more protected area.

Condensation in the winter on the glazing is worth thinking about before it happens.  The interior can get pretty humid as well so making sure your house siding and other wood doesn't start to rot is worth some planning as well.

Any strategy you would advise me to read up on regarding condensation on the glazing, or is just something you have to deal with and make the rest of the build rot resistant? I'll consider treated plywood for the floor and maybe plastic paneling for the ceiling. Siding is vinyl so I'll just have to hope that's enough to protect the wood beneath it.

The main strategy is to just plan for it.  The glazing will be wet and dripping about 1/4 of the time.  So where that water runs down to is where it will cause problems.  I make little gutters on my glazing with J channel and it seems to be containing most of the problem.  The condensation is mainly where the low R value materials are (warm humid greenhouse and cold outside interface).  The other materials will just experience up to 100% humidity.  That might be just fine for exterior grade stuff.  I just wouldn't want it venting into my attic or possibly rotting out wood siding.

Matt, you'll get a lot of heat on the western end of the porch, more than the eastern, especially in spring and fall.  So when the direct rays of the setting winter sun are angled away from the southern side, they will be more direct on the western end.

So where is all the water going to go on the floor, the overflow from pots/containers, etc., and will the high humidity of that greenhouse room bring in too much moisture to the main house?

Gnats are an issue where I am, they love the soil and heat.

I do not get any condensation in my attached, converted sun porch with greenhouse attributes, which is what you are doing.  part of this may be that it is open to the main house every day, which is how I get the heat, and so any moisture evaporated from the relatively small amount of plants ( wet soil) do not make a noticeable change to the house humidity.  In mine, I open a door to get the connection, looks like you will open two windows.  

I am right now getting lots of good heat as it is a sunny day.  

Maybe you will have more plants.  For me, the plants change seasonally.  right now it is onion starts and about to start peppers.  I should have a flat with cutting greens, but I was away.  Later in the spring I will have added tomatoes, sweet potatoes, various veggie starts.  But I have never had moisture build up.  

The cats love to hang out there in the morning as it gets hot sooner than the house itself.   My area has single pane windows which are in screen frames and held in with screen clips and can be swapped out in the summer with screens.  There is a sliding door to the outside at one end, with a screen, and yes, in the shoulder season as it starts to get hot, you must make sure to plan ahead that the "greebhouse" is open either to the house, wehn we need heat, or the sliding door open some amount to let excess heat out.

I removed roofing on mine and replaced that part with corrugated clear panels, so mine can get quite hot, and yes, this means hot in the summer.  SO, it must be left open with just screens in the summer.  I could have a grape vine, vine part planted outside, vine growing inside the greenhouse, to provide summer shade, but my area is smaller I I never got around to it.  

Cristo Balete wrote:Matt, you'll get a lot of heat on the western end of the porch, more than the eastern, especially in spring and fall.  So when the direct rays of the setting winter sun are angled away from the southern side, they will be more direct on the western end.

Thanks, the west side would be much smaller since the front door is closer to the west side of the porch and I want to keep that clear. I'm coming around to the idea that it will be more practical though, doesn't need to be as big as I had planned for the east side.

What you say about East/West sunlight makes sense for my site in particular because of trees to the east (still an issue, even when bare in winter) but I feel like you're telling me something new here that I'm curious about. On a neutral site with no obstructions, wouldn't the eastern morning light be the mirror image of the western evening light so either way the heat generated would be the same?      

Matt Todd wrote:

Cristo Balete wrote:Matt, you'll get a lot of heat on the western end of the porch, more than the eastern, especially in spring and fall.  So when the direct rays of the setting winter sun are angled away from the southern side, they will be more direct on the western end.

Thanks, the west side would be much smaller since the front door is closer to the west side of the porch and I want to keep that clear. I'm coming around to the idea that it will be more practical though, doesn't need to be as big as I had planned for the east side.

