Our SIP House Build

[JackJester]

Per suggestions from @skyking1 and others, I started a thread that documents our small house build using Structural Insulated Panels (SIPs). If you are not familiar with SIPs, they consist of an insulating foam core sandwiched between two structural facings, typically oriented strand board (OSB): What Are Sips
….so in a way they use a similar principal as Insulated Concrete Forms (ICF); see the @skyking1 and @rmcelwee threads for detail: Construction has finally started on the "Big House" (formerly Bunny Ranch)

Building our new retirement place

---with the primary benefit of combining structure and insulation into one unit, which quickens construction time and reduces labor costs. And both are much more energy efficient than traditional timber framed batt insulation houses since there is very little thermal bridging and air leakage through the exterior. That’s a quick overview, and I’m defiantly not trying to sell one approach over the other, but SIPs is the approach we chose; primarily due to build time and our preferred architect's exclusive use of SIPs for exterior walls, ceilings, and floors in her designs.

I’ll break this thread up into smaller parts to limit the size of the posts.

 

[JackJester]

Part 1 (background):

We are building a small 800 sqft single story house in the Pacific Northwest; but unlike @skyking, we are not doing the work ourselves (we have a General Contractor to manage all aspects of the build). We have downsized from a 3000 sqft house. We knew after lots of deliberations… a history of living multiple weeks in vacation condos, and calculating the amount of space we actually ‘lived’ in and used in that 3000 sqft home, that an 800 sqft home would work for us. We even mapped out that size rectangular area in tape on our lawn to walk through the space and visualize how it would work.

A year ago (Oct 2024) we found and purchased a 1/4 acre lot in the town that we want to live in. Our prerequisites for the lot location were that we wanted to use city utilities and infrastructure. And wanted some nature (wood or sea views). After 25 years living in the cascade foothills up a narrow private mountain road we had had enough of those ‘challenges' (septic, well, propane, road maintenance, and difficult access by delivery and large trucks). We immediately worked with our architect/GC on the design. It was nice using modern 3D computer modeling tools to do a virtual walkthroughs of the house; we could focus on the location of light switches and how they would be accessed as you moved from 1 room to the other, and visibility through windows, etc.

One of the most important aspects with using SIPs is that window size and location, and electrical & plumbing locations must be well defined. The SIPs are built based on these specs and window/door holes are cut into the SIP walls at the factory. Channels are formed into the insulation foam at the factory to feed electrical wires. For our house, all the plumbing is run inside the house in ‘plumbing walls', which are traditional 2x4 / 2x6 stud frames that most of us are used to. Thus there are no channels through the SIP foam to run plumbing except holes from the crawl space into the SIP floors and access to a Utility room for the heat pump water heater..

Here is the design of our house:
It is L-shaped with an open living room/kitchen/and dinning room. There is 1 bedroom, a walk-in closet, 1 bathroom. There is a large covered outside deck with direct access to a hot tub. The focus is on living with nature to maximize views of the woods behind the house. There are a lot of windows. The walls are high 10 to 12 ft to make the space feel bigger. All of the rooms (3 of them ..bedroom/closet//bathroom plus the hallway) are framed with traditional wood studs. We will use the deck 9 months of the year and it will have a ceiling-mounted electric heater, as well as a propane fireplace.

 

[like2]

Looks really nice! Looking forward to seeing the progress!

 

[JackJester]

Part 2 (Site Prep):

After waiting for building permits to be approved (4 months) we broke ground in June 2025. We cleared out some trees and did everything to retain the bigger pines, and of course the majestic Madrona (a.k.a, ‘Pacific Madrone') trees.

Here’s the site after clearing and marking out the foundation:

Our first major design change was to increase the height of the foundation. Our site was down slope of the sewer system (sewer pipe was 9 ft below the street) and we could not achieve the required 2 deg slope for gravity drainage to the city sewer. So we raised everything by about 6 ft. This was a costly change, but the right decision. The other option would have been to add a Grinder pump system to break up the crap and pump it up slope to the sewer. That was just a septic system all over again to us (maintenance, etc) which was a pre req to avoid, so building up the elevation was the best solution for us. We ended up adding 580 yds of fill dirt ... yes, 58 dump truck loads! Now its like being in a tree house .
Foundation:

We put in a rat pad on the foundation inside so we have lots of unplanned storage. This pic also shows how a base of pressure treated 2x12s are used to provide the support for laying the SIP floor panels.

