2018 IECC / Stretch Code Code Compliant Home
General recommendations for building a Stretch Code compliant home.
We include design support as part of our HERS Rating service.
We also offer detailed thermal envelope design consulting and plan review services.
Building a code compliant home does not require an all spray foam insulation scope or complicated design details. In fact, the simpler the building form the easier and less expensive it is to build an energy efficient, comfortable, healthy and code compliant home.
Below are some recommendations for a relatively low cost home built to the 2018 IECC MA Stretch Code. Of course each home is different and without a HERS Rating energy model, we can’t say for sure if a home is designed to meet the current required HERS index of < 55 (less than 55) . Moreover, there are many other factors that make a design decision appropriate - skill of builder, maintenance, occupancy, aesthetics, health/air quality priority, ecological impact awareness…etc etc.
Again, these are code minimum recommendations…NOT CODE REQUIREMENTS. Code currently requires that the HERS Rating is 55 or lower. This is typically one way to get there. These recommendations are based on observing hundreds of projects, seeing where they sometimes go wrong, and understanding construction costs in the MA market.
If your project goals and budget is for a high performance home, your thermal enclosure and mechanical systems will deviate from these recommendations in places. We can help with that too.
General guidelines
Attic flat, not cathedral ceiling. Low pitched vault ceilings are okay, if can be insulated like an attic flat
Basement is fully insulated, but not necessarily finished.
All mechanical equipment and duct work is ‘inside’ the thermal envelope (insulated space)
Heating and cooling equipment is right-sized using Manual J
Window sizes are not excessive and solar gains are considered.
Garage is outside the building, not under the home
The primary air-barrier must be understood by all contractors on site. For the recommendations below, the airbarrier is as follows:slab> foundation wall> sheathing>ceiling drywall…down the other side. Sounds simple and it is! All penetrations and framing connections at the airbarrier must be airsealed sealed.
Home Siting
Consider orientation for future solar PV and solar heat gain through windows
Attic Flat
R60 blown cellulose - 16-18” loose blown. Attic fully airseaed. Hatch insulated with R40 rigid board.
Exterior Walls
R21 fiberglass batts, 2x6 framing ,insulated headers. Zip sheathing recommended unless very experienced with airtight sheathing strategies.
Windows / Glass Doors
0.28 U-value or lower. SHGC is critical- higher = more sun’s energy enters as heat.
Basement / Foundation
R15 Thermax rigid board on foundation wall, seams taped. Occasionally R10 ThermalStar Intergrade board can work if HERS rating can support the trade-off
(basement ceiling insulation can often work instead , but it is not recommended due to air sealing challenges, loss of function of basement space, moisture issue potential, code implications for airtightness testing and duct leakage testing)
Rim / Band
Good place for 3” of closed cell spray foam. OR airseal completely and install R21 fiberglass batts/ or rigid board. Seal the bottom plate of the home
Slab / Slab Edge
See this great guide here on this.
R10 XPS (blue/pink board) - at Slab Edge and under all
If basement is conditioned, or will be in the future, now is the time to insulated under the entire slab
If basement is unconditioned, only the slab edge of walk-out walls need to be insulated
Heating / Cooling
Electric heat pumps should be considered for every project, due to excellent rebates in Massachusetts.
These systems must be right sized - oversizing will limit dehumidification in the summer. Undersizeing will risk heating needs are met.
Alternatively forced air systems that are 95%+ AFUE with ECM motors is recommended . FOr A/C, 14 SEER+ .. RIGHT SIZED…Do not oversize the A/C system!
Hot Water Heater
Electric heat pump hot water heater - if in insulated space
Ventilation
Balanced ventilation (HRV/ ERV) will provide much better air-quality than an exhaust only bath fan. But this is not required for code. Bath fans can meet ASHRAE 62.2 ventilation requirements- Panasonic Whisper Select bath fans with speed control, are highly recommended
Want more input or design support? Contact us today
