Self-builder
· Östergötland
· 1 837 posts
Hi, I have a house from 1910 that turns out to consist of vertical timber planks in the exterior walls, about 3" thick, and over the years it has received some organic materials on the inside like some fiberboard and masonite. Soon I plan to add external insulation to the wall and replace the facade. I talked to an insulation company nearby, but I'm not sure if they understood my reasoning. They claimed that I should put wind barrier on the exterior wall after removing the outer paneling, then build up cross-layers with CC60 45x45 studs, then wind barrier again on the exterior, followed by battens and paneling. I accept this reasoning since you then get a vapor brake on each side of the insulation, and today there is nothing apart from potentially some wind barrier in the wall (which should be on the outside). At one point, I considered nailing 17mm tongue-and-groove boards onto the wood frame with maybe CC40 to support the insulation against, but do I need to worry about moisture against the old wood frame in the middle of the wall? The idea is that any moisture formation should occur in the insulation and then migrate outward. I am considering using cellulose insulation iCell boards, as I can obtain these easily. Previously, I’ve used wood fiber boards in several new constructions and then used wind barrier on both sides of the frame with good results. What do you experts think? 
External additional insulation is clearly the best when you have a timber frame. Mainly because this increases the time delay that always occurs with a heavy frame. Today's solar heat comes in at night and the night's cold during the day. This reduces the heating requirement, at least during certain parts of the year. Moreover, it's a way to conserve floor space.
Cellulose insulation is also good as it eliminates concerns about potential condensation in the new insulation. A vapor barrier should not be placed on the inside of a plank wall. You might consider the thickness of the insulation, but 45+45 is probably a reasonable balance. It should also look sensible. If you estimate that 3-inch planks are equivalent to 25 mm of high-performance insulation, then the total is 115 mm of insulation. It seems to me that the insulation company knows their job. Remember that the window frames should be moved out as much as you additionally insulate. It's also a good opportunity to review the caulking between the frame and the wall. It's usually not good in houses with plank frames.
Cellulose insulation is also good as it eliminates concerns about potential condensation in the new insulation. A vapor barrier should not be placed on the inside of a plank wall. You might consider the thickness of the insulation, but 45+45 is probably a reasonable balance. It should also look sensible. If you estimate that 3-inch planks are equivalent to 25 mm of high-performance insulation, then the total is 115 mm of insulation. It seems to me that the insulation company knows their job. Remember that the window frames should be moved out as much as you additionally insulate. It's also a good opportunity to review the caulking between the frame and the wall. It's usually not good in houses with plank frames.
Self-builder
· Östergötland
· 1 837 posts
But you can put a wind barrier on the outside of the plank and again outside the insulation, i.e., a layer on each side of the new insulation and directly against the old plank, or is that a bad idea? The plan is to replace the windows and move them out to the edge with the panel. I want 45+45 cross-battening because it results in few thermal bridges and is easy to build. However, I do not expect to recoup the cost of the renovation, but I think some renovation is needed after 107 years.
No, it is not a bad idea to place wind barrier on both sides of the insulation.
Self-builder
· Östergötland
· 1 837 posts
No risk that there will be moisture against the outside of the framework plank with wind barrier and insulation lying directly against it, do you think?
No. The cellulose insulation is as hygroscopic (moisture-absorbing) as the plank frame. The wind barrier should be windproof, not vapor-proof.
Self-builder
· Östergötland
· 1 837 posts
Should work well. Thanks for bouncing ideas!