Possible Modifications based on Passive House Standard

Since studying the Passive House standard of energy efficient design, we have been trying to determine what we can incorporate into our project without blowing the budget. Below are some of the ideas we have so far to improve the energy efficiency of the home after consulting the Passive House Standard.

Insulation

1. Increase SIP wall panels to 6.5″ (R-25) thick from 4.5″ (R-17)
2. Increase SIP ceiling panels to 10.25″ (R-43) thick from 8.25″ (R-32)
3. Look into increasing insulation under the slab (currently ~R-14). If we keep our radiant heating system it may be beneficial to leave a hole in the insulation in the center of the slab in order to utilize the ground as a heat sink to maintain a more constant temperature in the slab. This needs further investigation.
4. Investigate ways to further reduce thermal bridging with SIPs manufacturer
5. Investigate whether we can afford bolstering the insulation of the walls on either side of the SIPs panels. A 1-2″ layer of foam board insulation on the exterior before the cladding is installed could boost our R-value by as much as 14 to bring us to R-39. A half inch of EPS foam board on the interior walls could replace drywall, adding another layer of insulation and allowing us to use an American Clay type of product to finish the walls that would also further improve the indoor air quality.
6. Investigate a radiant barrier layer under the roofing material and above the SIPs.

Efficient Windows

1. Investigate fiberglass windows with better U-values than the currently spec’ed Pella Proline series. See this window post for more info on options. Marvin Integrity is looking good right now as far as value but may still be a premium compared to the Pella’s.
2. Replace the existing spec’ed sliding glass door with an energy star rated model.

Mechanical Ventilation with Heat Recovery

1. Implement and HRV or ERV system as cost effectively as possible with minimal ducting.
2. Investigate the possibility of using earth cooling tubes under the foundation that feed the HRV/ERV that will pre-heat or pre-cool the incoming air naturally prior to entering the home. The main issue here is the fear of condensation building up inside of the tubes under ground that could lead to mold formation.
3. Investigate the possibility of incorporating a dehumidifying element into the HRV/ERV system that would allow us to eliminate a separate air conditioning system in the summer.

Efficient Heating System

1. Radiant heating still seems to be the best way to go for our home as we will not be able to reach the full passive house standards in all other categories that could allow us to use the HRV/ERV system only with a post heating element. We also really like radiant heat and think it will be a great feature of the home.
2. The heating source is still not nailed down as it depends on whether we will need air conditioning or not. If we do, then it may make sense to use a heat pump capable of cooling and heating the home and the water supply. If we do not need air conditioning then we will lean towards a gas, tankless unit with the option to add a solar thermal array.

As you can see, we don’t have all of the details nailed down yet. This will come in the next few weeks as we look at the budget in more detail and finalize the construction drawings. We may also look into hiring a consultant that is familiar with passive homes and efficient heating, cooling and ventilation systems for them.