Your architect should be able help you make these decisions. If you want my opinion I would need to read the ordinance to know if the requirement is for a UL Lab tested fire-resistant-rated exterior wall or just for non-combustible siding. There would be a big difference in the construction of each.

Only complete tested wall and floor assemblies have fire-resistance-ratings not individual materials. Plywood is combustible but can be fire retardant treated (FRT). Some codes will consider FRT wood to be non-combustible.

The requirement in the IRC is for a wall that has received a 1 hour test rating (using ASTM E119 or UL 263) with exposure from both sides. That requires finding a published design from a testing agency like UL Labs etc. One that should work is UL Design No U330. It consists of 5/8" type X interior GWB, 2x4 wood studs, mineral wood batt insulation, 1" foam insul. board, 1/2" plywood sheathing and whatever siding you like. Look up the design for more detailed information.

But whatever is required must be clearly stated in the ordinance or clarified by the building dept.

This post was edited by Renovator8 on Thu, Sep 18, 14 at 13:46

Since building codes usually only require residential exterior walls and eave projections to be 1 hour fire rated when they are LESS THAN 5 feet to property lines or other structures, why not simply have the architect redesign the bump-outs and eaves so that they are at least 5 feet5 feet... (not 4 feet)... from your property line... and then NOTHING has to be fire rated at all!

Or locate the house 1 foot closer to the opposite property line to avoid the fire rating issue altogether!

This sounds more like your real issue is the designer who is either being too inflexible or not creative enough to solve your setback problems without resorting to costly (and totally unnecessary) fire rated designs....

Above should read:

"...why not have the architect redesign the bump-outs and eaves so that they are at least 5 feet...not 4 feet...from your property line...and then NOTHING has to be fire rated at all!?"

This is an inner city, urban build. A standard lot is 25'. The setbacks are 4 feet on either side. The bump outs can be up to 3 feet, and could potentially be on both sides. So, if I squish the house to fully within the setbacks, my house would be less than 11' wide. 9' if I made the setbacks 5'.

The architect spec'd the minimum required. When I confirmed with him that's all that's required, he suggested we might want to do more. So, is there a benefit to doing more than is required in this case?

Only benefit would be if your neighbors house caught on fire. Realistically if your house is going to catch on fire at 4 ft it will catch on fire at 5 ft. The other side to that is if your neighbors house is really burning, fire rated sheathing is not going to do very much anyway.

It's difficult to advise you with confusing statements and no code text or reference.

Wouldn't the width between the setbacks be 17 ft not 11 ft. I can think of no reason to not follow your architect's advice. The fire risk is a serious issue. But my concern would be any windows in these side walls.

What is confusing about this post is that in the US FRT sheathing has no fire-resistance rating only a flame spread and smoke contribution classification and it does not improve the fire endurance of a fire-rated assembly such as a one-hour exterior wall to any significant extent. Why it would be specified or required inside of a wall assembly that might be exposed to a fire in an adjacent building is puzzling.

The only time I have needed to use FRT wood framing was in a non-combustible multi-family structure and it would not have been acceptable in many others states.

In a wood framed building typical US codes are concerned with limiting the temperature of a wall surface on the opposite side of a fire for a specific amount of time and for the assembly to still be intact after a hose stream test.

If I were the architect I would not be concerned with FRT sheathing where not required but the construction of the wall to provide adequate fire protection which so far appears to be missing.

The use of a wood fiber and concrete composite siding would have little or no effect on the time inhabitants or the fire service will have to do what they need to do. If the goal is to save property a sprinkler system should be installed.

This post was edited by Renovator8 on Fri, Sep 19, 14 at 13:11

I just checked and saw that the project is in Canada so the mystery is perhaps solved. However, I would not change my advice about the design of the wall.

Fire does not penetrate a wall by burning through layers. High temperatures can reach the inside materials before that happens. The best non-masonry material is gypsum wall board because it releases water vapor at high temperatures. FRT panels are for exposed wood not fire protective assemblies. Your architect should understand this.

This post was edited by Renovator8 on Fri, Sep 19, 14 at 14:08

I'm in Canada, so that's why US codes are confusing you.

But, it's been cleared up this morning. I don't actually need fire protected sheathing in the finished home. But I need it while the house is being constructed, until the siding is on.

I'm told that if a fire starts on my site, the inside of the fire rated OSB will burn faster than the outside, and it'll collapsed inwards, and not spread to the neighbour's house. The fire department doesn't give a rat's ... if my partially constructed house burns, but they don't want to have to deal with it spreading to the finished house next door, where people are living.

The important issue is what is the fire-resistance rating of your completed wall. The fire department is responsible for protecting occupied buildings; you are responsible for protecting yours with the assistance of your architect and contractor. Good luck with it.

Since your lot is so narrow, why not make the most of it by building with noncombustible construction rather than conventional wood framing?

Poured concrete, concrete block or concrete panels could be used to make the exterior of the structure virtually fire 'proof'...especially if covered with brick or stucco.

This way you can maximize the width of the house providing maximum interior usable space while also providing the maximum fire safety for you and your neighbors.

That said, window and door openings on the sides should probably be eliminated in that case or be truly fire rated protectives

Other openings such as vents and open soffits would need to be eliminated on the sides for the most part.

But by doing a non-combustible design, you could get more usable space and a quieter and safer structure at the same time....and doesn't need to break the bank.

Again, this all goes back on the designer.

I would be interested to see how a 17 foot wide house could have no windows on the side walls.

I doubt these issues would be determined by the designer since windowless spaces would most likely be determined by owner preferences and building code requirements.

In these inner city lots, 17' wide homes are very common. And there are very few windows on the sides. In my case, I have 1 window, and it's a clerestory window in the bathroom. The rest of the rooms on that side have closets, a fireplace (no issue whatsoever with fire safety there, apparently), and kitchen cabinets. The neighbour's house has some small, frosted windows in the stairwell. We minimized them on that side as we'd just be looking at the neighbour's house anyway.

Another common style is a semi-detached home. On the minimum 25' wide lot, you have to build 4' from the property line, unless you're attached to the other house. So developers can put in 21' wide homes if they build them semi-detached. So there's absolutely NO windows on the one side. The other side has minimal windows as it's just a few feet from the neighbours.

Windowless spaces are entirely allowable and permitted under US International Residential Codes... provided that:

A) Illumination is provided by electrical means or through adjacent spaces...(R303 2009 IRC)
B) Ventilation is provided by mechanical means or through adjacent spaces...(R303 2009 IRC)
C) Emergency Escape and Rescue openings are provided in bedrooms...(R310 2009 IRC)

Within these rather 'broad' code parameters, it is entirely conceivable and permissible and even practical to design 'windowless' rooms given the circumstances.

That said, a build of this type, remains largely at the mercy of the designer...and in my humble opinion....this designer could do far better given the restriction of the space.

But if the designer has no willing client to accept his recommendations, then what can any of us hope to say?