Passive House goals can be achieved for retrofits under the EnerPHit certification. Meeting Passive levels may become trickier when retrofitting, but the retrofit standard is ambitious and achievable.

Passive House Institute Founder, Dr Wolfgang Feis launched the EnerPHit standard at the Passive House Conference, and pointed out that the energy consumption of old buildings can’t usually be brought to the level of new build Passive House standard, precisely because of those unavoidable thermal bridges.

“But,” he notes: “The same components as for new Passive House buildings can be used, and the building substance can thus be protected and sustainability can be improved significantly. In numerous projects, a reduction of 90% in the heating demand could be achieved.”

Thus, there is a realization that retrofitters face many challenges, and, as a result, the Institute has in-built an important level of flexibility into the EnerPHit standard. The thresholds are looser, and there are fewer to meet. Moreover, certification is achievable even if these minimums are not met.

EnerPHit—“Quality-Approved Energy Retrofit with Passive House Components” Certificate—for certified energy retrofits include an opaque building envelope, windows, external doors, and ventilation. Now, installing a continuous insulated envelope is much more difficult on retrofit, as cavity walls or block walls descending all the way to the foundations, thermal bridges cannot be designed out as they can on a passive new build.

What happens with the passage of thermal current? Heat moves from the warmed space to the outside, following the path of least resistance. Thermal bridges are localized areas of building envelopes in which that flow of warmth is different—probably heightened—compared to contiguous spaces (in terms of a differential internal and external temperatures). Thermal bridges result in altered or decreased surface temperatures, which at worst can yield moisture penetration in building components and the spread of mould. There is often heat loss.

Passive Houses avoid such bridging because the interior surface temperatures are so high ubiquitously that moisture levels can not occur—yielding additionally unimportant heat loss. If the losses are smaller than a limit value [at .01 W/(mK)], then the “thermal bridge-free design” criteria are satisfied.

Should these criteria be met everywhere, planners, builders and construction managers no longer need concern themselves with cold/damp spots. Subsequent to this, less effort will be made calculating the heat-energy balance, which means appreciably improved elements, just as the construction’s sturdiness and durability are increased while saving heating energy is conserved.

To put it bluntly, measurable energy savings—between 75%-90%—can be achieved in existing buildings, following these guidelines:

  • Better thermal insulation (“if it has to be done, do it right”)
  • Improved airtightness (adumbrated with regard to thermal bridging, above)
  • Effective use of high-quality windows(should be SOP with Passive House standard)
  • Ventilation with high-efficiency heat recovery(again, Passive-House-suitable)
  • Efficient generation of heat, as noted
  • Utilization of renewable energy sources

These are proven measures—they work in new construction. A number of examples demonstrating the application of high-efficiency technology in existing buildings have become available already. The Passive House Institute has advised on the implementation of several projects and carries out measurements in modernized buildings.

The materials that can fit the standards are also important to note for Passive House retrofits. The first is the Intello Air Barrier Membrane, a smart vapor retarder furnishing a first-class air barrier for thermal insulation in roofs, walls and floors. This gives structural systems a previously unachievable degree of protection from structural damage (condensation, later mould) even under extreme climatic conditions, due to the retardant properties. The benefits:
• High diffusion tightness in winter (0.17 Perm, protection against condensation)
• Maximum diffusion openness in summer (13.20 Perm, facilitates rapid drying to the interior)
• Particularly suitability for structures with lower permeability on the exterior that prove difficult to protect from condensation (flat or grass roofs; metal siding/sheathing)
• Compatibility with a wide range of insulation elements, such as fiberglass, BIBS, mineral wool and many others
• Translucent properties allowing dense packed blown-in cellulose insulation to be inspected after installation
• Lightweight, easy installation—especially compared to OSB/Plywood, and fully recyclable, with air permeance per ASTM E2178 0.00005cfm/ft2
• Class A material per ASTM E84 test (0 FS, 35 SDI)
• Roll width: 59-1/16” (1.50m); Roll length: 164’-1/2” (50m); Roll area: 807 SF (75 m2)

Additionally there are Pro Clima Tapes. These air-seal without losing critical efficiency over time. Comprised of solid acrylic in a patented formulation, Pro Clima also have a proven track record from the past three decades in automobile and aircraft construction: A long lasting seal in conditions markedly more challenging than typical building construction.

