Insulating a Converted Farmhouse
Hey everyone. I have some insulation questions for y’all. For starters, this is more of a “restoration project with a twist” than a “go green” project.
My wife and I moved a 100-year-old house onto our East Texas property (Zone 2A). This will be our weekend house, so energy efficiently isn’t necessarily our top priority. Our number one priority is to avoid doing something that will cause moisture/mold/rot issues.
The house was originally 30’ by 30’ feet. To move it, they had to cut it in half. So, when they set it down, we had them set the halves 20 feet apart. Then, we added to the middle. Instead of going into a ton of detail about the construction, I uploaded a video to YouTube here so you can see it for yourself. But here are the highlights:
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There is no insulation anywhere in the house
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We are keeping the original T&G walls and ceilings
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The new construction will get matching T&G walls and ceilings
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We are keeping/restoring the original windows
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The original attic has gable vents, but they won’t work anymore because the middle section now blocks airflow
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The new roof has ridge vents, but there are no soffit vents
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The AC unit is a Single-Phase 5-ton unit. It has a zone for the upstairs and downstairs
Here’s what I’m thinking in terms of insulation:
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Spraying closed-cell foam underneath
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NOT adding any insulation to the original walls with two exceptions
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We have removed the T&G walls in the kitchen and original bathroom (you can see daylight through the siding in the bathroom). In those areas, I’m thinking about using 2” rigid foam sealed in the wall cavity of the exterior walls. Then the walls will be greenrocked.
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Spraying closed-cell foam in the wall cavities in the new construction followed by T&G interior walls (no sheetrock).
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For the attic, I’m thinking of putting down a layer of craft paper then spraying in fiberglass insulation.
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Adding soffit vents to the old section
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Adding gable vents to the new section
I’d be interested in your thoughts and ideas on this project. And in case the link above doesn’t work, you can copy/paste this one.
Thanks in advance for your insight!
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Replies
Wow, Adam! This project blows my mind. I just shared your video with my team at Fine Homebuilding. They will appreciate it too. If you'd ever like to discuss it with me for possible coverage on my Green Advocate blog, I'd bet a lot of readers would enjoy learning about it. Also, that's one sharp-looking house--nicely done.
Anyone? :)
Here’s a video of moving it onto our property. Maybe someone will chime in???
Thanks!
https://youtu.be/A2dwmhelLU0
Cool looking house!
I would think for the attic area you could install an inch of closed cell spray foam to air seal and then blow cellulose over the top. Your gable vent and ridge vent will still somewhat work, although at a somewhat reduced capacity.
I think you’ll really regret not installing wall insulation or doing anything to tighten up the leakiness. Are you able to install an inch or more of rigid foam on the inside of your walls and then reinstall the tongue and groove over the foam? This would at least air seal the walls and give you some insulation.
Otherwise maybe someone can chime in on the effectiveness of aero barrier and if it would leave visible residue. If aero barrier would work to seal up your exterior cladding you could then install blown in cellulose, fiberglass, or open cell foam. Without getting the clapboards sealed I’d be very hesitant about installing cavity insulation.
Thanks for the reply.
For the walls, I’ve considered removing the T&G walls and installing foam board. We may do this little by little in the future, but I don’t think it’s likely. We may just consider the air leaks (drafts) part of the farmhouse charm. But I still want to minimize them as much as possible.
It’s how to insulate the attic that I’m most concerned with. I like the idea of spray foam to seal it, but at the same time, I don’t want to do anything that will potentially cause damage. And can’t be undone.
Another idea we’ve bounced around is to spray foam the roof deck over the old sections of the house with open cell foam. And do blown in fiberglass over the new section.
The thought is that moisture could still escape through the ceiling of the old section.
Do y’all have any thoughts on that? Thanks again!
And Kiley, I’d love to talk about this with you. Just let me know the best way to communicate. Thanks!
Or maybe what I need to do is hire a building science consultant. If anyone has a recommendation, I’d appreciate it. Thanks!
That is a very neat project!
