the roof aspect of an addition to a mobile home

[maryella1]

I'm aware of the need to have the addition to my mobile home on it's own foundation. What I would appreciate is any advice as to how to attach the roof to the existing mobile home. At present, I have a metal roof. Can i just "flash" the roof to the addition? thanks you. and I live in Vermont, so snow is always a factor. mary

[JD]

Hi Mary,

First of all, I have next to zero experience with snow or ice dams on roofs but this is what I have learned from working on mobile home roofs for over 20 years. As you mentioned, a built add-on room needs to be free standing and not structurally connected to the main coach. This means, no ledger boards and the wall framing of the room is not to be anchored directly to the framing of the main coach. The side walls can be sealed with trim or flashing.

For the metal roof, I recommend that there be some amount of "step down" from the main coach roof to the add-on room roof. Basically, if you try to line up the two roofs to be on the same plane, you are asking for chronic leak problems. This step down does create a problem when designing your add-on room. You usually need as much height as you can get at the main coach's eave wall to be able to maintain the minimum 90" ceiling height in your add-on room. Usually I will keep an add-on room or awning height at least 1" below the main coach's roof drip edge. See drawing below. That 1" leaves enough room to fit the flashing in under the drip edge of the main coach. This allows me to totally seal the flashing as well as perform maintenance on the drip edge and flashing.

Trying to install flat flashing from the top of the main coach to the top of the add-on room is just like installing a metal patch on top of a roof. It can work for a while, but eventually they fail. Some people might get lucky, but most of the ones I see create problems.

JMO
JD

[Greg]

JD is right about the step down roof, and you may want to think about a step down for the floor also depending on what you will have for head room.

I'm thinking that we need to get JD "Up North" for a while so he can claim a little more experience with snow & ice dams. Greg

[DoubleWideDrama]

JD can come to my house... we have plenty of issues with snow and ice dams!!! Then I'll put him to work while he's here ;o)