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Community and Q&A

Managing Moisture and Insulating a Complicated Old House

OldMAHousing | Posted in Energy Efficiency and Durability on

Hello!  My name is Jason and I’ve recently acquired an old summer home in MA (Climate Zone 5A).  We’re considering making the building inhabitable in the winter.  Key facts:

– Built in 1927
– 4,666 sqft
– Extremely large, unvented attic (sloped roof).  Walkable throughout, floored, absolutely opposed to filling it with 10″ of loose fill and rendering it unusable.
– Built into the hillside.  Soil is sandy loam and well draining.
– Multiple basements: One finished with boiler, heaters, etc with an accessible dirt floored crawlspace, the other a walk in but unfinished, dirt floored space, with  the slope exposed, and a second crawlspace accessible.
– No insulation in any part of the home.
– Original 1927 cedar shake siding
– 2011 asphalt roof replacement with solar.
– 68 single paned, original wood windows.

Why did I just list all these facts?  Well, everything I’ve studied on the subject of winterizing & insulation stresses the importance of considering the entire system of the home.

My struggle: Most advice you read focuses on solving one piece of the puzzle.

So far I’ve brought in some insulation contractors and also participated in a “Mass Save” evaluation (virtual thanks to COVID).  Neither of these have inspired any confidence in me that they are considering the home as a system.

I apologize for making this a multipart thread and I know many of these subjects have been covered in individual threads and articles.  My hope here is to find resources, advice, or referrals to help us tackle this home as a system.

Our goals for the home:  (1) Do no harm.   (2) Invest in the highest returns and work our way down until we arrive at an efficiency level we are comfortable with.  (3) Get to a point where the home can be climate controlled.

Our current plan.  Places marked with [??] I am uncertain on but welcome criticism/advice on any stage of the plan.

First Steps:

–  Do something with the drafty old windows.  Not really a question for this board but welcome any advice there.

– Keep current, unvented attic.  Apply closed cell spray foam to underside of roof sheathing.  Supplement with [??] insulation to achieve code R value and cover with drywall.

–   Insulate rim joists with closed cell spray foam.
–  (Mass Save recommendations): Apply vapor barrier to dirt floors (plastic sheathing).  Apply [??] insulation to the basement ceiling then cover with a thermal barrier.

Primary concern here is the basement.

(Q1) The foundation walls are currently allowing water to seep in during heavy rains.  Preventing this given the hillside will always be a challenge.  If I cover the dirt floor with sheathing, won’t that moisture just collect on it?  Should I also line the concrete walls with a vapor barrier?

(Q2) What is the right way to handle the insulation of the basement ceiling as proposed by Mass Save?  I presume it is unlikely they will achieve a consistent vapor barrier, so I should be careful what insulation I allow to be put up there?

Second Step: Walls 

I will be re-doing the interior walls on the 2nd floor of the home – replacing old lead painted paperboard with proper drywall.  The rest of the home has has beautiful wood shiplap which I would like to avoid removing.

(Q3) While I have the 2nd floor open, I have an opportunity to insulate.  Is there any safe way to insulate here?

Can I put some sort of moisture permeable, breathable insulation that won’t change how the home functions?

I’ve also seen a setup described here: essentially creating an airgap and then an air barrier on the interior of the wall, then insulating behind that.  Seems like a lot of work that could go wrong however.

(Q4) If all else fails, we’re also considering waiting on the walls until we re-do the siding.  At that point we’d insulate from the exterior of the home.   Is this just the right thing to do?  Live with higher heating bills for a few years until we decide it’s time to spend the big money on redoing the entire exterior?

I welcome any and all advice & criticisms.  Thank you in advance!


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  1. Austin G | | #1

    For the basement, your first objective is going to need to be controlling the water ingress. Perimeter drains and a sump pump can be a good step. Once the moisture issue is taken care of, you need to decide if you want the basement to be a part of the home (conditioned envelope) or unconditioned space (outside). If you plan to have any equipment in the basement, it should be encapsulated with the WALLS insulated and sealed, but not the ceiling. If it’s going to be completely unconditioned, it needs to be separated from the house with an air barrier and insulation on the ceiling and we’ll vented to the exterior. I would suggest the former.

