Retrofit an existing exterior wall to 1-hour rating
salarch
| Posted in Building Code Questions on
I have a small garage conversion project that is within the side and rear yard setbacks and requires one-hour rated walls, eaves for approval. Any thoughts and solutions that balance compliance and a small budget (i.e. demo and rebuild, exterior versus interior modification). USG wall assemblies suggest 1/2″ Ply and then exterior wall board (but the garage is now sided with lap siding).
Thank you
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Search and download construction details
Replies
Robert,
I don't know much about fire ratings for wall assemblies, so I'm hoping that a GBA reader can help. If no one shows up with advice, an architect could certainly help you.
Robert, some details of the current construction would be helpful. I'm not an expert on fire rating either but I know that Hardie makes fiber cement siding that is pretty much fireproof. I'm assuming the fire rating you are after involves fire spreading from neighbors structure and to neighbors structures. The fiber cement would definitely help with that. Whether that is both an economical or sufficient option for a 1 hour rating I just don't know. If you have to strip the existing siding to put up 1/2" plywood then it would definitely beat that if it was possible to put fiber cement over the existing siding. I'm talking about labor only because my understanding is it's somewhat expensive stuff.
It may be that there is really no cheap way of accomplishing what you are trying to do.
The answer may depend on what code or bylaw is driving the 1 hour rating. Our code only uses fire rated assemblies between differing occupancies or attached dwelling units. Structures too close to a property line are required to be of non-combustable construction. Municipal bylaws may take another approach.
Fire rated assemblies are often measured from both sides, the idea being they will resist the fire moving through the wall wherever it starts. Depending on what code requires the rating you may find the rating has to protect both your house from the neighbour and your neighbour's property from fire originating in your house. It's worth looking into as the implications may be you are tearing off not only siding but drywall too.