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Detail for covered entry door and exterior rigid foam with brick veneer

whitenack | Posted in Green Building Techniques on

Hi all,

There is plenty of discussion out there about proper techniques for window installation on thick wall construction, but not much, if any, for door installation.

Here’s my situation…

I’m going to have an entry door, flanked by sidelights, under a full covered porch, on a house with 2×6 studs and 3″ of exterior rigid foam, then an air gap, then brick veneer.

I haven’t decided on a porch material yet, but there is a strong possibility it will be masonry which I know is a large thermal bridge, which means I still need to the rigid foam between the house and the porch floor. How does one bridge the gap over the foam?

The sidelights take away the concern about innie vs. outie installation and whether the door can open fully, but I think I like the thought of an innie installation anyway so the door can sit on solid foundation as opposed to figuring out how to support the door system over the rigid foam.

So, considering an innie installation, what is typical in terms of threshold design, where the porch meets the door, etc? I see aluminum thresholds are typical in new construction, but I’m not sure I like the look.

In old houses with solid masonry walls, I’ve seen some homes lay a stone threshold under the door which bridges from under the door to the porch like a small step. See the picture below. Obviously the stone would be a thermal bridge. I have also seen wood thresholds but I worry about maintenance and keeping paint on it.

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  1. whitenack | | #1

    Oops. Forgot the pic.

  2. GBA Editor
    Martin Holladay | | #2

    Q. "I haven't decided on a porch material yet, but there is a strong possibility it will be masonry which I know is a large thermal bridge, which means I still need to the rigid foam between the house and the porch floor. How does one bridge the gap over the foam?"

    A. I'm confused. What does "there is a strong possibility it [the porch material] will be masonry" mean?

    Do you mean that you want to build brick walls to support your porch floor? Or do you mean that you want to use bricks for your porch floor? Or both?

  3. whitenack | | #3

    Yes, I mean the surface of the porch will probably be brick or concrete, with the walls of the porch certainly being brick or concrete. As opposed to a wood plank porch, which would not be quite as bad.

  4. charlie_sullivan | | #4

    The extent to which the material of the threshold matters for thermal bridging is a complicated question because it is a 2D heat flow problem. The ability of that material to conduct heat from the porch toward the door doesn't really matter, unless you add a storm door, because the part just outside of the door is exposed to the outside temperature anyway. But you would like the layer just under the surface skin there to have good insulating capability. And you'd like the part literally under the door itself to have low thermal conductivity, as well as sealing to the door well.

    So if you want an inch-thick stone slab there you can do that without thermal problems, as long as what's underneath that layer is good insulation. That underlayer could probably be ordinary rigid foam, perhaps higher density than you might require elsewhere. But some other stronger options would be Compacfoam super-high-density foam, imported and sold in the US by, or foam-core tile backer board, such as ProPanel or Johns Manville GoBoard. Propanel has a high density EPS core; GoBoard has an even higher density polysio core, and is rated at 200 psi.

    You could also put tile on top of the tile backer board, resulting in a thinner overall stackup for the same insulation thickness underneath.

    But I think wood is fine too, especially given that it's a covered porch. People make decks out of wood, and that's much more severe duty. So if you paint it with deck or porch-floor paint it should hold up well.

  5. SwitchgrassFarmer | | #5

    I faced a similar problem. I wanted a direct transition from our entry porch onto the ground (radiant slab) floor of our home.

    We had already jackhammered out the initial porch slab as it was too high to lay bluestone on top of. The bluestone is on Schluter Ditra too, more height. (The previous slab also hadn't been constructed/poured to factor in an outer perimeter step that the architect subsequently designed.)

    The new (and old) slab was thermally isolated from the house with dense insulation board and/or intersection with the ICF foundation. Trying to be as good I fussed and pondered how to break the thermal bridge under the door. I looked at thermal break thresholds from the likes of Zero, thin strips of high strength insulation, etc.

    In a flash of inspiration I realized that the carpenters could take a MultiMaster to the prehung door threshold so we could thin it up and make it less ugly. We then used a concrete saw to cut in towards the house so that we could hide a thermal break under that now thinner pre-hung door threshold. Still though, somehow it just didn't all want to work, particularly with how to be sure the bluestone would be supported correctly.

    Finally, when the day of reckoning came, the mason turned to me and said "Andy, go up to the barn for a couple hours." I did, and am happy with the appearance. I don't know what is going on under there, and I probably don't want to know.

    (The little divot in the one piece of bluestone; of course that was our last piece of matching stone wouldn't you know. Couldn't justify driving 80 miles roundtrip and the subsequent remobilization to get a replacement. I consider it a beauty mark!)

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