I need to choose the technology for building a gable roof, on a rectangle 2 story box. Should I go with SIP? How does SIP roof compare to a traditional stick roof, with a good insulation (price and R value)?

Thanks,
Beno

Beno,

There are a lot of factors to consider. It depends on your price, shipping and whether you will need a second truck, labor and skil of labor, your expected energy savings, etc. You will probably find that labor is more expensive unless you find an experienced crew. SIPs is probably the way to go if you are considering vaulted ceilings and live where it is very cold or labor costs are very high as you can help offset cost with precuts. As a rule of thumb, sticks are going to cost around $2/ft and SIPs are going to cost around $4/ft so you will have to count on the upgrade to give you some cost savings on energy. In my area where the cooling is more of an issue the heating, I built a 1400 sq ft structure with 6" walls and a stick roof with tech shield on my OSB. I have figured my HVAC cost to be less then $20/month as averaged across 12 months. This is done after the fact when I can see my bill without the system turned on. It is unreasonalbe to think I could save the whole $240 per year as there is obviously a cost to heat and cool. So even if I were able to reduce what is left in my bill by 50%, I can only expect to save $120 per year. At 30 years that is only $3600. If interest and energy costs are tradeoffs, then I will end up footing the bill for the upgrade unless I stay in the home for at least 31 years which is not my goal. That and the fact that it would have cost me more for labor and would have required a crane led me to the decision to go with stick. I believe I would have done better to have sealed the ceiling with 2" of spray foam and then add blown in, but I was already pushing the envelope with costs and what the bank would finance for the project which is probably the greatest concern in building as the presumption is that those financing a project will not want to pay for upgrades out of pocket.

Now there are those that will blast me for not building a SIP roof, but I can't justify it in my location. This is not to say that I am not looking to use it in other locations. Our other concern here is mechanicals as we usually build on slab.

Beno,

It really boils down to the type of roof you want. If you want the look of vaulted ceilings, with exposed beams. Then a SIP roof is the best way to go.
If you are wanting flat ceilings. Then traditional trusses are the way to go. But, to get close to the same performance as a SIP roof. You do need to do the 2" of spray on foam over the bootom cords, with dry cellulose over the top. This way you will get the sealed envelope for energy efficiency.
Of course there are other options. Fo example: Some people want flat ceilings, but also want a conditioned attic area. In this case, you would use traditional trusses, and install a double sided SIP roof panels over the top of the trusses. Thus venting the attic area from the interior of the home.

Beno;

I believe that mmacgowa's assesment of energy savings are not accurate, Most SIPs builders would claim 30 - 50% saving, some 70% and I know from my own Steel SIPs home it is closer to 60% of the TOTAL utility bill.
They also allow you to downsize the HVAC system - my 2,400 sq. ft. home would normally need a 4-1/2 ton unit but instead only has a 2-1/2 ton unit and the calculations actually said it could be done with a 2 ton but we bumped up for additional air flow
Using steel sips no crane is required.
The most energy efficient design is to have all ductwork in conditioned space

Chris,

Perhaps I wasn't clear in the assessment I was making. My point was after the fact. I already have SIP walls and Tech shield OSB on trusses for the roof with no spray foam. My highest utility bill ever paid was $99. My lowest bill without any HVAC turned on is $65. There are four month out of the year when I don't use the system at all. So at most my entire bill for HVAC = (99-65)=39. 39 * 8 months = 312 total yearly bill/12 months = $26/month average. I am already realizing a signfiicant savings with the SIP walls and tech shield. My point was that at best I would get an additional 50% savings and that would be pushing it because my numbers are already tight with a very good system as opposed to excellent. If I saved 50% of what is left of my cost, I would only gain another 13 *12 or $156/yr. That is less then 5k over a 30 year note. My SIP roof upgrade is thus going to cost me more then my savings. So if design, energy costs, and interest rates are held steady, my upgrade is most likely going to cost me money rather then save me money. So I better have a different justification for a SIP roof.

In the example above using your numbers, I would already presume that I am saving 50% or more. Even if the roof netted me the additional 10% of the total energy bill, that would only give me 10% of 99 or 9.9 * 8 months =$80/yr. That is less then $2400 over the lifetime of the loan. I am not sure I could even cover the interest on the upgrade for that kind of money.

Thus the question is really regarding the additional savings over adding the SIP roof rather then the savings achieved of total SIP vs stick. And this is only for my situation. I am not trying to suggest that it wouldn't work in others or that the SIPs might be useful in the roof design.

Since most energy loss/gain is in the roof/ceiling ....Should have gone with the SIPs roof too

Is the most loss/gain truly in the roof/ceiling?

If I am not mistaken, this theory is based on heat rising, but if you calculate the amount of surface area exposed to the outside elements, I believe the walls have the greater amount of loss/gain. I could be wrong, but its food for thought.

By the way, I'm an advocate for roof panels. They're truly ideal if you're in a climate where gains potentially outweigh the cost of materials.

