Townhouse fire wall... contractor screw up

[Jmeng1026]

See the attached detail. The contractor used purlins instead of plywood so the 4' of fire retardant plywood was not installed. So a fire could burn up and over the fire wall due to the purlins. Is there a way to remedy this other than removing the metal roof and plywood and installing the four foot fire retardant plywood? Some kind of fire caulking?

Thank you for the help.

 

[Aesur]

I don't follow what they actually built, could you provide a sketch of what was built as well?

As for firewalls, this should also be coordinated with the architect as it's their assemblies as well.

It would also help to know which code provision you are looking at for the 4' requirement as there are a few locations in the code that have that requirement. It appears you are referring to 706.6?

 

[SwinnyGG]

So the contractor installed purlins to support the roof, parallel to the page (90 degrees to the wall shown)?

How thick are the purlins? Is the head of that wall shorter than it should be by 3 1/8"?

If so, you may have bigger issues than just the fire rating of the assembly, depending on how packed with utilities the plenum space is designed to be.

If that's not a problem, there's probably some type of spray applied fire protection that will get this assembly up to whatever rating is required, but it's going to be expensive. If the contractor truly had this detail, they should bear whatever costs it takes to get the assembly up to its design rating, or tear it apart and build it back correctly.

 

[Jmeng1026]

Attached is a detail of what they installed. Basically instead of fire retardent plywood on top of the trusses the installed 2x4 purlins.

This is in regards to R302.2.4 Parapets for townhouses.

Why should the head of the wall be shorter by 3 1/8"?

 

[Brad805]

Your architect most likely used a ULC tested assembly, so they would need to review this change.

 

[Jmeng1026]

I am from a small town where there aren't really architects. Engineers prepare the plans and stamp them.

The firewall is based on a UL assembly.

The code official will want some documentation that it meets the 2 hour fire separation.

 

[Brad805]

I am from a small town as well. We work with out of town Archs frequently. I assume the building is of a size that this is permitted.

I talked with someone from my office and they thought you would need to block between the 2x4 and extend the GW to the U/S of the roof. You could check the UL or ask the contractor to hire an Architect to provide you a report stating his substitution meets the requirements dictated in your dwgs.

 

[SwinnyGG]

Why should the head of the wall be shorter by 3 1/8"?

The detail shown shows a sheet of fire rated ply capping the wall assembly, and then (I assume) roof assembly directly on top of that ply.

2x4 purlins are taller than 1/2" ply. So either the head of the wall moved down to accommodate the added depth of the purlins, or the bottom of the roof assembly moved up.

 

[Aesur]

Interesting installation, what threw me off is the use of the word purlins instead of decking. I don't typically use the IRC, but suspect short of a UL assembly allowing such construction that the only option may be to rebuild it.

It should also be noted that you should review lateral as replacement of sheathing with planks doesn't yield similar capacities - again though this is when it's an engineered solution, not sure how the IRC handles this.