Foam is for sound wood. First find out which you have.
Rim joists have become insulation’s favorite target, and for a dry, sound rim that is fair: sealing it cuts real drafts. But a rim that is already wet or soft needs a carpenter before it ever meets foam, because foam over rot seals the failure in and hides it from every future flashlight. The ten-minute probe that splits the two cases is free with any visit, and the repair side prices off the published guide.
The split, in plain terms
Insulate when the rim probes firm everywhere, moisture readings run dry, there is no active water source at the wall outside and no staining that a probe contradicts. That house should absolutely seal its rim bays; it is one of the better efficiency dollars an old Connecticut home can spend.
Replace first when the screwdriver sinks, when staining pairs with softness, when the outside grade or gutters have been feeding that wall for years or when a floor above already bounces. Sections run $1,500 to $4,000 on the guide, the moisture source gets fixed in the same scope and the foam crew comes back to a rim worth sealing. Wood decay simply stops progressing when the wood stays dry, the point the USDA Forest Products Laboratory’s durability research at fpl.fs.usda.gov has documented for decades, which is why drying the assembly is half of every repair we quote.
Meriden Sill & Joist Repair plays one position in this: the structural gate. Sound rims get a written all-clear you can hand any insulation contractor; failed rims get carpentry first. The damp-basement stock around Southington and the older frames of Berlin are exactly where the ten-minute check earns its keep.
Foam-and-rot questions, answered
The insulation company wants to foam our rim joists next week. What should happen first?
A probe, this week. Ten minutes with a screwdriver along the rim line tells you whether the wood under that future foam is sound. Foam over sound wood is a fine upgrade; foam over soft wood hides an active failure and makes the eventual repair harder and costlier. Any insulation crew worth hiring will welcome the check.
Does spray foam cause rim joist rot?
Not by itself, and the building-science argument runs both ways: closed-cell foam done right reduces condensation on the rim. The real risk is sequencing, foaming wood that was already wet or already rotting, which locks moisture against the failure and blinds every future inspection. Structure first, insulation second is the whole rule.
We already foamed years ago and now a floor feels soft. Can you even inspect it?
Yes, it just costs more honesty: the foam gets cut back at the suspect bays, the wood probed and the foam patched or replaced after. Finding rot under old foam is common exactly because the foam hid the early symptoms. Soft floors above a foamed rim earn the look regardless.
If the rim turns out sound, do you sell insulation?
No. We are the structural half of this conversation; when your rim probes sound, the written result says so and you hire any insulation contractor you like with confidence. Being the honest gate in front of foam jobs is worth more to us than pretending to be two trades.
Get the probe before the foam
Tell us the house age and what prompted the insulation plan. The structural answer comes back in writing.