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Historic renovation

twoodson | Posted in Energy Efficiency and Durability on

This might be the first of many questions I for this community. I’ve been lurking for awhile and heard about this site from the guys on FHB.

Here’s the backstory: I own (for 2 years) and live in the bottom unit of a 1905 all brick 3200 sq foot 2 family flat in a historic district (national register of historical places) in St Louis, MO. My upstairs tenant of 20 years just moved out and I’m weighing my options on what to do. The until is in rough condition. Kitchen and bathroom are 50’s. Drywall tacked on top of bad plaster. Electricalical is a disaster. Basically the only updates over the years have been to the plumbing. I have completely updated my until (minus windows), btw.

Goals.
1) Heating/Cooling was more than half of the rent and I want to remedy that.
2) Completely update the finishes of the unit to get higher rent. This is a higher rent area, so it’s not unreasonable that I could get 3x the rent I was getting.

Here’s my first questions: There is basically no insulation in the flat roof. There is a drop ceiling that needs to be replaced with some fiberglass batts stuffed in between that I’m pretty sure are pointless. There is metal lathe and plaster original ceiling under that. I need to do a scope still, so I’m not sure of the space above the plaster. The roof probably needs to be replaced in 5-10 years, but there isn’t much space against the parapet for rigid foam above.

What should I consider doing? I was thinking about gutting the ceiling and doing sprayfoam/fiberglass batts.

My second question is on windows. They are 14 75″x36″ original single pane double hung windows in bad condition with trashed storms in front of them. I’m considering going with wood sash replacements and scrapping the storms. Is this a good choice?

My final question: Mechanicals are in the basement, however, the ductwork is original and leaks badly (it was a coal gravity/octopus furnace). The furnace (condensing gas) and AC are newer (6 years old). I’m viewing my options as mini-splits or updated ductwork. Not sure what to do there.

Thanks!

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Replies

  1. GBA Editor
    Martin Holladay | | #1

    T. Woodson,
    It sounds like you are contemplating a gut rehab job. The gives you many opportunities to fix things correctly.

    The window question is fairly easy. Replacing windows in an older building is routine, and lots of contractors can give you bids. Make sure that your window contractor understands how to flash a rough opening. Before you choose your contractor, study up on this issue, so you can ask your contractor questions about the flashing plan.

    The only wrinkle in the window replacement issue concerns your local historic preservation commission. Negotiating with those people has nothing to do with building science; it's a political issue. Good luck.

    HVAC contractors can advise you about options for heating and cooling, although you need to be wary of their advice. If you feel uncertain of your options here, you might want to hire a mechanical engineer to advise you.

    It's certainly possible to install closed-cell spray foam on the underside of your roof sheathing. The main issues on an older brick building with parapets are (a) hidden air leakage paths, and (b) thermal bridging through the parapets.

    Now that I've raised the question of thermal bridging through the parapets, we come to another issue: How do you insulate the walls of an older multi-wythe brick building?

    Here are links to two articles you should read:

    Insulating Low-Slope Residential Roofs

    Insulating Old Brick Buildings

  2. twoodson | | #2

    Hi Martin, thanks for the response.

    Zeroing in on the insulation issue, I re-read the articles you mentioned (I had seen them before, great material), and I hadn't considered the difficulty of air sealing the flat roof cavity and the thermal bridging issue seems to segway to the wall insulation issue in my mind.

    Are there specific areas to have my contractor watch out for when air sealing the roof cavity? A more economical option that I was quoted was dense pack cellulose in the roof cavity without removing the steel plaster and lath ceiling. They would use a smart air barrier over the plaster (paying close attention to interior walls, strapping and drywall over that.

    As far as the walls are concerned, my takeaway from your article was to NOT insulate the walls given the risks. In addition, the number/size of windows (35% of the wall surface) and difficulty in re-trimming them, I'm considering leaving that out of the rehab equation. Is the thermal bridging issue a larger energy drain than uninsulated walls? Should I expect that not insulating the walls or parapet will disproportionately offset the insulation in the roof?

    Thanks again!

  3. GBA Editor
    Martin Holladay | | #3

    T. Woodson,
    Q. "Are there specific areas to have my contractor watch out for when air sealing the roof cavity?"

    A. In addition to all of the usual problems -- utility chases, wiring penetrations, plumbing vent penetrations, etc. -- the contractor should pay attention to the perimeter of the attic. In old brick buildings, there is sometimes vertical strapping on the interior side of the brick walls, and this vertical strapping sometimes extends into the attic. If that's the case on your house, these are superhighways for air movement.

    Q. "A more economical option that I was quoted was dense pack cellulose in the roof cavity without removing the steel plaster and lath ceiling."