    For the walls, I like to use rock wool/mineral wool in old homes. It’s still allows the walls to dry in both directions and is unaffected by moisture. In can be put in as batts (which will need to be cut and cobbled to what are surely non standard spacing) or blown in. Blown in allows you to insulate walls you don’t plan to open.

    I mention the above as you said you first, wish to do no harm. If you want to air seal the walls, it’s all or nothing. No halfway measures. Those walls have to stay dry and free from moisture if you go beyond adding rock wool.

    Personally, I’d start with the basement. Control the moisture, lay the air barrier, insulate the walls (and floor if possible). Then I’d go to the attic. Since you can’t use exterior insulation (given the new roof) I’d suggest several inches of closed cell spray foam in the rafter bays. Next hit the rim joists with the same. Only then would I consider insulating the walls.

  2. Expert Member
    Akos | | #2

    Usually in these old houses the lowest hanging fruit is air sealing not insulation. When I had a similar vintage home tested, about 60% of the heat loss in the place was from air leaks, fixing those will go a long way in getting your home more energy efficient.

    Since it is sounds like its not a simple structure, you'll probably be looking at a some SPF. I agree with Austin, the best way to insulate and air seal the attic is closed cell spray foam between the rafters for condensation control (40% of total R value), the rest can be fluffy or open cell SPF. This will also go a long way in sealing up the attic, walk ups are typically huge air leaks in older houses. Make sure to test with a blower door after the SPF and touch up any areas that leak, lot of times the installers can miss tricky ares such as behind short knee walls or interior partition walls.

    A big air leak is also your rim joists and any windows in the basement. Make sure to seal these up and replace the windows as needed.

    If you have balloon framing, make sure to check that the there are top and bottom plates in the attic and basement. Lot of times these are missing creating a nice air passage through your house for heat to escape through.

    Wet basements are moldy basements, no matter how much you air seal, that will get into the house. The best is to deal with the moisture first. Occasional flood is not a problem provided the basement is not finished. You can still insulate the walls with rigid foam or SPF as it doesn't mind a bit of water.

    From energy saving perspective, usually the best is to bring the basement inside the conditioned envelope. Since the soil is much warmer than outside air, you don't need much insulation plus any heat losses from your boiler and piping now stay inside your house. Insulated basements also mean much warmer floors above.

    About the only time I would consider insulating the floor and keeping the basement unconditioned is if there is a lot of radon.

    As for the walls, it gets a bit tricky. These older houses relied on leaky walls and the airflow behind the siding to keep it dry. Sometimes insulating the walls can cause the paint on the siding to start flaking off. Since you are looking at re-siding, this might be less of an issue. Just make sure you deal with flashing details around your windows. These are non existent in houses of your vintage, leaks there mean moldy insulation. Most likely you have real 2x4 which are hard to insulate with batts since the bays are not standard width. Usually the best is to dense pack the walls with cellulose. This has also the benefit if tightening up the walls and buffering moisture to deal with small leaks.

  3. Tyler Keniston | | #3

    Since your discussing the broad strategy of the 'system' I would suggest searching 'deep energy retrofit' for big picture stuff. There's tons of info here on GBA (use google or such as your search engine and include greenbuilding advisor in search terms.)

    There are advantages to doing everything from the outside due to the fact that many old buildings don't have adequate flashing details for an insulated structure. And if you're eventually replacing all windows, it fits nicely with that step.

    >"Apply vapor barrier to dirt floors (plastic sheathing)... If I cover the dirt floor with sheathing, won’t that moisture just collect on it?"
    You probably mean 'sheeting' such as 6mil (or thicker) polyethylene / polyolefin.
    If you have water coming into the basement, trickling down the walls, you indeed should create drainage paths to send that water beneath the sheeting, and eventually out of the building. Search for interior french drains (there also happens to be several active threads right now discussing this very issue.)

  4. Jonathan Blaney | | #4

    How are the gutters? Managing the water coming off the roof will go a long way toward keeping the basement dry.

