I'm in the planning stage for a SIPS house with 6-1/2 (r-22) walls & 10-1/4" (R-37) roof. Wondering what air change rate (@ACH50) people have found with a SIPS house and what HERS ratings you have received. Thanks Bob

Participants in this forum includes a number fo SIPS profesionals, so I'm wondering why none have responed to my simple question. Could it be that none of these professionals have ever had their homes rated by an independent third party HERS rater? None have done blower door tests? Seems hard to believe that in an industry directly related to performance no one has or wishes to share what should be impressivbe results. ??
Bob I

We have all our turnkey homes tested and rated, blower door and duct blaster

Good morning Bob I,

As one of the SIP professionals you referred to I think you may want to double check the rating requirements for SIP structures. If my memory serves me correctly I think you will find the SIP structures are exempt from the blower door test. Of course this would not preclude an owner from obtaining a HERS rating (or doing a blower door test for that matter).

Best of luck,

Matt B. Phelps, P.E.

Hi Matt WHY ON EARTH WOULDN'T YOU WANT TO TEST? This is from SIPS LEARNING CENTER by GBT at the top of the column: "I've tested two SIP walls-only houses that were only marginally tighter than the average home" he also says: "The only reliable tightness inspection includes a blower door-a mechanical device that mechanically exhausts air out of the home, pulling it in where leaks are still unsealed. Talk is cheap; testing is proof." That seems to say it all. Bob

Bob;

Most of our homes tested are at least twice as tight as conventional, the area most seceptable in any home is the sill plate connection

Oak Ridge National Laboratories (ORNL) Whole Room Air Infiltration Test. 4 1/2 SIP walls and ceiling vs 2 x 6 framing @ 16" O.C. with OSB sheathing, fibergalss insulation, and drywall: Air "leakage" results: (Blower door at 50 pascals of negative pressure) SIP structure= 9cfm; "sticks" = 126 cfm (one discrepency on the page that describes the test: The graph that illustrates the test results indicates that 2 x 4 studs were used to construct the "stick" box, and the text indicated thst 2 x 6's were used, either way another pretty impressive case for SIPs. (about a 90% better performance in this particular test criteria)

For more details on this test: www.r-control.com/air-tightness.asp

Obviously the SIP manufacturer's installation manual was adhered to precisely, thus little, or no, air leakage at the sill plate connection, nor at any other connection for that matter.

Chris and Sipper: the normal method for listing air change rates is "X ACH50". The problem with using CFM is that CFMs vary with volume, so 9cfm may be great in a large house, it could be less so in a small house. In talking to local raters, they have seen ACH50 rates in new construction of anywhere from "19 ACH50" to ".1 ACH50". Passive House, for example mandates ".6 ACH50. Saying SIPS are 50% of conventional rates begs the question: 50% of what exactly? 50% of 10 ACH50 or 50% of 5 ACH50? Do either of you have real data from the houses you have constructed? Thanks Bob

Bob;

 

our houses have typically tested between .14 to .22 ACH

Hi Chris
An ACH rating is not the same as an ACH50 rating. This is from Home Energy magazine: "In this formula, ACH50 denotes the hourly air change rate at a pressure difference of 50 Pascals between inside and outside. Thus, for a house with 15 ACH at 50 Pascals (ACH50 = 15), one would predict an average air change rate of (15/20 = ) 0.75 ACH."

I'm lousy at algebra, but by this formula I think your ratings would be 2.8 ACH50 and 4.4 ACH50.

You can apply for an Energy Star rating which means that your utility pays for the house to be tested and will give you the test results and HERS rating at no cost to you.
Bob

Bob;

In our area we have several power companies, some have never paid for the HERS rating and Florida Progress Energy discontinued doing their own ratings , so as builders we pay for our own. Typically costs about $450.
But thats OK,  we build energy efficient homes
The only upside are some progress energy rebates, but they never compensate fully for money spent.

But on the other hand we can make the claim that our homes are 50-60% more energy efficient, it does set us apart.

Bob,

We just completed a house in Arlington VA using Insulspan SIP panels. We did not do any in-progress blower door tests like we prefer, just the final Energy Star / LEED verification.

Project: Metro Green, Arlington VA

Final HERS rating: 46
Certified LEED Platinum & Arlington Green Home Choice
Final ACH50: 1.85
Final CFM50: 1043
Final ACHnat: 0.10

The worst of the leakage seemed to be around the spot where the geothermal installers cut their exterior ductwork penetrations with a chainsaw. Wish we'd caught that before drywall...

Jesse;

 

nice looking project, congradulations!

Thanks Jesse, those are the numbers I was looking for. Very impressed with your portfolio - nice to see smart buildings that aren't all built for the very rich. I'm curious about your thoughts on the comparison between the double stud/ extra deep rafter approach that you show (cellulose?) vs SIPS. Not trying to subvert this SIPS forum but the real choice in high performance building isn't between 2x6 walls & SIPS, but SIPS vs well thought out alternate methods.

I noticed one project had individual window overhangs, presumably for summer shading. As Passive House has demonstrated these details become more important as the homes' energy requirements becomes lower & lower. We all have to learn to use these "new" building techniques to get to where we need to be.
Bob Irving
RH Irving Co Inc., Homebuilders

I've had a good conversation with an energy star rater from Missoula MT who said local SIP builders there were regularly getting below 0.6 ACH50, he talked like it had become normal practice for them once they started trying for it. He has seen as low as 0.2 ACH50.

I can't imagine it's that hard to get to that tightness if you use a blower door once windows and doors are installed, there aren't that many seams to deal with. The "Alaska SIP failure" story shows why it's so crucial to catch any un-sealed seams, as well.

We love working with SIPs when we get the chance, getting buildings up quickly and weather tight is crucial, and a nice set of pre-cut panels from the factory is a great thing. As a designer, it really lets you get your window placement the way you want it, the framers can't box you into 8 stud corners just because they feel like it.

Stick framing is still substantially cheaper in our area, so a client has to see value in faster and more accurate for it to make sense. An R-40 2x4 double stud wall is tough for SIPs to beat on price alone.

In parts of the country with milder climate, SIPs are much more competitive. A 2x6 SIP was perfect for Arlington VA, but we wouldn't recommend them for Maine.

Jesse:
I'm working out details with my local stick frame panelizer; - I'm trying for 2-4 days to weathertight with either SIPS or 2x, but we'll see. I'm quoting a SIPS house & he's anxious to preassemble the wall sections as he's doing with the floors & interior partitions.

When I posed the question about HERS ratings & air change I thought I'd see several in the .5 ACH50 range, so I've been surprised that there haven't been any. Good to know that those numbers are out there.
Bob

The real people to talk to are your local Energy Star raters, they're the ones who do air tightness testing on piles of houses, and see everything, from SIP to ICF to stick. They'll know the real range that's out there in your area.

However, it's still not common practice yet to treat air-tightness as a challenge. I do see that when builders start to see it as a challenge, it turns into good bragging rights for them. Finish carpenters are used to being able to show off their skills, but air tightness gives framers and SIP installers a chance at bragging rights as well. "I got 200 CFM50, what did you get..."

I think it's changing quickly. The Alaska cover story in this month's JLC talks a lot about low ACH50 buildings: nstalling Exterior Insulation in Cold Climates The attention Passivhaus is getting is creating a lot of chatter around it as well.

Now all we need is ASHRAE and the codes to change...