How’s my cabin build approach?
Hi, I’m still in the planning stage of my cabin build and wanted to get some thoughts from the green building community on where I can improve my design, save costs, or build better.
It will be located in Virginia: a mixed-humid climate (zone 4a) where temperatures range from ~20-90 Fahrenheit. Here are the details:
– 1.5 level, 16×24 cabin with saltbox style roof and a loft at the higher end
– Foundation: Frost protected slab, Sonotube piers, or helical piles
– Subfloor: 12 16ft long floor trusses, Advantech sheathing
– Subfloor insulation: ?? Advice appreciated
– Walls: 2×6, Advantech sheathing, Mento 1000 WRB, Tescon Vana tape, Interior Rockwool, Exterior Rigid Rockwool (Comfortboard 80)
– Rain screen: ?? Wood cladding maybe? Advice appreciated
– Roofing: Advantech sheathing, metal roofing
– Roofing framing: 2x rafters with a bearing wall where the roof lines meet
– Roofing insulation and WRB: ?? Advice appreciated
– Flooring: solid hardwood
– Paneling: birch plywood or tongue and groove pine
– Heating / cooling: Wood stove? Ductless mini-split? Window unit? Advice appreciated
– Plumbing: PEX
– Driveway: Road stabilization fabric, a whole lot of gravel
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Replies
Looks like a fun project :) A couple of questions from me while the experts are waking up.
What’s your ventilation approach? Crucial to sort out now since ducts required and that needs planned chases. I’d want to deliver fresh air to bedrooms. Ditto kitchen hood. Duct layout before framing plan :)
Consider a standalone dehumidifier? Key for long shoulder seasons. Perhaps the split system from ultra-aire is enough Cooling for bedrooms in summer, with a single mini-split doing the rest.
I used helical piles. Figuring out your air barrier line at the ground is key. Is it the floor sheathing? Is it the underside of the joists? How seal plumbing penetrations etc. Termite shields needed in the piles? There is a recent story in GBA about using a material lift to raise floor system for comfortable air sealing then lower back to low. Might work even at your size.
James, any recommended articles on using helical piles for houses/cabins? I see a lot of articles about using them for decks or to support old house footings, but not much about their use in new construction for houses.
Thanks for the reply! :) I hadn't though much about ventilation yet. Would an HRV be a good option for that? I was trying to go ductless to keep things simple, but am open to suggestions. As far as the kitchen, would a kitchen hood vented straight through the wall to the outside of the house make sense? Likewise with perhaps an exhaust fan from the bathroom to the outside?
Could you expand on the dehumidifier? I'm not sure I'm completely following on what a split system plus mini-split would be.
How would I figure out the air barrier line? What do you mean by material lift?
A couple of links for yah:
Material lift are the things lifting up the floor system here: https://www.finehomebuilding.com/2019/07/09/air-sealed-and-on-piers
Split dehumidifier: https://www.ultra-aire.com/dehumidifiers/sd12/
Yes, HRV for ventilation.
Air-sealing line means a continuous line in the plans that you say, “this is the air-barrier” and you can run a pencil all the way around without lifting it off the plans. Lots on that in Martin’s guides on the site :)
Thanks James! Reading the links now :)
If the first floor is a concrete slab why do you need piers and sub floor insulation?
To my eye the loft looks small relative to the space you lose to the staircase needed to access the loft.
I am getting old and do not want to climb a latter or a steep and narrow stair. If you have acreage put it on one floor.
The sloped ceiling force you into foam insulated roof that is best located on the exterior.
Walta
User...307,
To get useful advice you need to make some more choices so you can get advice on whether they make sense or not. As Walter said, right now there is no point in commenting on the structure if you d0n't know what the foundation will be - and that carries on though your list. For example: You won't have any floor trusses if you use a slab. You can't have a load-bearing wall under the ridge if you have continuous floor trusses below.
The decisions all flow from one another. You can't make them in isolation.
Malcolm and Walter, the reasoning behind the ambiguity is that I haven't picked out a plot of land yet to build on. I guess I'm trying to plan for all possibilities right now. I'd rather have a (flexible) plan thought out before buying land than to buy it only to find out I picked a poor choice of a lot or my budget runs way too short.
User... 307,
The problem is it sets up so many permutations. The answer to one question changes the answer to many of the others. it's sort of like saying: I'm thinking of serving pasta or chicken or fish for dinner. The starch will be potatoes or rice. The wine will be red or white.
Ah, I understand Malcolm. I appreciate the analogy.
Anything you or others would recommend I look for in a plot of land in general then (especially in terms of cost savings/simplicity)? I've heard flat is generally better/cheaper to build on, but having some slope is good for septic. Ideally, I'd like to do a good chunk of the building myself.
