I just read the SIPs article by John Ross. The system seems very interesting, but I am left with some questions:
1. STRUCTURAL insulating panels. How do they work? Does the skin take the load studs would otherwise take, or do they have to be part of a separate framing system? Who engineers it? What about lateral loads?
2. I was quite taken by the idea of the efficiencies of putting up pre-cut panels, and then in the sidebar we read SIPs cost TWICE what insulated framed walls cost. TWICE!! Isn’t there a savings in time? How does the cost of a SIPS house compare to the cost of a stud built house?
3. Why use SIPS? If it costs more, and requires special skills and special detailing and special HVAC design and air to air heat exchangers, are we to understand that we should use it for energy savings alone to be realized over a decade or more?
4. What does that ridge detail for the cold roof look like in a design suitable for snow country?
Replies
You can google some sites on SIPs, I can't remember but the costs didn't seem to be way out of line something like 10% overall. Energy savings is a big draw you have no thermal loss/gain through studs, the panels act more like a continuous blanket wrap. Savings in labor and time to get the house framed is another plus. Electrical can be a challenge but it just requires a bit more planning.
I don't have all the answers but have looked into building useing sips it seems like a viable way to go.
Jeff
Thanks for your reply. Do you mean 10% premium overall including labor or just for the materials? I am trying to get at the comparison of more expensive parts plus less labor for SIPs compared to stick built.
Starfish,
I’ll try to answer some of your questions.
1) SIP panels are an engineered system. The combination of the three elements (outer skin, foam core, and inner skin) work together to create a structural component that is stronger than each element separately. Generally speaking for the load to be transferred properly both skins of the wall panels need to come into contact with the floor and roof systems. Typically there is 2x lumber inserted at the floor and at the top to help transfer the loads. Each SIP manufacturer will have specifications about spans and lateral loads.
2) The cost I figured do not include labor costs since that depends on the proficiency of the crew putting up the panels. The materials costs of SIPs can cost twice as much but this is where SIP manufactures start to get riled up. It is very difficult to come up with a apples to apples cost comparison. A SIP wall tends to outperform a stud framed wall to the point that if one were to build a stud framed wall with the same insulative capacity as a SIP wall and no thermal bridging that stud framed wall might cost just as much as the SIP wall. I tried to compare walls that would be built rather than walls that were equal in performance.
3) The premium paid for SIPs can be gained back (allowing for a ton of variables) can be returned through tax breaks and lower operating costs in 1 to 4 years.
4) The cold roof should be vented at the top with a typical ridge vent. Though not complete this website is a good place to start http://www.winterpanel.com/manuals/stresskin/manual.html
If you check out the blog (link on the FHB homepage) there will be more to come.
jross -- FH Editorial
John
Thank you for your reply. I have Emailed a SIPs site for more info, but I expect to get generic promo material, and thought I might get more specific experience related info here, plus the benefit of not coming from the manufacturer's point of view.
I can see why you didnt' compare equal thermal performance walls. That raises the question of whether with SIPs one is buying higher thermal performance than is needed. What are the tyical R values of SIPs walls? I want to build in a climate that gets down close to zero in winter, so this might be academic for my project, since I do need high thermal performance, and probably even an air to air heat exchanger.
I have seen other articles concerning systems in which the authors threw up their hands at obtaining a cost comparison between a system bulit house vs stick built, because estimating is not an exact enough science, as many low bidders learn to their sorrow. Unfortunately, cost is a do or die element with this project, so I need to get as accurate an idea as possible of the relative costs.
One problem is that system builders have an idea what typical construction costs are, or what real estate values are, and if there is a savings, they are tempted to try to keep it for themselves by edging costs up to just below the norm.
I have also considered trying to use the 24" stud spacing concept of Lstibruk, which makes sense but requires an engineered design. My only concern with that approach, which seems assured of being cheaper on a materials basis alone, is that my experience is that asking many if not most contractors to do something out of the ordinary often produces a sense of unease which results in an unreasonable dollar value being assigned to his uncertainty. This cancels the potential savings from the bright idea. No disrespect intended, it just seems to work that way.
