SIP vs 2x6 with spray foam (energy efficient home building)

[MN Gardener]

We are preparing to build this year and was considering SIP construction, but have heard framing 2x6 framing with spray foam can be just as effective. Does anyone have an SIP home? What are the pros and cons? We will be building on a slab with in floor heat and hopefully geothermal heat. Any information or suggestions on energy efficient buildling would be great!

[Windy in Kansas]

Don't have a SIPs home but I did do quite a bit of studying up on them. The 2X6s will conduct heat through the walls as they go clear to the sheathing and drywall with no thermal break. The SIPs on the other hand have no such conductive material---unless the design you look at has such. http://www.r-control.com/ Those don't.

The SIPs will be higher in cost, but when you factor in labor savings probably not.

With energy costs on the rise and with the probability of the cost only going higher get what you can afford even if it seems like overkill.

With either house so tightly constructed I urge you to consider an air to air heat exchanger to continually provide fresh air while expelling the stale humid air. They do go by a different name than I learned a number of years ago and I don't remember it.

Best wishes on figuring out what will work best for you.

[MN Gardener]

Our neighbor's roof is spray foamed and you can see where the rafters are after it snows....the snow melts where the framing is! What about plumbing and electrical through out the house? We will definately be getting an air exchanger.....I don't want moisture problems!

[cfabe]

It's not going to be as efficient as SIP due to thermal bridging. There are ways you can frame the wall to avoid some of the thermal bridging. I think by the time you get done trying to get a crew to build you a custom wall and then spray foam it, you'd be close on cost to SIPS once you factor in the labor savings.

Is this going to be in MN? You don't see slabs often up there, any reason going with a slab over a basement? You'll be digging down, what, 4 feet anyway for footers? Basement might not be much more work, and you can still do radiant floor heating.

[MN Gardener]

I want to do a full basement but DH does not. We also might have some water table issues if we do a basement. We are in Northern MN and the heated slab thing has been really picking up here for quite awhile now. I would much prefer a house with one bedroom on the main floor and 2 in a walk out basement. I think it would be most efficient, but DH wants one floor living.

[artificer]

I haven't priced SIP's, but the spray foam quote I received last year was $2/bd-ft for the first inch, and $1/bd-ft for each additional inch. 2" thick is $3/sq ft, 4" is $5/sqr-ft. On the other hand, 2" extruded polystyrene sheets (pink or blue) is around $.60/sqr ft, or $.30/bd-ft. Add more for great stuff to seal it in. You can do a 2x4 wall with 2" foam board infill, and then cover the outside with 1" foam. You get less thermal bridging that way.

If you are doing the work yourself, so no labor costs, material costs are the biggest expense. In this case, the foam board makes a lot of sense. If you are having the work done, the other two methods probably make more sense, but you need to get quotes to find out which is less expensive. Running plumbing and electrical is much easier with spay in foam. Do the work in the open studs, then foam in place. I guess it comes down to cost.

Originally Posted by cfabe

Is this going to be in MN? You don't see slabs often up there, any reason going with a slab over a basement? You'll be digging down, what, 4 feet anyway for footers? Basement might not be much more work, and you can still do radiant floor heating.

They could do a frost protected foundation for the slab. (insulation out into the yard) Even a properly done slab with heave free materials under the slab and proper drainage isn't that unusual. I remember some posts about high water tables from people in MN, so that might be the reason.

Personally, I prefer full basements, and especially ones that have an insulted floor and a couple inches of foam on the OUTSIDE of the walls. All that lovely thermal mass... In Wisconsin, they don't count towards you square footage as far as taxes go. Cheap storage, and the mechanicals can go down there.

Good luck on whatever you decide.

Michael

Edit: MN Gardener, you were posting before I finished mine The first thing to do is find out about the water table. If its high, then your basement is a moot point, unless you want to landscape the walk out basement. If the basement is possible, then I guess its a mater of compromise, and deciding what makes the most sense to both of you. I won't mention about the most stubborn winning...

[SolarGary]

HI,
You can estimate the actual R value for the 2X6 wall with this calculator:
http://www.ornl.gov/sci/roofs+walls/...rvalueinfo.htm
It comes out R16 if you use the closed cell (expensive) spray in foam insulation. The SIP wall would be more like R25, or more if you use the polyiso insulation in the SIPS.

