A fairly common question during the certification process is ‘What sort of construction documentation is required for a certified passive house?’
Required documentation for a Certified Passive House (Passivhaus) or PHI Low Energy Building is that sufficient to fully check the energy model and design quality and assure that the building was built as per the design. That sort of information is best split into two parts: the first part can and should be done before construction, while the second part of the information is only available after construction is completed.
RecommendedWe highly recommend the use of a Certified Passive House Tradesperson or an experienced Passive House Designer as the construction site supervisor. Being the site supervisor on a Certified Passive House project is no joke. Once it is built it you are stuck with the quality that was built. The building will either meet the certification criteria or not and when you consider that overseas buildings with third party certification are worth 7% more (California) that is a considerable sum of money. Our current construction work force has been focused on speed and cost over quality for many years and it can be difficult to change these habits. It is very easy to find examples of poorly installed insulation that will perform 30% worse than a good practice install with only a small increase in installation quality. Material substitutions are another common practice that can cause performance shortfalls and thus problems with certification. Knowing what is required for a Certified Passive House and where the typical industry shortcuts are is important.
As a first part before construction, the design and product information sufficient to support each entry in the Passive House Planning Package (PHPP) energy model should be provided. This is design information such as the drawings showing the floor areas and the wall areas, the materials that make up the wall and each of the thermal envelope’s constructions including two dimensional thermal bridge calculations if required. Detailed component specifications on the windows, ventilations system, domestic hot water (DHW) system and the heating and cooling system. Ideally this would include the supplier quotes to allow checking that the specified item on the drawing is actually what they intend to supply. It is surprising how often the quote is for an entirely different specification to that requested. All of this information allows the certifier to check that the building design matches the energy model; ideally at pre-construction when errors can be fixed on paper.
The certifier will often issue a pre-construction letter at this point which typically lists the open items that have not had data provided. Ignoring these exclusions the construction team can now focus on ensuring the building is built per the design with the specified products and quality high enough to achieve the air tightness. Success is clear and well defined.
RecommendedIt is good practice to have an air tightness champion on site. This is one person on the construction site who is responsible for the building air tightness. Often they will brief subcontractors on the importance of the air control layer and check that any time the air control barriers is pierced by anyone on site it is sealed properly. For example, a common place for air tightness failure is when the heat pump is installed. The insulated twin copper pipes that contain the refrigerant for the heat pump need to be sealed to the air control layer. Sealing the outside of the insulation on the bundle will result in a large air leak.
The second part covers what is done at the building site. This is primarily four things: photographs of the construction, construction site supervisor declaration, air leakage testing (blower door test), and ventilation system commissioning.
Photographs sufficient to support the process of construction are required. As the insulation measures are what impact the energy model this is the focus. Photographs of the insulation installation to each of the building assemblies are required: sub-slab insulation (thickness and type), wall and roof insulation layers (ideally showing installation quality). These are intended to show that the building is insulated as designed. Next most important are photographs of the junctions between the different building assemblies (floor-to wall, roof-to-wall, window details) showing how the junction was constructed in a thermal bridge free manner. Door sills are particular interesting, the way they are flashed and set into the wall-to-floor assembly. It’s not uncommon for someone to attempt to put metal flashing from the inside to the outside of a window or a door which is obviously not permitted in a Certified Passive House due to condensation concerns. Another detail that is particularly interesting is the thermal break in the concrete slab between the unheated garage and interior. Finally completed building interior and exterior photographs plus site surroundings for each orientation are required.
A signed and dated construction site supervisor (manager) declaration must be provided. A Passive House Institute (PHI) supplied example is at this link. This declaration states that the construction site supervisor (manager) supervised construction and the building is built per these drawings except for these a list of changes. It is really bad practice to sign this stating no changes when there have been changes. One option on smaller projects is to keep a set of drawings be on site and marking changes. These can then be scanned and supplied as ‘as built’ drawings and are sufficient notification of changes.
Final air leakage testing (i.e. blower door test) report must be provided. This test must be after the building envelope is completed with all penetrations. PHINZ has released a good guide to the air leakage testing and I recommend reading this closely. Ideally the test would be performed by someone independent of the building owner or construction team but sometimes this is not practical. This is permitted provided the testing person or firm clearly takes legal responsibility for the test results. Common mistakes in the air leakage testing are not signing and dating the test report, not noting that the building volume used was confirmed by the tester, neglecting to note which door the blower door is installed into and what was sealed or left unsealed for the test.
Commissioning of the mechanical ventilation with heat recovery system (MVHR) or any other sort of ventilation system must be performed at the PHPP energy modelled flow rates. It is much easier to ask the PH designer for the correct airflow rate to commission the MVHR to than to go back and re-commission another day. The common practice in the commercial building ventilation commissioning world is to commission at the peak flow rate. Passive Houses are to be commissioned at the ‘typical’ flow rate – which is almost always lower. This is a very common mistake. Note that the commissioning report also needs to be signed and dated. We recommend use of the PHI provided template and instructions. Note that in single family homes acoustic measurements are always recommended but are typically not required by the certifier unless a problem is suspected but they are required in commercial or multifamily buildings.
Of course all of these requirements are detailed in the latest Passive House detailed building certification criteria. Located here.