Passive retrofit in 71 year-old home
So, I bought a house in Halifax, NS, Canada. It’s old, 71 years to be exact, but a major retrofit was done in 2002. It’s horribly inefficient and prior to buying for location, my intention was to build a new passive build.
Here are the details currently:
– Solely electric baseboard heat
– 2×6 walls – fiberglass (poor job), no rigid foam board on exterior, no concern for air sealing
– attic – R20 cellulose, no concern for air sealing at all, single hip roof, ok ventilation currently.
– basic air exchanger installed
I’ve reached out to my passive builder partner and they don’t really want to be associated with the retrofit as they can be complex and not yield the desired results unless the home is taken down to the studs (not the intention here).
My initial plan is:
– Attic – R80 cellulose, after air sealing – should I attempt to seal with poly before blowing?
– Walls – Dense pack existing 2×6, take off vinyl siding, add 3″ foam board, and re-install siding – again, air sealing on walls… presumably impossible, but what considerations should I have?
– Mechanical system – I intend to upgrade. What considerations would you take into consideration?
Would the all knowing group here have any suggestions for such a project?
…I presume in the coming years this will be a hot topic, considering the government here just announced 40K interest free loans on envelope efficiency upgrades, at least in Canada.
Thanks, all.
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I don't blame the passive builder, well I kind of do. But after doing a renovation for the last several years, everyday I wake up and ask myself why I didn't tear down and start new... Lessons learned, future projects will only be full teardowns.
However, for your project, I just wanted to mention that I see some contradictions. You mentioned you don't want to take it down to the studs, but also mention removing existing wall insulation and adding cellulose. That sound like taking it down to the studs to me.
Since I'm a beaten dog with renovations. I would suggest sticking to a few "best bang for your buck" solutions and live with a "not the best house". You'll save from pulling your hair out and still have a good level comfort and emergency efficiency.
Things like leaving the wall insulation so you don't have to tear down drywall, kitchens, baseboards etc. But instead, take the siding down. Do all your sealing from the exterior, 3" inches or more of exterior insulation (rockwool if you have an interior vapour barrier), new siding. Airseal the roof from the attic and add additional insulation. Or consider making the attic a conditioned space and spray foaming the roof rafters and removing the attic cellulose. (If spray foam gets approved in the grant for envelop stuff, its not green but it's also significaltly easier, timely and energy efficient than alternatives). You'll probably have to get an energy auditor for a before and after. Maybe see if you can get a blower door test done for the after. And also consider aeroseal (expensive but fast and easy ie worth it for a reno).
For heating. Since you only have baseboard and assumed no existing ductwork, I suggest doing some ductless minisplits for the fastet easiest and also very effecient. The only downfall of ductless minisplits is difficulty with many rooms, especially bedrooms with closed doors. You should post your floor plan and a lot of people on here can help you with an effective minisplit layout.
I havent gotten into the weeds of the federal grant you mentioned. But please post a link of what it involves. I remember Ontario had some energy incentives a few years ago but it was a REAL pain in the ass to get funding. Ie it wasn't a grant, it was essentially you hired their certified contractors if they have the time to do your job, and they applied the grant to their own invoice, which usually meant they priced higher. Since I do my own work, I wasn't allowed an incentive.
For what it's worth,
Jamie
This ^ is basically the process that we're going with on our 90 year old farmhouse. A Pretty Good House :) Thx Jamie and others here for pointing out their experiences.
If you want to achieve something "certifiable", a local architect suggested skipping Passiv and LEED, because you'll save $ on certification fees, and instead shoot for Living Future's Zero Energy certification. You'd think that retrofits could try for the DOE's Zero Energy Ready b/c it's suppose to have a performance path not just a prescriptive path, but I've not seen any raters actually say that they would come in and certify a retrofit home :/ If anyone has heard otherwise, I'd be all ears, b/c I actually like the DOE's ZER ... it's a poorly named program b/c it includes WaterSense and IndoorAir requirements in addition to net zero onsite.
Thanks, all. For us, I was more thinking about applying the "Passive concepts" or "pretty good house" concepts rather than going full certification. There's certainly a good argument for licensure, but viability is not always there in residential - like ours.
The thing I still struggle with most is how to make sure I am not making a huge mistake with my water and vapour barriers as I attempt to increase the tightness and overall insulation.
I will update the thread more once I get moving along in the project in the coming weeks - perhaps leaning on the knowledge here to get through the sticking points.
>huge mistake with my water and vapour barriers
I struggle with the same. From leaky to tight -- what could go wrong?! :)
As we've tightened the house, the indoor relative humidity has gone up. We 1st noticed this in single pane glass on an original exterior door condensating (all the other glass had been upgraded to double pane) after the roof was air sealed and that cold snap blew up a few weeks ago. Maybe some GBAs would cry out that we should have noticed earlier! with a humidistat or similar, but we already had a dehumidifier going in the basement. Basically our air sealing had outpaced that dehumidifier and we didn't realize that until "winter" temps blew in early.
