Where do fire and pest resistance fit in?

Building science question, and of course I'm interested in how this applies to materials and methods that fall under the "natural building" umbrella, though I'm also curious about how you'd approach this in conventional construction.

I feel like fire and pest resistance don't get talked about much as much as other aspects of house construction, leaving me with some knowledge gaps. This thread will hopefully fill some of those gaps.

Let's start with the theoretical "perfect wall"--see the diagram below. Ideally every exterior wall, and the roof too, would be formed like this.

Where do fire resistance (both from fires outside and fires inside) and pest (wood-destroying insects in particular) fit into the perfect wall? What sorts of products, treatments would be used, and if it isn't obvious, how do they work?

PS. In the US at least, modern houses with attached garages are required to have drywall on all garage walls and ceilings, ostensibly for the aim of fire prevention. I'm not sure, but some OSB sheathing products might be required to have a fire retardant treatment as well. (Fire-treated OSB is definitely required in some commercial construction applications.) But I don't want to put drywall or OSB in my house, so what are alternatives?

PPS. In Australia, aren't all the exterior-wall structural members of houses commonly treated for termites? And if they are, how are they treated? In any case, such treatment is not common in the US. Should it be?

Cob and plaster meet the fire resistance need.

The air barrier is the tough one for natural materials. Most of the other issues can be addressed by methods more than materials.

Ned, I think this is another one of those situations where people want a "building code" or a "best practice" that works for a whole country.

Alas, there's a *huge* difference in what a house needs in coastal BC, vs Ontario. A local builder friend told my son that many of the houses built here after 2000, used things like "house wrap" and "sealed everything", rather than the leakier houses built in the 1970'd. So what's happening is that these new, sealed houses are getting mold in the walls and are rotting from the inside out.

A concrete example: I kept getting black mold on the aluminium window frames in the bedroom. I'd clean it up, but it would just keep coming back during the winter rainy season. I finally insisted that Hubby move the portable dehumidifier up to the bedroom. I run it for 1-2 hours every morning in the rainy season and no more mold problem.

Similarly "code" says that so long as you have a window in the bathroom, you don't need a fan, so that's what the ensuite bathroom is like. A window doesn't actively exhaust the humid shower air - in our climate, it's just as humid outside as in! So that dehumidifier now gets pointed at the bathroom and run for 30-60 min after a shower. (We save the dehumidifier water and use it to wash our laundry, so it's not wasted!)

This is completely opposite to my sister who is always trying to *add* humidity to her house in the winter.

TLDR - how you manage risks is dependent on your ecosystem. I am considered to be in a fire risk area. Plastic siding would be out of the question. Concrete boards, or mud would be much safer! Metal roofing with very careful vent protection is also critical in fire areas.

Wood/plastic will always burn, because it's flammable. Wood will also attract pests and they will always find the way, because they are small, patient and come in thousands. Any cavity in framed building will be inhabited sooner or later.
Solid masonry solves these problems.

In terms of fire protections, you really should not be focusing as much attention on the walls as you should the roof.  Here in California entire towns are burning down even though they have stucco walls and clay roofs.  The biggest problems are exposed rafter ends that overhang the walls to keep the rain drip away from the foundations.  Blowing embers get lodged in the exposed nooks and crannies, and fire eats it's way into the building via the undersides of the roofs.  Keeping embers from getting caught is how you will stop a fire from spreading.  Also focus on ladder fuels right next to your building walls.  That means no plant grow immediately under the eaves of the roofs that can catch on fire, and bring fire up to the eave level.

Also have a fire-proof zone on the ground immediately off the walls.  I poured concrete sidewalks 360 degrees around my cabin to keep fire at least 4' away from the walls.

I think most of the strategies for keeping away fire will also help keep away pests.

Historically, cob, plaster, wool, bricks, ... and there was about 6 other wall "ingredients" we had to memorize for history class in university as suitable building materials under differnt medieval town charters specifically for fire prevention.  Towns were really big on enforcing fire prevention as every home in the middle ages had an open fire and several open flames like rush lights.

There was alot of restrictions on roof building.

Later, when fire places and chimney technology was accepted into England, there was a much higher risk of fire for about 300 years as people got used to how chimneys needed to be built, cleaned, and maintained.

When i lived in england, the house was built in the 1500s.  It was extremely comfortable, with only the baseboard heading and double glazing being upgraded in the 1990s.  It was more comfortable than any north american building.  I never found out how the walls were built, but they were beam and plaster like a tudor building.  

There are also examples from east asia of codification of prescribed building materials and practices in towns. The book Just Enough, is a good starting place.

A museum i visited in japan had houses that were 900 years old.  Construction was primarily wood and staw, with something like daub walls.   Each house had a fire within to prevent damage to the house.  A real fire in a house nearly a thousand years old!  In a recession in the middle of the floor.  The guid said the fire protects the house from decay due to weather, insects, fire, and some other things that didn't translate well.

I find it useful to look to history for solutions as there were thousands of years to get it right. What we consider modern building materials don't really reach the shape we know them until well into the 20th century.

r ransom wrote:... A real fire in a house nearly a thousand years old!  In a recession in the middle of the floor.  The guide said the fire protects the house from decay due to weather, insects, fire, and some other things that didn't translate well.

