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Community and Q&A

Porch Insulation

Faulted1 | Posted in General Questions on

This is another of those porch attic insulation interface questions–
Zone 4 – New construction
A couple of attached 3 season porches are created by overhanging roofs. The roof is truss built and the area over the conditioned space will be an unvented conditioned attic insulated with spray foam.

The main question is how to handle the attic space over the porches–

Due to the porches being created by the overhanging roof trusses and since the attic is unvented, it is not practical to vent the porch attic. Let me clarify, it is not possible to vent the top of the attic space through the roof with ridge vents etc. but soffit vents are possible.

Since the porches are not large, the expense to bring them into the conditioned attic space is not a killer. If this option were chosen, I would continue the insulation of the underside of the roof deck with the spray foam and then cover the porch ceiling with cellulose to create a continuous insulation barrier.

But would it be better to stop the insulation envelope at the connection between the living space and porch ? This would create a “separate” minimally accessible attic space. I don’t see any practical way to vent this space. Is venting necessary, if it was “cut off” from the main conditioned attic? Should the porch ceiling still be insulated to lessen the heat transfer to the porch?


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  1. Foamer | | #1


    We have worked with a large number of porch "attics" on older homes in our area (zone 5). Typically, they are neither vented nor insulated and we have yet to find any structural issues caused by lack of ventilation. Since the porches are unconditioned, the usual moisture and vapor flow concerns that we have for between the inside of the house and the main attic are eliminated.

    If this were my project, I would stop the conditioned attic space at the point of the insulated walls of the house. Install a solid surface such as OSB or foam board that reaches from the wall sheathing to the roof deck. Your spray foam contractor can then continue the roof insulation down to the top plate of the wall.

    If you want to reduce the radiant heat reaching the porch from the roof above it, it is certainly worth while to foam any roofs with sun exposure but leave the porch ceiling alone.

  2. user-659915 | | #2

    100% agree with Torsten. Extending the insulation into the porch roof will needlessly increase the area of heat transfer through the insulated surfaces.


    We did have an inspector who was "uncomfortable" with leaving the attic over the porch un-ventilated. Rather than argue we simply installed vented soffit on both sides of the porch and the inspector was willing to compromise and not require the ridge vent. This is the one place where we use foil backed roof decking to keep the heat out of the roof attic.

  4. sarlindo | | #4

    I just had a new un-ventitlated porch overhang attached to my house and this winter (live in toronto, canada) I am noticing ice build up along the side of the wall. Now I am not sure if its caused by heat/venting issues or roof or gutter issues. I was thinking of maybe putting some vented soffits? I have attached a photo of my current issue. Any advise would be great.

  5. GBA Editor
    Martin Holladay | | #5

    Does the roof include kick-out flashing?


  6. sarlindo | | #6

    I do not have any kick-out flashing, but now that the weather is warmed up a bit, I decided to record what was happening with the water and I think it's simply a poor job done with the eavestrough and down spout. I think they accidentally over shot the down spout to line up with the bottom eaves and restored to some sort of macgyver to direct the down spout into the eaves. I have posted a video here

    let me know your thoughts.

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