I'll also through out that SIPs can make more sense to the contractor than the client, or visa versa.
Small crews like SIPs because they go up fast so the job and the final check comes sooner. If they are working cost plus or T&M the cost of the SIPs doesn't have as much impact on profitability as does speed to completion.
A crew with a number of good framers won't benefit as much from SIPs because their core skills aren't being used. Sure, teaching new skills can be valuable, but it can make more sense to teach the $15/hr guys and save the $30/hr. roof cutting wizard for what he's best at.
The clients benefit from a tight house with good insulation, but the saved utilities payback can be discounted using time value of money and all the sudden other building methods become just as economical over the life of the building.
Some SIPs use cheaper foam and the final cost delivered can be substantial, although it's at a lower r-value. This sounds seductive, but it's lowering the long-term value of the SIP as a good insulator.
Equal r-value can be had for less money with other building methods, but SIPs are cool, trendy, easy to sell to clients that want an upgrade, and are user friendly.
In some designs the engineering provided by the SIP supplier saves hiring an independant structural engineer for conventional framing, which can easily amount to a few $k.
Cheers
Beer was created so carpenters wouldn't rule the world.
Thanks for your reply.
Time value of money cancelling the energy cost savings is not something that had occurred to me. The benefits of SIPs seem to be narrowing down to just seeing the building volume enclosed in a hurry, but then saving time can be very important, especially if your contractor is juggling several projects.
What kind of wall assemblies are you thinking of when you say you can get equal performanc for less money? High thermal performance is important for this project.
What kind of wall assemblies are you thinking of when you say you can get equal performanc for less money?
If you look to cold states that need a great deal of insulation as a minumum, the methods they use translate well to high performance in more moderate climates.
For instance the SIPs we put up a few months back used foam that's only about r-4 per inch so a 5-1/2" wall is about r-22. With very few thermal bridges it is better than a stick framed wall with equivelent r-rated insulation. However, a 2x6 wall with r-19 bats and 2" of polyurethane foam (r-10) run horizontal (with horizontal sheetrock nailers 2' oc.) is less expensive and I'd bet tomorrow's lunch money it insulates better.
That design is one recommended by a governmental agency in AK for most bang for the buck.
Other designs out of AK include walls with 6"-8" or more of ridgid foam in the walls and floor, with twice that in the ceilings.
Double walls, with two 2x4 walls spaced apart goes up quickly and affords room for as much insulation as you care to pour in. I friend's brother has such a house and the utility bills are as low as any super insulated ICF or SIP house in the area.
Even 2x8 walls in an otherwise standard method of construction sounds pretty good with r-26 insulation and an inch or two of spray foam to seal the stud bays.
Heck, even pole barn construction with full depth spray foam is every bit as energy efficent as a SIP house. In the rocky mountain region more and more commercial buildings super insulated with spray foam are turning up. Can't say I'm excited about the long-term health of the burried section of the poles, but if done well there isn't any reason it shouldn't last indefinitely.
OSB is really pretty fragile over the long term if any moisture at all gets to it, and SIPs rely on osb extensively. I'd be surprised if many SIP houses don't start having significant damage when they hit the 50 year mark if maintenance is at all lacking. It's very hard to tell if anything is leaking until a large section is rotted out.
ICF's will most likely be the number one way to build a house to last indefinitely. I'd love to see an ICF producer come out with a few more inches of foam on the exterior.
Best
Beer was created so carpenters wouldn't rule the world.
Thanks for your reply.
I have heard OSB is sensitive to moisture, but have also heard that criticism rejected by some contractors. The size of the chips is so small compared to the full size laminations of plywood that the integrity obviously depends much more critically, if not entirely, on the manufacturing process and the adhesive.
Can others shed any light on this from their experience?
Starfish ,
I can speak from actual experiance.. My home is clad in SIP's. The roof due to a vairity of conditons could not be sealed up for over four years.. That's four years of exposure to the full effects of Minnesota winters ,spring rains (er, floods) summer heat and fall variables.. This particular area was on the north side so it never really got exposure to sun. It's only saving grace is the panels weren't constantly immersed in water..
