Room Addition Construction Questions

[travispremo]

Hi everyone. My family and I moved into Shores earlier this year and we're already dreaming up our room addition. I have a background in residential construction in California, but I am unfamiliar with several building methods used on the Big Island. After years of building homes and room additions with 36" deep full perimeter footings, concrete grade beams, steel/laminated structural members, and a full envelope of structural sheathing, it is quite relieving to see the light-weight methods used here. This is likely my first question of many, but I'll get the ball rolling.

When framing up the roof of a room addition, what methods are used to tie the existing roof in with the new? In California it was as simple as placing 2x nailers to the exposed roof sheathing along the new valleys, providing a post on the existing home's exterior wall to carry the ridge beam, then stick framing the rafters between the nailers and ridge beam. With many of the homes here lacking roof sheathing completely, opting for sheet metal roofing directly on purlins, and the use of trusses, how do builders do it out here? Is it necessary to remove the existing roofing material to expose the purlins and existing trusses, then frame on top of that? Is it possible to frame on top of the existing metal roofing in the interest of keeping the existing home watertight during construction?

Thanks in advance everyone.

[hotinhawaii]

You don't want to frame over the existing metal roofing. It is not able to bear structural weight for one thing. Also, it makes it impossible to flash the new addition properly. And you are creating a nightmare for whoever replaces the roof in 20 years. You have to take the metal off.

[travispremo]

As I suspected; and thanks for the reply. I've seen it done with asphalt shingle roofs. Of course asphalt shingles are thin and dense enough to not be affected by the weight, and can be cut with a utility blade when it comes time to stitch in the valley or install valley flashing.

Can a local truss builder (like HPM) manufacture a truss system for the portion that extends over the existing trusses or must this be stick framed?

As far as that framing over the existing roof goes, I guess speedy framers, with roofers close behind, is the way to protect against rain? Or do builders simply have plenty of tarps ready to cover it over at the end of the work day?

Thanks again for the response. It's great to finally have access to people with first hand experience.

[hotinhawaii]

HPM can build whatever trusses you want. Speedy framers, roofers and tarps are the way to go.

[DanielP]

What are the details? Are you adding a gable roof butted perpendicular to an existing shed or one side of a gable roof to form 2 new valleys?