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# ASHRAE 160 DA07
We get asked a lot of questions about **DA07 Criteria for Moisture Control Design Analysis in Buildings**. That's **ASHRAE 160 Criteria for Moisture Control Design Analysis in Buildings** for the rest of the world outside of Australia! And yes, it's the same thing!
Some questions are about what the standard actually overs, some about what it actually requires you to do to meet code compliance, and plenty about where the default numbers come from and why they are what they are.
So... we've collected the twenty we hear most often into a single list. Consider it a starting point rather than a finished document. As new questions come in, and they will, we'll keep adding to it.
These are the twenty questions we get asked most often about applying DA07. We've put them in one place rather than answering them one email at a time, and we'll keep expanding the list as new ones come in.
What is ASHRAE 160/DA07?
It's the AIRAH DA07 standards sets the assessment method for moisture control design analysis in buildings. It is called up in the National Construction Code and is a modified adoption of ASHRAE Standard 160. In practice it tells you what inputs to use, what analysis method is acceptable for residential and commercial buildings, and what result counts as a pass.
What counts as an acceptable analysis tool in ASHRAE 160/DA07?
It has to be transient, with a maximum time step of one hour. It must handle energy transport including phase change, material properties that vary with moisture content, and liquid and vapour transport covering capillary transport, surface deposition, storage, vapour diffusion, and water leakage. Ventilated cavities have to be modelled as cavities. Outputs must include temperature and surface relative humidity at every surface and material interface, plus average temperature and average moisture content for each layer. Steady-state hand calculations do not qualify.
What does ASHRAE 160/DA07 actually cover?
New buildings, retrofits, renovations, all building types, all materials, and all interior and exterior zones and envelope cavities. It's deliberately broad. If you're modelling an assembly, DA07 has an opinion about it.
What does ASHRAE 160/DA07 not cover?
It doesn't address thermal comfort or indoor air quality, and it doesn't address designing components to resist liquid water leakage from rain, groundwater, flooding, or ice dams. Keeping bulk water out is still your job. DA07 tells you what happens to the water that inevitably gets in anyway.
What are the weather data requirements in ASHRAE 160/DA07?
A minimum of ten consecutive years, or the moisture design reference years (the 10th-percentile warmest and 10th-percentile coldest years from a 30-year analysis). Hourly data, including dry-bulb temperature, a humidity measure, solar insolation, wind speed and direction, rainfall, and cloud index. Yes, all of it.\
\
It should be noted that such data is often impractical to source of create, so this particular requirement can be difficult to meet.
How do I set indoor humidity in ASHRAE 160/DA07?
If HVAC equipment and controls are part of the design, use the intended design humidity. If not, pick one of three methods: simplified (a function of daily average outdoor temperature), intermediate (a mass balance using moisture generation and ventilation rates), or full parametric calculation. Whichever you choose, indoor design humidity cannot exceed 70% rh.
What's the simplified method in ASHRAE 160/DA07?
Design RH is 40% below -10°C, then 40% plus (daily average outdoor temperature plus 10) between -10°C and 20°C, capping at 70% above 20°C. Crude, but it exists for a reason: it stops people inventing indoor conditions that flatter the assembly.
What moisture generation rate should I use for a house in ASHRAE 160/DA07?
Occupancy-based. Two occupants minimum, plus one for every bedroom beyond the master. That lands at roughly 7 L/day for one bedroom up to 11 L/day for four, adding 1 L/day per extra bedroom. And if there's a jetted tub in a room without a humidistat-controlled exhaust fan, add another 1.3 L/day.
What ventilation rate applies in ASHRAE 160/DA07 if the building has no designed ventilation system?
Default air exchange rates of 0.2 ach for standard Australian Building Code compliant construction, and 0.1 ach for airtight construction. DA07 also recommends a sensitivity analysis on infiltration, which is good advice. Better sealed buildings push internal humidity up, and the interstitial risk climbs with it, particularly in cool and cold climates.
What's the pass criterion?
Mould index must not exceed 3.00 on any surface, calculated hourly and accumulated over the simulation. The material surface gets assigned to one of four sensitivity classes (Very Sensitive, Sensitive, Medium Resistant, Resistant), and that class drives both the critical relative humidity threshold and the growth coefficients. Choosing the class is a judgement call, so ASHRAE 160/DA07 requires you to state your rationale in the report.
