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Vapor retarder, sealing and ventilation – what to do with an old 1960’s ranch?

Heih | Posted in Building Code Questions on


I am an owner builder and I have a humble question related to vapor retarders for the experts, nerds and a like on this forum. I have been reading about vapor retarders, sealing air leaks and ventilation here, building science website and elsewhere for a while and I have talked with the village building inspector about them.

But let me start with a little background information of the house just incase it makes any difference and helps some one in the future who is looking for similar information. Maybe some of it is irrelevant to my questions but… at least it is out there. Bare with me.

  • 1960s ranch in South-East Wisconsin
  • main floor area is around 1800 sqft (total 2150 sqft)


  • exterior wall is either chicago pink brick or painted cedar board and batten siding with plywood and tar paper on the backside
  • no rain screen/air gap with siding
  • low pitch roof with architectural asphalt shingles (medium tone, but not dark enough to be a heat sink, but makes them dry faster than a light colored roof)
  • vaulted ceilings in the kitchen, living room and foyer
  • an attic in the dining room with lowered ceiling/soffits, no air circulation
  • second attic in the rest of the home which has louvered vents at the end of the gables
  • attic insulation is an old mix of loose fill rockwool and cellulose and very dusty (6″ height)
  • in the winter roof gets icicles
  • partial basement is half finished and relatively cool and dry
  • the rest is slab on grade
  • located downhill and sump pump constantly on during spring/early summer, backup system is planned because sometimes get power outages
  • running a dehumidifier at 35% in the basement

Passive elements

  • large double pane window wall facing south east
  • house is shaded by three big locust trees
  • overhangs are 2-1/2 feet
  • two painted concrete brick fireplaces in the middle of the house, wall is shared with dining room being renovated (one on each floor, 1-story ranch)
  • painted concrete brick wall in foyer (facing east)
  • concrete subfloors all over (4-5″ thick)


  • in-floor radiant heat system that is about to get an upgrade by retrofitting on top of an existing slab a new one similar to a warm board system but as a DIY
  • no air conditioning, but in the future might install a ductless minisplit to the two attics, for now leaving a reserve for it
  • two bathrooms with loud contractor grade fans installed (50 cfm) and a laundry with Panasonic variable speed Whisper Green fan (80 cfm) that goes to full power when someone enters the room (motion sensor switch connected to a ceiling light) waiting to be installed
  • kitchen will have a Bosch downdraft (600 cfm) with an induction cooktop (no fumes from gasses)
  • radon system (RadonAway RP140) is going to be installed, cracks sealed prior, now at 7pCi/l

So last winter I started a kitchen and dining room renovation. I have since removed drywall and fiberglass insulation in these areas. I installed R-15 rockwool to exterior 2×4 walls filling the whole cavity and R-23 rockwool to the 2×6 the cathedral ceiling by lowering the rafter bays with 2x2s to leave an air gap on top. I took time and care in the installation to get to grade I. I understand that by code I should have done higher R-value in for example a new construction, but it is what we had to work with. On the eaves/overhangs are soffit vents and we are retrofitting a ridge vent in a month when we redo the shingles to get better airflow to the cathedral ceiling. I am not happy with the air gap space we have but that is what we had to go with. We decided to go this route based on what we had read on the GBA forum discussions and articles.

In case someone is still reading and wondering I didn’t want to go with the hot roof approach and install at least 2 inches of polyiso on to of the deck, because it would have meant replacing the fascia board metal flashings and other related recently installed by previous owner.

Note that the inspector’s point of view comes from the building code in Wisconsin no matter what type of insulation (cellulose, fiberglass, rockwool) you use and he has never heard of Airtight Drywall Approach, but neither have any of the drywall installers I have interviewed.

The inspector wants to see plastic as a vapor barrier or I will have to write a letter to the village and provide additional proof of usage if I want to use vapor retarder paint on the new drywall. He did say that “in older homes there are several layers of paint that act as a vapor barrier”, but in the renovated areas if I am replacing insulation he wants proof that a vapor barrier has been used and also to record it to village records. It doesn’t make a difference in the inspector’s mind if a vapor retarder is used only in one area and not continuously around the house. The walls were fine and dry when I inspected them after pulling out the grade II installed insulation, maybe it was dumb luck who knows.

Furthermore we are sealing air gaps with high quality caulking. The inspector feels no matter how well I seal the home’s air gaps I am still going to have air leaks so I don’t need to worry about supply air with the exhaust only system I am going with. He also hasn’t heard of passive air inlets that I have been considering for the supply/replacement air and I don’t want to twist his arm on that if I don’t have to. He only cares what the code says about moisture removal with bathroom fans and stops there. He did mention I could put in an HRV, but personally I don’t think it would be the right choice given the lifetime costs and having an old home with exhaust only ventilation.

Anyhow, I feel I am between a rock and a hard place as I just want to do what is right and best for my home and be green about it. I feel if you are going to renovate or build you should do it by keeping in mind the next generations to come and making it better than what was, but I also need to pass the inspections to keep moving and I’d like to get things done right the first time. So that is why I am turning to you to find out what would be the best solution to my problem/challenge/opportunity

So now the questions:

  • What should I use as a vapor retardant considering my situation? Is putting plastic sheeting on the walls in this case asking for trouble. The home isn’t new or super-insulated, we are doing our best with what we have.
  • Is it going to make any difference by going with the airtight drywall approach in the renovated rooms and to seal around baseboards, windows and exterior doors on the rest of the home? I can borrow a thermal imaging camera from work to find temp differences.
  • And in any case I do get it sealed should I put passive air inlets to the bedrooms? For now I have been opening windows and using cross ventilation for couple of minutes to get fresh air in every day. Otherwise the air feels stale. I know that at least in Northern Europe (Norway, Sweden, Finland) the custom is to use passive air inlets in bedrooms and living rooms.
  • And furthermore how can I convince the village building inspector to approve it?

Any thoughts? Thanks.

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  1. GBA Editor
    Martin Holladay | | #1

    Q. "What should I use as a vapor retardant considering my situation?"

    A. To satisfy the building inspector, install a smart vapor retarder like MemBrain.

    Q. "Is it going to make any difference by going with the airtight drywall approach in the renovated rooms and to seal around baseboards, windows and exterior doors on the rest of the home?"

    A. Yes. It always makes sense to pay attention to air sealing.

    Q. "Should I put passive air inlets to the bedrooms?"

    A. It's up to you. Most bedrooms don't need them, but if the rooms feel stuffy and you like fresh air, go for it.

    Q. "How can I convince the village building inspector to approve it?"

    A. That's a tough one. You can always (gently) suggest that he read some articles on the Building Science Corp. website or GBA.

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