  5. Expert Member
    DCContrarian | | #5

    Lots of good advice above. My two cents:

    In modern construction the building envelope forms a barrier between conditioned space and unconditioned space/the outdoors. In older construction that wasn't really a concept, and in a lot of older houses the attic and basement were kind-of indoors, kind-of outdoors. As part of your systematic approach you have to decide where the boundary between the conditioned space and unconditioned space is. You should be able to take a plan of the house and draw the boundary without ever lifting your pencil from the page.

    Joe Lstiburek likes to talk about the "perfect wall" having four layers -- rain control layer, air seal layer, vapor seal layer, and insulation layer. He lists them in that order because that's the order of importance. If you can't keep the rain out all the other layers are useless. If you can't keep the wind out the vapor and insulation layers are useless. Insulation is useless without vapor control. So your first order of business is to deal with the water getting into the basement. The next is to deal with air sealing. As Akos notes above, just air sealing can make a huge difference. In general, the air, vapor and insulation layers will all follow the building envelope boundary that you developed in step 1.

    If you are quantitatively minded, it really helps to get one of the Manual J estimators and build up an energy model of the house as it exists. It's particularly good if you can get a blower door test and use the actual results to model air infiltration. From that you can plug in various improvements to the insulation and model what the impact will be.

    Single pane windows will never have great U-values, but they can be made air-tight. You may well find that the air leakage isn't so much around the panes as it is where the frame of the window unit is mounted to the wall.

  6. OldMAHousing | | #6

    Thank you all for your advice. I will definitely check out the suggested search terms for more information on thinking about the home as a system vs individual parts.

    How do others feel about Austin G's suggestion of adding blown in mineral wool / rock wool? Is this safe to do in our situation? I understand it may not be the most efficient, but as long as it "does no harm" it's a nice intermediary until I am prepared to tackle the insulation further on the exterior.

    Regarding the water coming in through the basement walls:

    Jonathan is indeed correct that this is currently, from what I can tell, resulting from the way water falls off the roof in one spot. I am trying to figure out why and it, along with some external sloping, are near term projects.

  7. Charlie Sullivan | | #7

    I think part of the decision process has to be around the budget. Do you have the budget for a full deep energy retrofit? If so, then you needn't choose the low hanging fruit, and can simply work through the whole envelope . But if you are not ready to commit to that, then priortizing based on avoiding moisture problems and getting the biggest band for the buck is the way to go.

    For the basement water problem, you may want to dig out around the foundation to install footing drains, add waterproofing, and while you are there, add insulation.

    A dirt floor might seem like a problem, but it's an opportunity: you can remove some soil, put down foam insulation, a vapor barrier, and (optionally) pour a new slab. Just make sure you don't remove soil to the point of undermining the footings.

  8. GBA Editor
    Kiley Jacques | | #8

    To piggyback on something Akos mentioned, if you do get to the point where you are devising a plan to insulate the walls and need to consider the details of flashing existing windows, consult this article (flashing existing windows is something that comes up quite a bit, which is why we decided to write about it): FAQ: Flashing an Existing Window. In terms of controlling moisture in the basement (I can hear Martin Holladay advising you to start there, as water is always the first priority), take a look at this article and the related resources for additional ideas: FAQ: Dampproofing and Waterproofing for Foundation Walls.

  9. OldMAHousing | | #9

    Thank you all again for your thoughts on this matter.

    Right now most of the energy retrofits we will be performing will be in conjunction with planned renovations. This will keep the cost manageable.

    The elephant in the room however is the closed cell spray foam in the attic. This will cost us ~$10,000 to get 4..5" covering the entire roof assembly (it's huge) and the basement rim joists. This provides no aesthetic or functional value - in fact it will aesthetically make the attic far worse (the existing exposed T&G sheathing is charming). As I've already ruled out blowing in loose fill over the floor and the ceiling is too shallow to provide sufficient R, it appears the only alternative would be re-roofing and insulating from the exterior. Only 4 years into the last roofing job it makes no sense (environmentally or financially) to do so, so it's either bite the bullet or wait until the roof needs to be replaced again.