BoloRock;

Most SIPs buildings have more roof exposure than walls

Also food for thought, is that if anyone thinks that energy prices will remain stable, they are not paying attention.

wind would seem to be a big factor for losses/gains. One of the real advantages of SIPs is the ability to have less breaks in insulation. On a stick home you can feel wind come through the outlets. At least when you use standard blown in insulatin in the roof, you can apply a coating that will cover the entire surface unlike the area between studs where there are likely gaps. But blown in is obviously inferior to a SIP roof. A recent demonstration of a sprayed foam insulation model showed how cavities heated by a light bulb could float a ping pong ball over a mini chimney on a standard fill but there was not enough heat rising to create the same effect on the side where there was a seal.

No doubt JC is write in suggesting that energy prices are going up. What is really needed is a better method of distinguishing between better insulated homes that doesn't add more cost to the equation. The energy bill credits is fine, but adds multiple layers and cost before realization of the value. And it will be over soon. Perhaps the real opportunity is to legislate the mortgage side. A one for one upgrade cost in the better materials to loan amount would be a good start if it could be adjusted with the sales price. For instance say you build a 300k house with 30k panels. The mortgage amount is 330k and a buyer qualifying for 300 would be approved. the list price is 300k. That way a builder is not penalized for adding the 30k in panels. If we are really in the business of prepaying utility bills, the purchase price should be adjusted to reflect that. Maybe a separate thread could be started to suggest some gret ideas to lawmakers so that buiders could build the way we should as opposed to trying to get a comp to justify a price.

They are called energystar mortgages and have been available for years with homes that meet the "Energy Star" criteria the following link is for 89 companies in all 50 states offering incentives
http://www.energystar.gov/index.cfm?fuseaction=new_homes_partners.showIncentives

Chris,

That is a great link. Thanks. It starts to solve some of the problem but I think there needs to be legislation to regulate the purchase price adjustment and mass marketing to provide the education. Until a customer knows they can buy a better product in their price range, a shopper is not going to shop for cadillacs when looking at volkswagons. Now if a buyer could look at the same model as identical (SIP vs stick) but see a list of upgrade options that are the different with monthly payments calculated to be equal, the industry would be off and running!

mmacgowa:

If you are a builder you should join as an Energystar Builder ITS FREE and they will hot-link your website, the only requirement is that you have one rated home per year.

chris,

That sounds good. I sent you an email regarding the availbability of plans for one of your models. Did you get it?

I understand the concepts involved in the energy savings. What I am unclear about is the structural part. I will have a 2 in 12 pitch roof with vaulted ceiling, each panel needing to be 30ft long. The local supplier says he can make a 10x35 foot panel. We haven't involved an engineer at this point, but it seems to me the panel will need 2x6 if not 2x8 members to give it the needed strenghth. Using polyurethane, this is getting pricey, but let's leave that aside for now.
Any body done any prelim calculations on the engineering required?
Bill Chaleff has some ideas in his article, but I need more concrete advice.

bob

I have yet to see a PU manufacturer that embeds structural lumber within their roof panels. Even if they did, there isn't a lot you could do with 6" of thickness(structurally). In most PU roof applications, the support for what you have described would come from below(trusses).

A thick EPS panel or maybe steel SIPS might be your best bet.

The local manufacturer says he can make them to any spec. They essentially use dimensional lumber and OSB (or steel) to frame a "wall" which they then shoot full of foam. To prevent thermal bridging they can insert a piece of foam in between the stud and the OSB, using , say . a 2x6 and foam on top to make an 8in SIP. Steel could be used as the "stud" if it would need to be stronger. They say that for this roof, you would still need a ridge beam, but I would certainly have an engineer stamp the system!

advancedpanel.com

is the website. Isn't he problem with anEPS panel the fact that 4x8 foam panels are glued into a frame, or amm I missing something on the construction process...?

bob

I certainly haven't seen a 2 x 6 that could span anywhere near 30'.


It is standard practice to embed structural lumber in EPS panels. Yes, EPS panels are manufactured with adhesive, and many manufacturers create 'jumbo' 8' x 24' panels.

Beno;

If you want real economy use steel SIPs (raw), we have done commercial projects and several homes where roof is not highly visable.
The steel sips also create a finished white soffit at the same time.

http://southernsips.com/job_batz.html

http://southernsips.com/madeirabeach.html

mmcagowa, need to redo your math,

 

"Perhaps I wasn't clear in the assessment I was making. My point was after the fact. I already have SIP walls and Tech shield OSB on trusses for the roof with no spray foam. My highest utility bill ever paid was $99. My lowest bill without any HVAC turned on is $65. There are four month out of the year when I don't use the system at all. So at most my entire bill for HVAC = (99-65)=39. 39 * 8 months = 312 total yearly bill/12 months = $26/month average. I am already realizing a signfiicant savings with the SIP walls and tech shield. My point was that at best I would get an additional 50% savings and that would be pushing it because my numbers are already tight with a very good system as opposed to excellent. If I saved 50% of what is left of my cost, I would only gain another 13 *12 or $156/yr. That is less then 5k over a 30 year note. My SIP roof upgrade is thus going to cost me more then my savings. So if design, energy costs, and interest rates are held steady, my upgrade is most likely going to cost me money rather then save me money. So I better have a different justification for a SIP roof."

Need to do some math here! First off $99. - $65 is only $34. $34 X 8 months would be $272, total yearly bill/12 months = $22/month average.

If I saved 50% of what is left of my cost, I would only gain another $11 X 12 months or $132/yr. that = $3960 over 30 years...