John Straube replies:

You suggest two solutions,
1. the interior insulation approach and
2. the part inside, part outside approach.

Both approaches presume you install draining fill and drain tile near the base.

Both solutions can work. The interior insulation approach has many benefits, but one large risk factor – the brick, mortar or even stone could be damaged by freeze thaw because of the added insulation. The second approach can be designed to reduce the risk of F/T but is somewhat more complex and may have less thermal performance.

Do you need to reduce the risk of FT? I don’t have enough information. Is there any sign that the masonry and mortar are susceptible to damage? If so, we must be careful. If not, we don’t still know.

Solution one could be used by ensuring that the masonry remains dry, e.g., we don’t care about cold if it is dry. Excellent draining backfill (crushed stone with no fines) could possibly keep the below grade components dry enough (although even ¾” exterior insulation like drain board would help a lot). How the brick above grade would be protected is unclear -- perhaps by a good washboard projecting out 1.5” at the top of the wall, or by a good paint coating (I can recommend some specific products). The ground to brick interface would be critical, and may be helped by a crushed stone bed (even 4” wide) or concrete curb.

Solution 2 is slightly different. By placing a significant amount of drainboard on the exterior, the stone masonry from 6” below grade to footing would be completely protected from FT because it would be both dry and warm. The problem is the above and at grade By lapping the interior insulation below the point at which the exterior insulation stops, we can likely keep some heat flowing to the critical at grade region. This should be designed using THERM or FRAME to ensure that the interior surface temperature remains high enough to stop condensation, that the brick/conc remains a few degrees higher than if fully insulated (the temp difference will dry the brick/mortar). We could also answer the question of what the real R value of the assembly was. The same above-grade brickmoisture protection measures would still be used.

I would not worry about ground water control much, since both of your solutions will do this well.

So the decision is still yours, and really depends on the susceptibility to FT damage of that at-grade portion. If the materials are assumed to be suscreptible or the exposure to moisture thought to be high, solution 2 would be better. If you have reason to believe this is not the case, solution 1 would save more energy and likely be easier to build.

JS