04 November 2015

Structural Insulated Panels (SIPs) Tiny House

There are many ways to build a house and many ways to build a tiny house. Most tiny houses go down the path of traditional stick frame construction due to its relatively simple construction and easy access to materials. But is this the best approach to build a floor, walls and roof? Like most things there are multiple options, each with pros and cons. One option that is a fairly new-ish approach in NZ is (SIPs) or Structural Insulated Panels. SIPs are reasonably common for tiny house construction in the States but not so much in NZ yet. Lets find out the pros and cons, look at some examples and hear what approach we have taken.



What are SIP's?



SIPs are generally referred to as panels made from a thick layer of foam (polystyrene or polyurethane) sandwiched between two layers of Oriented Strand Board (OSB) or Magnesium Oxide (Mag). The result is an engineered panel that provides structural framing, insulation, and exterior sheathing in a solid, one-piece component. They can be used for many different applications, such as exterior walls, roofing, floor and foundation systems.


What are the benefits of SIPs over traditional timber construction?


  1. Better energy efficiently - because the construction method is very precise a near zero air leakage is achieved meaning no drafts. Due to zero thermal bridging your energy bills will be less, saving money over the long run.
  2. Durability - improved structure strength, great for a mobile tiny house.
  3. Speed - due to the standardized and all-in-one nature of SIPs, construction time can be less than for a frame home, as well as requiring fewer tradesmen.
  4. Cost -  Less man hours are required during the build but the material is generally more expensive. However the running cost will be less in the long term. These factors vary between countries, regional, location of building and local labor costs. As with any build a cost analysis would need to be conducted to compare. In general SIP's seems to be more cost beneficial. 

SIPs Specifications

Typical product specifications are:

Width: 300mm, 600mm, or 1,200 mm wide
Length: 2.4, 2.7, and 3 m long, with roof SIPs up to 6 m long
Thickness: 100mm-300mm
Density: 15−20 kg/m

They are not limited to these sizes as custom panels can be constructed.


Examples of SIPS tiny houses include. 

Minim Homes


Brian and Joni's Tiny House under construction

Leaf Tiny House


Monarch Tiny Homes


New Zealand SIP's Manufactures


There are a number of NZ SIPs manufacturers which include and not limited to:

Formance
Magroc
Method

Our approach to SIPS's


We think SIPs is an excellent option for building a tiny house for the reasons above. However we investigated this option for a long time and after some careful thought we decided for our budget this method wasn't for us, A do it yourself build methodology was a better fit for us and was better for green reasons.  

Cost: After getting quotes for a single level foot print approx 8m x 3m we were getting quotes in the order of $15k to install yourself. For a total house budget of $25k, this was not feasible for us. If you build you own I don't think you get the cost savings from the reduced labor time.   

Build mythology: We want to build as much of the build as possible to gain experience. Although possible to build your own SIP panels it did air on the risky side and required equipment and plenty of space to construct.  

Green : Not all but many SIP's use polystyrene for insulation and structure. We were not comfortable using in this material in our tiny house, see here for why. Having said that there are more green SIP alternatives available. 

We decided on a different approach that uses polyurethane and plywood sandwich see here. You might be thinking these are not the greenest materials, but there is always tradeoffs. Polyurethane and plywood do off gas initially and then become stable, and seem to be a much better option than polystyrene. The structure is lined inside and out reducing this risk also.



To conclude we would recommend building a tiny house or any house from SIP's if you can get the cost at the right point.


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