    A. Remember, you can't insulate this type of roof (a flat roof) with cellulose unless either (a) there is a sufficiently thick layer of rigid foam on the exterior side of the roof sheathing, or (b) there is a well-ventilated attic that is at least 8 inches high above the top of the cellulose.

    Q. "Is the thermal bridging issue a larger energy drain than uninsulated walls?"

    A. No.

  4. Expert Member
    Dana Dorsett | | #4

    If you are up for re-roofing soon, in US climate zone 4A (that's you) as long as at least 30%+ of the total roof R above the roof deck, it's OK to dense pack the cavities on the under side of the roof deck.

    Measure the amount of space you have for cellulose at the deepest point, multiply x R3.7/inch. Whatever that number is, divide it in half an assume that's how much rigid foam board needs to go above the the roof deck. Fortunately there is a fair amount of trade in USED 2lb density fiber faced roofing polyiso, and it can be assumed to be at least R5/inch, often R5.5-R5.7/inch, at a fraction of the cost of virgin-stock goods.

    So just for yuks...

    Say you have 11" of space between the metal lath and roof deck, determined by probing drilled holes with a wire. Dense packing that would yield ~R3.7 x 11"= R41

    Half of that would be R20, R21, which at R5/inch would be 4" of reclaimed roofing polyiso, or 5" of reclaimed EPS. The stuff is out there and it's 1/4-1/3 the cost of virgin-stock goods. There's one company (Nationwide Foam) that will ship from regional depots if you can't find a local reclaimer.

    Even a skinny inch of continuous EPS behind new plaster on the walls can make a huge difference with an uninsulated brick wall, and with unfaced EPS the risks are pretty minimal. With the additional inch it would usually mean all new interior window trim, but if you're replacing the windows and completely updating the interior that's probably already in the budget.

  5. twoodson | | #5

    Resurrecting this old thread now that we are almost ready to actually build (demolition is almost done)

    A few corrections/changes to the above to the above.
    1) The is roof of the "low-slope ... with attic access on only one side of the building" variety (https://www.greenbuildingadvisor.com/article/insulating-low-slope-residential-roofs)
    2) We are reroofing with TPO.
    3) We are saving the original windows and installing Quantapanel low-e storms.

    I was hoping to get comments on my roof assembly and wall assembly and things to watch out for.

    1) The roofer will install 5 inches of polyiso insulation above the board sheathing (2 layers of 2.5 inch with staggered seams). R5.9x5 = R29.5
    2) My carpenter will frame out the inside of the exterior brick walls using 2x4's turned flat with a small (1/2 inch) gap to the brick (10ft ceilings).
    3) My insulation contractor will spay form between the new framing to fill the new cavity (1.5-2 inches of Icynene ProSeal) for ~R10 final assembly and up the parapet walls where the joist are pocketed in. I'm somewhat concerned about the brick getting too cold and the joists getting wet, so I do not want to go any higher (thanks to Martin on the articles on those two topics). The exterior brick parapet and chimneys are in good condition, so I think the exterior brick is good, but I know insulting can be risky. I'm do not think I'm willing to go any higher.
    4) My insulation contractor will install R38 fiberglass batts between the 2x12 roof joists. Total roof insulation R67.5 with a ration of foam to fluffy of ~44%

  6. walta100 | | #6

    What is your plan for air sealing? My opinion sealing is more important than insulation.

    If a blower door test fits your plan I used this guy he works in St Louis.
    https://www.betterbuildinginstitute.org/

    If you do not have a metal cap on your parapet consider add one. Some Soulard bricks are pores. As is they dry to the inside your spray foam will stop that.

    Walta

  7. twoodson | | #7

    Can you explain more what you mean by metal cap? I currently have clay/concrete caps and the roofing contractor is wrapping tpo over that.

    As for air sealing, I’m expecting the spray foam to take care of most of that. They will spray foam around the windows behind the casing. I am adding bulb seals to the doors and integral metal weather stripping to the windows.

    Do I need poly on the roof deck before the rigid foam? I guess there is a question about the sheathing to brick, but I think the spray foam is going to seal that?

    I do plan on getting a blower door test done.

  8. walta100 | | #8

    My friend thinks his moisture problems come from the parapet.

    What looks like a very good foam install turns out to have a lot of leaks.
    This YouTube really shows the problem.
    https://www.youtube.com/watch?v=EOQFivxaG7c

    Walta

  9. twoodson | | #9

    This was very helpful. I'll definitely be getting a blower door test done. I want to seal the second floor from the first floor as much as possible as well. Should be interesting.

    1. twoodson | | #10

      Any suggestions on how to air seal the brick wall/parapet to the foam/ single ply tpo? I have board sheathing and pocketed roof joists. I am framing the brick wall below and filling with spray foam to the underside of the roof deck. Seems like there is still a weak spot in the gaps between roof deck boards.

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