How To Look At A House
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site-built, mobile/manfuactured and modular homes
Why is it a dangerous mistake to attach a carport, porch, or room addition directly to the roof of a mobile home?
Tuesday, May 14, 2019
When the roof structure of an addition is attached directly to the roof of a mobile home, failure of the addition under the uplift force of high winds will often strip off the roof of the mobile home and cause other major damage to the home. Here’s couple of examples documented by the Federal Emergency Management Agency (FEMA) in a 2007 report on the performance of mobile homes in “high wind events."
Here’s what the FEMA report says:
"The potential for damage to manufactured homes increases significantly when additions like carports, awnings, or porches arefastened to the home. These additions concentrate wind forces where they are fastened to the home.The increased forces can overload connections used to hold the home together and cause failure of the members or connections in the home.
Most home manufacturers prohibit attachments to their homes unless special provisions to support attachments were incorporated into the home when it was manufactured. The attachments themselves, unless engineered, also violate local code requirements in many jurisdictions."
Mobile homes are not ordinarily engineered and manufactued to accept any additional loads on their walls, so there are two ways to correctly install an addition to a mobile home:
- Have the manufacturer install a “host beam” in the wall framing of the home when it is built and specify piers and tie-downs rated for the added load imposed by an addition, but both by gravity and windstorm uplift, so that is ready to accept an addition. To learn more about this option, see our blog post What is a "host beam" at a mobile/manufactured home? Or, if your home was not pre-engineered for an addition, then...
- Build the addition as a freestanding structure, not bearing on the walls or fascia of the roof of the mobile home, and install a flashing to connect the old and new roofs. Here’s an example below.
And an example of the wrong way to do it.
Also, see our blog post What do I need to know about building an addition to a mobile home?
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