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Community and Q&A

Retrofit insulation

Cedar90 | Posted in Energy Efficiency and Durability on


I’ve been scouring this website and its been a huge help in understanding where we should be trying to go in terms of home efficiency. So thanks to all the contributors!

We have zone 5 – 1.5 story balloon frame home constructed in 1900. This has nominal 2×4 framing and minimal insulation. It is currently clad with wood siding -> asphalt siding -> 1.25″ foil foam non taped -> vinyl siding. This whole structure has a single story 1980’s addition and now another 1 story addition planned. So lots going on.

With this comes a full gut and a re-evaluation of how we are choosing to prepare for efficiency and trying to reduce our ecological impact.

We’ve been quoted for a full EPS nailbase wrap of the original structure bringing our wall insulation to R37, and a closed roof with a deck R value of R49 from foam only. This puts us well above the minimum foam thickness ratio as provided by Martin in his Combining Exterior Foam with fluffy insulation.

Is a smart interior membrane like Majrex or Intello plus still a wise application here? my building department will not allow us to go without.

Should the exterior asphalt siding be removed? is there any concern with its vapour permeance  as it sits essentially in the middle of my new assembly?

The EPS mfg requires 6 mil poly installed directly on the warm side of their product. This seems odd in regards to the ability to dry in one direction?

Is anyone accounting for increased snow load on highly insulated roofs given that we are getting little to no melt?

While we expect to continue the same wall nailbase around the additional structures the roofs/attics will be traditionally vented and blown in. Should we expect to see any moisture concerns between the buildings?

I understand there are some green impacts from foam manufacturing however looking into larsen truss (or cascadia system) with rock wool insulation is dramatically more expensive and the application to our 6/12 roof is concerning for our local engineer. 

Looking forward to hearing your thoughts

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