What is a Barndominium?
A building technique that uses the shell of a typically less expensive barn or post and frame structure to be used as a home. (Don’t confuse post and frame with timber frame.) This “house” often includes a large garage or shop space, or maybe a better description is the garage or shop area includes living quarters.
I’ve seen and been involved with several of these structures, many were simply large storage spaces converted into a home. One particular structure kept the original skin of the barn and built an entire cabin inside. This cabin overlooks a small lake, the original sliding doors on the lake side of the barn could be closed when the cabin is not occupied, completely hiding the cabin inside.
The photo shows one that I worked on in 2009. This was a barn built, I believe, back in the 1930’s. The owner had the top roof section of the barn removed and placed on a slab. We were hired to complete the shell. We used closed cell spray foam outboard of the original roof on this project.
How are post and frame structures built?
Post and frame structures typically have buried posts that act both as the foundation and wall system. Posts are set in a drilled hole that extends below the frost line; this is 5 feet in my climate zone. Posts can also be set on poured concrete footings, usually sonotubes or a continuous footing. Another option is to use a thickened edge slab. Once the posts are set, horizontal wall girts are fastened directly to the posts. These wall girts are installed both inside and outside the posts and become the “wall sheathing”. Spacing between the wall girts will depend on engineering specifications, but 2-foot centers are common. Roof trusses are set next, usually fastened to the posts. Much like the walls, 2x boards are nailed on top of the trusses, these purlins become the “roof sheathing”, 2-foot centers are again common. Once the framing is complete, the frame is covered both on the walls and roof by a corrugated steel panel, 3 feet wide by usually whatever length is needed.
Why do this style of construction?
Post and frame structures were originally built as an inexpensive structure used for storage, usually in agricultural areas. They would be used to store farm machinery, hay and other items used in farming. More recently, post and frame buildings have evolved to include businesses other than agriculture and have also moved into the residential market. There is a couple reason to choose this type of construction over normal traditional framing, the ability to have a large area under roof and cost, though I would argue that using a true post and frame building for residential use usually won’t save a lot if trying to achieve a high-performance building. Where it does make more sense is if a large garage, shop or storage area is needed and is connected to the living space.
Specifications for the Barndominium Build.
I am a consultant on a new barndominium project that we are attempting to make very energy efficient and durable. I am also providing the labor for the wall insulating and making sure the air control layer meets the goals, including all testing. The homeowner has a list of requirements for this structure.
- Increased performance-better than code air sealing and insulation levels
- Durability-this is a generational property, to be handed down to future family members
- High performance heating and cooling system-ground source heat pump-in-floor and forced air
This barndominimium project is a residential structure, the residential building codes of the area are required to be followed. This includes insulation and air sealing, heating, cooling, and ventilation, details that typically aren’t included in a “barn”. Every home I am involved in has an emphasis on the four control layers, water, air, vapor and thermal, in that order. The first challenge is the construction style of a true post and frame structure. Wall framing, the posts are 4’, 6’, 8’ or more on center, usually with no sheathing. In the case of this current project, the 8,700 square feet of floor space has 6 x 8 posts 6 feet on center with an 18-foot side wall height. How do we apply a water resistive barrier to framing 6-foot on center, and then maintain the integrity of the WRB with planned openings and mechanicals that need to penetrate the layer?
Another challenge, how do we make the structure air-tight? There are two distinct areas, the living space and storage/shop area. The goal is less than 1 ACH50 in the living space and 1+ ACH50 in the shop area. The overhead garage doors are the challenge in the storage/shop area.
How do we address vapor? The conditioned shop/storage area of the structure will have snow covered vehicles coming in and melting off. This will increase humidity levels during the heating season, along with it, an increased chance of vapor moving in undesirable areas.
Lastly, thermal. How do we insulate a structure that has 6-foot on center framing? How do we increase thermal performance beyond code minimums?
These are the challenges of the barndominium. The project began during the summer of 2021 with preparing the lot and bringing in utilities, as of this writing in mid-January, the roof steel is almost complete. We still have a long way to go before completion. Stay tuned for more detailed posts on each of the control layers along with other details of this build as the construction continues.