When I went to put the roofing on the SIP's were solid and showed no sign of coming apart.. they held nails just like new! 4 years later!
Nothing to protect them except what the factory used to make them.. I've heard longer times thru the grapevine..
Frankly there is no other roof system I would ever use..
I should tell how just how strong they are as well. While I keep hearing they are 200% stronger than the same stick built wall, I never realized thatcould be used so many ways..
I was building my house whenI started on the tower.. because of the way it was built I basically had to build the roof with SIP"s and then stand on the SIP's to work on the tower..
this is a really steep roof.. 17/12 pitch. I'd built a platform that All I did was spray Great Stuff, the insulation in a can? as an adhesive to extend a work platform out from the roof.. One end was proped up with a couple of 2x4's the other end was "glued" together with the Great Stuff.. No nails, screws or anything else.. The next day when I was working at the end of that SIP nearly 6 feet from the roof I noticed that my buddy had removed the 2x4's because they were in the way of his task..
250 pounds and I was lifting timbers that weighed over 100 pounds into place on a panel held in place by foam.. cantalevered out nearly 6 feet held up with foam! No flexing, no shaking ,nothing to indicate that I wasn't walking on a side walk!
Thanks for your reply.
Yours is the kind of first hand experience I was hoping to hear about. Your [positive experience regardig performance is very encouraging. How about costs?
starfish,
As I said my costs were right in line with stick building costs.. The cost of studs etc. was about 2/3 of the cost of SIP's locally but when you added the cost of insulation back in the costs were even. My actual numbers varied a lot,, I did this over a several year process (did it all myself), so what I statrted out paying for panels is less than what I finished paying for them.
I don't think I got a great deal.. I mean I simply walked into the plant and asked for a quote (told them I was doing it myself) Yet nearly every detractor claims the price they would pay for SIP's is dramatically higher!
So much higher in fact that it doesn't account for material cost increases etc.. We're talking about way more than triple what I paid..
I'll try to look up the recepts from a few years ago and get back to you wiith costs tonight..
When looking at R values, one thing you need to keep in mind is that whole wall R values are less, sometimes quite a bit less, than the value of the insulation batts themselves. Steel stud walls are particularly susceptible to thermal bridging and normal stud walls also have their problems. There are a number of websites that give figures for various whole wall assemblies. Given the way SIP houses are constructed, there would be much less thermal bridging than with standard stud or even most advanced stud framing techniques. One example of reduced R value in a whole wall assembly:" Actual R-value for 2x4 wall insulated with R-2.3 (R-13) fiberglass batts (nominal
R-value of R-2.6 m2W/K –(R-14.5)) is in the range between R- 1.5 to 1.6 m2W/K
(R-8.5-9.0 hft2F/BTU).
This is 35 – 40% reduction of nominal wall R-value
This is equivalent to R-value of additional 3.8-cm. (1.5-in.) of EPS
6
This means that houses built in this way would require approximately 10-12%
more energy than it is predicted by currently used energy calculation tools."http://www.ornl.gov/sci/roofs+walls/NewRValue.pdfFor an improved stud wall assembly, you might want to do a search on Breaktime for a "mooney wall".
http://forums.taunton.com/tp-breaktime/messages?msg=65624.1
one thing you need to keep in mind is that whole wall R values are less, sometimes quite a bit less, than the value of the insulation batts themselves.
I already said that.
Beer was created so carpenters wouldn't rule the world.
after reading and seeing them online for 3-5 yrs.... saw my first one this morning
not a great area.. and not a big house.... i'm guess'n 20x40 footprint... was a slab yesterday... was a lockable dryed in site today.... they had not cut out all the windows... had a truss roof system and no sips on the roof... i know this house could be framed in a day anyway but.... i can still see where speed of sips could save you $$ plus the other +++'s
they are building 2 side by side... 6 panels total per house...
p
Thanks for your reply. I guess SIPs still has an edge here even if it could could have been framed in a day, because SIPS was framed and sheathed and insulated in the same time.
