Insulation for a 1914 stucco wall, tile roof bungalow in New England
Hi,
I’m new here but have read a lot and am hoping for some input on a question that’s been nagging at me! We are updating a 1914 bungalow with a stucco exterior and a Spanish barrel tile roof. This is in New England (zone 5A). I’m the homeowner. The house previously had basically no insulation of any kind whatsoever. I need help deciding what sort of insulation to use for the roofline/attic.
The eaves and attic crawlspace (but not the rest of the plaster walls) are open to the studs at the moment, so we have a lot of options. But of course, in an old house, we have a lot of limitations too. We have been working with a GC, an insulation contractor, and an energy consultant/HERS rater, but have not gotten what we feel is a confident answer. My priorities are a) avoiding creating moisture issues where none existed before, and b) longevity. And of course functioning insulation.
1. The house is currently heated with oil-fueled hydronic radiators, no air conditioning. We are adding a zoned, ducted mini-split heat pump system for cooling and mild-weather heat as well. The air handler for the mini-split system is going in one of the eaves upstairs (with insulation around it and the ductwork). There is an attic crawlspace, but it’s very small.
2. We are not going to be insulating the exterior walls, for the most part, because there is no opportunity to add a vapor barrier. The horsehair plaster is in good shape, and the last thing I want is to introduce a moisture problem into the wall cavities in a 105 year old house. The exception to this is the kitchen, which is down to the studs. We will put in a vapor barrier and insulate the exterior walls in there before the walls go back up.
3. The tile roof is 105 years old and is not being replaced, but tile is a permeable material so the wood to which the tiles are nailed does get wet and needs to dry. Relatedly, if the roof leaks, it’s difficult or impossible to notice from the outside. We have been doing a bunch of roof work to repair cracked tiles, but this is likely to be an ongoing maintenance type issue. For this reason, we have been advised not to insulate the underside of the whole roofline.
4. Therefore, the current plan is to insulate the living space envelope (meaning the floors and inside walls of the eaves and above the ceiling of the second floor), except for areas where the living space ceiling is angled because it is part of the roofline (e.g. the ceiling of a shed dormer on the front of the house and the angled walls between the eaves and the attic). In those places, the roofline would be insulated with baffles and an insulating product TBD. In order to keep the insulation dry and avoid ice dams, we will use baffles running from the soffits below the eaves (which are full of air leaks) up to the attic crawlspace and install vents at the roof peak.
Where I am stuck is on the actual insulation material. Our GC has suggested using batts in the eaves and ceiling, with open cell foam sprayed over the baffles in the places where we would be insulating the roofline. I am wondering if we should instead do Roxul/mineral wool everywhere (including in the kitchen walls) and no open cell foam or fiberglass anywhere. Our GC has said he doesn’t have a preference. I am having trouble getting good advice on this topic as to old houses; the insulation guy and HERS rater seem to just want to foam things, and don’t seem well informed about different materials and their performance over a longer period of time in old house.
So…any help would be extremely appreciated. Please go easy on me…I’m not a building professional, just a layperson.
Thank you!
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Replies
Emho,
First of all, can you tell us your name? (I'm Martin.)
You are using the word "eaves" is a way that I don't understand. The eave is the bottom lip of the roof -- the part of the roof where water drips off. When you talk about the "inside walls of the eaves," I have no idea what you are talking about. Can you explain?
Hi Martin! I'm Emily. Thank you!
When I say "eaves," I mean the the kneewall spaces, sorry. I've circled one of ours in the photo attached here. This is part of the second floor of our house - we have two small spaces like that on the front side (on either side of the dormer you see in that pic, painted pink), one of which contains the chimney, and one much bigger one in the back of the house that runs all the way across.
Emily,
The 4-foot wall is called a kneewall. The area behind the kneewall is best described as "the triangular attic behind the kneewall."
Got it. I've always just called them the eave spaces, which explains why no one ever knows what I'm talking about. Ha.
An oil filled hyronic radiator?
Or was that meant to be an oil fired boiler, serving hydronic radiators?
Are the tiles on "skip sheathing", planks with spaces between the planks, or is it ship-lap or square cut planks butted up against one another, no gaps?
Do the walls have exterior plank sheathing with some sort of tarpaper or rosin paper and an air gap between the sheathing and stucco, or is it stucco applied to lath attached directly to the studs? (This is important- if it's the latter you can't just slap up a vapor barrier over the insulation and expect it to survive.)
Rock wool is at least somewhat preferable to fiberglass in most locations. But open cell foam may be the easiest way to air seal and insulate other locations. Some pictures would be useful here.
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OK! It's not letting me post photos at this time. I will try again later!
The attachments didn't seem to attach... ( I getting one pixel resolution :-) )
Drilling a small investigation hole into the shiplap/plank wall sheathing might be in order here. The fact that it's sheathed rather than lath-on-studs may be encouraging. If there's even a tiny gap between the stucco and next layer it's a good capillary break, making insulating less risky.
Even if it happens that you have the necessary capillary break and drain plane material, an interior side vapor BARRIER increases risk with stucco siding, since it blocks drying toward the interior. Installing a "smart" vapor barrier such as Intello Plus or 2-mil nylon (Certainteed MemBrain) on the interior side is a lot safer than 4 or 6 mil polyethylene vapor barriers.
I will ask our GC if he knows whether there is an air gap. A couple of new exterior wall penetrations are happening for things like HVAC and vent fans, so he may already know.
What you're talking about is exactly my concern though. I'm really glad to even start to learn the right questions to ask.
Trying again with a photo of the interior side of the outside walls...
OK and here is the one of the underside of the roof...
Emily,
There are lots of questions here, so it will be necessary to chip away at the questions, one step at a time.
Q. "We are not going to be insulating the exterior walls, for the most part, because there is no opportunity to add a vapor barrier. ... The exception to this is the kitchen, which is down to the studs. We will put in a vapor barrier and insulate the exterior walls in there before the walls go back up."
A. There is no requirement in building codes for a vapor barrier -- only (in cold climates like New England) a requirement for a vapor retarder, a less stringent layer than a vapor barrier. You can meet this requirement with vapor-retarder paint. For more information, see "Do I Need a Vapor Retarder?"
Thanks Martin. I will admit to being less concerned about code compliance (as regards insulation) than about doing the right thing for the house. The building inspector is being pretty flexible, as this is an old house and not a complete gut job. In terms of adding insulation to the intact walls, I am most concerned about having to patch a million more holes in the plaster, and about inadvertently causing a moisture problem along the lines of what Dana mentions above (lack of sufficient air circulation behind the stucco or introducing a new surface in the wall cavities upon which vapor will condense).
Worst-case it's usually possible to install an air barrier 1/4-1/2" away from the plank sheathing, and insulate toward the interior from there. Even 1/4" is a very good capillary break, and provides a bit of drying channel for the plank sheathing.
You may be able to see through the seams in the plank sheathing as to whether there is a rosin paper or tar paper layer external to the sheathing.
I will take a closer look next time I'm over there. My GC said he doesn't know, but we will know soon when he drills the holes for the new kitchen and bathroom exhaust fans.