 

[JackJester]

Part 3 (SIP Installation):
This is probably the most exciting part for those new to the concept of SIPs. It was fascinating to watch. All the floors, ceiling, and walls were installed in 5 days. A crew came in for the week and their company specializes in installation of SIPs across the PNW ...from N CA to ID, OR, and WA. They used a crane to place the SIPs. The floor SIPs were anchored to the foundation 2x12s and the SIP wall attachment seams were sealed together with glue. I had read that some SIP designs use mini-SIP spleens to attach one panel to the other, but that was not done for our build. All the individual SIP panels are labeled per the design specs and they just put it together.

The SIP floors were attached somewhat similar to this diagram. However, this diagram shows how a SIP wall (without a SIP floor) would attach to the foundation 2x12s. But in our case we had SIP floors, so essentially the left (outside edge) straddled the 2x12s and the inner SIP was shaved off to be flat. Hard to describe, sorry, but I don't have a good pic of that install.

Here are the SIPs being delivered on a trailer.

SIPs are placed using a crane:

 

[rmcelwee]

It is interesting to me that you went the complete opposite of the way we went (3000 to 800sqft vs 750 to 5500sqft, wood to the city vs city to the woods). My parents travel and go out with friends constantly and we only leave our property once every two weeks and don't have any family or friends in a seven hour radius of us. I guess everyone is just different. One suggestion on your build thread - don't give to much info at one time. There are people here, including me, that are very interested in it and you don't want to tell too much now because you won't have anything to say next week. Best of luck with the build! We broke ground one month before you did and expect to be moved in by March/April. When do you think you will be finished?

BTW, we have some friends back home in their 60's who sold everything and moved into a small studio apartment, I think around 650sqft. They said it was the best decision they have ever made. I look forward to hearing how you adjust to this.

 

[rmcelwee]

Here are the SIPs being delivered on a trailer.
View attachment 59459

I didn't see on the plans or in your description (I don't read very well) how thick the walls are

 

[skyking1]

casual observation on the trailer looks like 8" overall, about 7" of foam core.
Thanks a bunch for posting up, @JackJester
Looks great!
I do the earthwork thing and can appreciate all you went through to get gravity sewer. I *almost* had it, but the development next door is now at least a year or two out.
Those rat slab crawls are sweet. Perhaps you can do some infrastructure down there?
Did your SIPs come from Canada?
I stopped by Insulspan in Delta BC and spoke with Tristan there about re-purposing SIP scrap on another project. Very cool stuff.

 

[JackJester]

Thx for the feedback. Yea, 25 years of having 8 acres backed up to 100s of acres of state forest land and too big of a house for 2 people, we went small for our final decades on this earth. I was just trying to get a quick catchup as to where we are after the past year's journey. Now things are slowing down. We are at the stage of having all SIPs installed and a metal roof coming next week. The electric and plumbing rough-in are complete. We also did a "cold roof" which I will talk about in a later update. So we'll be dried in by Nov. Then its a matter of... exterior siding (a cool product called "Lunawood"), dry wall, painting, flooring, cabinets, final plumbing, final electric. I am told this is when things slow down with all the sub contractors to manage. Our GC is saying we'll have certificate of occupancy by Jan or Feb. Hopefully all of the change orders are over and we just stick to current design.

 

[JackJester]

I didn't see on the plans or in your description (I don't read very well) how thick the walls are

SIP Floors: 10 9/16"
SIP Roof: 10 7/16"
SIP walls: 6 1/2"

 

[Koolau]

As someone mentioned, we're all different. I could live in 800SF and even live with one BR. I could never do without at least an extra half bath. (Once in a while - you're both in a hurry AND every toilet will stop functioning at some point).

If you are going to add a garage, you might add a half bath out there. Just a thought.

Love your concept. Thanks for sharing the execution with us. I'm betting your utility bills will be next to nothing! Congratulations on your project.

 

[levindb]

I second the idea of needing a second bathroom...it seems as we age, the time on the throne tends to get longer. The builder of a new home in our neighborhood installs an electrical outlet next to the toilet in master bathrooms so you can charge your phone while sitting and waiting for something to happen.

There is also the value of isolating the aroma of the potty...when something does happen.

