Table 2: Sample house data fields

Table 2: Sample house data fields

Field

ID

Community Address

Storeys Basement

Bd

Example Meaning

1 A unique index Wells, MB Community, province 123 Main St Street address

2

0

4 Number of storeys above grade Storeys below grade Number of bedrooms

Ba 3 Number of bathrooms

Sq ft

2,184 Living area in square feet by real estate listing standards Year built 2017 Year built Year built est FALSE Is “year built” an estimate based on data collector's judgment of its architectural style? Plan aspect ratio 1.3 Approximate ratio of longer plan dimension to shorter, for estimating exterior wall perimeter as a function of plan area Exterior wall area 2,666 Exterior cladding area in square feet, estimated using sq ft, storeys, plan aspect ratio, and estimated storey height

Roof matl

Comp Roof material Roof matl est FALSE “Roof material” is an estimate from a photo Ext wall cladding Stone Exterior wall cladding material Ext wall cladding est FALSE Exterior wall cladding material is an estimate from a photo Foundation and deck enclosed or treated TRUE Is the deck either enclosed or treated for fire resistance Glazing surface area 0.3 Fraction of exterior wall area that is glazed Homes in neighbourhood < 100 Number of homes in the neighbourhood Access routes 1 Number of access routes per Chapter 4 Enough access TRUE Do the number of access routes satisfy recommendations? Access route length If another access route were added, what would its shortest practical length in feet be? Fuel 0–100 m F3 Fuel type according to National WUI Guide Table 2, within 100 m of the sample building Fuel 100–500 m As above, but 100 m to 500 m from the sample building Hazard High Hazard level according to Figure 6 in the National WUI Guide Exposure High Exposure level according to simplified method of National WUI Guide Section 2.6.3.1

Paved TRUE Is the road in front of the sample house paved?

UG elec

FALSE Is the electricity distribution system at the sample house underground? Wood poles TRUE If the electricity distribution is on above-ground poles, are they made of wood? > 5 m clear wires FALSE If electric distribution is on above-ground poles, is there at least 5 m clearance between the wires and vegetation?

Hydrants FALSE Are there fire hydrants within ~500 feet of the sample house?

One then groups the records by hazard level. Within each hazard level subset, one calculates median values of parameters that seem to matter most to cost and benefit, such as storeys, square footage, cladding material, and roof material. One then chooses a sample from each subset that comes close to the median attributes. That sample is then used as the archetype existing building for that hazard level.

To select an archetype to represent new buildings, one limits the samples in each hazard level to recently built houses, for example, built in the last 10 to 20 years. One calculates medians in these subsets and again selects a sample from the subset that comes closest to the median; that sample is used as the archetype for new houses in that hazard level.

The project team selects archetypes from real houses to avoid unnecessary recourse to judgment. Real houses offer some advantages over idealized ones with the desired same sample attributes. Real houses offer greater credibility: one can show photographs of them, imagine them more clearly, and estimate important quantities more defensibly. People can relate to images of a real, existing house and compare it to their own. While judgment can be used to check archetypes, an archetype cannot be reliably selected by judgment. The project team has seen more than one study deeply undermined by designing so-called index buildings using judgment or to take advantage of convenient pre-existing models. In one case, this approach resulted in costly experiments that were essentially representative of two-storey homes, while most homes that the study addressed were single storey.

Figure 9. Example of an existing home in high WUI hazard

In the present study, existing homes in high-hazard, moderate-hazard, and low-hazard areas may differ in size, height, and other important attributes because WUI hazard might correlate with other economic factors and regional preferences. And since home construction economics and architectural styles change over time, new houses may be larger than older ones.

The project team selects a stratified sample of 102 existing homes at random in the high, moderate, and low WUI hazard as defined in Figure 6 of the National WUI Guide. Here, “stratified” means 34 homes in each hazard stratum, deliberately selecting locations to include several samples from each province that have significant land area in the hazard stratum.

The project team estimates quantities for each house using Zillow.com (for most attributes) and Google Earth (for perimeter and footprint area). For example, an existing home for sale in Thunder Bay, Ontario (Figure 9), has the following attributes (not all attributes from Table 2 are shown here).

Note that this archetype selection process generally satisfies the principles proposed by the Canadian Home Builders’ Association (2020), as detailed in Appendix A. Location: (address omitted for owners’ privacy) Thunder Bay, ON Year built: 1975 (est.) WUI hazard level: High (National WUI Guide Figure 6) Fuel type: F2 within 100 m (see Figure 10 for FBP system fuel type M1. Figure 4 and nearby images from Google Earth suggest at least 25% conifers. By the National WUI Guide Table 2, these attributes imply field type F2.) Exposure level: Moderate (National WUI Guide Table 3) Storeys: 1 Square footage (sq ft): 1,280 Bedrooms, baths: 3, 1 Exterior wall area (sq ft): 1,900 (est.) Roof: Composition Exterior cladding: Vinyl Basement: No

Figure 10. Forest Fire Behaviour Prediction System (FBP) fuel types (National WUI Guide, Figure 16, after Beaudoin et al. 2014).

FBP Fuel layer V7-2

C-1 C-2 C-3 C-4 C-5 C-6 D-1 D-2 D-3 O-1 M-1/2 C25 M-1/2 C35 M-1/2 C50 M-1/2 C65 Non-fuel Water Urban

In some cases, some vulnerability attributes may not be visible at the house location. Zillow provides photos of sample houses, enough to observe most attributes of the house itself. One can observe the number of access routes from Google Earth satellite view. Google Earth Street View provides most or all of the other attributes (fuel type, paving, electricity, and hydrants). In some cases, Google Earth Street View is not available at the house address. In those cases, the project team observes the missing attributes from the nearest accessible location on Google Earth Street View. The nearest accessible location is usually less than a mile away, so fuel type is reasonably accurate. Paving may be observable from the nearest intersection, where one can see whether the street leading to the house is paved. Electricity and hydrant features at the nearest point are probably reasonable estimates of the conditions at the house, or possibly conservative, meaning that the farther one is from a place that is accessible from Google Earth Street View, the more likely that features like paving and vegetation control are to be poorer than at the point of observation. However, for present purposes – statistical estimates of houses in general rather than well-documented features of specific houses – the approximations used here seem reasonable.