Insulating and Metal Roof

[rubantin]

I just bought an old home... The detached 1 1/2 car garage is made out of rough cut thick and thin lumber and barn boards. The framework is rough cut 2x4 at 24" centers. live in northern MN.

I put firing strips (2x2s) on the wall studs, R19 6.5X23 in the walls with barrier & 3/8 osb for the interior.

There is no attic. The barn boards on the roof have rotted some and are showing some signs of white. The center of the ridge is bowing down some. It looks like the metal roof was installed a couple years ago to stop the leaks in the rotten roof. They actually installed a cable to help keep the side walls together.

I have purchased 4 2X8X20 boards to act as joists and will use some 1/2 plywood pieces to gusset the joists to the rafters. I have to figure some way to lift the roof to straighten it before I install the gussets though. But that is a later issue.

I have attached firing strips to the rafters so I can put in some of the R19 6.5X23 in the roof as well...

The real issues for me are how to construct/insulate the roof and avoid major moisture problems. Where or if to have a moisture barrier... etc...

I have also considered rigid foam insulation as well...

 

[tyme2par4]

It's unfortunate that they put the metal roof on without shoring up the ridge better. I think it may be difficult now without damaging the roofing.
As for lifting, a good 20+ ton bottle jack with a long stud on top should work to jack it up.

For insulation, I believe spray foam is probably your best option.
Or provide more ventilation in the eaves and peak and insulate the ceiling.

 

[rubantin]

It's unfortunate that they put the metal roof on without shoring up the ridge better. I think it may be difficult now without damaging the roofing.
As for lifting, a good 20+ ton bottle jack with a long stud on top should work to jack it up.

For insulation, I believe spray foam is probably your best option.
Or provide more ventilation in the eaves and peak and insulate the ceiling.

It appears as the metal roof ridge is stressed so the bowing may have happened more after the metal roof was installed.

Spray foam is too expensive to use on this project...

 

[TractorJeff]

5 ton jack is more than plenty!
There was/is a guy not to long ago pushing up a roof under General Garage Discussion

 

[DC73]

The real issues for me are how to construct/insulate the roof and avoid major moisture problems. Where or if to have a moisture barrier... etc...

Most building scientists don't like regular insulation (fiberglass, mineral wool, cellulose, etc) in direct contact with the underside of the roof deck. Regular insulation generally requires a vent channel between the top of the insulation and the bottom of the roof deck of about 1". There are exceptions depending on your climate.

You can definitely use closed cell spray foam. You might be able to use open cell spray foam depending on your climate.

Go to GreenBuildingAdvisor and search for how to insulate a cathedral ceiling. There's a good article there. You can also search there and BuildingScience.com for articles on unvented attics which will give you quite a bit of good information. You could also post your questions on the Q&A forum at GreenBuildingAdvisor as there are some building science gurus who hang out there and could give you better info.

DC