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Converting a porch to a greenhouse

Posted by tropicofcancer 6b (My Page) on
Wed, Feb 22, 12 at 14:03

We have 10ft deep and 14 wide porch with a concrete floor. The roof is actually our bedroom so I would have to put some glazing on the south and east facing side. The north and west sides are walls of two different rooms. In the winter the porch is pretty well lit and so I was wondering if converting it into a greenhouse of a sort is worth while. I will be housing mostly tropical plants so it cannot probably go below 45 or so.

Currently, the ceiling is supported by wide (about 2ft) brick columns. The header is on top of these columns and the joists end on the header. I was thinking to replace the brick supports with say 6x6 posts very 4 feet or so. This is mainly to increase the amount of exposure to the sun. Do you think that is a good idea? Any advise will be appreciated.


Follow-Up Postings:

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RE: Converting a porch to a greenhouse

Your approach to swap out the 2 ft brick columns with 6 x 6 wood supports may be pragmatic, in terms of increasing the amount of glazing + sunlight. However, it seems as though the brick columns may be aesthetically important to the house's character - "character defining elements" as we call them in historic architectural venues.

It's difficult to pass judgement on this without seeing photos showing an overall view of the east and south facades, and interior views of the porch. Additionally, although, a 10 x 14 structure is not huge and 6x6s 4' o.c. would probably suffice, what does the upper roof area consist of. These total roof and floor dead + live loads need to be assessed to qualify whatever columns you are considering.

Without knowing the house design, my recommendation would first be to try and retain the (two?) brick columns, then infill with a combination of glazing and an exterior glass door. Even considering the concrete slab as a heat sink, solar heat storage devices may not be possible without some overhead glazing, and your floor area does not allow much space for water tanks. So, consider providing some form of supplemental heat for the times with no sunlight - as well as adequate insulation.

Sounds like a great project - best of luck with it.


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RE: Converting a porch to a greenhouse

Thanks for your reply. I had been thinking about brick facing, especially since this is the front face of the house. The previous owners had already altered the looks though. Nevertheless it is a good point.

This is not a plain attached porch. Those brick columns do support the upper floors. The floor joists run from the front of the porch to the back wall and supported by two more internal walls about every 12 ft or so. I was going to consult some structural engineer for the design. I am sure I would need a permit too. I will have to talk to my neighbors too to see if they have any objections.

The porch would definitely need some extra heating. I doubt that keeping the window (to the porch from the living room) will be sufficient.

Any concerns with humidity, insulation? All the walls and roof to the rest of the house are insulated. I can remove the insulation in the ceiling or should I leave the insulation as it is?


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RE: Converting a porch to a greenhouse

Wouldn't the bricks also create some radiant heat that they absorb from the sun? I think that would be beneficial for your plans.


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RE: Converting a porch to a greenhouse

toc,

Been away for the past few days and don't frequent these forums very often - sorry for the delay in replying to your questions.

Perhaps I wasn't clear - my comment referencing your 2 ft brick columns was not a suggestion to repeat the brick as a veneer over your house' facade. I was questioning your proposal to remove the brick and replace with 6 x 6 posts.

Again, it is difficult to make design recommendations without knowing the existing house design - but, it may be that retaining the columns because they are character-defining elements to your home's architecture, should at least be considered in your planning - especially since it is the front facade. Also, rafor makes a valid point concerning the potential thermal storage mass properties of the brick columns. They are excellent for storage of passive solar heat.

Additionally and typically, columns in this application are continuous with brick piers which support the ground level floor deck. Removal of the upper columns and replacing them with spindly wood posts may be incongruous to the house's intended and original design. This is especially critical at the outside corner - which should (visually and structurally) be substantial. But then again, I am assuming the house currently has architecture worth preserving . . . photos, please.

Putting all that aside, there are always concerns with moisture permeating the wood structure between a greenhouse and living space. There are so many variables to consider - depending upon your home's particular circumstances.

Moisture barriers are crucial, as are minimum insulation r-factors, both governed by building code standards as well.

Consider this. If the porch space you are converting to a greenhouse becomes a "habitable" space by enclosing and heating it (as defined in local building code definitions - interpreted by the building inspector), the exterior walls may need to comply with the minimum energy codes stipulated by your area.

It is advisable to retain the insulation between the porch and bedroom floor above - with a moisture barrier on the greenhouse side . . . for a variety of other reasons as well.


