Sorry for the long post. (newbie)

I am looking for opinions on the pros and cons on various methods of constructing a SIP structure.

I am a firm believer in the Keep It Simple Stupid philosophy. I have looked at numerous articles and posts and would appreciate the insight of those who have experience working with these materials on a daily basis. My main goals are to reduce on site labor costs, maximize SIP capability (while still being practical) and think long term on cost/return.

First, the design should maximize the use  of the SIP. Window placement and utilization should be within the entire SIP panel (3'x5' conventional window). I do not know if windows can be installed at the SIP plant or only the cutouts for them.  Both electrical boxes and chases can be placed in PU panels, only chases can be placed in EPS panels. Also, I believe one manufacturer either fabricates  a special corner piece or has a special process for corner installation. (uncertain of this statement). The corners and the fudge factor should panels not be exact are another area of concern.

If permissable by code wireless lighting systems could be utilized in the SIP wall (uses RF device only, no hard wiring) . Also, air admittance valves (used in the PATH concept house) could eliminate certain vents.

In the building phase doesn't it make as much sense to conventionally frame certain features(e.g. dormers, entrance doors, large blocks of windows, etc. ) or not.

As far as the roof goes is it economical (time/money/return) to place a SIP roof versus a highly insulated conventional roof (trusses) unless the design truly dictates (open spaces/cathedral ceiling). Also, if it is a SIP roof, should it be made out of EPS due to deflection and panel sizes.

With regards to HVAC would a geothermal unit be warranted. If the structure is sealed tight, an air handler system is already necessary, does it make sense to add the geothermal. Where is the tradeoff between efficiency and overkill?

Lastly, I belive theat EPS is less expensive than PU per sq. ft. I also believe the R value of PU per inch is greater than EPS. EPS walls would be thicker to get same R value at less cost than PU which can be based on conventional framing dimensions. Where is the tradeoff betwween special jam sizes, cost of materials, and greater inclusion of prepackaged features (electrical outlets). Which is the better system, most bang for the buck, in the long run.

I guess what I am looking for isyour opinion on  the ideal way to build a SIP structure and the  ideal SIP (specifications, material, thickness, chases, window placement, R-value). 

Clancy,

Personally, I have a lot more questions than I have answers myself. But one of my pet peeves is the misconception that EPS is less expensive than Polyurethane. Even if you just consider the R-factor comparison where it takes twice as much 1# EPS to equal the r-value of a 2# density PU foam. So, you need twice as much EPS to reach the same r-value. At that quantity, EPS doesn't have a cost advantage over PU.

Additionally, when you factor in the added cost of larger dimensional lumber for splines (if that is what you are using) for the thicker panels, then EPS starts to look considerably less attractive.

Then consider the cost of transporting and handling preexpanded EPS. Expanded EPS is very light weight, but takes up a lot of space, so trucking the stuff arround becomes much more expensive. Then it must be warehoused until it is used, and handled several times along the way - and these are ongoing costs. With PU, it is possible to expand the foam in place within the panel, so the only handling for PU (aside from moving around large drums of unexpanded resin which occupy 1/30th the space of EPS foam - and 1/60th for the same R-value) is the handling associated with the fabricated panel. And, EPS panels have even less of an advantage here due to the fact that the same r-value panel in EPS will occupy twice as much space as a PU panel.

The final consideration that I will mention is the fact that EPS must be laminated to the SIPs skins using glue. Even using inexpensive Polyester glues, can add as much at 5% to 15% to the cost of EPS. PU doens't need additional adhesive, because it adheres to the skins naturally.

Dick Mills

Using your goals as stated, you would want to use prefabricated(lumber installed) SIPS. If you will be fabricating the panels the items that you mention become more important.

With prefabricated panels, window placement is not an issue(unless the placement is purely energy related). Chases aren't either, as most companies EPS & PU can customize them. Material is your preference, as is desired R-value.

If cost is the sole factor(and sadly, many times it is), you won't find a great deal of difference between EPS & PU. But, there may be a sizeable difference between manufacturers of the same type!

So, I don't think that anyone can make the decision for you. All we can do is answer explicit questions.

This post comes across as 'You'd be a fool to consider EPS'. Anyway that's the way that I read it.

When you look at the whole picture, EPS has advantages over PU, and PU has advantages over EPS.

So, I don't think that anyone can make a solid case that one type foam is superior in all cases over the other type.

I fully and completely agree with you. And, I didn't mean to suggest that considering EPS is foolish, just that the when making a decision, one should realize that what may look to be a bargain at first glance may not necessarily be the best economic choice. But I am the first to admit that there are cons as well as pros for using either foam product.

There are some out there who believe that PU foam can be used in SIPs without spline material. Instead they embed camlocks in the PU and use them as the only means for fastening adjoining panels to one another. I have heard that this can lead to panels where the OSB begins to separate at the edges from the PU. It may be possible to repair these (perhaps with a good epoxy), but I happen to think that is the height of foolishness, myself. I wouldn't trust a structure built that way, but that imay just be me.

Dick Mills

For use as insulating material over framed structure, PU has greater values.  For a combination of shear wall and insulating EPS, hands down.  Apples to apples, PU is 40% more expensive to manufacture and still cannot the shear values.

I will accept your shearing point, though manufactuers like Murus seem to have a different take on it. I only know what I read. But again, in terms of PU cost vs EPS cost, the raw material cost is only one consideration in terms of the total economic cost.

