What is the right prescription for southern high performance residential architectural design and building?
In our evolving practice we now recommend a prescription of high-performance solutions on every project. From a humble renovation to custom new home built to Passive House criteria we consider features in an following order of priority according to our client’s budget.
Tighten it up
The first priority is to seal the house to provide 1 air change per hour or less minimum. We use zip wall or OSB sheathing with Siga Wigluv air sealing tape to create the air barrier. You can also think about how to sequence construction to make sealing easier. One a lake house built to Passive Criteria on Lake Martin, AL we constructed the heated box without overhangs to allow complete house sealing. We then added on overhangs supported by brackets to achieve a .49 air tightness result of a blower door test before insulation.
Don’t forget the blanket
Provide continuous insulation at the floor, walls and roof. If possible add another layer of continuous insulation outside the framing as well. Even a ½ layer of insulation will limit thermal bridging through the wood studs to the exterior. Using produces like R-Zip allows for the sheathing, insulation and vapor barrier to install in one application.
Provide fresh air
Since house is now tight you need bring in outside air to ensure good air quality. In the south we recommend providing fresh air through a whole house ventilating dehumidifier instead of an ERV. We install the whole house dehumidifier tied into the duct work of the mechanical system. The dehumidifier operates when the AC is off to keep humidity at your set point between 40% and 50%. The AC system is just needed to change temperature. Clients can typically raise their temperature set point 4 to 5 degrees and are still comfortable. It is an awesome experience to walk into a 40% RH house in the middle of summer.
Remember if you extract air to provide air
In a tight house you need to keep positive pressure by providing make up air for hoods, bath vents, and fireplaces.
Use good windows
Use windows with a thermal break and U-Value of .25 or less unless you want European tilt turn window that typically have a better U-Value of under .15. We like Galhoufer for low U-value and either Marvin Integrity or a combination of Andersen E series with A series since the colors coordinate across the lines for different project conditions.
Design your HVAC system
We want our systems energy modeled with the conditions of the house . Perform a blower door test after the house is dried in to provide to the mechanical system designer measured results they need to confidently specify the capacity of the mechanical system for actual loads and not over capacity loads.
Be open to heat and AC system choices
Once humidity is controlled as a separate system the Air Conditioning choices become simpler. Do you need an expensive system to run slow to remove humidity when the humidity is already gone? Are less costly two speed units possible ? Are point source heat pumps possible if you duct your ventilation system?
Be ready for solar panels
On a new project stub up conduit to allow for the easy addition of photovoltaic solar panels (PV) later if the budget will not allow now.
After you have made your home sip energy instead of gulping it it is time to invest in solar PV arrays, battery back up systems and EV car charging. Think about where you can locate arrays to maximize the remaining Income tax credits. Can you locate the arrays on a porch so the cost of the panels and the structure to hold up the panels are eligible for the tax credit?