I have an unheated porch area and I would like to cover the roof with
cedar shingle. I am told that for a roof the shingles should be exposed
7" only, and that they should be installed over slats so that air can
flow underneath the shingle.

What's on the roof now is tarpaper over 1x12 wood roof boards.
Can I install the cedar shingle directly over 1x12 boards? I would
remove the tarpaper, nail the shingles directly to the board with
7" exposure, and afterwards cover the shingles with Thompson's wood
sealer.

I have build a shed roof like this 5 years ago and the shingles seem
to be holding out fine, so I'm not sure if it is absolutely necessary
to have the air space under the roof shingle. The shingles are
expensive
and I would not want them to fail after 5 years. Thanks,

--
Jeff