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RE: Converting a porch to a greenhouse

Great point by both rafor and archdiver on brick as heat storage device. I was sort of obsessing with increasing amount of sunlight since there is really no roof for the light to enter. In winter the sun is low enough in Pittsburgh that the porch itself is quite brightly lit and I wanted to use that.

I am including some pictures. The first one is looking at the house from front. The left side was converted into a small room by the previous owner. You can probably notice the lighter colored mortar on the new brick surrounding the window. I am planning/dreaming to convert the right side into a greenhouse for mainly winter use. I am looking almost straight north. South is behind me.

Front of house

The next two images are taken from inside looking outside. The first is one looking straight out and the next one is looking at the corner which is about south-easterly direction. The corner brick support is bulky about 30x30 measure from outside. The next column is about 22 inches. The wall comes up about 29 inches from the porch floor. The east side opening is about 92 inches and the two openings in front are about 72 and 68 inches wide.

Looking at the corner:

Porch corner

Looking at the front entry way:

Porch corner

One option, I was thinking is to just remove the brick wall in between the two supports in the front to the floor and leave all other brick intact. Then cover the rest in windows/door to let in light. This is the cheapest and least intrusive of all options (I think). What do you folks think? Any other brilliant thoughts/ideas/alternatives for a rookie? I am pretty handy with tools but with structural changes I do not want to take any chances.


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RE: Converting a porch to a greenhouse

Your photos clear up many unknowns regarding roof massing as it relates to the walls and masonry openings. Odd, that the house is similar to the mental picture I had formed, based upon your description.

I concur that removing the brick half-walls between the two columns will be relatively easy - since they are non-bearing. This would increase the amount of potential glass area and should improve appearances of the "solar room" as well. You can then be creative with the fenestration (glazing + door arrangements).

If you use a masonry blade on a circular saw, you may get a clean edge to the outside brick corners. I would form a reveal - or slight setback, between the brick face and new glass panel frames. The remaining cut sections beyond the frames, can be concealed by the use of cedar extension jambs and/or bench supports.

As a means of introducing more natural sunlight, I would seriously consider opening sections of the roof, from the upper intersection of the second floor shed dormer, down to a vertical plane intersecting the inside face of the porch header.

This distance appears to be about 3 feet - measured horizontally, and will enable the use of either custom, fixed double insulated glass panels, set into cedar frames or aluminum channels. Or, size the openings to receive four stock skylight units. If you have standard 16" framing centers, simply head off every other rafter bay.

Since the second floor joists also serve as porch ceiling joists beyond the second floor south wall, and bear on the south side header, you would need to size new headers under the second floor south wall. These joists seem to cantilever over the first floor south wall - which is set back from the second floor wall, so the loading is relatively light.

Then either create individual light shafts at each opening - up to the skylight frames, or open up the ceiling along the full porch width, up to the underside of the roof rafters. The section of ceiling remaining under the bedroom floor, would form a soffit of sorts over the sunroom. This of course, is an ambitious task, but relatively simple for anyone with basic carpentry skills.


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Correction -

On further thought and after a closer look at the photos, those joists are not clear-span and do not cantilever over the first floor wall. The second floor wall bears just beyond midway on the joists, and even though structural calculations are simple, I would advise you to seek professional engineering assistance with the framing design - or hire a local architect.

Could be a nice project for very little expense, if you do most of the work.


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RE: Converting a porch to a greenhouse

Thanks archdiver for a very detailed and thoughtful answer. I am a bit confused primarily because I am still not familiar with all the terminology. Here it goes:

If you use a masonry blade on a circular saw, you may get a clean edge to the outside brick corners. I would form a reveal - or slight setback, between the brick face and new glass panel frames. The remaining cut sections beyond the frames, can be concealed by the use of cedar extension jambs and/or bench supports.

What do you mean by remaining cut sections? Are you referring to the fact that the cut will not be clean all the way through?

Is it worth taking the brick wall on the east side too. We get a few hours (may be 3 hrs) of morning sun on that side or is it better as it is to capture heat instead?

I had thought about putting skylights. I thought I will first remove a portion of the tounge and groove ceiling in the front to check how it is all put together. This is an old house (1920) and it is full of surprises. Your guesses are very close to what I think it is. The second floor wall is set back about 2ft from the inside of the porch header. The rafters are 16" apart. Are you suggesting putting in skylights every other rafter space? That is I think quite doable. I can also paint all the wood white so as to reflect more light inside.