    There's no way I'll achieve a Pretty Good House if I don't proceed here right?

    Moving on to the wall assemblies, here's where it appears we'll settle exterior --> interior

    3rd floor: cedar shingles --> tar paper --> 1" T&G planks --> True 2x4s with 1.5" polyiso furring strips added & 5.5" cavity mineral wool batts --> 0.5" drywall.

    The walls on this floor are presently exposed so this is an easy way to add r23 to the cavity. We'll add the furring & fill with mineral wool batts then drywall.

    1st & 2nd floor: Cedar shingles --> tar paper --> 1" T&G planks --> True 2x4s --> 1" T&G vertical paneling

    These floors are a nightmare. The existing paneling is beautiful antique wood that would be a nightmare to get off and re-attach, and would likely be damaged by doing so. Furthermore, the presence of knob & tube wiring means the state programs for blown-in cellulose are likely off the table. So what to do?

    Well, I need to replace the siding on the southwest (long side) of the home. It's the exposed side and the wind & rain coming off the lake and up the hill batters it. When I do so, I think I will attempt to add 1 - 2" of exterior insulation. Critically, I have no plans to redo the siding on any other side of the house right now so it may be 5-10 more years before those need replacing and we extend the insulation the rest of the way around the home. My only alternative in the meantime would be paying for non-subsidized blown in mineral wool (no fire risk with the knob & tube I guess), adding substantial cost (I haven't received quotes here yet).

    In summary, would love the expert's opinions on my choices:

    Bite the bullet on the big ticket attic insulation, right?

    Faced with the bare walls I have on the 3rd floor, do you agree with my proposed assembly?

    Is this all for naught given the long time horizon before I'm able to add even the 2" of exterior insulation to the 1st two floors?

    1. artampone | | #12

      Just a thought on the attic, look at it from the long term. If you want to preserve the charm of the attic then insulate from outside. If you don't want to do this now due to the recent roof and solar, maybe give up the attic space for now temporarily and just lay down bat on the floor. It will insulate the floors below and can be pulled up later doing no damage when you're ready to do a well insulated above sheathing roof and at that point solar panels will be double the watt/sf so you'll upgrade anyway, hopefully your inverters will still work.

      If you want to use the attic space and retain its charm I'd do what you can to preserve it. Details like that are impossible to replicate and do ad value at the cost of energy maybe. But you're upgraded solar system will just run your heat pumps so its carbon neutral anyway right?

      As others have said, start at the basement. I just commented on another GBA article where Peter Yost mentioned

      "The building science cardinal rule is to honor the unavoidable relationship between heat and moisture flows. That means:
      Manage moisture first.
      Manage air leaks second.
      Insulate third."

      He couldn't be more right.

      1. Charlie Sullivan | | #13

        This is a great idea. The batt insulation won't cost much, will be easy to do, and will help substantially between now and the future exterior insulation.

      2. OldMAHousing | | #14

        That's an interesting idea - will consider this option as well!

        Yes the more I look at it the more I think the homes current, #1 problem is the vented crawlspace beneath half the home. Built into the slope side, dirt floor, etc, it will not be an easy place to get right but I think it could have a big impact on the home's energy performance.

  10. Wooba Goobaa | | #10

    Sounds similar to my reno + 1/3. We did 6" closed cell spray foam under the gambrel roof deck with full ice/water shield and asphalt shingles above. All the exterior walls ended up being taken down to studs and the board sheathing. New wall structure is cedar claps over 1/4" air gap over Blueskin-ed board sheathing. I really want to do dense pack mineral wool for the 2x4 cavities, but even the local blown insulation jocks are telling me to foam the walls due the irregular stud cavities.

    Knob and tube might be a problem for insurance.

    How is the plumbing?

    1. OldMAHousing | | #11

      Sounds like you went a bit deeper than I'm hoping to go! The sheathing is in great shape - old wood T&G no moisture damage or rot anywhere we've seen.

      The plumbing is what you would expect - corroding old cast iron drains, lead traps, etc. The plumbing is all getting redone as we're re-doing and adding new bathrooms.

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