Sheathing/insulating balloon-framed
In the process of bringing a two-story, balloon-framed home to a better level of functioning. The house was probably built in the late 1800s in a little Kentucky River town (zone 4), maybe starting life as a grocery or butcher shop (according to every other person who stops by to talk). 2×4+ framing, with plaster and lath, sometimes topped with a layer or two of drywall. Some early/original windows, some replacement, none of them performing well. Exterior is wood lap siding, with a second layer of vinyl siding nailed over top.
For a blend of cost and performance reasons, I’m thinking of siding tear off, then sheathe with OSB topped with recycled polyiso, then housewrap and lap siding. Because the roof overhangs are only 10″ and the fact that the available sheet insulation is, at the least, 1.75″ thick, I think I’m limited to one layer of polyiso and either no rain screen, , or one of minimal depth (I’ve done 1X rain screening in the past which has worked well, but don’t think that’s an option in this case). I’d use mineral wool between studs and drywall finish. All new outie windows.
I think I’ve looked at just about every GBA question and answer about similar situations, as well as FHB and GBA articles on the subject, but either I haven’t absorbed well, or there isn’t a consensus reached. The concerns I have focus on the OSB layer, since my experience with the material is limited to not-good occasions building Habitat houses where, to be fair, it was exposed for way too long due to the start/stop nature of the builds.
So first, assuming competent installation (I know this isn’t a given, but otherwise we devolve), can this arrangement and these materials result in a trustworthy, sleep-allowing wall? Where are its weak points? Is it worth being mindful of staggering OSB joints with polyiso joints? Is the integrity of a peel and stick housewrap worth the bump in cost/effort compared to a properly-applied tyvek or other similar product? Would CDX plywood be a significantly better sheathing material in this scenario? Cost is a real concern, but could give way if a demonstrably better result could be obtained with different materials or different approach.
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Replies
A full ¾” or 1x rain screen is the gold standard for keeping siding dry and allowing the wall to breathe. However, if your overhangs are too small to accommodate it, even a minimal ¼” gap (using something like a drainage mat) can provide significant benefits. If you can fit it in, I’d strongly encourage it.
Sounds like this project is really a deep energy retrofit.
Consider from a dollar and cents point of view this kind of project fail in that the costs of working around the existing old building are just so high that bulldozing the place and rebuilding a modern recreation on the same spot gives you a better building for less money.
If you make a realistic budget for EVERYTHING you are wanting and needing to do it will exceed the cost of a rebuild. Note doing smaller projects as you have the cash only make the total cost higher in the end.
The truth be told what are you going to keep and use in the end? Not the windows, doors, siding, electrical, plumbing or the lead paint incrusted interior. So, you keep the leaky cobbled together foundation with its 3 additions the less than ideal old framing layout, covered by an old roof with a few leaks.
The “river town” thing scares me to death. Has it ever been flooded?
Is there sentimental value that might add preserved value?
Sorry if I am to harsh in the end real estate is 100% about the numbers and the math has to work.
Walta
I am a home improvement contractor, and a serious lover of old houses. My current house is a late 1700s farmhouse (timber-framed), with an 1800s addition (balloon-framed).
I recently completed an interior gut rehab of my house. I have learned a lot through this process. Going at the house from the exterior simply did not make sense from a financial standpoint.
I’d be willing to chat with you about your plans for your house if you wish.
I think you have a solid plan there that will make an efficient assembly when done.
A couple of details with balloon framed houses. When the walls are open, make sure to install and air seal blocking where it is missing. This is typically at the bottom of the wall in the basement, at each floor and in the attic. This is important for fire safety but also prevents the wall from acting like a giant chimney and carrying all the heat out of the house.
For any floor joists, make sure to install blocking at the end of the joists bays as well, you don't want the joists space connected to your walls for similar reasons.
Most older houses have 1" sheeting, so if you go with 1/2" OSB, 1.75" rigid and 3/4" rain screen, you are not adding all that much extra thickness. Your 10" overhang would still be plenty.
In zone4 that 1.75" of rigid is way more than what you need for condensation control. The OSB underneath will always be warm, so there is no issues with moisture on the OSB.
Detail your windows well, make sure you have a solid air barrier (ie taped sheathing) and you'll have a great performing 100 year old house.
I've done an interior retrofit on a similar construction house in zone 5. Air leaks dropped from 22Ach to 8 and fuel use to a 1/3" of what it was. This was even without any exterior rigid.
Older, I'd very much like to talk about this with you.
I understand that, if I were to have each of the steps done by others, I could probably tear down and build a new home for the same or less money. I'll be doing the work, though, something that brings me some joy and satisfaction, so the material costs are the focus. Because of this, I expect to have a decently performing two family (2BR/unit) for a very reasonable dollar investment ($125-130k, including acquisition costs). And I admit that I value the maintenance of the existing streetscape and the continuing use of the embedded materials to a greater extent than others would.