Questions about a stick built barndominium
Hello. I’m located in cold central Iowa 5A with no codes or inspections.
I’m now considering a 80×40 stick built barndominium on a concrete stem wall where the old barn stands. A 30×40 one bedroom living quarters on the east (right) side, and the 50×40 garage/shop on the west side with separate slabs poured later. I know attached garages may have problems with IAQ and resale, but the advantages are proximity to the home, one simple roof that’s not cut up, and the west 40′ wall of the living quarters will have a even higher R-value since it’s inside the garage protected from NW winter winds. Plus, I would have the barndominium professionally built, and then slowly build the interior myself as Ive worked in and around the trades most of my life. Owners pay much more attention to details.
Questions are..
A) Having the 80×40 building professionally built with taped plywood over 2×6 studs on 24″, how would you recommend I achieve “pretty good house” standards from the inside, after it’s built not using foam..
B) Could I achieve a higher R value than PGH 10-20-40-60 standards with this building with a double wall built inside off the slab or another method? I don’t want to remove the steel siding to install roxul over the plywood sheathing, and rather not pay the contractor to do so at the beginning. But I’m also concerned about the plywood sheathing adsorbing moisture associated with the double wall method. I need this building to withstand the test of time.
C) A little off topic, but is there any information or blog about the construction methods of Martins off grid house?
Thanks!
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Replies
Provided the barn is built with siding that is naturally ventillated (ie corrugated) and the WRB is properly applied with the sheathing seams taped underneath, the easiest would be to treat it as a double stud build.
The barn with the 2x6 studs is one wall, interior 2x4 wall offset 3 1/2". Batts in the exterior wall, batts in the air gap, either batts in the 2x4 wall or leave them empty. Smart vapor barrier on the inside, air tight drywall over that. Make sure the roof can be vented and install your interior celing supports low enough that you can get the right amount of blown in insulation above it while keeping the vent gap (this might be a lot of furring down from the trusses).
Getting some insulation on the ground really helps with comfort. Even 1" to 2" makes a huge difference.
Deleted
Your barndominium title implies this will be a condominium with mutable owners from multiple families. Is that correct?
If so check with your local government for multifamily zoning requirements. the requirements can be very different with fire walls and sprinklers.
Often rural county will have some version of a model code on their books but make no effort to enforce it for single family residences. There feeling is if you decide to do something dumb and kill your family who are we to stop you. That thought process often changes for multifamily building where you could be killing others.
Walta
Thanks Guys. No codes or inspections in my area.
Akos.. I'm reluctant to build a double wall inside after reading "Lstiburek’s Ideal Double-Stud Wall" which encourages building your second wall outside and separated to reduce thermal bridging from the structure. Another good article is "Is Cold Sheathing in Double-Wall Construction at Risk? by Allison Bailes. This double wall method is so new, I don't want to find out myself if building "in", caused my sheathing to rot unless there's new information I'm not aware of. And yes I plan on insulating under the slab and inside the stem wall with rockwool not foam.
Walta.. A barndominium is a term I believe originated in Texas referring to a pole barn or steel commercial building with living quarters built in half or less of it. It usually has steel corrugated siding and maybe a porch at the living quarters, but the porch is simply to disguise the pole barn for what it is. I find it hard to believe someone would actually build a house in a building that has a average life expectancy of 60 years since it has wooden posts in the ground. I don't like that mentality, or the performance of a conductive metal buildings, so I'm building with wood on concrete for longevity long after I've passed away.
But I'm also concerned with resale value, and many "second half's" wont live in a machine shed.
Here's a quick sketch I made of my idea of a barndominium, shome, or shouse or whatever you want to call it, where the 24x56 garage has a 17' ceiling in the back half for my car lift, yet still looks like a regular house for resale and ease of insurance. Plus, if someone wanted to expand the living space of the house, they could install a floor over the tall part of the garage.
Double studs walls do have some condesation risk. There has been a number of studys that show that the sheathing moisture content increases in the winter but quickly dries out in the spring.
The key take ways there is:
-have a decent warm side air barrier (air tight drywall)
-use plywood or densglass for the sheathing not OSB
-have a vented cladding (rain screen)
There are a lot of houses out there built with this setup, your area is not cold enough to get you into trouble if you pay attention to the details.
If you are worried and if you are building it yourself and labor is not an issue, there are many ways of building a double stud wall with a vapor and air barrier in the middle of the assembly.
This article confirms my concerns..
https://www.energyvanguard.com/blog/77957/Is-This-the-End-of-the-Double-Wall-Cold-Sheathing-Scare
"4/22/15 This just in: I spoke with Joe Lstiburek today, and he wants to make sure it's clear to readers that he does not recommend this wall assembly. "I would never build that wall because I consider it too risky," he said. This was a research project for BSC, not a building that incorporated their design."
Allison addresses that article:
https://www.greenbuildingadvisor.com/article/lstibureks-ideal-double-stud-wall-design
https://www.finehomebuilding.com/2015/09/16/lstibureks-ideal-double-stud-wall
Also relevant:
https://www.buildingscience.com/documents/enclosures-that-work/high-r-value-wall-assemblies/high-r-value-double-stud-wall-construction?topic=doctypes/enclosures-that-work/etw-high-r-value-enclosure-assemblie
See Figure 7
https://www.buildingscience.com/documents/insights/bsi087-chubby-checker-fat-man-do-permeance
Thanks Jaccen.
And then Allison later states.. "Yes, exterior insulation is the better way way to go. It eliminates more of the thermal bridging, is less expensive, and keeps the sheathing warm. The diagrams in this article show Joe's preferred double-stud wall, but the superinsulated wall he likes best of all is one with exterior insulation.
Glad I didn't spend more time on this like this guy..
https://www.youtube.com/watch?v=2fj-7Vpb-l4
NP. Not that it matters, but my upcoming house build will be done with external insulation. That does not have to do with a preference one way or the other. It simply boils down to used polyiso being quite cheap in my area and I'm willing to put in the sweat equity to prep it.
Both designs have their pro's and con's. Drilling long screws into studs also isn't "all that and a bag of chips." Can turn out to be "snap city."
No it does matter because I consider what other people are/have done and why.
My main reason for not using polyiso is that bugs like to tunnel in it. So maybe using rockwool for the foundation and polyiso for the walls might be a option to reduce costs..