They are based on a solid acrylic, whereas other tape manufacturers use acrylic glue with emulsifying agents and water solution, and therefore may be adversely affected if put in contact with moisture. Consequently, Pro Clima boast a higher resistance to moisture on-site—they can be applied in very humid conditions, and will even maintain a reliable seal when exposed to water. They can, in addition, be properly applied in temperatures as low as 15°F. They are also rapid-age tested, a method independently verified by the Center for Sustainable Construction (Zentrum fuer Umweltbewusstes Bauen; ZUB).

Yet another construction material, STO-Gold Air Barrier, StoGuard with Gold Coat, is a code recognized, vapor-permeable fluid-applied membrane designed for application under EIFS.

As a substrate treatment part of the StoGuard air barrier and moisture barrier assembly, it combines the Sto Gold Coat sheathing treatment with StoGuard joint/rough opening treatments. Roller- or spray-applied through standard airless appliqués, it ensures continuous air and moisture barriers that prevent air infiltration and fluid ingress within the building, protecting moisture-sensitive components, and providing a solid, secure base for an energy-efficient wall assembly. It may be used on gypsum and wood-based sheathings, or CMU.

Further sealant can be found in Dense Packed Cellulose, which prevents air infiltration while offering superb sound insulation. The dense pack provides an effective air barrier, slowing down and (often) stopping the overall movement of air through the buildings envelope. Up to 33% of a building’s air leakage, as measured with the blower door, can be eliminated using dense pack cellulose, according to extant studies.

And, as a carbon-conscious material, cellulose insulation is created from recycled newspaper and reconstituted wood pulp. Treated with Borate, a naturally occurring mineral compound, the cellulose then has the added advantage of greatly increased fire-, moisture-, mould- and vermin-resistance. When installed properly, cellulose insulation’s thermal barrier is far superior to traditional fiberglass or other insulations.

Dense pack installation cellulose comparative facts are important to consider: It has 38% stronger sealing properties, as compared to fiberglass; offers 24% reduction in air infiltration; yields 22-55% greater fire resistance; provides superior moisture, vermin and mold resistance; and greater soundproofing and vibration-dampening potential.

Roxul Mineral Wool is also a crucial insulation element. Roxul makes mineral wool insulation for cavity walls and sheathing board—it is noncombustible, water-repellent, fire-resistant, sound-absorbent, and has a thermal resistance of about R-4/in. The R-value can range from 4.0 to 4.2 per inch. These products are produced with a urea-extended phenol formaldehyde binder, though heat processing during production drives off most of the formaldehyde, resulting in extremely low emissions.

The advantages of ROXUL are manifold, as ROXUL insulation goes beyond what most conventional insulations offer. The main ingredient is stone. Thus, the above advantages are that it delays the spread of fire, providing time, in the event of fire. It won’t burn, or release toxic gases or smoke when exposed to high heat (as it may withstand temperatures of up to 2,150˚F or 1177˚C—well above levels of typical house fires). As it is water-repellant, after exposure to moisture, the wool won’t slump in the wall cavity, as many conventional batt insulation products—and the R-value will not be affected.

Importantly, it is an inert substance that does not support mould or fungal growth, which means a safer indoor environment for the home, as it is made from stone. Created from a unique combination of stone and recycled slag—a by-product of steel production that would otherwise go to landfill—the nondirectional fiber structure and higher density offers better dimensional stability and an efficient barrier against noise.

Finally, Aerogel Thermablok, a flexible, nanoporous aerogel blanket insulation that reduces energy loss as it conserves interior space in building applications, features unique, extremely attractive/useful properties. Its extremely low thermal conductivity, superior flexibility, compression resistance, hydrophobicity, and ease of use combine to make it a worthwhile choice for those seeking the utmost in thermal protection.

Patented nanotechnology combines a silica aerogel with reinforcing fibers to deliver industry-leading thermal performance in an easy-to-handle and environmentally safe product. As a proven, effective insulator, Thermablok affords the highest R-value of any insulation material for maximum energy efficiency in walls, floors, roofs, framing and windows.

If retrofitting buildings poses difficulties according to Passive House standards, the EnerPHit certification is not an unreachable goal, due to available materials and their use. They will reduce the heating and cooling load while making the refurbishment environmentally sound—reducing the carbon footprint in the long run, which is what Passive House’s measures are designed, in the first place, to achieve.

– Alessia Pilloni