As for insulation, by placing the ducts and air handler in the attic, you pretty much eliminated most easy options.
Since it won't be occupied full time, I would focus on making the place just more comfortable and resilient to moisture issues.
The safest and simplest approach is the spray your roof deck in both areas as well as the gable walls with 2" to 3" of closed cell spray foam. This would bring your hvac inside the conditioned space, put a nice tight "cap" over the house to limit some of the air leakage and take the edge off the heat from the sun. Make sure to run the spray foam down all the way to the top plate of the walls and seal any openings to the outdoors.
In a regular house that is conditioned all the time, open cell foam can also be used in your climate, however I don't know how it will hold up with occasional occupancy. Closed cell SPF doesn't have any of the moisture issues and I think it is the safest approach in this case.
This way, if you ever want to convert the house to full time occupancy, you can always easily add in some additional insulation to the rafters (either batts or open cell SPF) to bring it up to code.
Without taking the T&G form the walls off in the old section, there is not much you can do to seal the house, it will always be a big air leak. T&G moves too much to be reliably sealed any way, I doubt something like aero barrier will work.
Thanks for the reply. I like the idea of spraying the roof deck. But I do have a couple more questions.
1. I had the load calcs done based on using traditional insulation in the attic. Based on that info, we installed a single-stage 5-ton unit. Will that unit be able to condition the additional space? I can share the load calcs if it would help.
2. Would I need to add additional registers and/or returns into the attic spaces.
3. Other than bringing the house to code, would adding additional insulation to the rafters otherwise be beneficial?
Thanks!
1. Since your air handler and ducting is currently in the attic, somewhere around 20% to 30% of its output is lost. By bringing the HVAC inside the conditioned space, you are reducing the load on your AC.
2. Sealed attics need to be conditioned, this is typically 50CFM per 1000 sqft but check your local code. Lot of times the leakage from the ducting and ceiling registers is enough. With closed cell SPF, conditioning the attic is not critical as you are not relying on it to keep the foam dry.
3. In the summer typical roof gets up to around 160F. Your 1500sqft house probably has around ~2000sqft of roof. Assuming the inside is kept at 75F.
Through an roof you gain:
R15 roof: 2000*(160F-75F)/15= 11300 BTU
R30 roof: 2000*(160F-75F)/30= 5666 BTU
R49 roof: 2000*(160F-75F)/49= 3469 BTU
Most your cooling load reduction is somewhere around R20 roof, above that it still saves some energy, doubt it is enough to have any ROI for a weekend house.
This is really helpful information. I sure do appreciate it. But I’m not sure I fully understand point 3. If the roof deck is insulated, does adding insulation to the rafters help the rest of the livable space stay cooler?
Thanks again!
When you insulate the roof deck, you bring the entire attic into conditioned space, so any insulation there will also help the rest of the house.
The one you want to avoid is split insulation where there is insulation both under the roof deck and also the attic floor. Make sure You are insulating only one or the other.
Ahh. Got it. I want to put enough foam on the roof deck to get at least R20. I understand now. Thank you.
Here’s another thing I’ve been thinking about. I have taken the T&G off of three walls (exterior walls). Two walls are in the kitchen and one wall is in the original bathroom. Since the T&G is already off, I’m going to insulate them.
In the bathroom, there is no tar paper between the studs and siding (you can see daylight coming through in the video) so I’m thinking of putting 3/4 foam board in each cavity, sealing it with can foam, then filling the rest of the cavity with foam.
In the kitchen, one wall has tar paper and the other wall has tyvek between the siding and studs (no OSB). Can I just spray foam directly onto the tar paper/tyvek, or should I put foam board in there first?
Thanks again!
Recent article about your situation:
https://www.greenbuildingadvisor.com/article/managing-water-and-insulating-walls-without-sheathing
If you are in an area with a lot of rain, I would build an air gap no matter what. Also with older siding it is important to provide a lot of drying to keep the paint from peeling.
The safest is to always install foam with 1x1 spacers to provide the air space.
Got it. Thanks so much! I really can’t thank you enough.