What affects cost the most is typically providing services, space and perc for a conventional septic field, and the cost of access. The difference between building a house like the one you have shown on a sloped or flat lot, or the different building assemblies you listed is generally not significant enough to worry about.
My suggestion is to think about the things I posted, but more importantly find somewhere you will love to live, and make sure you site your house where you preserve the parts of the lot you like most, rather than cover that spot with the house.
I totally agree from a cost perspective, that location and utilities will trump all. It's an interesting question from a system simplicity perspective though: assuming a low square footage (say less than 1000), what kind of changes to general climate recommendations might there be (let's say outside of those areas in the country where neither heating nor cooling are particularly important)? Some systems might be overly expensive (ERV/HRV/VRF), and some expensive technologies might come into play with so few square feet to apply, or some issues might become moot for the same reason. Cooling a small space (or even dehumidifying?) can't be done with a wood-stove, so ducting become an issue. Anyway, I think this is an interesting thread.
Matt,
Yeah, the systems and the architectural response to both the climate and the site will vary. I find responding to those more fruitful as the starting point of any design, rather than beginning with a house and then finding an appropriate site for it.
Matt, that's sort of the idea I was getting at. Keeping in mind that this will not be a full-time residence and more of a getaway cabin, how can I build it with budget and simplicity in mind, while still keeping quality reasonable?
Will over-insulating result in a requirement for expensive ERV/HRV/VRF? Is a ductless mini-split worth the cost for a cabin or is there a better way to heat/cool? Leaving the loft open would remove the need for heating it separately in winter, but make it harder to cool in summer. Closing the loft off means a need for ventilation and heating/cooling there. The list of decisions goes on...
Malcolm, I get that some of these variables will change once I pick out a site. If nothing else, I am learning about a lot of different aspects of building design that I knew nothing about before I started.
Now we are talking about real estate. Location location and location are the 3 most important things.
Is there any chance this location could flood? Lots of people build a house down by the creek and are shocked that 2 inch deep 3 foot wide creek is suddenly 30 feet deep and 600 feet wide.
How many minutes is it to n
the nearest emergence room? Most people end up going at some point.
What likely to happen on the adjoining properties? Will the highway get widened? Will they start a 500 head hog farm? The only control you have is to buy large and not build near the edges or buy in an a HOA but then you have to live with those rules.
What will you see when you look out the window?
I love my well and septic being off the electric grid is a deal killer for me.
Walta
Walter, I've been trying to do my research on locations. So far I've been (probably overly) picky about rejecting locations for various reasons (part of lot in flood plain, difficulty of access for heavy construction vehicles/equipment, alternative septic system requirements/cost, distance from where I live, minimum sq footage requirements that are bigger than I want to build, nearby chicken / turkey / hog farms, budget, etc.).
What size and type is your septic system (if you don't mind sharing)? I'm trying to stay conventional to save costs, but find that health departments are getting stricter about requiring alternative septic systems.
As others have pointed out, it's hard to make recommendations without having some site information, but it's still (to me) an interesting thought experiment. I think simplicity, durability, and using techniques that are familiar to local craftsmen are good ideas. But some ideas come to mind: forget about ERV and dehu and make sure there are plenty of operable windows - there might be some sticky/humid days, and you may find yourself adjusting windows more, but a simple bath fan on a timer plus having all the windows a few steps from each other means that opening and closing the whole house is not a chore. Eliminate ductwork and have a more open plan (it's a cabin) so that a single minisplit will work. There's your HVAC in an nutshell . A woodstove will introduce a few wrinkles, but again - an operable window is only a few steps away...
ERV and dehumidifier forgotten :) My concern with relying on windows too much is that this will be a weekend cabin, so I wouldn't be there all the time to open/close windows for ventilation. Not sure what that would leave me with as options.
I think when you walk the right bit of land it will speak to you and you will know it.
I think planning a house before seeing the land is a mistake. I think the slope of the land and the views should drive your design and not force your will on a site.
Do not reject a site because it does not face south. Computer modeling showed very little difference in what way my house faced.
My septic may have been the one think that came in under budget. We had a system bid. The contractor ID a location for a conventional drain field. All seemed well most of the house is built, we call the contractor to get him started. He says he is not able to put a system on our lot! Let the scrambling begin. A new contractor came back with a lower bid for an ARC system.
Understand the health department rules can be very different when you cross a county line.
Walta
I sure hope so Walter. I get what you mean as far as waiting until I have a site for the exact plans for the house (in case extra height is required, different orientation, wind design, etc.).
A reasonably priced alternative septic system? My mind is blown. ARC looks pretty neat. I imagine it requires certain soil depths and conditions, but definitely going to keep it in mind as an option.