The details below reflect observations from RDH’s wildfire testing, forensic investigations, and code development work.
1. Loads vary around a single building.
The wall facing the forest carries a different load than the wall facing the parking lot. The window at the bottom of a slope carries a different load than the window facing the driveway. Uniform treatment of every elevation over-protects some parts of a building and under-protects others.
2. A one-hour wall with a one-minute window is wasted effort.
Enclosure performance is governed by the weakest link. Upgrading one assembly while leaving adjacent weak points untouched is the wildfire equivalent of a thermal bridge. The rated wall’s contribution is limited by the unrated window beside it.
3. The eighth-of-an-inch gap standard matters.
Embers that pass through a quarter-inch gap carry enough heat intensity to ignite what they land on. Embers that pass through an eighth-inch gap generally do not. Vents, louvers, joints, and screen mesh all need to hold that dimension.
4. The five-foot zone comes first.
No enclosure detail compensates for combustible material touching the wall. Mulch, bushes, wood fences, wood decks, patio furniture, and stored materials within five feet of the building are direct ignition paths regardless of what the wall is made of.
5. Fences and decks are conduits.
A wood fence that runs into a wood-sided house is a fuse. So is a wood deck that meets an operable window or a door. Non-combustible transitions in the last five feet break the fuel path.
6. Windows are usually the weakest link.
Glass fails under heat and wind-blown debris. Frames deform, glazing stops fail, and vinyl distorts. The minimum wildfire guidance for windows is a single layer of tempered glass with a screen, and that is genuinely a minimum.
7. Where the tempered pane sits in an insulated glazing unit matters.
Two tempered panes outperform one. When only one is possible, RDH testing supports placing the tempered pane on the interior rather than the exterior. An exterior tempered pane that breaks and falls out leaves an annealed pane exposed, and annealed glass fails within a minute.
8. Open windows during evacuation are a common failure mode.
Summer evacuations often happen with windows open. Screens on operable windows offer meaningful protection when the closure step gets missed. They are a fallback worth designing for.
9. Class A depends on the whole assembly.
A Class A roof rating depends on the covering, the underlayment, and the deck working together. Substituting a component can move the assembly out of Class A even when the covering itself is unchanged. This is where roof consulting overlaps directly with wildfire consulting.
10. Foam plastic insulation is vulnerable above grade and below.
Foam plastic insulation on exterior walls needs to be protected by mineral wool or gypsum. The vulnerability continues below grade, where exposed foam at slab edges and ICF walls can disappear under fire load. Wildfire resistance has to run from the roof through the wall to the ground.