Do I need to think of perhaps to be able to open one of the skylights to vent excess heat?

Does cantilever refers to the joist being one piece pivoting over the first floor wall? I was a bit confused about the structural suggestions since it seemed these changes are not modifying any load bearing elements?

My guess was that the ceiling joist spans between the first floor wall and the porch header and then extends a bit for the eaves. The second floor wall is sitting on the joists about 7 ft or so from the first floor wall. (I had made an pretty accurate drawing and I cannot find it now.)

I think this plan will work. Waiting for spring and planning away.


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RE: Converting a porch to a greenhouse

I thought the brick columns were thick - at least 16", therefore - a 7-1/2" masonry saw blade can only cut a minimal slice off each face, leaving a rough section which needs to be chiseled out. Looking closer at the photos, they're only one course, or 8". You should be able to clear that.

I'm not able to spend any time answering your other questions right now - heading out. Wiil check back later.


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RE: Converting a porch to a greenhouse

Thanks. The brick columns are as you say 8 inches. A little more than that but that is what it is. Yes, I think I can cut those fairly clean. The ridge left in the middle I can chisel/cut but will not be very smooth.

Thanks, I will await your answer whenever you can. This has been helpful to say the least.


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RE: Converting a porch to a greenhouse

toc,

You should carefully consider the skylight placement, spacing and alignment, so the overall effect is balanced, ordered and of course, best directs sunlight onto your plants. What I would attempt, is to space 4 units equally, so they align with second floor windows and open spaces between the brick supports.

You could also consider grouping them into 2 separate groups - mulling 2 units together alongside a double rafter (for added support). There are optional standard flashing channels available for this purpose. The end result would align one group over the stairway/entrance and the other over the adjacent bay, centered on the opening below.

It is a good idea to order operable skylight units to vent during warm weather. You might also consider incorporating a horizontal wood rail into the glazing assembly - perhaps aligned with tthe plant bench. Additionally, consider placing operable windows, such as awning units, along the lower portion of each glazed window opening - south and the east sides. This will allow natural convection to cool the space.

It's your choice to decide whether to remove the east side bricks - although this may look more consistent with the front and function better as well.

I just noticed a little deflection on the center brick column - seems as though the center area may be bowed out of plumb. This is something you really do need to check out - may be just lens distortion, but after enlarging that area - it appears there may be a potential problem.

deflected-column

By removing the span of bricks between the columns, the problem (if it is indeed bowed) may be exacerbated. Of course additional support will be introduced, by building rigid wooden rails (horizontal) and stiles (vertical), required for the new windows to the east of the center column, and entrance door/side panels to the west of the column.

Another point to consider, is how your family and guests use the front entrance in cold months. As you know, opening/closing the new doorway will allow heated air to escape and cold air to enter. One solution to this problem is to provide either a double door air lock (vestibule) perhaps 4 feet inside the new doorway - which enables users to close one door before opening another accessing the greenhouse area. Or, create a separate full depth hallway to the existing front door. Naturally, this plan reduces your sunroom space, considerable.

Hope this helps.


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Another thought . . .

Meant to say "considerably". I hate the spell predict on this computer.

On the topic of airlock entry - you could also consider not enclosing the area west of the center column and simply build a wall separating the porch into two spaces, an open entrance porch and enclosed sunroom.

You need to decide if the smaller space is worthwhile - which seems as though it may equal the room to the west, the previous owner had constructed.


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RE: Converting a porch to a greenhouse

Just saw your message and I immediately went out to measure the deflection with a 2x4 and my 4ft level. The center column is pretty plumb. I guess it is lens distortion. Damn nikon lens at 18mm focal length.

On the other hand the corner is not plumb. The L shaped brick has deflection towards the top. The column is about 94" and the top is bowed out about 1.5" on the east side only. The south side is plumb. I presume over the years there had been some outward pressure because I can see some of the bricks are shifted.

Is this a problem that needs to be fixed? I am sure it will show up when I frame the openings for windows on the east side.

I thought of a double door system. This is back when I wanted to extend the greenhouse in the front adding around 6ft of depth. But soon I found out that I need a variance for that and got discouraged. One of my neighbors is not very keen about it and the others could care less. I am leaning towards using the back patio door during the winter months. Much simpler.

