Need a book? Engineering books recommendations...
[SEAOC] Re: [SEAOC] ridge vent in wood roof diaphragm[Subject Prev][Subject Next][Thread Prev][Thread Next]
- To: seaoc(--nospam--at)power.net
- Subject: [SEAOC] Re: [SEAOC] ridge vent in wood roof diaphragm
- From: BCASE1356(--nospam--at)aol.com
- Date: Thu, 12 Sep 1996 02:30:47 -0400
Rick, Take a look at section 1505.3 of the 1994 UBC which covers the requirements for required ventilation area at the eaves in the attic space. In custom homes this can be a problem since you may only be able to place the vents in two of the walls because of gables at the other two ends of the roof or because of stepped changes in roof elevations adjacent to interior rooms. You may want to make the vent opening in the block larger (5"x12" in a 2x8 block and cover with a screen) and require that only every third block can be a vent space. This may require that the roof sheathing boundary nailing will have to be spaced closer together since you have fewer blocks for the shear transfer. You might have four different nail spacings: boundary, continuous panel joints, edge and field. Also make sure to provide shear transfer at blocking not directly above the shear wall since the top plate is going to have to act as a drag. The framers often seem to forget A35's at blocks not directly above the shear walls. Ideally you may want to try and get some of the vents placed furthur up the roof towards the ridge as allowed by the code to reduce the number of vent spaces. On one job, when I got the permit set from the architect, I found that he had placed a vent opening (3"x12") in every other block (rafters are at 16" on center) to satisfy the code requirements. Also, if you are using a raised foundation, you may also want to take a look at where the vent holes are located. Most likely they are right under the shear walls, especially if you have lots of doors or full height windows along the perimeter walls. Depending on the number of vent openings, you may no longer have the shear transfer capacity that you thought you had to the foundation Michael Cochran Brian L. Cochran Associates Los Angeles ------------SEPERATOR------ In a message dated 96-09-11 16:00:39 EDT, you write: << ubj: [SEAOC] ridge vent in wood roof diaphragm Date: 96-09-11 16:00:39 EDT From: rburchpe(--nospam--at)worldnet.att.net (Rick Burch) Reply-to: seaoc(--nospam--at)power.net To: seaoc(--nospam--at)power.net (seaoc(--nospam--at)power.net) On pitched (gabled) wood roofs using plywood sheathing over either prefabricated wood trusses or stick-built rafter framing there quite often is a continuous ridge vent, which requires a continuous opening in the diaphragm a couple of inches wide along the ridgeline of the roof. 1. Does anyone have advice on how forces in the diaphragm are handled at this opening? In conjunction with the ridge vent (for air flow out), there often are continuous soffit vents (for air flow in) to provide the code-required ventilation of the attic space. Blocking in the spaces between the trusses for tranfer of diaphragm forces to the top plate unfortunately blocks this air flow. 2. Does anyone have advice on how these two conflicting requirements (structural force transfer vs. architectural ventilation requirements) can be handled? Rick Burch Columbia, SC ...
- Prev by Subject: [SEAOC] Re: [SEAOC] ridge vent in wood roof diaphragm
- Next by Subject: [SEAOC] RE: [SEAOC] Rigid frame with masonry walls
- Previous by thread: [SEAOC] Re: [SEAOC] ridge vent in wood roof diaphragm
- Next by thread: [SEAOC] Comply Sturdi-Floor