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Enclosed “3-season” porch in front of 16 foot sliders

user-1140356 | Posted in Green Building Techniques on

Enclosed “3-season” porch in front of 16 foot sliders: Where to put maximum r-value?

For a house in south Jersey, I will be enclosing a porch with some sort of glass or plastic. The porch is in front of a 16 foot wall of sliders that lead into the great room of the house. The porch is on the south and has 1.5 foot eaves. The porch is 10 feet deep by 28 foot long. It is in the Pine Barrens. The house is being constructed with 12″ double stud walls filled with cellulose (r-40). The windows that are not looking out on the porch are Inline windows with u factors of either .16 or .20 and high SHGC values of .5. Because the house is in a deep pine forest, the amount of pollen is nothing short of unbelievable. My neighbors do not use their porch from late April until late June (they are considering enclosing their porch).

What I would like to know is the value of different options. Obviously, the interior 16 foot sliders would not benefit from the high SHGC since they are completely shaded by the porch. So I can get a low u factor for those doors and not worry about a high SHGC.

But how can I determine the value of enclosing the porch with different kinds of windows? I can cheaply add a storm door system all around the porch, or I can enclose it with plastic. Or I can get more sliders. How would .3 u-factor sliders in both the interior sliders and the exterior sliders work for energy efficiency?
The goal is to keep out the pollen and still be able to open the porch up in July and do it as efficiently as possible.

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  1. GBA Editor
    Martin Holladay | | #1

    I'm not a fan of south porches. I'm a fan of west porches. (That's where you want shading for your windows.)

    It seems a shame to design a superinsulated house with high quality walls and windows, and then to mess up the design with a south porch.

    Is there any chance that you can move the porch to a different orientation?

  2. user-1140356 | | #2

    Thanks for your thoughts but I'm afraid we are tied to an existing footprint. It's Pine Barrens riverfront and fairly protected. I'm looking for a way to maximize the benefit from the need to enclose the porch to avoid the massive pollen in the spring. It is on the south west but the tall pine trees are already shading the porch by afternoon.

  3. GBA Editor
    Martin Holladay | | #3

    Here's my thought: If you enclose the porch with windows, it's not a porch any more. It's now a sunroom or an addition with inadequate heating and cooling.

    Before you can decide how to specify your windows and wall insulation, you have to think about how the room will be used.

    Frankly, a south-facing "three-season room" will be too hot when it's sunny, and too cold when it is cloudy.

    Perhaps what you really want is a screened porch.

  4. user-1140356 | | #4


    You are absolutely right. I do want a screen porch. But the amount of pollen is too much. Last year, we were forced to hose the porch off every day for 3 months. We could not leave our wicker furniture on the porch as it had to be scrubbed with a stiff brush before any use. The pollen is pretty nasty.

    So we need to somehow enclose the porch with sliders (or something) from April until June. Since we definitely will be enclosing the porch, we are looking for the best, most efficient, cost effective way to do so. The porch looks out on the river and the interior sliders look through the porch. If this were not the case, I think we would be using roll-up bamboo blinds (or something similar) on the porch. Right now, we are thinking cheap vinyl sliders. I'm wondering how the insulation value from sliders on the outside of the porch will effect the overall insulation. The interior sliders will most likely have a u-factor of .3



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