How can one add extra insulation to a cabin with tongue and groove wood walls and ceilings? Do you have to tear the walls out or is there another way?

You can have extra insulation blown in to your ceilings.The only way I know of to get extra insulation in to your walls,would be to drill small holes through out your walls and blow extra insulation in between studs and then have holes corked up.

There might be a way to use expanding foam insulation using small holes. Not sure if anyone can do this in the area.

Using Cellulose insulation to blow in the walls would be the way to go(imo).If you're handy this could be a job you could do yourself and rent equipment from Homedepot.It would be a lot of work though going around looking for the studs in your outside walls and then drilling holes in between each.You also would need to know if there are purlin's in between your studs,if so you would have to drill 2 holes in between each stud to make sure the blown insulation gets top and bottom.

What I would do first is take off a couple of receptacle plates and try and see/measure what is already in the walls. I am assuming that the builder installed fiberglass batt in the exterior walls. If you have an attic then measure the average of insulation in several areas to determine your R-Value. Batt is about R-3 per inch. Blown cellulose is about R-3.2-3.7 per inch. You want a minimum of R-19 but R-30 is the norm now. If you have a vaulted ceiling then you might be able to see what is installed from a soffit area outside. Do you have any floor insulation? Do you have a crawlspace or basement? Let me know I can help further. I will be a BPI, RESNET certified energy management consultant/auditor by March. I just have some field work left to finish or I would come take a look. But this is the extent of help I can give at this point. Let me know if you have more questions.