GBA Logo horizontal Facebook LinkedIn Email Pinterest Twitter X Instagram YouTube Icon Navigation Search Icon Main Search Icon Video Play Icon Plus Icon Minus Icon Picture icon Hamburger Icon Close Icon Sorted

Community and Q&A

Porch converted to living space, floor insulation solutions? traps?

andy_ | Posted in General Questions on

My friend’s 1930’s bungalow had the front porch converted to be part of the living room at some point at least 50 years ago. I was helping out replacing the rotted front steps so of course I had to poke my head into the crawl space and check things out. Turns out the space that was once the front porch has no under floor insulation whatsoever. No wonder their living room is nearly unlivable mid winter!
The easy solution is to put in some Rockwool bats and call it done, but here’s the wrinkle; since it was once a porch the original floor (now subfloor in the crawlspace) was pitched to shed water. Tapered sleepers to level the floor were put in so there is now a space of about 1″-2″ that is not easily accessible. 
I realize that this “dead space” between floor surfaces will reduce the effectiveness of any insulation, but what am I missing? Is there a good solution here? Is there a reason to not insulate the space?
Edit: Zone 4 PNW. The comfort issue is mostly the floor being cold underfoot.


  1. Expert Member
    DCcontrarian | | #1

    I'm trying to understand the porch construction from your description.

    It's off the ground -- there are steps to it.

    This bit, "the original floor (now subfloor in the crawlspace) was pitched to shed water," I take to mean the floor joists are pitched, there's an old porch floor on the joists, then sleepers on the old floor and a new finished floor above the sleepers.

    First, I recommend this article for details on insulating above a crawl space:

    To the question of what to do about the gap between the new floor and the old floor, we need more detail. How are the walls finished? There is a concept of the "building envelope," which is the barrier between the conditioned part of the house and the outside world. You want the building envelope to be continuous on all six sides of the house, providing a barrier to water, air infiltration and vapor, and having insulation. So you want the insulation in the floor to meet up with the insulation in the wall. If you can do that, the gap is entirely within the building envelope and inconsequential.

    If you can't make the building envelope continuous on all sides any insulation is going to be marginal at best. It's like waterproofing half of the hull of a boat.

    1. andy_ | | #2

      DC, I'm well aware of the building envelope concept yet forgot to give any detail on that part.
      It's a 1930's bungalow so originally would have no insulation. Remodeled a few times over the years so the walls are now typical 2x4 with fiberglass. Roof over this section has blown in cellulose. The rest of the house sits on a semi finished basement that has insulated walls. Some other parts of the house are spray foamed, others blown in cellulose. Basically a hodge podge of different attempts at improving comfort and efficiency but somehow insulating this one part of the living room seems to have been completely forgotten.
      The specific part I'm working on was originally a covered porch with stairs up to it from the sidewalk. 2/3 of the porch was closed in to make the living room bigger. Since a porch floor is sloped to shed water, another floor was built over sleepers to make it level. This left an air space.
      The crawl space under the porch (now living room) is separate from the basement. The walls of the crawl are a mix of brick and wood with no insulation.

      1. Expert Member
        DCcontrarian | | #3

        So what happens where the floor meets the wall?

        If the wall was built on the original, sloped, floor, that's basically normal construction and so long as the wall is insulated you don't have to do anything special. If the wall is on top of the new floor, there is an uninsulated space between the bottom of the wall and the top of the old floor -- unless wood blocking was put in. You'd want to fill that gap. Which might be as simple as drilling holes and spraying in spray foam.

  2. walta100 | | #4

    Before you open this can of worms consider the old porch may not have any real foundation. The porch posts may well be just setting on the 4 largest rocks they happened to find.


    1. andy_ | | #5

      Oh yeah, I've seen that scenario before but this one was fully restructured underneath as part of a seismic retrofit, which is likely the reason the insulation is missing. When the seismic crew reframed the whole underside they probably had to pull whatever insulation was in there, but then never put anything back in when they were done.

  3. andy_ | | #6

    So I guess the real question here is just this: Will a 1"-2" air gap between two layers of flooring create problems if insulation is added and the void is not filled?
    I'm guessing that the overall effect of the insulation will be less, but is there a danger of this gap become a moist moldy mess?

    1. Expert Member
      DCcontrarian | | #7

      Moisture isn't going to be the problem.

      If the gap is entirely within the building envelope it shouldn't be a problem. And it should be entirely within the building envelope. The problem is if the gap bypasses the building envelope and allows cold air in and a path for it to circulate. You're going to have a very cold floor, essentially uninsulated.

Log in or create an account to post an answer.


Recent Questions and Replies

  • |
  • |
  • |
  • |