 

[old medic]

Very nice... We considered SIP back in the 90s to build our timber frame house we designed.
Found an AWESOME deal on a doublewide modular instead.

 

[Ronstar]

Very nice! I like the design, and the lower level storage. How do you access the lower level storage area? And the plan shows attached shed?

 

[B-Guy]

Your place looks great! I can visualize your house. I would love to see what your view looks like from your house, maybe from the deck in addition to the construction photo’s. I look forward to further discussion and pictures as you continue your build. Your place reminds me of our cabin up in the mountains near Jesfferson, CO. It was perfect at about 800 sq ft for an escape from the city. It was butted up against the national forest, which gave us great access for hiking and a basecamp for exploring the area. We spent a lot of time up there.

At the time we built our home we had large family gatherings here 30+ frequently so we built for that in mind. Seems like many following this thread move from the city to the farm or vice versa. We moved from the city (Denver) to our very rural farm, that is two and a half times bigger. Now I joke we live past the sticks, but there’s truth in jest. We only go to town once a week to deliver eggs, honey, pick up groceries and rarely without fail we stop at the hardware store.

 

[Flieger]

Very cool! What is the cost comparison to "traditional" build?

Flieger

 

[JackJester]

This table is from the SIP manufacture to compare the R-values of various SIP panel thicknesses. It is my understanding via wikipedia that most R values are reported as measured at 70 deg F. So, if an industry standard stick framed batt insulation house is R-21, then my walls are an R-28ish and my roof and floor are an R-45ish.

R-value (insulation) - Wikipedia

en.wikipedia.org

Here's a better pic of the SIPs install almost complete:

Here's a more recent pic (from the side) in which all windows are installed, and the thermal barrier wrap (Henry Blueskin VP100) is up and is ready for siding:

Yes, there will also be a 10x10 ft storage shed that will match the look and feel of the house. It will have a covered roof and porch for a grilling station, and in addition to having a small tool storage and workbench, it will contain our standup freezer.

Here's a view from inside (living room) with the same windows pictured above:

 

[finnski1]

Very Nice. We built our 1947 square ft timber frame home 27 years ago. We used "curtain walls" that attached directly to the outside of the timber frame. A curtain wall is basically a SIP but with the inner surface being drywall. This sped up the process as the interior walls just needed a little mud on the seams and then paint. No extra step or contractor to hang drywall. I do not have any thermal bridges in the walls or roof. I believe that equates to a much better r value than a traditional wall built to R21. If one measured the traditional build they would probably find it effectively isn't achieving R21 but somewhat less. I do know our house is very "tight" and our energy use is fairly small for the house size.
Your layout looks great. You should have some pretty minor utility bills. You made need to add an ERV to ensure fresh air exchanges because of the house tightness if you haven't already thought about that. Enjoy!

 

[Montecfo]

Looks great JackJester. Thanks for letting us all ride along!

 

[JoeWras]

I am so glad I landed on this thread. Thank you for sharing, JackJester.

Really fascinating. I first heard of this like 40 years ago. Glad to see someone doing it. And it looks nice.

And... I can see DW and I moving to 1000 sq. ft. or so in about 5 years.

 

[B-Guy]

I can hardly believe how fast the exterior is coming along. I think you said 5-ish day's to go up, but wow!

 

[Fermion]

Any concern about the amount of trees near the house? We initially tried to build with minimal tree cutting, sort of tuck our house in between the large trees but after having 2 fall in wind storms and just miss the house, we have had 6 of them removed. We are in eastern Washington though with mostly Ponderosa. The western Washington trees are maybe a bit more robust.

 

[JoeWras]

Sometimes they don't miss. I think we may get off-track talking about trees near the house. I personally have had them fall on my house and did not enjoy the experience, and would recommend a buffer. But that has nothing to do with SIP builds.

 

[skyking1]

Agreed. I would never invite a tree to fall on my house, but if you're talking about strong, SIP plus metal roof is really tough!!
I mean seriously, that's some strong stuff.
I've played around enough with it to know that you can throw a sip down and use it for a bridge for light vehicles.

 

[NameTaken2]

House looks great -found no garage or outbuilding mentioned?
YMMV item, but an attached garage is a necessary convenience for me, especially later in life.
AFAIK there's a fair amount of rain and some snow there(?)