What you say about East/West sunlight makes sense for my site in particular because of trees to the east (still an issue, even when bare in winter) but I feel like you're telling me something new here that I'm curious about. On a neutral site with no obstructions, wouldn't the eastern morning light be the mirror image of the western evening light so either way the heat generated would be the same?      

The eastern sunlight is more valuable, to me, because that is when I need the heat the most.  The house and sunspace are cold in the morning, I want that east sun, if I can get it, to start the place warming up.  By the late afternoon, getting more heat, while fine, is not as needed as the house has been heating all day and is warm.  

My opinion from eeking out passive heat over the years

Glazing will be complete this weekend! It occurred to me that if I cut a hole in the porch floor and build a box to connect basement air to the porch, I can start a whole-house convection.
Air in the porch gets heated by the sun, flows into the first floor window, gives up heat in the house and flows back down the basement steps, and gets drawn back into the porch.
I welcome any design feedback.
I plan to configure the house window to open at the top half so the hottest porch air enters there. Not sure if I should direct air from the basement into another part of the porch though, or if it will still stratify just fine coming in directly below the house window.

Matt Todd wrote:Glazing will be complete this weekend! It occurred to me that if I cut a hole in the porch floor and build a box to connect basement air to the porch, I can start a whole-house convection.
Air in the porch gets heated by the sun, flows into the first floor window, gives up heat in the house and flows back down the basement steps, and gets drawn back into the porch.
I welcome any design feedback.
I plan to configure the house window to open at the top half so the hottest porch air enters there. Not sure if I should direct air from the basement into another part of the porch though, or if it will still stratify just fine coming in directly below the house window.

My only concern with that would be the large amounts of humidity that the greenhouse air will pipe into the house.  I would be very cognizant of mold issues and the like when you are first trialing this.

I would duct the basement air to the furthest point from the open window into the house to create air turbulence.  If you send the basement air into the greenhouse directly beneath the open window, I believe it will take the path of least resistance and go straight from the basement into the house without circulating air through the greenhouse.

I re-read the thread, and see others have mentioned the humidity.  Sorry for the redundancy.

Trace Oswald wrote:
My only concern with that would be the large amounts of humidity that the greenhouse air will pipe into the house.

My thinking is that there would only be a humidity issue if it were full of plants and their wet soil, so I won't try to load it up like a jungle right away. Need to see how it does  as a heat generator and how stable the temps are at night first.

I'm kinda with you on the fear of "path of least resistance" with air intake right below the output. But struggling to figure out where to direct the air instead. The easiest way might be to run insulated ducting between the floor joists under the porch to take air straight out to in front of the glazing.

Matt Todd wrote:

Trace Oswald wrote:
My only concern with that would be the large amounts of humidity that the greenhouse air will pipe into the house.

My thinking is that there would only be a humidity issue if it were full of plants and their wet soil, so I won't try to load it up like a jungle right away. Need to see how it does  as a heat generator and how stable the temps are at night first.

I'm kinda with you on the fear of "path of least resistance" with air intake right below the output. But struggling to figure out where to direct the air instead. The easiest way might be to run insulated ducting between the floor joists under the porch to take air straight out to in front of the glazing.

I don't think I would bother with insulated ducting under the floor, I think I would just use any old ducting or cobble something together out of plywood or something and run it inside the greenhouse.  You would lose a little floor space, but you will probably want a table or bench or shelves or something in there anyway, you could just run your "duct" under that.  You could run it along the walls to pretty much anywhere I think.

The use of Louvre windows set between the veranda posts would allow you to control air flows.
Having a combination of fixed and moveable glass would be easier to insert as panels between the posts.
Maybe think about a roof hatch to get rid of extreme heat or humidity.
Would the floor need to be made waterproof to prevent rotting?

It lives! And more importantly, it works. Thanks for the feedback. Here are the details: https://permies.com/t/173304/Solar-Porch-Passive-Solar-Retrofit