Wildland Urban Interface

How Wildland Urban Interface Affects Your Remodel

What is WUI

What is the Wildland Urban Interface?

The area between where we live and nature is where fires happen and where fires are more prone to affect us. WUI is the zone of transition between unoccupied land and human development. It’s the area or zone where structures and other human development meet or intermingle with undeveloped wildland or vegetative fuels. 

If you’ve ever seen the movie Frozen, Olaf is a snowman who really likes the sun. Olaf probably shouldn’t be hanging out in the sun. Maybe we shouldn’t be building houses in these locations, but we’re doing it anyway. We have to know the code that has provided ways for us to protect our structures against wildfire. To some extent, it’s going to be impossible to protect a structure with a massive raging fire next to it. But these are an attempt to slow things down. 

Fire hazard zones

Is My Remodel a WUI Project?

How do we know if a project is in the WUI? Basically, we’re using maps. Cal fire has a map on their website. I provided a link here. What we’re looking for is any colored zone. So there are three zones. There are very high, high, and moderate fire zones and WUI applies to any of those. There are some very mild nuances to how WUI is applied depending on if it’s a high hazard zone or a very high hazard zone.  I think it might only have to do with roofs. I will back up to say, I’ve known enough to get through WUI in the past, but I’ve done quite a bit of digging in the last week or so to put this together. And there’s stuff that I didn’t know and have learned through putting this together. 

The other nuance to this is even though this viewer shows everything, or seemingly everything, that should be in a fire zone and would require WUI, there’s also a county or Local Responsibility Area, or an LRA as opposed to the SRA, which is the State Responsibility Area. And there could be an area that the state is not responsible for. That’s not going to show up on this map. 

fire hazard designations

This is just a slide showing the different designations for the fire hazard severity zones, very high, high, and moderate. If the project falls within any of those zones, it requires that we comply with the code section for WUI.

designing in wui

Designing in the Wildland Urban Interface

If you know that we are designing a project in the WUI, then we use chapter 337 of the California Residential Code, which contains those standards. To be honest, looking at standards in the code, doesn’t really help a lot, because once, you know something’s in the WUI, you understand how to design for it. Knowing what those codes are, is helpful for understanding roughly what needs to comply. An important note for everyone is that WUI does not require specific fire ratings, meaning it’s different, than the standard fire separations that we use in the code. The standard fire separations that we use are one-hour fire-rated walls, typically in our construction that we do in our office.

With WUI, it does not necessarily mean that we are using any fire-rated walls.  WUI is a completely different approach and a different section of the code. What we’re really looking at within the WUI is some level of fire protection, not necessarily tested by the number of minutes or the number of hours of fire resistance. They have their own way of testing and approving products for WUI compliance. That includes roofs, the roof material, the underlayment of the roof sometimes, eaves, and other projections. In this photo, there’s a canopy that comes out over the door. That’s something that we would want to make sure is compliant. The eaves are obviously part of that. If you have a bay window that’s coming out on the second floor, the underside of that bay window would need to be fire-rated.

If it’s not coming all the way down to the ground,  I shouldn’t say fire-rated. It should be compliant with WUI code using an approved assembly, your product,  and exterior walls and siding. And again, that’s where it’s important to remember, we don’t just throw a one-hour fire-rated wall into the assembly. It’s really more about the exterior cladding, windows, exterior doors, exterior decking, and stairs.  We’re looking at all the stuff that on the outside of the building that we’re designing, and making sure that all of it is going to be compliant. Once you know that we’re in the WUI zone, and you are familiar with the code, you know how to proceed.

Calfire listing

It’s a bit of a question as to whether that’s even required, the shingle is going over the valley flashing. So, that’s not something that we have to put in our drawings. We can have the city issue a comment if that’s something they’re worried about. The code says spaces created between roof coverings and roof decking are fire stopped by approved materials or have one layer of minimum 72-pound mineral surface. That’s probably just for Spanish tile roofs, where you have a gap and embers would be able to blow in underneath.

fhsz roofs

This goes into more detail about the listing service, and what to look for in those listings. It is mostly siding.

Decking is another product that we would look for. You could take this listing number, slap it on the drawings, put a box on the elevations, and if we’re calling out a particular siding, put a little box for exterior siding to be bodyguard wood products, rustic siding part number,  listing number 814 0. And that’s this number you can see here at the top of the listing. So that way, when it goes through plan check, and the contractor’s trying to build it, everybody’s on the same page and knows exactly what the plan is for addressing WUI requirements.

Wildland Urban Interface

So to get into the specific categories, the first category is roofs. Most of our projects are going to have a class ‘A’ composition shingle roof, which is going to be compliant with WUI. I was doing my research, and I found that there was part of the code that says, valley flashing should be at least 26 gauge, and installed over one layer of minimum 72-pound mineral surface, nonperforated cap sheet, and at least 36 inches wide. So basically, that’s saying we are supposed to have this sheet of very thick roofing felt underneath the valley flashing, which  I have never seen in a plan check comment.

