Seeking input - DIY 800sqft ADU project planning - LEED + fire + flood resilient goal -
Last Post 08 Dec 2023 02:07 AM by alex_angel. 4 Replies.
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alex_angelUser is Offline
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06 Dec 2023 01:53 AM
Hi, I've lurked for a while but only recently decided to create a login and start asking questions. I've got a seemingly ambitious pet project that I'm looking for input at the brief phase:

Elevator pitch: "remember those house kits you could buy from Sears Roebuck and have delivered to your house via railcar? And they were actually GOOD, and not crazy expensive, and you and a friend or two could build them in not too much time? Yeah, that. But modern. I couldn't find anything that fit the bill, so I did it myself. And documented everything. And if you want to, you can do it too."

Target audience: Everyone who A: has a house, B: wants to put a smaller house in their backyard (either for their kids, or for themselves to age in place, or for rental income, etc etc), and C: can't afford to do so because builder fees are north of $450/sqft here.

Must-Haves:

-$125/sqft budget ($95/sqft USD) all-in, including permits, foundation, servicing, appliances etc.

-Buildable in <1600 untrained labor hours, aka two guys' weekends for a year.

-LEED Gold or PHI certified. Leaning towards LEED, there's more brand awareness and is cheaper to obtain.

Want-to-haves:

-fire resilient construction

-water resilient construction

Ok, some of the "why" questions:

-why LEED? Credibility. I'm not a builder, and selling this concept is far more credible if I manage to A: get LEED certified and B: get some press for it.

-why $125/sqft? Because at 800sqft that's $100,000 all-in. People can wrap their heads around $100,000 cost for a rental property, ($2000/month would actually be a low range lease). That's a 24% ROI, and that's a small enough investment that a huge portion of existing homeowners will seriously consider it for themselves. It also seems doable. Tight but doable.

-Why fire resilient? Protection of investment, and credibility.

-why water damage resilient? Again protection of investment, and credibility. The more "forgiving" the construction method, the less risky it is for people to DIY.

Oh and for both fire & water damage resilient, that's a pretty big sell for an investment property. Less risky.

At present I'm researching and talking to manufacturers & suppliers both in Canada and abroad (US & Europe, China). At the same time I'm learning relevant code and building science and reading up on the LEED certification process.

So, overall I'm looking for *helpful* tips and suggestions. There have been a few seemingly super obvious likely decisions already:

-frost protected slab on grade foundation (dirt cheap), with polished slab floor (again dirt cheap)...possibly with hydronic heating (less cheap but tankless water heaters that can drive a radiant system are surprisingly affordable, and pex is dirt cheap. oh and concrete isn't combustible, and is resilient to spills / water damage of the irresponsible renter variety).

-Some species of SIP framing. (super fast, fewer steps to get wrong, contributes greatly to LEED, and if I *carefully* use the right skins & core materials, I can achieve fire rating & water resilience. Leaning towards MGO (sulfate not chloride) panels with PUR cores. PUR handles better in a fire, MGO is super fire resistent and MGO interior skin can be mudded & taped allowing me to skip drywalling, and MGO is more water resilient than gypsum board.

-Pex or "hyperpure" PE-RT for the plumbing, and go with a manifold plumbing setup to minimize fittings (and thus failure points).

-mostly concrete "wet room" bathroom. Accessibility, simplicity of materials, mold/mildew damage is easier to remedy, and if I don't like it I can always tile over it.

-Windows from Poland...or China. Whatever works out. Poland is where you get European glazing for cheap in Europe, and China is where you get European...style... glazing for the rest of the world. We'll see. Some of the Chinese manufactures like Doorwin have US warehouses and showrooms so it's less sketchy than at first glance.

Let's start off I guess with some questions, see if the brain trust has answers?

1 - anyone have a lead on energy modeling software I can use either for free or for cheap? PHPP is NOT cheap and while I might use it if I must, I wasn't planning on it.

2 - has anyone put this whole "MGO chloride vs oxysulfate" thing to bed yet? It looks like there's a few MGO (sulfate) suppliers in the USA, but the only one in Canada (ZS2 Technologies) was telling me $17+/sqft for their SIPS, and that's beyond my budget envelope.

3 - Anyone know foam glass aggregate manufacturers near me? I very much want to use foamed glass aggregate for my subslab drainage and insulation as a "two birds, one stone, and better green bonafides" win. But I can't find any supplier anywhere near me. One's in Ottawa (6 hour drive) and hasn't answered my email in 2 weeks, and the other I'm aware of is in Vermont, and that's quite a distance to truck it over. I WILL buy the damned stuff from China if I have to (a shipping container's only about $3000 for transit) but I really want to skip the whole "fly there to actually make sure the product I ordered is what's shipped and it actually gets put on the container" step.

Anyway, updates will follow as this comes together :)
newbostonconstUser is Offline
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07 Dec 2023 02:08 PM
Say NO to MGO......way to many problems and if your starting out and trying to build a name then definitely wouldn't take that chance.
Sip has a bad history as well but better then MGO
Wish you luck....I would skip on the glass aggregate as well.
"Never argue with an idiot. They will only bring you down to their level and beat you with experience." George Carlins
alex_angelUser is Offline
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07 Dec 2023 02:53 PM
Newbostonconst, can you go into some of the reasons for your particulars? I'm at the investigating options and pitfalls of approaches stage. MGO (at least the oxysulfate kind) seems like a solid alternative to drywall for a few reasons: screw holding power, damage resistance, and water resiliency. And the glass aggregate, if feasible to obtain, seems like it'd give me insulation plus base for the concrete slab at the same time, and increase the green bonafides as the alternative would be EPS.
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07 Dec 2023 09:48 PM
MGO has tons of negatives on here and other places. The people saying it is good are the people involved in selling it. Buy a sheet of MGO and put a nail and then a screw in it and see how it holds up. It also isn't in the US code book and will likely cause you to have to get an PE to sign off on it here in the states. I know you are in Canada and don't know your code.

Sips had a roof rot problem years ago so research that. especially in colder moist areas....Canada?

As far as the substate trucking is the majority of the cost in aggregate so unless it is around the corner I am guessing proven stone and insulation is going to be the best.
"Never argue with an idiot. They will only bring you down to their level and beat you with experience." George Carlins
alex_angelUser is Offline
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08 Dec 2023 02:07 AM
I'm aware of the roof rot issue, vented cold roof assemblies solve for that, something to know but not a problem. Also if using an inorganic skin board like mgo or metal, rot wouldn't be a problem anyway, but regardless I'd just go with the better process and do a vented cold roof.

With regards to screw holding, are you referring to the fact that overdriving the screw reduces holding power? If screwed in correctly, a 12mm board is rated to over 200lbs of shear holding for a #8 screw, which pretty much means you don't need backer boards for grab bars or cabinetry.

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