I find it useful to look to history for solutions as there were thousands of years to get it right. What we consider modern building materials don't really reach the shape we know them until well into the 20th century.

Like my coastal environment, many areas of Japan will have damp on-shore breezes regularly or seasonally. I can understand them needing a safe indoor heat source that is considered a "dry heat".

Some of the pressures which has led to poor house building in North America is 1) the push for a "mobile" workforce, 2) the sudden increase in the number of humans in the last 2 generations, and 3) the shift from multi-generational homes to nuclear families. I know of several communities where many houses were built post WWII that are solid and have lasted, but they clearly were rush jobs and rely on cheap energy to be comfortable to live in. They were also around 1000 sq feet on the main floor which is considered very small for a modern family even though our modern families are much smaller than the average 1950's families were.

Adding on to what the others have said, and responding to the wall construction diagram....because different materials bring different properties to the table you end up combining or dropping various elements of that construction.

Strawbale is famously incompatible with a vapor barrier, for example. It *must* be vapor permeable.

Other materials may give you fire or pest resistance, but require an additional layer to keep the sun or rain off them.

Rather than thinking of a wall as a collection of replacable parts which do different jobs, it seems more common to think of a set of wall materials as a system designed to work together, with the various materials metaphorically leaning on each other to get their strengths and offset their weaknesses.

People's comments on traditional building techniques being more fire resistant than modern ones are generally correct (cob and strawbale and lath/plaster all greatly outperform wood framing with concrete siding, i can find the test data to prove that if people need it) but not all natural systems are better.

I think japanese building in particular traded heavily for other benefits (airflow is a major design consideration leading to movable walls but also entire house designs built to induce crossflow drafts...) but those houses are famously fire prone. Japanese cities regularly burned to the ground in the pre-industrial era, and they gave up on putting fires out, favoring demolition of whole blocks to starve the fire instead of trying to put it out. Japanese firefighters were more demolition experts than fire fighting experts. I think that speaks to how fire prone the wood and paper construction approach is.

Premodern tokyo burned so often it became known as the "city of fires" and a whole culture of spending lavishly developed because nothing in your home could be counted on to last. https://en.wikipedia.org/wiki/Fires_in_Edo I remember this contributed to the development of expensive geisha houses, who could make a dinner worth spending on, if you had the money.  People preferred to live loudly with the experience that the city was going to burn down and they would all start over sooner or later. The city lost huge portions of its buildings by fire 85 times in 350 years.

Thats a ridiculous tangent, but just more attempts to show that not all premodern building styles are more fire resistant than stick frame and plastic.

Indeed, good comments. I meant to specify in the OP that, for hypothetical purposes, let's assume wood framing.

Some natural building techniques have other drawbacks unrelated to performance. For example I think adobe is really cool, it's amazing actually, but an adobe wall has to be something like 18" thick for every 10 or 12 feet of height. (I might have the exact numbers wrong but that's in the ballpark.) That is pretty limiting if you want multi levels, and it really eats into the liveable floorspace of your footprint.

Traditionally for adobe it's assumed for the height to not exceed 10 widths of the wall, because the material is rather weak. Multilevel adobe does exist in Sanaa, but in most cases it's used for single floor construction. If I needed to build higher than one level I would use fired bricks/stones and either heavy timber ceiling/floor or vaulted ceiling/floor (which would require sufficient wall thickness, buttresses or bond beams to resist vault's spreading forces).
SIRE rammed earth allows for quite tall buildings. This one is 51 feet (15 m) tall:
https://sirewall.com/project/brinton-museum/
but it uses concrete slabs for floors so they definitely help to stabilize it. I think that SIRE wall could be the future of building materials, but at the same time I do not like it, because it's better fit for modernistic architecture and it would difficult to add architectural details within rammed wall that can be easily created with block by block (and brick by brick) construction.

For fire resistance adobe or solid fired brick walls (exterior and interior) would be the best. For stones - variation of their crystalline structures could make them behave in less consistent manner. Concrete, concrete blocks or lime block would be less resistant, because cement/lime starts decomposing around 400 C.

Masonry vaulted ceilings would be the best protection, followed by heavy timber roof structure. For timber - hardwood would be more difficult to ignite than softwood.
If timber is used for the roof, it's crucial to protect it by continuous masonry cornice traditionally built in the past from stone and in second half of the millennium from bricks. Not only it protects, but it makes the house looks next level better - by creating geometric border between the walls and the roof surfaces.

The roofing material of choice would be ceramic, followed by stone, concrete tiles and then metal. In case of masonry roof structure it would not matter much, but for timber one, the ceramic/stone tiles would be the best, especially if laid on clay mortar that would provide a lot of mass to absorb heat.

The next defense would be external metal shutters which protect the interior of the house from quickly heating by the sun (in fire prone areas usually extremely intense) but also protect the windows/interior from flying embers and heat radiation (if neighboring house is on fire). They would help immensely and are in regular use in southern Europe, but in US they were reduced to some plastic, non-functional, "decorative" gimmick. Very sad.

Painting the house white also helps to lower house overheating, but would also make it more resistant to infrared ignition. I'm astonished to not see more houses painted white in the sunny West//Southwest.

I call it "passive" fire proof design that will work without any maintenance, electronics, water, etc.

Of course no vegetation close to the house, would be the first and easiest area of improvement.