I am also seriously thinking of taking up the space in the little room for the greenhouse. Actually it is two rooms. One powder room that is about 4 ft wide and a little reading room about 5ft wide. I think I can eliminate that reading room. The problem is that reading room is my office where I am sitting and typing this post. I think the best option will be to put my computer in the greenhouse and work from there. It will be funny but I will be happier and my wife will go nuts.


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RE: Converting a porch to a greenhouse

Sensible choice, all considering. Maybe you can convince the wife to at least agree on installing a skylight over the south facing window. But don't push it too far though, after 35 years of marriage to the same woman, I am very astute to the establishment of mutual agreements in marriage relations. Fortunately, My wife shares my joy of gardening and indoor propagation. ;-)

Best of luck.


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RE: Converting a porch to a greenhouse

Good points. We are 22 years together and I always collaborate. I focus on strength, durability and function. She focuses on looks, beauty and simplicity. Works out great. She has become good with power tools but a single earthworm can still make her jump 2 feet in the air.

So I presume that 1.5" deflection on the east of the corner column is not a big deal or should I consult an engineer?


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RE: Converting a porch to a greenhouse

In most situations involving masonry supports which show any form of deflection beyond normal, it is advisable to investigate why. Even 1-1/2" in a 7'-10" high structural support is significant.

Does the foundation show any signs of upward thrust, or frost heaving, any cracks in the porch slab? It's my guess there is no crawl-space or basement under the porch, but if so, check the underside for anything which appears unusual.

In this application where you have an 8" support wall, there's a double thick coursing of brick. It's apparent the columns are solid brick, so the bricks should have hollow cores, vertical rebar and filled with concrete. If not, it would be difficult for the original mason to install vertical re-bar within the coursing. This is standard practice for preventing outward deflection.

It's obvious that without anything to anchor the bricks together, such as reinforcing bar, any significant downward force will cause the bricks to thrust outward. You cannot rely simply on mortar joints to do this. Unfortunately, hard to tell unless you have access to an x-ray, or metal detection device.

It appears your neighbor has a similar house - could be this design was repeated as a planned community back in the 1920s. Check other homes for visible problems and if other owners had made corrections through the years.

It would be wise to hire an engineer for his opinion, but most will suggest an overkill solution, even if unwarranted. Where there's doubt, at least contact a knowledgeable local builder for his recommendations. He may even do it as a complementary service.


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RE: Converting a porch to a greenhouse

I will probably need a picture for this but it is raining here. The cement floor shows no sign of cracking. It is, I think, sitting on dirt/fill. The brick wall foundation is only around the porch area. On the east side I can see there had been shifts and the mortar joints were refilled. So there must have been some shift. The rest of the house has a limestone and mortar foundation that is about 20 inches thick with no apparent shift. Exposed part of the foundation are these huge cement blocks. In my opinion the corner probably sank a bit and it did not happen in the last 30 years or so. This is how long our neighbor has been in their house and they say they have noticed the black mortar fix ever since.

Yes, our next door neighbor is the same type of house. In fact in our block there are 4 groups of 3 identical houses. I find this strange way of building houses. The two other that are next to me do not show any shifts.

Those bricks are solid not hollow core held by mortar. I am pretty sure of that. I ma pretty sure there is no rebar there. I always wondered how is it able to support the house.

What would be an overkill solution?

I was thinking may be somehow put an extra support inside the corner would be sufficient. I am going to try find a local builder but I doubt anyone will do it as a complimentary service :(


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RE: Converting a porch to a greenhouse

If you decide to convert the porch, then solid (4x4 min) pressure treated wood jambs for the windows - from header to slab, should support the load and prevent the brick wall sections from deflecting any further. This is assuming sections below windows are removed.

If you don't remodel to porch and are just looking to support the second floor + roof, it's important that whatever is used makes positive contact between the existing structural header/or beam and a firm base - such as bearing on the slab as close to the wall as possible.

Whatever you decide to do will be a balance between your budget and acceptable aesthetics. It really boils down to using a basic knowledge of physics, taste and common sense.


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RE: Converting a porch to a greenhouse

Thanks a lot for your input. I think I have a project in my hand for spring/summer. May be I will post an update in the future when the conversion gets a bit farther along.


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