So I've scaled back our air sealing projects a bit lately until we can be more confident that condensation isn't happening inside the exterior walls & roofing. Does that mean being paranoid and installing more insulation than code requires? Probably. But how to get at insulation that can achieve those R values when restricted by an old houses build characteristics?
I'm not sure if it is your intention, but you can also dense pack over the existing batts in the walls. This also does a decent job of limiting air leaks, not passive house levels, but much better.
If you are dense packing the existing walls, for high R value retrofit, Larsen truss type setups are much cheaper than rigid foam install. You can air seal your sheathing when your take the siding off. You probably have board sheathing, a full layer of peel and stick over the exterior walls is best way to seal it up.
Air sealing old attics is messy, if you have the access, it might be easier to lay a layer of 1/2 OSB over the existing insulation and rafters. You can tape that for air seal and blow in the rest of your insulation on top of that. This also has the benefit of supporting the weight of thick insulation which would bow drywall ceilings. The air barrier transition from the OSB to your walls would be a tricky detail, probably best with spray foam. This would also leave your ceiling free as a service cavity for wiring and HVAC.
re: dense pack - This is the plan, exactly. I intended to pull off the vinyl siding as it is in good shape, dense pack, wrap/seal, add foam board, reapply siding, with bug screen at the bottom.
This does present two other challenges though - re framing the windows and butting up to the roof line with he additional 3-5" of wall....
Open to suggestions there...
You don't need to re-frame the windows if you keep your WRB at the current sheathing. Just go with flanged innie windows. Details here:
https://www.buildingscience.com/documents/insights/bsi-085-windows-can-be-a-pain
With the WRB under the foam go with crinkly house wrap. This helps a lot with drying.
More work, but I'm a big fan of outie windows, the deep interior sills make the windows and room feel bigger and are great spot for plants. Those a bit more work as you would have to make window bucks to extend past the foam.
If you have decent overhangs, taking 5"6" off it is not an issue. If your overhangs are small, you can sister your rafter tails, cut back the roof sheathing and install new sheathing to bridge and extend.
Matt,
I applaud you for seeking energy efficiency. Harold Orr described superinsulation at the 2007 Passive House conference as heating degree days for your location divided by 120 for ceiling R-value and 180 for walls. I would suggest at least 1/2 of the wall R-value for continuous foundation insulation. Set a target of 1 ACH50 for airtightness. This will set you on course for a residence that will use approximately 1 Btu per square foot per heating degree day (Btu/sf/hdd).
Why Passive? It has nice sound to it I agree.
If you choose to call it a pretty good house the only goals you need to meet are your own. The only downside is you don’t get a certificate unless you print one.
What is the passive wall requirement for your region R65 or more? You plan sounds like low 40s?
What is the passive slab/ foundation requirement for your region and what is your plan?
Do you really have room for 20+ inches of cellulose around the eves?
Reinstalling the old siding over the new foam is that a realistic plan? Every wall is now a 6 inches longer than it was. What percentage of the 17 year old siding will be damaged when it is removing? Be careful if you move siding from one side of the house to another as they will have all faded to different colors over the years.
Are you planning on living in the house while doing this work? If so under the vinyl siding is likely the original siding coated in lead paint and exposing any person no less a child to that amount of lead would be a bad idea.
Walta
I should have been more clear - what I am really looking to do is apply Passive concepts to a retrofit, a la the "pretty good house".
Eaves will be an issue to insulate to those levels, yes. The rest of the attic should be a-ok. open to suggestions on best practise here...
Re: siding - we plant to reface the front of the house so if there is some breakage we should be able to accommodate. I don't see this being a huge issue but thank you for pointing it out.
Lead paint - possible... but TBD
Just to pile on for readers who might not understand the distinction:
"Passive" is not a catch-all term for energy efficiency, it's a portion of a proper noun denoting the most stringent, results-oriented set of standards that exist for green homes.
A certified Passive House is an incredibly hard thing to build in a climate significantly colder than western Europe in a way that's going to last, requiring a sizable additional financial outlay, many design compromises, and an exquisite plan & coordination during build for specific construction detailing. There are only a few of them on record in colder climates, and many people question the purpose of building one now that rooftop PV is cheap. The more insulation you have in a house, the less energy you have to work with to dry the house out, and the more devastating small mistakes are.