Dick Mills

Hi Jeff,

Me again. I don't mean to be argumentative, I am just here to learn. But, I have been looking for support for your statement about PUR not having the shear strength to compete with EPS, and have only been able to locate evidence to the contrary. I will include a couple of links here. Maybe I am missing something. Please send me your links about PUR vs EPS that indicate the superiority of EPS for shear loads.

Thanks, I appreciate your help.

Dick Mills

EPS http://www.benchmarkfoam.com/benchmark/poly/properties.asp
PolyUrethane http://www.sipsupply.com/PURmaniteX.pdf

These links seem to indicate that in all structural structural properties 2.5# PUR (I haven't been able to locate data for 2# yet) is stronger than EPS. Maybe there is something about the adhesion of the OSB that is different between PUR by itself vs. EPS w/ a polyester adhesive??? or something like that???

The type of insulation in a shear wall typically adds little or nothing to the allowable shear values for the wall. The real shear strength comes from the sheathing (skin) on the wall. The attachment of the skin to the internal wall structure (studs, EPS, PU, straw, etc) is important in distributing the shear through the wall. How the skins are attached to the top plate and sill plate is also very important. EPS pressure glued to the skins and PU that glues itself to the skins will have about the same shear strength for the same skins. The reason that PU panels are thought to have lower shear values is that there is testing on factory built EPS panels and little is done on field applied PU walls. There is also a question of quality control for PU walls filled in the field which limits published minimal shear values. Both types of walls are good and have pros and cons and should be considered for each project.

Now, back to the original post. SIP building is a living, growing industry. If you ask 10 SIP builders the best way to build a SIP structure and what type of SIP to use, you will probably get 20 different answers. The scary part is that most of them will be correct but a few will be really bad ideas. I suggest you make a few decisions on what you want from the SIP construction and how you want to build it. Then throw those ideas out here to the wolves and see what happens.

I will try and descibe my choice(s) for product and the rationale behind it and would appreciate any comments and insight that others may have.

Basement- Superior wall(s) -precast wall walk out basement (basement area (approximately 2500-2700 sq.ft).

Walls 6" PU (actually 5 5/8 (PU)/ 7/16 OSB skins based on regular framing with 2 horizontal and 1 vertical chase per segment.This seemed the more costly choice to me but since it will be built for Northeast winters and energy costs are on the rise I felt that there would be an eventual return on theadded R value over the 4" walls. Windows to be within each panel to design. Utilizing 2',4' modules in design process.

Gables (4) built out of SIP, 6 dormers built on site by regular framing/building methods

Open web floor joists - to facilitate electrical plumbing, hung internally with Simpson strong ties or similiar product. Trying to keep the building envelope tight.

Roof- conventional truss roof, no cathedral ceiling, Sprayed insulation

HVAC- geothermal from ARIT (plug/play models). Only because already need an air exchanger and the do it yourself version is considerably more cost effective than other HVAC quotes.


This is just my opinion on the way to build the mousetrap(structure).Like Avant said ask 10 people and get 20 different answers. Any opinions pro/con would be appreciated.

Clancy,
I agree. Super Insulating is not for everyone, but I love the concept.

How are you handling the rim area?

It sounds like you on on the right track.

I'm an old school simple way of doing things but when using the panels it is better to thinkl new school. The rim detail that I would prefer is tying the SIP externally with the rimboard and floor joist. This would tie into the foundation with anchor bolts and a pressure treated sill plate.

The other choice is old school: mounting the wall on the floor joist/subloor. This would create a thermal gap area. This is why I suggested hanging the second floor joists internally.

That being said I had hoped to have 9' internal walls. This would mean that I would need an 11' panel (via two internal joists; means of construction). I believe standard panels are 8', 10' and 12'. Does anyone know if an 11' panel is considered custom or is it better to just plan for 10' internal walls.

Balloon framing with steel SIPs:
since steel skin are run off coils it makes longer length panels available at no additional cost up to 40ft. long. This makes it possible to build 3 story buildings in one continuous piece. You can then stitch screw a 14" steel rim joist receiver made by trade ready http://www.dietrichindustries.com/products/ the steel is far superior to OSB in accomplishing floor systems that do not compomise the insulation integrity at the floor. In addition you have the ability to place the ceiling heights any were you want.
Zurich Insurance is also giving huge builders risk discounts for builders building with steel framing.
In addition to providing an energy efficient structure, you are also providing a fire and termite resistive building as well. This construction also bodes well with the "green" building as the steel skins are painted and FDA approved, providing a clean start for good indoor air quality.
From the builders perspectivie these panels are, lighter, need no splines, snap together easily, require no fasteners at sline joint, can withstand the elements for extended periods of time ( nothing to warp, split, swell when they get wet)

If any one is interested in a floor/wall connection detail I would be happy to provide it

That would depend on the manufacturer. To be honest, for the manufacturers that I've worked with, everything is custom.

In fact the majority don't even make 'stock' panels. And as I've stated before, for these manufacturers, the price per sqft is the same no matter what the length/height.

The SIP manufacturers that I work with have stock size panels that they produce and then cut these stock panels to size. Their stock panels are 4’-0” or 8’-0” wide and 8, 9, 10, 12, 14, 16, 18, 20, 22, and 24’-0” long. If you are using 11’-0” high walls (or even 10’-1” high walls) , they charge you for a 12’-0” panel and then charge you to cut it shorter. When we design structures we design for stock lengths where possible. For 9’-0” ceilings, we use 10’-0” exterior wall panels and 11-7/8” TJI’s for the floor/ceiling system hung on the inside.