How much rain does ASHRAE 160/DA07 assume gets through the cladding?
One percent of the water reaching the exterior surface, deposited on the outer face of the water-resistive barrier. That's the default in the absence of full-scale test data for the as-built wall system. It sounds pessimistic until you've opened up a few walls. If there's no water-resistive barrier, you have to nominate the deposit site yourself and justify it.
Do I have to model air pressure differentials and airflow in ASHRAE 160/DA07?
No. The analysis is optional under ASHRAE 160/DA07.
If I do include air pressure in ASHRAE 160/DA07, what values do I use?
If the pressure differential is actively controlled, use the controlled value. Otherwise pick one of two alternatives: calculate it from design ventilation rates, airtightness, wind pressures, and stack effect, or use the default of +5 Pa when the 24-hour running average outdoor temperature is below indoor design temperature and -5 Pa when it's above. For buildings taller than three storeys you also calculate stack pressure at the top of the top floor wall and use that instead if it exceeds 5 Pa, unless each floor is effectively pressure isolated.
What airtightness do I assume in ASHRAE 160/DA07 if it hasn't been tested?
0.1 for airtight construction and 0.2 for standard construction. At a 5 Pa design pressure that works out to roughly 0.016 L/s per m2 and 0.084 L/s per m2 respectively. If you do know the measured airtightness, use it, and describe the airflow pathways and why you chose them.
What initial moisture content do materials start at in ASHRAE 160/DA07?
For new construction, twice EMC90 for concrete and twice EMC80 for everything else. If the project specifies procedures to dry materials or protect them from wetting during construction, you can drop to EMC90 and EMC80. For retrofits, EMC90 and EMC80 apply unless you have measured values. The doubling is a nod to reality: materials arrive on site wetter than anyone would like.
What indoor temperature should I use in ASHRAE 160/DA07?
If the design, operating specification, or applicable code sets one, use that. Otherwise DA07 ties it to the 24-hour running average outdoor temperature. Below 18.3°C outdoors, indoor design temperature is 21.1°C. Between 18.3°C and 21.1°C, it floats at outdoor plus 2.8°C. Above 21.1°C it stays at outdoor plus 2.8°C for heating-only buildings, or caps at 23.9°C where air conditioning is present.
What happens to indoor humidity in ASHRAE 160/DA07 when the building is air conditioned?
If the equipment runs on thermostat control alone, indoor design humidity ratio is 0.004 plus 0.4 times the mean coincident design outdoor humidity ratio for cooling at the 1% annual basis. If the equipment has humidity control, use the specified setting or that calculated value, whichever is lower. No setting specified? Assume 50% rh.
How is wind-driven rain calculated in ASHRAE 160/DA07?
Rain deposition on a vertical wall is the product of the exposure factor, the deposition factor, an empirical constant of 0.2, hourly average wind speed at 10 m, the cosine of the wind angle to the wall normal, and horizontal rainfall intensity. Exposure factor runs from 0.7 for sheltered low buildings to 1.5 for anything over 20 m, with severe exposure covering hilltops, coastal sites, and funnelled wind. Deposition factor is 0.35 for walls under a steep-slope roof, 0.5 under a low-slope roof, and 1.0 for walls taking runoff from above. That last one is a fourfold jump, which is why parapets and unflashed transitions keep showing up in failure investigations.
Is mould the only performance criterion in ASHRAE 160/DA07?
No. Corrosion gets its own treatment. Requirements are meant to come from the properties and function of the specific metals used, and where that information isn't available, DA07 falls back on the 30-day running average of hourly surface relative humidity at the metal. Worth noting the extract you've supplied cuts off mid-sentence at that threshold, so check the source document for the actual limit before quoting a number.
What do I have to include in the ASHRAE 160/DA07 report?
More than most people expect. A description of the assembly (type, orientation, surface coefficients, air space locations and ventilation rates, material list with data sources), full material data for every layer (thickness, density, conductivity, specific heat, vapour permeance, sorption isotherm, liquid diffusivity, suction isotherm, initial moisture content), general building information, and a record of every methodological choice you made: which humidity method, whether airflow was considered, weather data source, exposure and deposition factors, mould sensitivity class and decline coefficient with rationale, and the name and description of the analysis software. The reporting section is effectively an audit trail, and it's the part that separates a defensible assessment from a screenshot of a graph.
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