Basement Sprayfoam vs vertical fireblocking

SERDIYER

I searched for an answer to this particular problem on this site and several others. This question gets asked, but is usaully de-railed by another well meaning DIYer who clouds the issue by asking other important questions.

I'm about to start a basement finishing project. I've researched enough to know that I will be building 2x4 studded wooden walls about 1" off of the poured concrete foundation walls. I will be having a spray foam insulation contractor spray foam the rim joist area and all basement walls with 2" of closed cell spray foam. The often linked Building science articles have convinced me that this is the best insulation approach for this project.

Local building code requires that I place a fireblock every 10 ft. along the studded wall. So using standard fireblock techniques I must use 1/2" drywall or other suitable wood / metal product every 10 feet and have it touch the concrete wall of the basement for the entire height of the stud wall. So here is my question: Won't having wood or galvanized metal touching the concrete wall every 10' the entire height of the wall violate the design principles outlined in the building science report on basement insulating?
Even if we spray foam everything wont we have a moisture/mold/rust issue every 10' ?
This vertical fire block is not optional. Any suggestions / comments?

mae-ling

That is new to me. Usually fire block goes at a height of 10' not every 10' along the wall.
Maybe you are misunderstanding? Or you might have a different code.

SERDIYER

I guess I may have misread the requirement. Are you saying there are no requirement to place a fireblock behind a basement wall to prevent fires from horizontal propagation?

SERDIYER

2006 IRC - R602.8 Fireblocking required.
Fireblocking shall be provided to cut off all concealed draft openings (both vertical and horizontal) and to form an effective fire barrier between stories, and between a top story and the roof space. Fireblocking shall be provided in wood-frame construction in the following locations.
1. In concealed spaces of stud walls and partitions, including furred spaces and parallel rows of studs or staggered studs; as follows:
1.1. Vertically at the ceiling and floor levels.
1.2. Horizontally at intervals not exceeding 10 feet (3048 mm).
2. At all interconnections between concealed vertical and horizontal spaces such as occur at soffits, drop ceilings and cove ceilings.
3. In concealed spaces between stair stringers at the top and bottom of the run. Enclosed spaces under stairs shall comply with Section R311.2.2.
4. At openings around vents, pipes, ducts, cables and wires at ceiling and floor level, with an approved material to resist the free passage of flame and products of combustion.

SERDIYER

Thanks for the reply, but I have read and re-read this and I do not think I have misread it.
This is the section of building code requirement that I am concerned about:
Snipet from code:
Fireblocking shall be provided in wood-frame construction in the following locations.
1. In concealed spaces of stud walls and partitions, including furred spaces and parallel rows of studs or staggered studs; as follows:
1.1. Vertically at the ceiling and floor levels.
1.2. Horizontally at intervals not exceeding 10 feet (3048 mm).

I read this to mean: I need to deal with potential fire propagation horizontally as well as vertically in the void space behind my stud wall that is 1" - 2" off the basement conrete wall. To address this I assumed that I must place a suitable fireblocking material that bridges the gap between the stud wall and the basement wall every 10'. This will stop horizontal fire propagation. I will of course also need to put a fireblock material at the top of the stud wall as well.


Am I reading this wrong?

Cerberus

Isn't the spray foam going to bridge the gap between the studs and the concrete wall? If so, why do you need a special firebreak? I know that canned spray foam insulation is used for firebreak purposes in closing off duct pass-through holes and so forth... why should this be different?

Anti-wingnut

You are correct, generally an area which may act as a fire plenum must be kept below 100 sq ft, or another measrement as per the AHJ.

1) The sprayfoam may have a flame spread rating, and be acceptable as a fire block

2) You are worrying way too much about thermal bridging. Way too much

Minich

They do have fire-rated spray foam that could be used at appropriate intervals.

SERDIYER

First: I am glad that I read the code correctly.

Cerberus: My thoughts exactly, but alas closed cell spray foam (at least the foam that I will have sprayed on the walls) is considered a combustible material. I assumed that the building inspector would fail me if I used the spray foam bridging that you just talked about.

I am more worried about this vertically mounted material (whatever I choose) being a moisture wick/mold problem.

Here is my current thoughts about how I'm planning to do this: (Not actually my thoughts, but the spray foam contractors thoughts)
He has seen other contractors use 1/2 drywall sheet about 4" wide nailed vertically along the full height of the stud wall every 8 ft (every 6 studs), and brought into close proximity of the basement wall, but not actually touching. The spray foam contractor then comes in behind it with the spray foam. The spray foam will fill the small gap along the edge of the drywall to minimize any moisture transmisison issues, and the rest of the space is filled with sprayfoam as normal. The entire studd wall and concrete wall will become one solid mass as the sprayfoam bridges the gap between the wall and the studs.

BTW: My wife agrees with the person saying I am too concerned with this. My wife thinks I am nuts!.

Does anyone have positive or negative comments on my proposed solution?

Anti-wingnut

So what if it considered a combustable material? So is wood, and fire blocking is typically wood.

Ask your inspector

Cerberus

My understanding of a fireblock is air and smoke control, not flame. Seems like foam should be enough?

SERDIYER

I think Anti-wingnuts had it right. Ask my building inspector and see what he will allow/not allow. I have this "the building inspector is not my friend" mental block that I must have developed from my early childhood days of watching my dad "work around the house"

TarheelTerp

The term "fire rated" doesn't mean fire proof.
It means the material used has a reasonable expectation of remaining intact for X hours before changing state (burn, melt, etc) which should allow time for people to exit safely after alert.

It is safe to say that 2" framing lumber will remain lumber in the presence of high heat (and even some flame) far longer than a styrene composite will remain... well anything even recognizable.

hth

leungw

Serdiyer, check out the thread below. It started with a different question but ended with fireblocking related topics.

Putting Up XPS On Basement Walls

I did rigid foam and used treated 2x4 every 10ft against the wall. (GBR later replied saying that wood's not required to be treated since it's against concrete and not on concrete.)

Hope this helps.

EvilNCarnate

There is a fireblock thread in the how to section of this forum and "Termite" would be able to answer all of your questions (based on my reading).