removing tin after trussed roof over?

[yukontrevor]

Hi I have mid 70's mobile with full length addition. At some point previous owners added another outside wall and trusses over top of whole thing. I want to add more insulation over the trailer part of the roof. A few local contractors have suggested the correct way to do this is take a skill saw up in the roof and rip the tin along the trusses and roll it up. This way the additional insulation is directly on top of the insulation that is already in the mobile home roof. This way there is no air gap between insulation layers. Does this sound reasonable and the correct way to do this.

I am removing ceiling tiles, strapping with 1 x 4 and then drywalling on ceiling and walls. Planning on using 1/2" drywall x 12 footers so limited joints.

On the walls I have choice of putting drywall in verticle and having no but joints or using longer sheets and putting them horizontal. Not expecting much movement in the trailer, which way would reduce the chances of joint cracking?

thanks

[JD]

It is hard to say how difficult it would be to "roll the metal" back. If the added trusses has a bottom cord on or near the metal roof, there will be very little room to work. The metal is not all that easy to open up in a closed space.

The next question would be "How effective would this insulation be?". Air moves like water and takes the path of least resistance. Ceiling insulation should be of consistent thickness and/or R value. If not, the cold or hot air (whichever you are trying to keep in the house) will bypass heavy insulated areas and flow to the less insulated area. In the end, the house is only insulated as well as these lesser areas. Now with the majority of air flowing to limited areas, it carries the air moisture for the entire room to these limited areas. Mobile homes with metal roofs only have about 2.5" of height at the eave wall where the edge of the metal is bent. This height grows as you move to the ridge area, but a lot of these homes only have 10"-12" of height at the ridge, so the rise is very small, about 1" in 12". Some homes will have more pitch, but the space is still limited, and extra space is non-existent at the eave.

So unless you are able to insulate evenly, the added insulation will have limited effect. It would mostly redirect the air loss. Also keep in mind that there needs to be some air flow over the insulation, within the closed space. I know that this is also non-existent at the eaves of metal roof homes, but that is just the way they were made.

JMO

[JD]

Joint cracks in drywall texture is a part of mobile home life. It is unlikely that you will get by unscathed. If the home is stable and there are no frost heave problems, you could go many years without cracks.

The main suggestion I would have is to plan out your drywall so the you won't have seams at the sides of doors and windows. The marriage joints and these doors and windows is where the cracks like to happen. I know this sounds too simple to talk about, but every factory drywall job I have seen slides full sheets or drywall up beside the windows and doors and then fill in the blanks over the tops and bottom spaces. This is the wrong way to do it as it makes cracks much easier to happen.

[yukontrevor]

I have tons of room to work above the existing roof. I can stand up at the apex. Bottom cord is 18" of so above existing roof. I can get more insulation pretty evenly layered. The big thing I am wondering is about the logic of removing the old tin or am I ok to leave existing tin there and add insulation on top of that?

[Greg]

Hi & welcome. I personally think the insulation R value would not make much difference if the tin is there or not, But one thing that would be there is a barrier should the new roof start to leak. Just my thoughts.

Greg

[JD]

>> am I ok to leave existing tin there and add insulation on top of that?

I have never done what you are asking about and don't consider myself on expert on permissive air loss, so I would be just guessing. Guessing, I would think that having insulation on top of the existing roof would work, in terms of insulation. I would think that insulating the original metal would keep that metal from developing a condensation problem. I would think that the top insulation would have to have some air flow over/through it and it should be protected from any direct contact with outside air.

I am never a proponent of actually eliminating the original metal roof. The roof adds to the structural stability of the home by locking in the side walls and offers some strength against horizontal racking at the top of the walls.

JMO

[Greg]

JD, is it too late for us to go Engineering school??

Greg

[JD]

Math?? Oh noooo