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Thinking About Your Prefab Green House Kit: Contractor Tips And Thoughts

We were hoping to head out to the prefab net zero energy green house kit this weekend, as we were snowed out last weekend... but check out the weather forecast, above.
I'm even hearing the words, "twelve to twenty inches" ominously, forebodingly whispered amongst colleagues when they speak about the upcoming weekend.

I am dying to see the interior walls that were built two weeks ago, yet there is still over a foot of snow on the land from LAST week!  Our carpenter, a Mennonite minister, is also leaving to move back to Haiti (where they lived for five years) to help their Haitian community in March, so I would really like to properly thank him in person before he goes... Danged this snow!

But good news: Ran the numbers last night - looks like our *own* prefab house kit we're building is still at around $100sf (actually less if it weren't for all the off grid stuff we're doing). Good to know you can be net zero off grid yet affordable!

Now we're in the final stages, and of course the systems will be very expensive to purchase and install, but you can see our own prefab zero energy green home tally here. Of course YOUR local material and labor costs and systems you choose will all be different. But this is what it's costing for us to build and complete the net zero off grid prefab house kit in rural Virginia as a net zero energy home, not tied to the grid.

But let's talk about you. A lot of you are in the process of permitting and getting ready to start foundation work. Here are some contractor tips I collected over the year to post during this long snowy week, information you might find helpful to think about when planning your own prefab green home.  Of course when you have the design documents and go over them with your contractor it will be easier to make your own choices for your own budget, but here are some "general contractor tips and things to think about."

I subscribe to the Good, Better, Best philosophy.
  • Best would be if I could all hire an in-house team of my house kit SIPs specialists to erect and complete the house kit from start to finish, then certify it to LEED and passive and BREAM standards.
  • Better would be where I choose a contractor with decades of SIPs experience to construct my house kit that was enthusiastic about off grid energy efficient homes.
  • Good would be where I find a fantastic, reputable contractor willing to 1. educate themselves with the manufacturer's manuals, 2. attend workshops, and where I, as the consumer, 3. also educate myself on SIPs and green building technology to then feel confident I, with my contractor, was making the best choices I could for my budget. 
In our own net zero energy house kit construction, it is clear we are in the Good category as consumers of our own house kit... once the modern house kit was erected, you even see us change direction on the interior a bit...isn't that real life? We're adding built-ins to where there's designated closet space, expanding that area to accommodate off grid systems and our own funky, bookcase lovin' lifestyle.
Many people ask why I don't just ship out a completely completed prefab house kit. Here's WHY I'm offering the house kits the way we do: My mission is to offer energy efficient house kits that are gorgeous but also affordable... attainable green design.
By having you order your windows and doors locally (we send you a list along with the design documents), you can then order them at a more affordable price than if we had to add them to your house kit shipment (adding to the cost of the windows the cost to store them at the factory), increasing the truck load weight and number of trucks, increasing shipping, increasing risk of damage and increasing cost.  

By leaving the house kit unfinished, I give you control: you choose your systems, your finishes, your appliances to your individual needs.
  • We CAN have the house kits finished more if you like, which we are working on with European clients. But it will cost a lot more; more than if you worked with a local contractor and supply store. But we certainly can include the windows, doors, framing in shipping containers.
  • We do have contractor firms we recommend who WILL travel and complete the kit for you, and are familiar with SIPs and our house kits, but it will cost a lot more. Just ask, I will send you names.
Now on to Contractor / Construction Tips And Thoughts!
  • ERV / HRV: Because of the energy efficient, tight structural insulated panels in the prefab green home, you will want to make sure you choose an appropriate heat / energy recovery ventilator that works for your area climate needs. We recommend two manufacturers and are happy to send you their contact information.
  • Roof panels: Do you want chassis ways or will you use a surface-wired mold? If you like, you may tell the factory where you want to run a roof chassis.
  • It's not just about the house kit: Are you keeping in consideration How To Keep Water Away From The Foundation?
  • Another tip: Copper pipes and galvanized duct work: Do not let them come into contact! They will deteriorate, then leak!
  • Framing: Your contractor will need to build anything that is not structural insulated panels. SIPs are the majority of the house kit, but there are areas (note along north and clerestory windows) that the engineer deemed it structurally better to have framed in. This is dependent on which house kit you choose. FOR THE CASA TI, here is what *our* contractor estimated:

    "Here is the estimated list of wood required to assemble the SIPs:

    Dim Length Qty
    2X6 8' 60
    2X6 10' 48
    2X6 12' 13
    2X6 14' 4
    2X6 16' 7
    2X8 8' 31
    2X8 10' 42
    2X8 12' 22


    5' 3 5/8 header 9 1/4 "
    16' 2 1/4 header 10 1/4 "
    3' 6 3/8 header 11 1/4 "
    3' 1 7/8 header 9" tall, design/measure on site
    2' 9 3/4 header 11 1/4"
    2' 9 5/8 header 11 1/4"
    2' 9 3/4 header 11 1/4"
    8' 8 1/4 header 2x6, wall thickness?
    8' 8 1/4 header 2x6, wall thickness?
    5' 9 header 2x6, wall thickness?
    2' 9 3/4 header 11 1/4"
    2' 9 5/8 header 11 1/4"
    2' 11 1/4 header 11 1/4"
    2' 6 3/4 header 9" tall, design/measure on site
    12' 3 header 2x6, design on site
    12' 3 header 2x6, design on site

    The following is not included in the above:

    - framing materials for interior load bearing wall/header
    - framing for panel H (row of small windows at transition of roofs)
    - framing for edge of parapet on north end of roof
    - framing between walls and roof

  • Filing this under, "Things your contractor should know":
    Obviously, make sure your contractor carefully READS THE SIP MANUFACTURER'S MANUAL...
    Because there is a *lot* of useful, critical information in there that is imperative to the success of your project. We also have workshops and schools we can point them to, and the factory is always ready to answer questions.

    But even if they follow successfully the SIP instructions perfectly, even if they're the *best* contractor, ever, don't forget they might have aesthetic differences than your love of modern design, so here are just some easy things you can point out/gently remind them...

  • Modern Design vs. Traditional Trim: The trim around the windows should be narrow- It should be “receiver trim” that catches the end of the cut siding.

    It's a very minimalist / modern look, not a traditional way of trim- not 3” wide but more ½ inch, flat, for corners and openings- see this as an example:
    And this:

  • MAKE SURE before you order cladding where everything is measured out individually by your contractor, despite what the plans say.

    Why? Because there are materials and decisions your engineer / contractor will make on site that might slightly change the dimensions- like adjusting the pitch of the roof or framing an overhang out more to accommodate the sun in your area.
  • If you're building a casa ti and using a rubber membrane on the north roof, we randomly came across a graphic that explained the parapet and scupper concept really well! Don't say we're not geeks!

    Flashing ("scupper") in the passages through the parapet BEFORE the rubber membrane is installed:
  • Cladding: Consider HardiePlank, cedar, galvalume (we can put you in touch with the manufacturer we used but make sure you also get a local quote), and I have one other solution that I will post more on in the next week... but cladding is totally up to you! Be creative!
  • Roof: Consider using white paint to reduce heat reflection.  We discovered a great paint application that increases energy efficiency, more on that soon!
  • The West Door: YES it is supposed to be painted black to line up with the window above it, I will do so as soon as I have time... : )

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    At 2/3/10, 2:46 PM , Anonymous Missi said...

    Hi, Thanks for documenting such a great project. I love seeing the updates and can't wait for the open house in April. FYI-Our VDOT crews in Charlottesville, VA got a weather report that we "could" get as much as 45" from this storm. So be prepared.

    At 2/3/10, 3:07 PM , Blogger Passive Solar Prefab Homes said...

    *THANK YOU* for your...oh wait: Thank you for the first half of your comment, it means the world to me!

    As for the second half... booo! hisss!!! *Whimper*
    Surviving Day THREE of NO SCHOOL


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