A lot of people improve the perfromance of the 2X6 wall by adding an inch or 2 of rigid foam board on the outside -- this keeps the thermal bridigng on the studs down.

There are some other high R value walls shown here:
http://www.builditsolar.com/Projects...tructionps.htm

Have a look at the "Mooney Wall", the double stud wall, and the Larsen truss. These all give high values with minimal thermal bridging.
Thick walls framed with TJI type engineered beams are another way to go == they have minimal bridiging because of the thin webs and you can get any thickness you want.

SIPs are good, but they are very subject to water damage. The wall construction must really protect them well from water damage.

Gary

[ErinP]

Another way to minimize thermal bridge, similar to SIPs, is something along the lines of a FirstDay Cottage.

[painterswife]

I live in a SIP home. Love it!

As others have said you need to ass a layer of board insulation on a spray foamed home to combat thermal bridging through the studs.

SIP should be less expensive then framed and sprayed.

[fishhead]

HUGS in Pine River MN is doing a lot of work on super insulated solar heated buildings.

I haven't crunched any numbers but what about a double wall filled with cellulose? The outer wall could be 2x4 for strength and the inner wall 2x2 to nail your wall covering. That would eliminate bridging for the most part.

[MN Gardener]

Originally Posted by fishhead

HUGS in Pine River MN is doing a lot of work on super insulated solar heated buildings.

I haven't crunched any numbers but what about a double wall filled with cellulose? The outer wall could be 2x4 for strength and the inner wall 2x2 to nail your wall covering. That would eliminate bridging for the most part.

Thanks for the info on HUGS, I am going to show DH. I would think that doing the double framing might cost more in labor and time. We are having a profession get everything framed up and we are going to finish the rest ourselves. I saw the R factors on the HUGS building and the are really good (R-38 for 12" walls - probably expensive though!). We have to sell our current home and have at least a shell to move into when we close. I am leaning towards the SIPs because it will be a tight timeline (probably 30 days).
As far as the water table, we did put in a sandpoint for the garden last year and I believe DH said they hit water at 11 feet.

Thanks for all the great information everyone, keep it coming!

[fishhead]

At the HUGS campus in Pine River they are using those big 400 lb bales of straw in their solar heated commercial buildings.

Yes there would be more labor in making a double wall structure.

I would have the water tested before you drink it. 11 feet is probably not protected by an impervious layer and is subject to contamination.

[MN Gardener]

Originally Posted by fishhead

I would have the water tested before you drink it. 11 feet is probably not protected by an impervious layer and is subject to contamination.

We don't drink out of this well, we just water the garden with it. We will do a drilled well for the house.

[ET1 SS]

I used spray foam on our house.

We love it.

Two-component foam; I sprayed our roof and walls with 2 inches of foam. It is structural, it deadens sound and is great.

[Mrrsteelers]

Originally Posted by ET1 SS

I used spray foam on our house.

We love it.

Two-component foam; I sprayed our roof and walls with 2 inches of foam. It is structural, it deadens sound and is great.

Spray foam is also a moisture barrier, it won't mold and bugs hate it. It is expensive though, we spray it, but not often because most people only care about getting things cheap.

I don't know anything about SIP though. (had to google it lol) So I can't say which is better.

[ET1 SS]

I sprayed foam and then laid 9 inches of fiberglass batting on top of it, both walls and roof.

Each type of insulation has it's strong points.

Using multiple types you can get the best of both.

[Roothawg]

What was the outcome on this? I am researching this myself.

[ET1 SS]

In nearly all wood-stick construction, you will see some thermal-bridging. It is hard to avoid when dealing with wood.

[mike554]

My house is covered with sips. It is very easy to heat. We don't need a/c here in the mountains of NC. I wouldn't live in anything else. I worked on a new home that had spray foam insulation installed. I noticed quite a few areas where the installers either didn't cover well or the 2x shrunk a little and you could see daylight.

[fixitguy]

I have a customer that has a SIP home. Its one level with no basement.
They installed 3 heat sources, In floor, pellet and forced air. IIRC, they said the gas bills were real cheap, but they have to pump in outside air because the building is so tight.