2015 IECC prescriptive insulation requirements

[Coder]

Hi all, I am working on the adoption of the 2015 I-Codes and am reluctant about accepting some of the requirements in the 2015 IECC. The big one (for here) is Table 402.1.2 Insulation and fenestration requirements by component. Specifically wood frame wall R-values for zones 7 & 8 requiring R-20+5 or 13+10. We currently require R-21. This allows for a continuous exterior insulation to be optional not mandatory. I am not comfortable with requiring every residence to be built with exterior insulation. I know that the designer can go the performance path or total UA alternative but in my simpleton contractor design build world, they just want to know how much they need in the wall. Any thoughts or suggestions? Thanks

 

[mtlogcabin]

We are in a zone 6 across the entire state and the state chose to modify the requirements because the pay back period versus the cost to comply where 8.3 to 13 years Our state belives the payback period should be less than 5 years.

http://www.mtrules.org/gateway/RuleNo.asp?RN=24.301.161

 

[Francis Vineyard]

Similarly with Virginia (zone 4) under the 2012;
Denied increasing ceiling R-Value from 38 to 49 on basis of impact on framing and benefit for savings.
Denied increasing frame wall R-13 to R-18 again based on framing would need to go from 2x4’s to 2x6’s in many cases depending on type of insulation materials used.

 

[tmurray]

We are 6 & 7a here (I think the "a" thing is Canada only?) and we currently require R22 or R24 depending on exterior cladding (we have to take into account isothermal planes under our code), but there is a potential to go to a minimum 1" continuous under the 2020 code.

 

[JBI]

I am not comfortable with requiring every residence to be built with exterior insulation.

Where does the Code require it to be 'exterior insulation'?
It is 'continuous' that is required. That could be on the exterior or the interior of the framed wall.
The intent is to limit the effects of thermal bridging - the wood studs don't insulate as well as the cavity insulation and create a thermal bridge that allows heat loss. Continuous insulation, even a thin layer, significantly reduces this effect. (There are actually builders using continuous insulation only with nothing in the cavity, and achieving great success with it.)

 

[tmurray]

Where does the Code require it to be 'exterior insulation'?
It is 'continuous' that is required. That could be on the exterior or the interior of the framed wall.
The intent is to limit the effects of thermal bridging - the wood studs don't insulate as well as the cavity insulation and create a thermal bridge that allows heat loss. Continuous insulation, even a thin layer, significantly reduces this effect. (There are actually builders using continuous insulation only with nothing in the cavity, and achieving great success with it.)

In the north of our province it's actually common practice to use interior foil faced insulation. When I used to energy audit homes, these things were very tight when I did the blower door test. Only thing better was ICF.

 

[mtlogcabin]

You can stagger the studs and blow it full and meet the continuous insulation intent the the only bridging would be on the top and bottom plates.
There are a number of ways to meet code for continuous and if it has more than a 5 year payback in savings our elected officials believe it is basically not worth the extra cost.

Determining the savings is a wag. When the code was going through the adoption process propane and fuel oil where about 30% higher than today's price. Electrical has been pretty stable. So for fossil fuel prices the pay back time is even longer than originally calculated.

 

[Coder]

That could be on the exterior or the interior of the framed wall.

I haven't seen an interior continuous insulation application yet. Interesting.

 

[linnrg]

we have seen it all been done. Some consideration needs to be done with interior vapor barriers when using continuous exterior foam. Uninsulated stud bays are never recommended up here in the cold climate due to stack effect. I do not know the payback periods but I think in terms of most performance it has been:
Full height ICF (very good sound performance)
SIPS (thickness can be specified and have good continuity if properly installed - Alaska has freight issues to deal with)
Exterior foam board Insulation (thickness can be easily increased)
Interior insulation (thickness has to be taken into account for electrical)
Insulated sidings (not usually a high R value)
2x6 studs with R21 or R19 or blown in fiberglass or blown in cellulose or sprayed in foam
2x4 studs with R11 or R13 or blown in fiberglass or fblown in cellulose or sprayed in foam

We also have one builder who has gone through the process of coming up with sandwiched logs that have gotten high performance. He has the operation set up in a factory based environment where he can control costs quite well.

We have several that have built out of a insulated Masonry called Penstar. http://www.davisblock.com/download/pdfs/Pentstar Brochures.pdf

We also have lots of log homes so stating the insulation levels is tricky business in my opinion.

Of the above we have had very few go with ICF above grade repeatedly due to it is very expensive. I have only had a couple of SIPS projects come through here and the last one I inspected was at least ten years ago - the other night I talked to a builder who just built his first one and I think he spent extra time just getting through the learning curve. The penstar is very durable and is costly but we did have two residential projects of it in the last couple of years.

I firmly stand with the philosophy that the amount of insulation should be at the choice of the homeowner.

 

[jwilly3879]

The problem with the r-5 continuous on the exterior is condensation in the wall cavity in our climate zone 6. The foam won't keep the sheathing above the dewpoint. You need at least r-11.25.

 

[tmurray]

Logs can be easily calculated from ICC 400 (the only ICC code Canada references).

Generally, even though the foam sheathing is sealed, it's not sealed as well as the interior vapour barrier. Since most of the moisture finding it's way into the cavity is through air leakage and there is the ability for more to get out than to get in, we've not seen any issues (climate zone 6 too). The oldest houses I've seen do it was built in the 80s. When we ripped it apart, we didn't find any degradation of the sheathing.

 

[Min&Max]

We wrote our own prescriptive energy code based on IECC. One page long and easy to understand for all concerned. I like it, the contractors like it, and homeowners are getting excellent value and finished product.

 

[Coder]

We wrote our own prescriptive energy code based on IECC. One page long and easy to understand for all concerned. I like it, the contractors like it, and homeowners are getting excellent value and finished product.

Would you be willing to send me a copy?