Today's Smaller, Tighter Lot Size Focuses More Attention on Fire Separation Distance

It’s no secret that many developers, architects, and home and multifamily builders are reducing lot size as one way hold down housing costs and maintain profitability. 

The rise of zero-lot-line homes, odd-lot/infill development, and compressed parcel spacing and size is helping shape a new housing normal for many communities:

• The nation’s leading new home research authority, Metrostudy, recently reported the average home size in the top 15 housing markets has fallen the past two years.
• The U.S. Census Bureau declared in late August the median lot size of a new single-family home has stubbornly remained at a record low size the past two years, just under 8 600 square feet. By contrast, the average lot size in the early 1990s was 10 000 square feet.
• In Nashville, older homes are being torn down and replaced with two “tall skinny” homes on a single lot.
• In California, a new class of detached homes are now offered in the 1 000 to 1 400 square foot range. Tiny, yes. But for housing-strapped California the modest 150 000 $ to 175 000 $ price tag is a revelation to homebuyers accustomed to prices many times that.

Emerging Housing Category

For many code professionals this trend line means unconventional lots and home configurations will become an increasingly common feature of residential development. In many parts of the country new terminology is taking root to describe odd lot variations and locations, including:

• Slice
• Triangle
• Leftover
• Alley
• Abandoned right-of-way
• Wedge
• Tandem
• Center block
• Undersized
• Back-lot
• Shallow
• Driveway
• Internal court
• Gateway

Affordable housing advocates, developers, architects, and builders now view the non-conforming parcels as new opportunity areas for residential construction. For example, Boston's downtown is widely viewed as densely developed. In fact, downtown Boston has a robust supply of odd lot parcels that have been overlooked for commercial development. Today, many of those lots may be prime targets for opportunistic housing developers.

10-Foot Wide Homes?

One of the leaders in this housing movement is Jonathan Tate. Tate is an architect and principal of New Orleans-based OJT, a design practice focused on infill housing development. Tate estimates there are more than 5 000 irregularly shaped empty lots in New Orleans. Where others see an unbuildable lot, Tate sees a new, affordable single-family home.

"There are a lot of land fragments embedded in these neighborhoods that you could probably mistake for somebody's side yard," Tate explains. "One of the first houses we did was on a lot 16-and-a-half feet wide. We ended up having three feet clear on either side, so it's a 9-and-a-half foot wide home. It's not for everyone, but it's a great home. We recognize now if a lot is any less than 16 feet wide, we move on."

2018 IRC Implications

Tate admits the dense building practices of New Orleans may offer some advantage at inspection time. Yet, the unusually tight lot lines do generate close scrutiny from code officials. Nonetheless, Tate has elected to avoid requests for waivers and variances. Rather, the rules are the rules. "What can we make within them?" Tate asks.

For urban infill construction, fire separation distance is a critical consideration. Section R302 of the 2018 International Residential Code – Fire-Resistant Construction – describes the requirements for fire-resistance within close proximity to adjacent property lines. Section R302,1 requires exterior walls within 5’-0” of a property line or adjacent structure to have a fire resistance rating of 1-hour, rated from the interior and exterior. Louisiana-Pacific has a load-bearing wall assembly, LPB/WPPS-60-01, that is commonly used in this application when a 1-hour fire resistance wall is required and is in compliance with Table 302.1.

ICC-ES Evaluation Report (ESR) 1365 describes a tested sheathing product that is compliant with the 2018, 2015, 2012, and 2009 International Building Code for surface-burning characteristics, durability, thermal barrier, component of fire-resistance-rated assemblies, and component of roof covering classified assemblies. As ESR-1365 states, “The product is a composite panel consisting of a layer of Pyrotite^® – a noncombustible inert, inorganic fire-shield – factory-applied to either plywood or oriented strand board (OSB) complying, respectively, with US DOC PS1 or US COC PS2.” The Report evaluated LP^® FlameBlock^® Fire-Rated Sheathing.  

Watch for Code-Compliant Sheathing

Today's growing emphasis on smaller lot sizes and compressed lot spacing casts an even brighter light on fire separation distance. More than ever, look for exterior wall sheathing products that meet ICC certification for flame spread and burn-through resistance.

 

The views and opinions expressed in this article are those of LP and do not necessarily reflect those of the International Code Council, or Hanley Wood.