Streamlining Passive House design

17 June 2024 by Sara Wareing
easyPH an option to streamline Passive House design

easyPH logo

There’s some anticipation about the release of easyPH, understandable given its promise to make Passive House design easier. Here’s some advice for new designers about how to streamline and simplify Passive House design, some of which is applicable to either PHPP or easyPH.

Firstly, make sure you’re familiar with the subset of projects that can be designed using easyPH. This very much overlaps with the type of project we would expect a new Passive House designer to be tackling. (We estimate experienced Passive House designers fluent in PHPP’s 40 worksheets and already using designPH for modelling would save little time by switching to easyPH. That said, it’s worth checking out the simplified input for kitchen extracts. We’re interested to hear what you think.)

There are multiple benefits to streamlining the Passive House design process. The advice that follows describes workflows and tips to save time, reduce complexity and produce more certainty and fewer errors. That makes design work less stressful and more enjoyable and saves clients money by avoiding multiple rounds at the pre-construction review stage.

As certifiers, our ideal outcome is every project submitted for certification passes on the first round of pre- and post-construction certification review. We’re with you (and your client): we want this to be fast, efficient and cost-effective. That’s why we share information like this and the many articles you’ll find links to below.

Streamlining Passive House design

1. Start in designPH then export

The benefits of using easyPH will be fully realised by working first in designPH, a plugin for SketchUp (it can be bundled with PHPP or purchased separately). The whole Sustainable Engineering team is sold on the benefits of using designPH, for reasons outlined here. That applies regardless of whether a design is being submitted in PHPP or easyPH.

Use designPH to create the geometry and shading. Draw the TFA over a DWG of your floor plan so that it’s easy for your certifier to check. Note that to use easyPH, you must enter the room-by-room areas and average room heights in the easyPH sheet. 

Here’s some detailed information about terrain modelling if you need it. Construction U-values and window details can also be included in the designPH file before exporting it into PHPP or easyPH. At that point, almost all of the remaining entries are on a single worksheet, a top-down checklist which is a convenient format for new Passive House designers.

When exporting the file from designPH, it’s essential to select “designPH geometry and components”. All other export options will break the PHPP file.

It is feasible to use easyPH without any work in designPH—you’ll need to enter the physical geometry of your house, the window properties (dimensions, install situations and surfaces they are installed in) plus rely on the classic method for shading, which in New Zealand underestimates overheating. But doing all of that is not at all easy! Classic shading is probably the hardest part of a PHPP submission (and we as certifiers don’t like it—see #2 in this post). 

2. Make use of built-in/linked databases. 

easyPH contains links to PHI thermal bridge catalogue. In either easyPH or PHPP, projects being submitted to Sustainable Engineering for certification can access thermal conductivity, window and glass databases our team has compiled. This makes it unnecessary to hunt down and submit supplier data sheets, saving you lots of time and hassle. It saves time at the certifier’s end too.

3. Design in some (not too much) margin

This means assumptions can be used rather than precisely calculating every input. Chasing down trivia and calculating every thermal bridge at post-construction review stage to earn back a few kWh to meet certification targets is painful. Target a result of 14 kWH/m2/a with a blower door test result of 0.64ACHn50 on the reasonable assumption your airtightness result will be better than this, which in term reduces your heating and cooling numbers.

4. Lean on known data

Use known Passive House construction details from the High-Performance Construction Details Handbook. The details have been proven and the modelling carried out, with the data needed for easyPH/PHPP available right there.

5. Avoid thermal bridges

A timber floor on piles requires no thermal bridge inputs (it’s also a winner from the point of view of minimising embodied carbon emissions). If using a concrete slab, go with an evaluated design from suppliers that have published Passive House calculations such as MAXRaft, QuickSet or others like Firth, Insulfound, Koolfoam, Resene and Megafound that will share data on a project specific basis. See our full list here. This will save chasing up thermal bridge calculations, doing hand calculations or paying a consultant to do them for you.

All of the above advice is offered from the perspective of streamlining Passive House performance. Architects and engineers may seek require more complex designs and different material choices. If the architect and Passive House designer are the same person (or collaborate closely), the trade-offs can be considered and tested. Passive House is a flexible system and almost any complexity can be accommodated. It just comes at a cost and it’s worth being clear on that from the outset.

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