In a retrofit setting? Energy retrofits are hard enough to begin with. Bringing a poorly constructed house up to certified Passive House spec in a way that's going to be durable is ludicrously difficult, and likely more expensive than a new build. Things like foundation insulation just are not things you get to retrofit, and many of the airsealing things you would want to do end up confronting the issue of "There's already something structural in the way".
Look at it this way:
"What can I do to improve efficiency for <$40k"
Here's what you need to begin:
An energy consultant with a blower door, a thermal camera, some weatherstripping and some spray foam.
Lots and lots of photos.
What does the design of your attic look like? One of the very easiest projects you can do is blow in a bunch more cellulose in an attic (dense-packing walls is much harder). There are potential trouble spots at the eaves, which ideally have a bit of a knee-wall.
The AeroBarrier process is another potential high-payoff option, in that after you've done blower-door-directed airsealing and checked for any big gaps and covered your bases, it can help to mitigate all the minute mistakes made during initial construction that are otherwise nearly impossible to catch and airseal by hand.
>"– Attic – R80 cellulose, after air sealing – should I attempt to seal with poly before blowing?"
In a NS climate a sheet of poly at the ceiling under a vented attic isn't mandatory from a building science point of view, but it might be from a local-inspector perspective. If you skip it and it comes up, vapor barrier latex primer under the ceiling paint meets the NBC definition of "vapour barrier".
>"– Walls – Dense pack existing 2×6, take off vinyl siding, add 3″ foam board, and re-install siding – again, air sealing on walls… presumably impossible, but what considerations should I have?"
When it's stripped down to the sheathing it's possible to get good air-sealing details on the exterior. If it's in too rough a shape for tape to work, using a fully adhered weather resistant barrier between the sheathing & foam board does wonders! (Think of it as 4' wide housewrap tape.)
The dense-packing will also tighten up the seams between the sheathing & framing, but pay attention to putting beads of caulk between doubled-up framing such as top plates & jack studs (whenever they are accessable), and between the bottom plate and subfloor, etc.
Akos is correct that dense-packing over the pre-existing batts is possible, and perhaps desirable, drilling from the exterior.
>"– Mechanical system – I intend to upgrade. What considerations would you take into consideration?"
First and foremost, do a good job of calculating the heating and cooling loads.
And, even though NS currently has the highest fraction of coal-fired power of any province (!), go all-electric, leveraged by heat pumps where it makes sense. NS is warm enough in winter to do the bulk of the space heating with cold climate heat pumps, and heat pump water heaters still work fine in insulated (if not fully conditioned) basements. The amount of world-class off shore wind resource in NS is huge, more than enough to replace all coal fired power, and it's only a matter of time (and regulation) before it becomes cheaper than operating existing coal plants. If Canada is going to meet it's greenhouse gas committments that coal fired power is going to be scaled way back, and sooner than most might think.
Thanks for all of this info. Very useful.
One follow up on mechanical - Basement is concrete with insulated walls, nothing known underneath. The mechanical is in an insulated room with laundry. If I use a heat pump hot water heater in the room, would it make it too cold in that space? What are your thoughts/is there a rule of thumb?
We had our plumber install a 50gal AeroTherm heat pump hot water heater in our basement at the end of last winter. Our basement still stays a constant 50F, we have plenty of hot water, and I've never noticed the unit go into electric resistance backup mode.
I've noticed GBA experts usually ask a few common questions to consider for HPHW:
1. how big is the space where the hot water heater sits?
2. what's the average and low temps of that space?
3. have other plumbing efficiencies been considered, aka. a core design, insulated piping, etc.?
I believe the rule of thumb is 1) don't install HPHW in utility closets, so you're good there, 2) most brands of heat pump hot water heaters aren't any more efficient than electric resistance if the temp falls below 40F*, and 3) take the whole plumbing system into a decision. But hopefully others can comment.
* BradfordWhite's spec sheet says our heat pump will not operate below 35F.
>"Basement is concrete with insulated walls, nothing known underneath. The mechanical is in an insulated room with laundry. If I use a heat pump hot water heater in the room, would it make it too cold in that space? What are your thoughts/is there a rule of thumb?"
If the room with the water heater has the manufacturer's specified volume it'll be fine. Depending on manufacturer & model that tends to run 700-1000 cubic feet. If the room is smaller than that, buying a ducted model could allow the water heater to access the full air volume of insulated basement, not just the laundry room.
eg: The Rheem Prestige series requires a minimum room volume of 700 cubic feet, but both the intake and exhaust can be ducted. See page 3:
https://s3.amazonaws.com/WebPartners/ProductDocuments/c2ba7801-ae70-4c6c-be6b-f5c2a3647577.pdf
Giving the water heater access to the full air volume of the basement has the added benefit of summertime dehumidification, lowering the amount of other mechanical dehumidification necessary to keep the "musty basement smell" at bay.