It’s the classic Catch-22 of building envelope design: By keeping water vapor out of a home through insulation and air sealing, you also keep it in. This conundrum is explored in depth by Passive House builders and architects.

To get a handle on moisture issues, many of them use the WUFI modeling program, which encompasses climate, construction, and material data and shows energy and moisture fluxes into and out of a home. The Passive House Institute US (PHIUS) has released an updated and improved version of WUFI Passive 3.0 software, the most advanced passive house modeling tool on the market.

With this upgrade, for the first time ever, a free version of WUFI Passive will be made available for download. The free version offers all the functionality needed to model passive buildings for the purposes of design and PHIUS+ project certification. Visit the Fraunhofer IBP Web Shop to download the free version (you must register for a free online account to download this version)

WUFI Passive couples the static passive house design methodology and a sophisticated hygrothermal dynamic building simulation tool. It offers instant energy demand calculations for the PHIUS+ certification process and dynamic simulations to guarantee long-term moisture-safe and hygienic conditions at the design stage. Both the dynamic and the static modules of the software have been improved and extended in this major upgrade.

Updates and new features of the static passive house design mode include:
--PHIUS+ 2015 climate specific certification criteria 
--Updated inputs for lighting and plug load calculations 
--Advanced geometry import options 
--Exhaust air appliance calculations

Updates and new features of the hygrothermal dynamic mode include:
--Inter-zonal airflow model
--3D-thermal-bridge calculation
--Parallelization for improved simulation performance