I'd use them in a heartbeat.... which i didn't say.... i use to build walk in coolers... and they were pretty much.... SIPS...
p
Starfish,
200% stronger than stick built!.. Satisfy yourself.. take a wall made of 2x4's and lay it across a sawhorse, say a 20 foot long wall.. sheet it with plywood, 3/4 of an inch if you insist. Now stuff insulation into the wall cavity and walk across it.. Let me know when it breaks.
Now put my fat butt on that same SIP wall and I'll walk across it.. I weigh close to 275 right now.. moderate deflection, almost none at all if you use a 6 inch panel..
Another interesting point.. if you stick build a wall you have a 2x4 every 16 inches,, plus some doubled up and worse!
That's why the rating for insulation is derated by 20% on a stick built wall.. yeah, the insulation package may be rated higher but the assembly is 20% lower and that's if the insulation was done perfectly..
Next is the quality of insulation.. Fiberglas and cellulose are both badly derated if wet. Foam isn't affected at all..
Fiberglas is extremely good at allowing air movement. that's why furnace filters are made of it.. Warm air rises cold air settles.. pure physics.. a little know fact is all insulation is rated at 70 degees. temp.. If you measured fiberglas at say zero temp. you'd see that it's R rating is dramatically down.. due to air movement washing warm air and replacing it with cold air.. inside the wall cavity there is cold air on the outside wall dropping and warm air on the inside wall raising. so a little "race track" forms on the inner walls and "washes" the heat outside.. foam doesn't let air move thru it..
Fire safety..
Due to it's poor transferance of heat a wall made of SIP's and with a proper sheetrock covering is capable of withstanding the 1500 degrees of an indoor bonfire in the corner while only gaining 50degrees in outside suface temp.. The factory I bought my SIP's from (AFM) has a video displaying just that fact.
A stick built wall will transfer that heat quickly due to a stud every 16 inches and quickly become engulfed in flame..
Twice?
Please do some reaseach!
I was able to buy my panels for less than the materials would cost me to stick build..
I loaded them in my truck and drove them to my job site myself thereby saving trucking charges.. I cannot accept that SIP's cost twice what stick building does.. Maybe if the SIP plant you choose to buy from is a thousand miles away and there are several middle men with their hand out but I compared the material cost of SIP's to the material costs of 2x6's etc.. and found them to be the same.. Now maybe the factory gave me a deal because I'm tall handsome rich and famous,... except I'm not.. I walked in asked them their prices and walked out with an order. They rasied the prices as the price of OSB soared at the early start of the Iraq war and had to delay me about six weeks once when the Borate treated OSB wasn't available but I honestly don't think I'm exceptional..
Savings? Well my old home cost me over $500 a month to heat during Dec. and Jan.. I reused the same furnace and added a lot of windows not to mention that the house has more than doubled in size.. plus I haven't carefully sealed up the house the way I had my old home.. I can see air gaps on many places that once I'm finished will get sealed up
My worst heating bill in Jan and Dec. is now $127.00 same furnace, twice as much house to heat,, probably 3 times the windows, and not properly sealed yet and I spend almost $400.00 a month less using SIP's
Having said all of that,, If I had it all to do over again I'd build with a combination of ICF's and SIP's as roof panels..
Thanks for your reply.
The cost info I got directly from the FH article. Your valuable feedback is part of my research on that point.
I understand the reasons foam performs better than FG batts, and it has the added value of not making an issue of condensation as well. Your anecdotes as to structural strength are encouraging. I am planning on a 2 story house, and will need to find out if it will require 2x6 panels.
Starfish,,
Look too at ICF's the more I've built with them the more I like their features. Right now you can build with ICF's for about what you can stick build.. the few local contractors add a 2% premium but that's there because of lack of competition I suspect more than any cost issue..
MY friend built his house (4000sq.ft.) using ICF's and SIP's on the roof he did it for $100,000.00 It only took him 30 days from teardown to weather in but it took him another 2years of nights and weekends untill the house was finished.