It’s a bit of a question as to whether that’s even required, the shingle is going over the valley flashing. So, that’s not something that we have to put in our drawings. We can have the city issue a comment if that’s something they’re worried about. The code says spaces created between roof coverings and roof decking are fire stopped by approved materials or have one layer of minimum 72-pound mineral surface. That’s probably just for Spanish tile roofs, where you have a gap and embers would be able to blow in underneath.

roof class levels

So in practice, most of our projects will use a composition shingle class roof. Make sure we call that out on the drawings. This is where it gets into the nuance of the different FHSZ zones. If it’s not in a very high hazard zone, we can use a class ‘B’ roof, such as treated wood shakes. That opens up some possibilities for design potential if a client really wants a shake roof or something like that. 

The last bullet is roofing materials like concrete and clay tile. We create a gap that would require that heavy building felt be used on the eaves and other projections. This is where it gets a little more nuanced. The science behind this, and the theory behind the fire science and this code requirement is that when you have a wildfire, and it’s blowing embers,  100, 200, or 300 feet away, even if you’ve built your defensible space, you’re required to keep that space clear of any fuel.

eaves projection wui

This is where it gets into the nuance of the different FHSZ zones. If it’s not in a very high hazard zone, we can use a class ‘B’ roof, such as treated wood shakes. That opens up some possibilities for design potential if a client really wants a shake roof or something like that. The last bullet is roofing materials like concrete and clay tile. We create a gap that would require that heavy building felt be used on the eaves and other projections. This is where it gets a little more nuanced. The science behind this, and the theory behind the fire science and this code requirement is that when you have a wildfire, and it’s blowing embers,  100, 200, or 300 feet away, even if you’ve built your defensible space, you’re required to keep that space clear of any fuel.

If there are embers that are blowing from far away and there’s a wind or some sort of vortex blowing up the side of your house, it’ll pull those embers up to your cooler attic, and then they get sucked in and catch your roof on fire. And that’s what this part of the WUI code is trying to avoid. We have a couple of different ways of addressing eaves. These are kind of all the specific code requirements. The way that we can address them is we can either do an unvented eave, which just means we’re not pulling any air into the attic from the eave, or a vented eave, which means we are pulling air into the attic, but we have to use specific products to do that.

vented unvented eaves WUI

For unvented eaves, we would typically want to use a closed-cell spray foam insulation in the attic that creates a vapor barrier so that no moisture is getting into the attic. And, therefore there’s no need to ventilate. The alternative, which seems a little counterintuitive, but still works, is that we can put roof vents down the roof. So typically we have Hagans vents, further up, or our ridge vent. We can have them closer to the eave, still venting the attic, but, just past the eave, and past the exterior wall. The way that the embers are going to go is up to the eave. If they hit the eave, they’re going to eventually cool off and fall back down.

The embers are not going to blow around the eave and then go up into the attic that way. If we want to do a vented eave, then there are products out there that are put on the screen. When there’s no fire, the air is flowing freely through this honeycomb mesh.  The mesh is painted with a special material that, when heated, will expand and then it closes the vent so no embers can get in. We found that it’s probably easier most of the time to not bother venting from the eave. But if there’s a particular situation where we want to have that venting, these can work, and then any projection, like an eave, or porch ceiling, or underside of a balcony or bay window.

We can use Densglass gold for the underside. Then we can cover that with a textured material, like beadboard,  for aesthetic reasons.

Wildland Urban Interface walls

For exterior wall siding, these are the specific codes. There are basically two ways that we can address this. 

exterior fhsz

In most cases, we’re going to try and specify a material that’s listed on the Calfire website in the listing service. That way, we can avoid using Densglass, which involves building the wall out a little bit thicker, which contractors dislike. If we can’t find, a product that we like, and we really want to use something like Cedar shake, it isn’t going to work for an siding material. We would have to do the Densglass gold underneath, which is what we would do with a one-hour rated firewall, but we’re not required to do the inside. We are just doing the Densglass gold on the exterior windows and doors. 

wui doors

Straightforward windows, as long as they’re tempered, are going to comply, and doors, as long as they are solid core, are compliant.

wui windows

Or, if you have a patio door, a French door, as long as it’s tempered glass, it’s going to comply.

exterior stairs WUI

For exterior decking and stairs, you might have to go to the listings service to find a product. As long as we’re using 2×6 joists and 2×6 decking, it’s going to comply. That’s all we really need for a WUI-compliant deck. So we would find the listing number, and put that on the drawings.

WUI decking

YOUR PROJECT STARTS HERE

Get in touch with us. We would love to help you get your project off the ground